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[openscop.git] / doc / openscop.texi

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@c %
@c %  /**-----------------------------------------------------------------**
@c %   **                           OpenScop Library                      **
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@c %   **                            openscop.texi                        **
@c %   **-----------------------------------------------------------------**
@c %   **                 First version: september 10th 2006              **
@c %   **-----------------------------------------------------------------**/
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@c % release 0.0: May 4th 2008
@c %

@c % /*************************************************************************
@c %  *                              PART I: HEADER                           *
@c %  *************************************************************************/
@c %**start of header
@setfilename openscop.info
@settitle OpenScop Specification and Library

@set EDITION 1.0
@set SPEC_VERSION 1.0
@set LIB_VERSION 0.7.0
@set UPDATED September 27 2011
@setchapternewpage odd

@c % This is to ask for A4 instead of Letter size document.
@iftex
     @afourpaper
@end iftex

@c %**end of header

@c % /************************************************************************
@c %  *                PART II: SUMMARY DESCRIPTION AND COPYRIGHT            *
@c %  ************************************************************************/

@copying
This document describes OpenScop, a specification of a file format and a set
of data structures for polyhedral compilation tools to talk
together. It also describes briefly the OpenScop Library version @value{LIB_VERSION}, 
a Free Software that provides an example of OpenScop implementation.

It would be quite kind to refer at the present document in any publication that
results from the use of the OpenScop Library:

@example
@@TechReport@{Bas11,
@ @ author =@ @ @ @ @ @ @{C\'edric Bastoul@},
@ @ title =@ @ @ @ @ @ @ @{OpenScop: A Specification and a Library for Data 
@ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ Exchange in Polyhedral Compilation Tools@},
@ @ month =@ @ @ @ @ @ @ @{june@},
@ @ year =@ @ @ @ @ @ @ @ 2011,
@ @ institution = @{Paris-Sud University, France@}
@}
@end example

Copyright @copyright{} 2011 Paris-Sud University and INRIA.

@c quotation
Permission is granted to copy, distribute and/or modify this document under
the terms of the GNU Free Documentation License, Version 1.2 published by the
Free Software Foundation; with no Invariant Sections, with no Front-Cover
Texts, and with no Back-Cover Texts. To receive a copy of the
GNU Free Documentation License, write to the Free Software Foundation, Inc.,
59 Temple Place, Suite 330, Boston, MA  02111-1307 USA.
@c end quotation
@end copying

@c % /*************************************************************************
@c %  *                 PART III: TITLEPAGE, CONTENTS, COPYRIGHT              *
@c %  *************************************************************************/
@titlepage
@title OpenScop
@subtitle A Specification and a Library for Data Exchange in Polyhedral Compilation Tools
@subtitle Edition @value{EDITION}, for OpenScop Specification @value{SPEC_VERSION} and OpenScop Library @value{LIB_VERSION}
@subtitle @value{UPDATED}
@author C@'edric Bastoul

@c The following two commands start the copyright page.
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@c Output the table of contents at the beginning.
@contents

@c % /*************************************************************************
@c %  *                     PART IV: TOP NODE AND MASTER MENU                 *
@c %  *************************************************************************/
@ifnottex
@node Top
@top OpenSCop

@insertcopying
@end ifnottex

@menu
* Introduction::
* Polyhedral Representation::
* OpenScop Specification::
* OpenScop Library::
* References::
@end menu

@c % /*************************************************************************
@c %  *                       PART V: BODY OF THE DOCUMENT                    *
@c %  *************************************************************************/

@c %  ****************************** INTRODUCTION ******************************
@node Introduction
@chapter Introduction
OpenScop is an open specification that defines a file format and a set of
data structures to represent a @emph{static control part} (SCoP for short),
i.e., a program part that can be represented in the @emph{polyhedral model}.
The goal of OpenScop is to provide a common interface to various
polyhedral compilation tools in order to simplify their interaction. 

Designing a single format for tools that have different purposes
(e.g., as different as code generation and data dependence analysis) may
sound strange at first. However we could observe that most available
polyhedral compilation tools during the last decade were manipulating
more or less the same kind of data (polyhedra, affine functions...) and
were actually sharing a part of their input (e.g., iteration domains and
context concepts are nearly everywhere). We could also observe that
those tools may rely on different internal representations, mostly based on
one of the major polyhedral libraries (e.g., Polylib, PPL or isl), and
this representation may change over time (e.g., when switching to a
more convenient polyhedral library).
The OpenScop aim is to provide a stable, unified format that offers a
durable guarantee that a tool can use an output or provide an input to
another tool without breaking a tool chain because of some internal
changes in one element of the chain. The other promise of OpenScop is
the ability to assemble or replace the basic blocks of a polyhedral
compilation framework at no, or at least low engineering cost.

The policy that drives OpenScop can be summarized by these three rules:
@itemize @bullet
@item  Embed the @emph{minimum} information to build a complete polyhedral
       compilation framework in the so-called @emph{core part}
       (to avoid as much as possible empty or useless information
       for each tool).
@item  Provide a @emph{very stable} core part (so users have some
       guarantee that they will not need to update their tool
       because of frequent specification evolution),
@item  Provide a @emph{very flexible} extension part (so it can also
       be used to test wild new ideas).
@end itemize

@noindent Another, more technical, rule may be added:
@itemize @bullet
@item  Avoid any need for external library or tool to support it
       (i.e., it's not XML or YAML or anything like that).
@end itemize

The success of OpenScop in meeting its goals totally depends on its
acceptance by the tool developers (that have to support it in their tools).
To help them, we provide an example implementation: the OpenScop Library.
This library (and in particular its API) is not part of the OpenScop
specification (which includes only the file format and the set of data
structures). It is licensed under the 3-clause BSD license so developers may
feel free to use it in their code (either by linking it or copy-pasting its
code). This document also describes this library briefly (readers are
invited to read at its technical documentation).
The current version of the OpenScop Library is still under evaluation,
and there is no guarantee that the upward compatibility will be respected,
even if we do think so. A lot of reports are
necessary to freeze the library API. Thus you are very welcome and
encouraged to send reports on bugs, wishes, critics, comments, suggestions
or (please!) successful experiences to the OpenScop mailing list
@email{openscop-development@@googlegroups.com}.

This document is organized as follows. First, we provide some
background on the polyhedral model and how it is used to represent and to
manipulate programs (@pxref{Polyhedral Representation}). Next,
we describe the OpenScop specification, from the file format
(@pxref{OpenScop Core Part File Format Specification}) to the data structures
and the OpenScop Library API
(@pxref{OpenScop Core Part Data Structure Specification}).
Finally we will detail how to install the OpenScop Library
(@pxref{Installation}).


@c %  ******************* POLYHEDRAL REPRESENTATION OF PROGRAMS ****************
@node Polyhedral Representation
@chapter Polyhedral Representation of Programs
If you are reading at the OpenScop documentation, you probably don't need any
explanation about the polyhedral model. It is unlikely that someone will read
this paper by mistake. However some vicious advisor may ask their poor
engineers/interns/students
to work for the very first time on this exciting topic. Most papers on
polyhedral compilation are hard to read. Despite my efforts,
mine are no exception according to some reviewers. Hence I give there a new
try to provide a comprehensive explanation of the polyhedral model without the
size and style limits of a classical research paper.

Be aware that to be able to understand the polyhedral model, there are a few
prerequisites. You should not read the following while you still ignore
what is:
@itemize @bullet
@item  a @code{for} loop construction in C programs (@code{do} loops in FORTRAN are OK too!),
@item  an @emph{affine expression},
@item  a @emph{vector},
@item  a @emph{matrix},
@item  a @emph{matrix-vector multiply}.
@end itemize
If you do not know those concepts, please do some search and come back
afterwards. And if you are courageous enough, send me a few lines that
describe them so I can insert them here!

@menu
* Motivation::
* Thinking in Polyhedra::
* What's Next?::
@end menu


@node Motivation
@section Motivation: Program Transformations

A direct translation of high level programs written, e.g., in C, to assembly
then to object code is likely to produce (very) inefficient applications.
Architectures are
quite complex, including several levels of cache memory, many cores, deep
pipelines, various number of functional units, of registers etc.
The list of such
"architectural features" is growing with each new generation of processors.
To achieve the best performance, the object program must use
these features in a smart way.
Programmers use high level languages for productivity and portability:
typically they do not have to take care of the target architecture but
to ensure they write programs which produce the right output. Hence,
the problem of mapping the program to the target architecture in the most
efficient way is left to the compiler.

The compiler may see a high level program as a specification
@emph{of an output}. The program is a list of instructions to be executed to
produce the output. As long as the output is guaranteed to be as the
programmer specified in his code, the compiler is free to modify
the program.
For instance, let us imagine we are working on an architecture with only
three registers and we consider the following statements written by
a programmer:

@example
@group
x = a + b;
y = c + d;
z = a * b;
@end group
@end example

It is easy to see that we can reorder the three statements in any way without
modifying the semantics (no statement reads or writes a variable that another
statement writes). Because of the lack of registers, the solutions such that
the first and the third statements are one after the other are better
because @code{a} and @code{b} will be put in the processor registers by
one statement and can be reused directly by the other one
without reading from memory (this is called a @emph{data locality
improving} transformation). Hence a better statement order is, e.g.:

@example
@group
x = a + b;
z = a * b; // a and b are still in processor registers
y = c + d;
@end group
@end example

We can also notice that it is possible to run the three statements in
parallel (possibly on different processors). The programmer may
explicit this in a way the compiler
and/or the architecture is able to understand. For instance,
we can use OpenMP to describe parallelism
(this is called a @emph{parallelizing} transformation):

@example
@group
#pragma omp parallel sections
@{
   #pragma omp section
   @{
     x = a + b;
   @}
   #pragma omp section
   @{
     y = c + d;
   @}
   #pragma omp section
   @{
     z = a * b;
   @}
@}
@end group
@end example

However, the right way to optimize this program is probably a tradeoff
between these two techniques. This is true if, e.g., the target
architecture has some limitations to run too many operations in parallel,
or, like in our case, when some data may be reused by some processors.
Hence, the best optimization for our small example is probably the
following:

@example
@group
#pragma omp parallel sections
@{
   #pragma omp section
   @{
     x = a + b;
     z = a * b;
   @}
   #pragma omp section
   @{
     y = c + d;
   @}
@}
@end group
@end example

This example is quite trivial because the statements are
executed only once. The real sport begins when we have to deal with loops,
as we will see momentarily. However, polyhedral compilation framework users
have to be conscious that we @emph{need} to transform programs to achieve
the best performance and that the best transformation  that has to be
discovered (at the price of many, many efforts) and performed may be
quite complex. Hence the need of powerful model and tools.


@node Thinking in Polyhedra
@section Thinking in Polyhedra


Since the very first compilers, the internal representation of programs
is the @emph{Abstract Syntax Tree}, or AST. In such representation,
each statement appears only once even if it is executed many times (e.g.,
when it is enclosed inside a loop). This is a limitation
for finding and applying complex transformations:
@itemize @bullet
@item It limits program analysis power. For instance if a statement
      @emph{depends} on another statement (i.e., they access the same
      memory location and at least one of these accesses is a write),
      we will consider both statements as unique entities while the
      dependence relation may involve only few statement executions.
@item It limits program transformation power. Loop transformations
      operate on statement executions. For instance, because they
      consider all statement executions at the same time, present day
      production compilers are not able to achieve loop fusion
      (that tries to merge the loop bodies of two loops) if the loop bounds
      of the two loops do not match (yes, that's ridiculous).
@item It limits program manipulation flexibility.
      Trees are very rigid data structures that are not easy to manipulate.
      Program transformation may require very complex transformations that will
      imply deep modifications of the control flow.
@end itemize

The Polyhedral Model is a convenient alternative representation which
combines analysis power, expressiveness and high flexibility. The drawback
is it breaks the classical structure of programs that every programmer
is familiar with. It requires some (real) efforts
to be smoothly manipulated, but it definitely worth it. It is based on three
main concepts, @emph{iteration domain},  @emph{scattering function} and
@emph{access function} that are described in depth in the
following sections.

A program part that can be represented using the Polyhedral Model is called
a @strong{Static Control Part} or @strong{SCoP} for short.

@menu
* Iteration Domain::
* Scattering Function::
* Access Function::
@end menu

@node Iteration Domain
@subsection Iteration Domain

The key aspect of the polyhedral model is to consider @emph{statement
instances}. A statement instance is @emph{one} execution of a statement.
A statement
outside a loop has only one instance while those inside loops may have many.
Let us consider the following code with two statements @code{S1}
and @code{S2}:

@example
@group
pi = 3.14;               // S1
for (i = 0; i < 5; i++)
  A[i] = pi;             // S2
@end group
@end example

The list of statement instances is the following (we just have to fully
unroll the loop):

@example
@group
pi = 3.14;
A[0] = pi;
A[1] = pi;
A[2] = pi;
A[3] = pi;
A[4] = pi;
@end group
@end example

Each instance of a statement which is enclosed inside a loop may be referred
thanks to its outer loop counters (or @emph{iterators}). In the polyhedral
model we consider statements as functions of the outer loop counters that may
produce statement instances:
instead of simply "@code{S2}", we use preferably the notation @code{S2(i)}.
For instance we  denote the statement instance @code{A[3] = pi;} of the
previous example as @code{S2(3)}. This means @emph{instance of
statement @code{S2} for} @code{i = 3}.
If a statement @code{S3} is enclosed inside two loops of iterators @code{i}
(outermost loop) and @code{j} (innermost loop), we would denote it
@code{S3(i,j)}, and so on with more enclosing loops.

The ordered list
of iterators (ordered from the outermost iterator to the innermost iterator)
is called the @strong{iteration vector}. For instance the iteration vector for
@code{S3} is @code{(i,j)}, for @code{S2} it is @code{(i)}, and for @code{S1}
it is empty since it has no enclosing loop: @code{()}. A more precise reading
at the notation @code{S2(3)} would show that it denotes the instance of
statement @code{S2} for the iteration vector @code{(2)}.

Obviously, dealing with statement instances does not mean we have to unroll all
loops. First because there would be probably too many instances to deal with,
and second because we probably just do not know how many instances there are.
For instance in the following loop it is impossible to know (at compile time)
how many times the statement @code{S3} will be executed:

@example
@group
for (i = 2; i <= N; i++)
  for (j = 2; j <= N; j++)
    A[i] = pi;             // S3
@end group
@end example

@noindent Such a loop is said to be @emph{parametric}: it depends on
(at least) a value called a @emph{parameter} which is not modified
during the execution of the whole loop, but is unknown at compile time.
Here, the only parameter is @code{N}.

A compact way to represent all the instances of a given statement
is to consider the set of all possible values of its iteration vector.
This set is called the @strong{iteration domain}. It can be conveniently
described thanks to all the constraints on the various iterators the statement
depends on. For instance, let us consider
the statement @code{S3} of the previous program. The iteration domain is the set
of iteration vectors @code{(i,j)}. Because of the parameter, we are not able to
achieve a precise list of all possible values. It would look like this:

@example
@group
(2,2)  (2,3)  (2,4)  ...  (2,N)
(3,2)  (3,3)  (3,4)  ...  (3,N)
...    ...    ...    ...  ...
(N,2)  (N,3)  (N,4)  ...  (N,N)
@end group
@end example

@noindent A better way is to say it is the set
of iteration vectors @code{(i,j)} such that @code{i} is an integer greater or
equal than 2 and lower or equal than @code{N}, and @code{j} is an integer
greater or equal than 2 and lower or equal than @code{N}. This may be written
in the following mathematical form:

@tex
$$D _{S3} =  \{(i,j) \in Z^2 \; | \; 2 \leq i \leq N \land 2 \leq j \leq N \}$$
@end tex

@ifnottex
@example
@group
D_S3 =  @{(i,j) in Z^2 | 2 <= i <= N && 2 <= j <= N @}
@end group
@end example
@end ifnottex

@noindent It is easy to see that this iteration domain is a part of the
2-dimensional space
@tex
$Z^2$.
@end tex
@ifnottex
@example
@group
Z^2.
@end group
@end example
@end ifnottex
We often use in our research papers a graphical representation that gives a
better view of this subspace:

@image{images/basic1,4cm}

@noindent Here, the iteration domain is specified thanks to a set of
constraints. When those constraints are affine and
depend only on the outer loop counters and some parameters, the set of
constraints defines a @emph{polyhedron} (more precisely this is a
@emph{Z-polyhedron}, but we use @emph{polyhedron} for short).
Hence the @emph{polyhedral model}!

To manipulate a set of affine constraints easily, we rely on a matrix
representation. To write it, we use the @emph{homogeneous} iteration vector:
it is simply the iteration vector with some additional dimensions to
represent the parameters and the constant.
For instance for the statement @code{S3}, the
iteration vector in homogeneous coordinates is @code{(i, j, N, 1)}
(we will now call it @emph{iteration vector} directly for short).
Then we write all the constraints as affine inequalities of the form
@emph{affine constraint}
@tex
$\geq 0$.
@end tex
@ifnottex
@code{ >= 0}.
@end ifnottex
For instance for the statement @code{S3} the set of constraints is:

@tex
$$
\hbox{$ \cases{  i         - 2  &$\geq 0$\cr
                -i     + N      &$\geq 0$\cr
                     j     - 2  &$\geq 0$\cr
                    -j + N      &$\geq 0$}$}
$$
@end tex

@ifnottex
@example
@group
    i - 2 >= 0
   -i + N >= 0
    j - 2 >= 0
   -j + N >= 0
@end group
@end example
@end ifnottex

@noindent Lastly, we translate the constraint system to the form
@strong{domain matrix}@code{ * }@emph{iteration vector}@code{ >= 0}:

@c Thanks to Harald Devos for the TeX :-) !  
@tex
$$
\left[
\matrix{
 1 &  0  & 0  & -2 \cr
-1 &  0  & 1  &  0 \cr
 0 &  1  & 0  & -2 \cr
 0 & -1  & 1  &  0
 }
\right]
\left(
\matrix{
i \cr
j \cr
N \cr
1
 }
\right)
\ge
\left(
\matrix{
0 \cr
0 \cr
0 \cr
0
}
\right)
$$
@end tex
@ifnottex
@example
@group
[  1  0  0 -2 ]   [ i ]    [ 0 ]
[ -1  0  1  0 ]   [ j ]    [ 0 ]
[  0  1  0 -2 ] * [ N ] >= [ 0 ]
[  0 -1  1  0 ]   [ 1 ]    [ 0 ]
@end group
@end example
@end ifnottex

@noindent @strong{The domain matrix will be used in all our tools to provide the
information on the iteration domain of a given statement (the iteration vector
is in general an implicit information).}

@node Scattering Function
@subsection Scattering Function

There is no ordering information inside the iteration domain: it only describes
the set of statement instances but @strong{not} the order in which they have
to be executed relatively to each other. In the past the lexicographic order
of the iteration domain was considered, this is no more true
(especially when using CLooG). If we do not provide any ordering information, this
means that the statement instances may be executed in any order
(this is useful, e.g., to specify parallelism). However, some statement instances
may depend on some others and it may be critical to enforce a given order (or
non-order). Hence we need another information.

We call @emph{scattering} any kind of ordering information in the polyhedral
model. There exists many kind of ordering, such as @emph{allocation},
@emph{scheduling}, @emph{chunking} etc. They are all expressed
in the same way, i.e., using @emph{logical stamps}, but they may have
different semantics.

In the case of @strong{scheduling}, the logical stamps are logical dates that
express at which date a statement instance has to be executed. For instance,
let us consider the following three statements:

@example
@group
x = a + b;   // S1
y = c + d;   // S2
z = a * b;   // S3
@end group
@end example

@noindent The scheduling of a statement @code{S} is typically
denoted by
@tex
$\theta_{S}$.
@end tex
@ifnottex
T_S.
@end ifnottex
Let us consider the following logical dates for each statement:

@tex
@example
@group
$\theta_{S1} = 2$
$\theta_{S2} = 3$
$\theta_{S3} = 1$
@end group
@end example
@end tex

@ifnottex
@example
@group
T_S1 = 1
T_S2 = 2
T_S3 = 3
@end group
@end example
@end ifnottex

@noindent It means that statement @code{S3} has to be executed at logical date
@code{1}, statement @code{S1} has to be executed at logical date
@code{2} and statement @code{S2} has to be executed at logical date
@code{3}. The target code has to respect this scheduling (the order of
the logical dates), hence it would look like the following where the
variable @code{t} denotes the time:

@example
@group
t = 1;
z = a * b;   // S3
t = 2;
x = a + b;   // S1
t = 3;
y = c + d;   // S2
@end group
@end example

@noindent When some statements share the same logical date, this means that,
once the program reaches this logical date, the two statements can be executed
in any order, or better, in parallel. For instance let us consider the
following scheduling:

@tex
@example
@group
$\theta_{S1} = 1$
$\theta_{S2} = 2$
$\theta_{S3} = 1$
@end group
@end example
@end tex

@ifnottex
@example
@group
T_S1 = 1
T_S2 = 2
T_S3 = 1
@end group
@end example
@end ifnottex

@noindent Statements @code{S1} and @code{S3} have the same logical date,
moreover, @code{S2} has a greater logical date than @code{S1} and @code{S3}.
Hence the target code would be:

@example
@group
t = 1;
#pragma omp parallel sections
@{
   #pragma omp section
   @{
     x = a + b;   // S1
   @}
   #pragma omp section
   @{
     z = a * b;   // S3
   @}
@}
t = 2;
y = c + d;        // S2
@end group
@end example

Logical dates may be multidimensional, as clocks: the first dimension
may correspond to days (most significant), the next one to hours (less
significant), the third to minutes and so on. For instance we can consider
the following multidimensional schedules for our example:

@tex
@example
@group
$\theta_{S1} = (1,1)$
$\theta_{S2} = (2,1)$
$\theta_{S3} = (1,2)$
@end group
@end example
@end tex

@ifnottex
@example
@group
T_S1 = (1,1)
T_S2 = (2,1)
T_S3 = (1,2)
@end group
@end example
@end ifnottex

@noindent It is not very hard to decypher the meaning of such scheduling.
Because of the first dimension, statements @code{S1} and @code{S3} will be
executed before statement @code{S2} (@code{S1} and @code{S3} are executed at
day 1, while @code{S2} is executed at day 2). The second dimension is not
really useful there for @code{S2} because it is the only statement executed
at day 2. Nevertheless it allows to order @code{S1} and
@code{S3} relatively to each other since @code{S1} is executed at hour 1 of day
1 while @code{S3} is executed at hour 2 of day 1.
The corresponding target code is the following, with some
additional time variables for a better view of the ordering (@code{t1}
corresponds to the first time dimension, @code{t2} to the second one):

@example
@group
t1 = 1;
t2 = 1;
x = a + b;   // S1
t2 = 2;
z = a * b;   // S3
t1 = 2;
t2 = 1;
y = c + d;   // S2
@end group
@end example

In the case of @strong{allocation} (in the literature we can find some
papers calling it @emph{placement}), the logical stamp is a processor
number expressing on which processor a statement instance has to be
executed. Typically, allocations are written in the same way as scheduling.
Here, we denote it @math{P_S} for a statement @code{S}.
For instance, let us consider the following allocation:

@tex
@example
@group
$P_{S1} = 1$
$P_{S2} = 2$
$P_{S3} = 1$
@end group
@end example
@end tex

@ifnottex
@example
@group
P_S1 = 1
P_S2 = 2
P_S3 = 1
@end group
@end example
@end ifnottex

@noindent The corresponding target code has to take into account that both
statements @code{S1} and @code{S3} have to be executed on the same processor
(they have the same logical number 1) and that statement @code{S2} has
to be executed on another processor (logical number 2). A possible target code
is the following:

@example
@group
#pragma omp parallel sections
@{
   #pragma omp section
   @{
     // Logical processor 1
     x = a + b;   // S1
     z = a * b;   // S3
   @}
   #pragma omp section
   @{
     // Logical processor 2
     y = c + d;   // S2
   @}
@}
@end group
@end example

@noindent We can note that no order has been specified for the
statements @code{S1} and @code{S3} that are executed on the same processor.
Hence any order is satisfying. For sake of flexibility, it is usual to build
a scattering whose various dimensions do not have the same semantics. A
typical construction is @emph{space/time mapping} where the first @code{n}
dimensions are devoted to allocation, then the last @code{m}
dimensions are devoted to scheduling. Typically, space/time mapping is
written in the same way as scheduling.
Here we denote it @math{M_S} for a statement @code{S}.
For instance, let us consider the following space/time mapping for our
example where one dimension is devoted to mapping and one dimension is
devoted to scheduling:

@tex
@example
@group
$M_{S1} = (1,2)$
$M_{S2} = (2,1)$
$M_{S3} = (1,1)$
@end group
@end example
@end tex

@ifnottex
@example
@group
M_S1 = (1,2)
M_S2 = (2,1)
M_S3 = (1,1)
@end group
@end example
@end ifnottex

@noindent Here we have the same first dimension as the previous example, thus
the allocation of the statements to processors is the same. The second
dimension precises on a given processor at which logical date a statement
instance has to be executed. Here, the statement @code{S1} is executed at
day 2 on processor 1 while the statement @code{S3} is executed at day 1 onto
the same processor. It follows this space/time mapping corresponds to the
following target code (we added an additional variable to represent the
local logical clocks):

@example
@group
#pragma omp parallel sections
@{
   #pragma omp section
   @{
     // Logical processor 1
     t = 1;
     z = a * b;   // S3
     t = 2;
     x = a + b;   // S1
   @}
   #pragma omp section
   @{
     // Logical processor 2
     t = 1;
     y = c + d;   // S2
   @}
@}
@end group
@end example

For the same reason as discussed for iteration domains
(@pxref{Iteration Domain}), it is not possible to define a scattering for
each statement instance, especially if the statement belongs to a
(possibly parametric) loop. The iteration vector fully defines an
instance of a given statement. Thus, a practical way to provide a scattering
for each instance of a given statement is to use a @emph{function}
that depends on the iteration vector. In this way the function may associate
to each iteration vector a different scattering. We call these functions
@strong{scattering functions}. Scattering functions are @emph{affine}
functions of the outer loop counter and the global parameters.
For instance, let us consider the following source code:

@example
@group
for (i = 2; i <= 4; i++)
  for (j = 2; j <= 4; j++)
    P[i+j] += A[i] + B[j]; // S4
@end group
@end example

@noindent The iteration domain of the statement @code{S4} is:


@tex
$$D _{S4} =  \{(i,j) \in Z^2 \; | \; 2 \leq i \leq 4 \land 2 \leq j \leq 4 \}.$$
@end tex
@ifnottex
@example
@group
D_S4=  @{(i,j) in Z^2 | 2 <= i <= 4 && 2 <= j <= 4 @}.
@end group
@end example
@end ifnottex

@noindent If you are still not comfortable with the mathematical notation, it
corresponds to the following graphical representation:

@image{images/basic2,3cm}

@noindent The list of the statement instances of @code{S4} (the integer
points of its iteration domain) corresponds to the following iteration vectors:

@example
@group
iteration vector
     (2,2)
     (2,3)
     (2,4)
     (3,2)
     (3,3)
     (3,4)
     (4,2)
     (4,3)
     (4,4)
@end group
@end example

@noindent Let us suppose we want to schedule the instances of the statement
@code{S4} (the integer points of its iteration domain) using the following
scheduling function:

@tex
@example
@group
$\theta_{S4}(i, j) = (j+2, 3*i+j)$
@end group
@end example
@end tex

@ifnottex
@example
@group
T_S4(i,j) = (j+2,3*i+j)
@end group
@end example
@end ifnottex

@noindent We only need to apply the function to each iteration vector to find
the logical date of each instance:

@example
@group
iteration vector       logical date
     (2,2)       -->       (4,8)
     (2,3)       -->       (5,9)
     (2,4)       -->       (6,10)
     (3,2)       -->       (4,11)
     (3,3)       -->       (5,12)
     (3,4)       -->       (6,13)
     (4,2)       -->       (4,14)
     (4,3)       -->       (5,15)
     (4,4)       -->       (6,16)
@end group
@end example

The polyhedral model users do not have to take care about the generation of a
target code that respects the scattering: the
CLooG@footnote{@url{http://www.cloog.org}} tool is there to
solve the problem quite easily. For the previous
example, the target code would be the following (@code{t1} and @code{t2}
correspond to the two dimensions of the logical date, the reader may
take care that this code actually implements the scattering function):

@example
@group
for (t1 = 4; t1 <= 6; t1++) @{
  for (t2 = t1+4; t2 <= t1+10; t2++) @{
    if ((-t1+t2+2)%3 == 0) @{
      i = (-t1+t2+2)/3 ;
      j = t1-2 ;
      P[i+j] += A[i] + B[j]; // S4
    @}
  @}
@}
@end group
@end example



Obviously with such a twisted scheduling, it is hard to see the "meaning"
of the transformation. To name any kind of program transformation as
a magic spell ("tile", "fuse", "skew"...) is an old bad habit which is not
relevant anymore in the polyhedral model: a scheduling may be an arbitrary
complex sequence of basic-old-good transformations. Nevertheless it is most
of the time quite easy to translate well known transformations to schedules.
For instance, let us consider this new scheduling function:

@tex
@example
@group
$\theta_{S4}(i,j) = (j,i)$
@end group
@end example
@end tex

@ifnottex
@example
@group
T_S4(i,j) = (j,i)
@end group
@end example
@end ifnottex

@noindent Using CLooG, we can generate the target code:

@example
@group
for (t1 = 2; t1 <= 4; t1++) @{
  for (t2 = 2; t2 <= 4; t2++) @{
    i = t2;
    j = t1;
    P[i+j] += A[i] + B[j]; // S4
  @}
@}
@end group
@end example


@noindent It is easy to see (and analyze) that it corresponds to a classical
@emph{loop interchange} transformation.

A very useful example of multi-dimensional scattering functions is
the @strong{scheduling of the original program}.
The method to compute it is quite simple (@pxref{Fea92}). The idea is to
build an abstract syntax tree of the program and to read the scheduling for
each statement. For instance, let us consider the following implementation of
a Cholesky factorization:

@example
@group
/* A Cholesky factorization kernel. */
for (i=1;i<=N;i++) @{
  for (j=1;j<=i-1;j++) @{
    a[i][i] -= a[i][j] ;           // S1
  @}
  a[i][i] = sqrt(a[i][i]) ;        // S2
  for (j=i+1;j<=N;j++) @{
    for (k=1;k<=i-1;k++) @{
      a[j][i] -= a[j][k]*a[i][k] ; // S3
    @}
    a[j][i] /= a[i][i] ;           // S4
    @}
  @}
@}
@end group
@end example

@noindent The corresponding abstract syntax tree is shown in the following
figure. It directly gives the scattering functions (schedules) for all the
statements of the program (just follow the paths).

@image{images/tree,6cm}

@tex
$$
\hbox{$ \cases{ \theta _{S1}(i,j)    &$=  (0,i,0,j,0)$\cr
                \theta _{S2}(i)      &$=  (0,i,1)$\cr
                \theta _{S3}(i,j,k)  &$=  (0,i,2,j,0,k,0)$\cr
                \theta _{S4}(i,j)    &$=  (0,i,2,j,1)$}$}
$$
@end tex

@ifnottex
@example
@group
T_S1(i,j)   = (0,i,0,j,0)
T_S2(i)     = (0,i,1)
T_S3(i,j,k) = (0,i,2,j,0,k,0)
T_S4(i,j)   = (0,i,2,j,1)
@end group
@end example
@end ifnottex

@noindent These schedules depend on the iterators and give for each instance
of each statement a unique execution date. Using such scattering functions
allows CLooG to re-generate the input code.

@noindent To easily manipulate the scattering function of any
statement @code{S}, we translate it to the matrix form:
@tex
@math{\theta_S}(@emph{iteration vector})
@end tex
@ifnottex
T_S(@emph{iteration vector})
@end ifnottex
@code{ = }@strong{scattering matrix}@code{ * }@emph{iteration vector}.
For instance let us consider again our previous example
@tex
$\theta_{S4}(i, j) = (j+2, 3*i+j).$
@end tex
@ifnottex
T_S4(i,j) = (j+2,3*i+j).
@end ifnottex
We write it in the following way:
@tex
$$
\theta_{S4}
\left(
\matrix{
 i \cr
 j \cr
 1
 }
\right)
=
\left[
\matrix{
 0 &  0  & 2 \cr
 3 &  1  & 0 
 }
\right]
\left(
\matrix{
 i \cr
 j \cr
 1
 }
\right)
$$
@end tex
@ifnottex
@example
@group
     [ i ]    [  0  1  2 ]   [ i ]
T_S4([ j ]) = [  3  1  0 ] * [ j ]
     [ 1 ]                   [ 1 ]
@end group
@end example
@end ifnottex

@noindent @strong{The scattering matrix will be used in all our tools to provide
the information on the scattering of a given statement
(the iteration vector is in general an implicit information).}


@node Access Function
@subsection Access Function

Before applying any transformation, it is essential to deeply analyze both the
original program and the transformation to ensure the transformation does not
imply any modification of the original program semantics. In the polyhedral
model, we are able to achieve
an exact analysis when all the memory accesses are made through arrays
(note that variables are a particular case of arrays since they are simply
arrays with only one memory location) with affine subscripts that depend
on outer loop counters and global parameters (note that @emph{subscripts}
are sometimes called @emph{index} or @emph{accesses} in the literature).

For instance let us consider the array access @code{A[2*i+j][j][i+N]}. It has
three dimensions, each subscript dimension is an affine form of some outer loop
iterarors (@code{i} and @code{j}) and global parameters (@code{N}) hence
it corresponds to an acceptable array access to be analyzed in the
polyhedral model.

Each array access can target a different memory cell depending on the
statement instance, i.e., depending on the iteration vector.
Thus we use access functions (or subscript functions, or index functions, as you
prefer to call it) depending on the iteration vector to describe an array
access. In our example, the access function would be written
@math{F_A(i, j) = (2*i+j, j, i+N)}.

@noindent To easily manipulate the access function of any
array @code{A}, we translate it to the matrix form:
@math{F_A}(@emph{iteration vector})
@code{ = }@strong{access matrix}@code{ * }@emph{iteration vector}.
For instance let us consider again our previous example. We would
write it in the following way:
@tex
$$
F_A
\left(
\matrix{
 i \cr
 j \cr
 N \cr
 1
 }
\right)
=
\left[
\matrix{
 2 &  1  &  0 &  0 \cr
 0 &  1  &  0 &  0 \cr
 1 &  0  &  1 &  0
 }
\right]
\left(
\matrix{
 i \cr
 j \cr
 N \cr
 1
 }
\right)
$$
@end tex
@ifnottex
@example
@group
    [ i ]    [  2  1  0  0 ]   [ i ]
F_A([ j ]) = [  0  1  0  0 ] * [ j ]
    [ N ]    [  1  0  1  0 ]   [ N ]
    [ 1 ]                      [ 1 ]
@end group
@end example
@end ifnottex

@noindent @strong{The access matrix will be used in all our tools to provide the
information on the access of a given statement
(the iteration vector is in general an implicit information).}

@node What's Next?
@section What's Next?

OK, now you have an idea about how we do represent a program part in the
polyhedral model. You know the three main concepts, namely: domain, scattering
and access. What can you do with this?! Well, pretty much anything related
to code restructuring! The core idea will be to rely on the mathematical
representation to extract useful information about your
code (data reuse, parallelism...) and to generate a scattering
to benefit from the properties you analysed.
However, OpenScop's documentation is not the right
place to learn at this (OpenScop is all about representation, not about
manipulation). Probably it is the right time for you to
have a look at:
@itemize @bullet
@item PoCC @url{http://pocc.sourceforge.net}
@item Pluto @url{http://pluto-compiler.sourceforge.net}
@end itemize

@noindent Have fun :-) !


@c %  *********************** OpenScop Specification **************************
@node OpenScop Specification
@chapter OpenScop Specification

OpenScop provides an explicit polyhedral representation of a static control
part. It has been designed by various polyhedral compilation tool writers from
various institutions. It builds on previous popular polyhedral file and data
structure formats (such as @emph{.cloog} and CLooG data structures) to provide
a unique, extensible format to most polyhedral compilation tools. It
is composed of two parts. The first part, the so-called 
@emph{core part}, is devoted to the polyhedral representation of a SCoP.
It contains what is strictly necessary to build a
complete source-to-source framework in the polyhedral model and to output a
semantically equivalent code for the SCoP, from analysis to code generation.
The second part of the format, the so-called @emph{extension part},
contains extensions to provide additional informations to some tools.

@menu
* Core Part::
* Extension Part::
* History::
@end menu


@c %/*************************************************************************
@c % *                             CORE PART                                 *
@c % *************************************************************************/

@node Core Part
@section Core Part

@menu
* Preliminary Example::
* OpenScop Core Part File Format Specification::
* OpenScop Core Part Data Structure Specification::
@end menu

@c %/*************************************************************************
@c % *                         PRELIMINARY EXAMPLE                           *
@c % *************************************************************************/
@node Preliminary Example
@subsection Preliminary Example
OpenScop is a specification for representing static control program parts in
the polyhedral model. Thus, we can translate some code parts to an equivalent
OpenScop representation. As an example, let us consider the
following matrix-multiply kernel:

@example
#pragma scop
if (N > 0) @{
  for (i = 0; i < N; i++) @{
    for (j = 0; j < N; j++) @{
      C[i][j] = 0.0;
      for (k = 0; k < N; k++)
        C[i][j] = C[i][j] + A[i][k] * B[k][j];
    @}
  @}
@}
@end example

The Clan@footnote{@url{http://www.lri.fr/~bastoul/development/clan/}}
tool may be used to translate this code part to an OpenScop
representation automatically. The @code{#pragma scop} is used here for
Clan, but some other tool may not need it. Here is the result of the
translation to an OpenScop textual representation.

@sp 1
@center @strong{DON'T PANIC}
@sp 1

@noindent Explanations will follow and it is not
as cryptic as it seems to be !
@sp 1

@example
<OpenScop>

# =============================================== Global
# Backend Language
C

# Context
CONTEXT
1 3 0 0 0 1
   1    1   -1    ## N-1 >= 0

# Parameter names are provided
1
# Parameter names
N 

# Number of statements
2

# =============================================== Statement 1
# Number of relations describing the statement
3

# ----------------------------------------------  1.1 Domain
DOMAIN
4 5 2 0 0 1
# e/i   i    j    N    1
   1    1    0    0    0    ## i >= 0
   1   -1    0    1   -1    ## -i+N-1 >= 0
   1    0    1    0    0    ## j >= 0
   1    0   -1    1   -1    ## -j+N-1 >= 0

# ----------------------------------------------  1.2 Scattering
SCATTERING
5 10 5 2 0 1
# e/i  s1   s2   s3   s4   s5    i    j    N    1 
   0   -1    0    0    0    0    0    0    0    0    ## s1 = 0
   0    0   -1    0    0    0    1    0    0    0    ## s2 = i
   0    0    0   -1    0    0    0    0    0    0    ## s3 = 0
   0    0    0    0   -1    0    0    1    0    0    ## s4 = j
   0    0    0    0    0   -1    0    0    0    0    ## s5 = 0

# ----------------------------------------------  1.3 Access
WRITE
3 8 3 2 0 1
# e/i  Arr  [1]  [2]   i    j    N    1
   0   -1    0    0    0    0    0    1    ## C
   0    0   -1    0    1    0    0    0    ##  [i]
   0    0    0   -1    0    1    0    0    ##     [j]

# ----------------------------------------------  1.4 Body
# Statement body is provided
1
# Original iterator names
i j 
# Statement body
C[i][j] = 0.0;


# =============================================== Statement 2
# Number of relations describing the statement
5

# ----------------------------------------------  2.1 Domain
DOMAIN
6 6 3 0 0 1
# e/i   i    j    k    N    1
   1    1    0    0    0    0    ## i >= 0
   1   -1    0    0    1   -1    ## -i+N-1 >= 0
   1    0    1    0    0    0    ## j >= 0
   1    0   -1    0    1   -1    ## -j+N-1 >= 0
   1    0    0    1    0    0    ## k >= 0
   1    0    0   -1    1   -1    ## -k+N-1 >= 0

# ----------------------------------------------  2.2 Scattering
SCATTERING
7 13 7 3 0 1
# e/i  s1   s2   s3   s4   s5   s6   s7    i    j    k    N    1
   0   -1    0    0    0    0    0    0    0    0    0    0    0   ## s1 = 0
   0    0   -1    0    0    0    0    0    1    0    0    0    0   ## s2 = i
   0    0    0   -1    0    0    0    0    0    0    0    0    0   ## s3 = 0
   0    0    0    0   -1    0    0    0    0    1    0    0    0   ## s4 = j
   0    0    0    0    0   -1    0    0    0    0    0    0    1   ## s5 = 1
   0    0    0    0    0    0   -1    0    0    0    1    0    0   ## s6 = k
   0    0    0    0    0    0    0   -1    0    0    0    0    0   ## s7 = 0

# ----------------------------------------------  2.3 Access
RDWR
3 9 3 3 0 1
# e/i  Arr  [1]  [2]   i    j    k    N    1
   0   -1    0    0    0    0    0    0    1    ## C
   0    0   -1    0    1    0    0    0    0    ##  [i]
   0    0    0   -1    0    1    0    0    0    ##     [j]

READ
3 9 3 3 0 1
# e/i  Arr  [1]  [2]   i    j    k    N    1
   0   -1    0    0    0    0    0    0    2    ## A
   0    0   -1    0    1    0    0    0    0    ##  [i]
   0    0    0   -1    0    0    1    0    0    ##     [k]

READ
3 9 3 3 0 1
# e/i  Arr  [1]  [2]   i    j    k    N    1
   0   -1    0    0    0    0    0    0    3    ## B
   0    0   -1    0    0    0    1    0    0    ##  [k]
   0    0    0   -1    0    1    0    0    0    ##     [j]

# ----------------------------------------------  2.4 Body
# Statement body is provided
1
# Original iterator names
i j k 
# Statement body
C[i][j] = C[i][j] + A[i][k] * B[k][j];

</OpenScop>
@end example


We will not describe here precisely the structure and the components of this
output, this is described in depth in a further section
(@pxref{OpenScop Core Part File Format Specification}). This format
has been designed to be a possible input or output file format of most of
polyhedral compilation tools. If you read the description of the polyhedral
representation of programs, you should already feel familiar with this file
format (@pxref{Polyhedral Representation}).


@c %/*************************************************************************
@c % *                 CORE PART FILE FORMAT SPECIFICATION                   *
@c % *************************************************************************/
@node OpenScop Core Part File Format Specification
@subsection OpenScop Core Part File Format Specification

The following grammar describes the structure of the first part of the
OpenScop file format where terminals are preceeded by "_". There can be
at most one terminal per line in the file. Each
relevant part will be explained in more details momentarily:

@example
OpenScop            ::= Start_tag Data End_tag
Start_tag           ::= "<OpenScop>"
End_tag             ::= "</OpenScop>"
Data                ::= Context Statements
Context             ::= Language Parameter_Domain Parameter_list
Statements          ::= Nb_statements Statement_list
Statement_list      ::= Statement Statement_list | (void)
String_list         ::= _String   String_list    | (void)
Relation_list       ::= _Relation Relation_list  | (void)
Statement           ::= Statement_relations Body
Body                ::= "0" | "1" Iterator_list Body_text
Parameter_list      ::= "0" | "1" String_list
Statement_relations ::= Nb_relations Relation_List 
Parameter_domain    ::= _Relation
Language            ::= _String
Body_text           ::= _Text_line
Nb_Relations        ::= _Integer
@end example


@itemize @bullet
@item  @samp{Context} represents the global information of the SCoP. It
       consists on the target language, the global constraints on the
       parameters and optionally the parameter names which may be necessary
       for the code generation process. The constraints on the parameters
       are represented as a relation (@pxref{Context Domain Representation})
       with zero input and zero output dimensions. The parameter name
       list starts with an integer: a @samp{0} means that we don't provide
       the names while a @samp{1} means that the name list
       is provided afterwards. The ordering of the names in the list is
       meaningful: it must reflect the ordering used in the relation.
@item  @samp{Statements} represents the information about the statements.
       @samp{Nb_statements} is the number of statements in the SCoP,
       i.e. the number of @samp{Statement} items in the @samp{Statement_list}.
       @samp{Statement} represents the information on a given statement.
       To each statement is associated a list of relations and,
       optionaly, a body. The list of relations may include
       one iteration domain (@pxref{Iteration Domain Representation}),
       one scattering relation (@pxref{Scattering Relation Representation})
       and several access relations (@pxref{Access Relation Representation}).
       There is no mandatory ordering, but for consistency reason it would
       be much appreciated that iteration domain comes first (if present)
       then scattering (if present), then accesses (if present).
       The statement body is an optional information. It is preceded by a
       boolean which precises whether it is provided or not. It is made of two
       parts: first, the list of surrounding loop counters in the original
       program and second, the text string of the statement. This
       representation allows to apply the substitution of the original
       iterators with new iterators in the target program.
@end itemize

The main parts of the OpenScop format (namely, iteration domains,
scattering and access information) are detailed in the next subsections.

@menu
* Relation Representation::
* Iteration Domain Representation::
* Context Domain Representation::
* Scattering Relation Representation::
* Access Relation Representation::
@end menu

@node Relation Representation
@subsubsection Relation Representation

As shown by the grammar, the input file describes the various pieces of
information based on strings, integers and @emph{relations}.
Each relation is defined as a union of convex relations, each in turn is
described by a set of constraints in an extended PolyLib format (@pxref{Wil93}).
The number of elements in the union is given by an integer
on a separate line, optionally followed by a comment starting with @samp{#}.
This number of elements can be omitted when there is only one element.
Each element in the union has the following syntax:

@enumerate
@item Some optional comment lines beginning with @samp{#}.
@item A line with the type of the relation, possibly followed by comments.
      The type can be one of the following:
      @itemize @bullet
      @item @code{UNDEFINED}: generic relation,
      @item @code{CONTEXT}: for context information,
      @item @code{DOMAIN}: for iteration domains,
      @item @code{SCATTERING}: for scattering relation,
      @item @code{READ}: for read accesses,
      @item @code{WRITE}: for write accesses,
      @item @code{MAY_WRITE}: for may-write accesses,
      @end itemize
@item A line with 6 numbers, possibly followed by comments:
      @enumerate
      @item the number of rows of the constraint matrix,
      @item the number of columns of the constraint matrix,
      @item the number of @emph{output dimensions},
      @item the number of @emph{input dimension},
      @item the number of @emph{local dimensions}
            (existentially quantified dimensions),
      @item the number of @emph{parameters}.
      @end enumerate
      The sum of the last four numbers should be equal to the number of columns
      minus two. The remaining two columns are the equality/inequality
      indicator and the constant term. The number of parameters should be the
      same for all relations in the entire OpenScop file or data structure.
@item The constraint rows. Each row corresponds to a constraint the
      relation has to satisfy. Each row must be on a single line and is possibly
      followed by comments. The constraint is an equality @math{p(x) = 0} if the
      first element is 0, an inequality  @math{p(x) \geq 0} if the first element
      is 1. The next elements are the coefficients of the output dimensions,
      followed by coefficients of the input dimensions, the existentially
      quantified dimensions and finally the parameters.
      The last element is the constant term.
@end enumerate

This representation is the basis for several purposes. Examples for
iteration domains (@pxref{Iteration Domain Representation}), scattering
relations (@pxref{Scattering Relation Representation}) and
access relations (@pxref{Access Relation Representation}) are provided in
further sections.

@node Iteration Domain Representation
@subsubsection Iteration Domain Representation

Iteration domain represents the set of instances of the corresponding statement.
OpenScop iteration domains are represented as relations with the following
conventions:
@itemize @bullet
@item the type is @code{DOMAIN},
@item there is 0 input dimension,
@item loop iterators correspond to output dimensions.
@end itemize

@noindent For instance, assuming that @samp{i}, @samp{j} and @samp{k} are the loop
iterators and @samp{M} and @samp{N} are the parameters, the domain defined by
the following constraints :

@tex
$$
\hbox{$ \cases{ -i     + M &$\geq 0$\cr
                    -j + N &$\geq 0$\cr
                 i + j - k &$\geq 0$}$}
$$
@end tex
@ifnottex
@example
@group
   -i + M >= 0
   -j + N >= 0
i + j - k >= 0
@end group
@end example
@end ifnottex

@noindent can be written in the input file as follows:

@example
@group
# This is an iteration domain
DOMAIN
1 # Number of relations in the union
3 7 3 0 0 2                  # 3 rows, 7 cols: 3 output dims and 2 params
# e/i  i   j   k   M   N   1
   1  -1   0   0   1   0   0 #    -i + M >= 0
   1   0  -1   0   0   1   0 #    -j + N >= 0
   1   1   1  -1   0   0   0 # i + j - k >= 0
@end group
@end example

@noindent Equivalently, it can be written in the following way as the number
of relations in the union can be omitted if it is 1:

@example
@group
# This is an iteration domain
DOMAIN
3 7 3 0 0 2                  # 3 rows, 7 cols: 3 output dims and 2 params
# e/i  i   j   k   M   N   1
   1  -1   0   0   1   0   0 #    -i + M >= 0
   1   0  -1   0   0   1   0 #    -j + N >= 0
   1   1   1  -1   0   0   0 # i + j - k >= 0
@end group
@end example

@noindent As an example for unions, let us consider the following pseudo-code:

@example
@group
for (i = 1; i <= N; i++) @{
  if ((i >= M) || (i <= 2*M))
    S1(i);
@}
@end group
@end example

@noindent The iteration domain of @samp{S1} can be divided into two
relations and written in the OpenScop file as follows:

@example
@group
# This is an iteration domain
DOMAIN
2 # Number of relations in the union
# Union part No.1
3 5 1 0 0 2          # 3 rows, 5 cols: 1 output dim and 2 params
# e/i  i   M   N   1
   1   1   0   0  -1 #  i >= 1
   1  -1   0   1   0 #  i <= N
   1   1  -1   0   0 #  i >= M
# Union part No.2
3 5 1 0 0 2          # 3 rows, 5 cols: 1 output dim and 2 params
# e/i  i   M   N   1
   1   1   0   0  -1 #  i >= 1
   1  -1   0   1   0 #  i <= N
   1  -1   2   0   0 #  i <= 2*M
@end group
@end example

@noindent As an example for local dimensions (existentially quantified
dimensions), let us consider the following pseudo-code:

@example
@group
for (i = 1; i <= N; i++) @{
  if ((i % 2) == 0)
    S1(i);
@}
@end group
@end example

@noindent The iteration domain of @samp{S1} is composed of all even
integer values between 1 and N. The "divisible by two" constraint can
be expressed as follows: there exists an integer @samp{ld} such that
@samp{i = 2*ld}. We encode this thanks to a new local dimension:

@example
@group
# This is an iteration domain
DOMAIN
3 5 1 0 1 1          # 3 rows, 5 cols: 1 output dim, 1 local dim, 1 param
# e/i  i  ld   N   1
   0   1  -2   0   0 #  i = 2*ld
   1   1   0   0   1 #  i >= 1
   1  -1   0   1   0 #  i <= N
@end group
@end example


@node Context Domain Representation
@subsubsection Context Domain Representation

The context domain is a particular case of iteration domain
(@pxref{Iteration Domain Representation}) where there are only
constraints about parameters (no loop iterators). Hence it is the same
as an iteration domain, with the following conventions:
@itemize @bullet
@item the type is @code{CONTEXT},
@item there is 0 input dimension,
@item there is 0 output dimension.
@end itemize


@node Scattering Relation Representation
@subsubsection Scattering Relation Representation

Scattering relation maps an iteration domain to a logical time and/or
space (and/or) anything.
OpenScop scattering information is represented as relations
(@pxref{Relation Representation}) with the following conventions:

@itemize @bullet
@item the type is @code{SCATTERING},
@item output dimensions correspond to scattering dimensions,
@item loop iterators correspond to input dimensions.
@end itemize

As an example of a scattering relation and
assuming that @samp{i}, @samp{j} and @samp{k} are the loop
iterators and @samp{M} and @samp{N} are the parameters, take for instance:
@tex
$\theta_{S}(i,j,k) = (j+2,3*i+j,k+N+1).$
@end tex
@ifnottex
@example
T_@{S@}(i,j,k) = (j+2,3*i+j,k+N+1).
@end example
@end ifnottex
We can represent it in the following way:

@example
@group
# A scattering relation
SCATTERING
# 3 rows, 10 columns: 3 scattering dimensions, 3 iterators, 2 parameters
3 10 3 3 0 2
# e/i s1  s2  s3   i   j   k   M   N   1
   0  -1   0   0   0   1   0   0   0   2 # s1 = j+2
   0   0  -1   0   3   1   0   0   0   0 # s2 = 3*i+j
   0   0   0  -1   0   0   1   0   1   1 # s3 = k+N+1
@end group
@end example

@node Access Relation Representation
@subsubsection Access Relation Representation

Access relation maps an iteration domain to an array space.
Each array accessed in the SCoP has a unique identification number.
OpenScop relation information is represented as relations
(@pxref{Relation Representation}) with the following conventions:

@itemize @bullet
@item the type is one of the following:
      @itemize @bullet
      @item @code{READ}, for read accesses,
      @item @code{WRITE}, for write accesses,
      @item @code{MAY_WRITE}, for may write accesses,
      @end itemize
@item output dimensions correspond to the array identifier and dimensions,
@item the first output dimension corresponds to the array identifier,
@item the (i+1)th output dimension corresponds to the ith array dimension (i>1),
@item loop iterators correspond to input dimensions.
@end itemize

As an example of a scattering relation and
assuming that @samp{i}, @samp{j} and @samp{k} are the loop
iterators and @samp{M} and @samp{N} are the parameters, let us consider
the array access @code{A[2*i+j][j][i+N]} (the identifier of @code{A} is 42),
and let us suppose this is a read access. Its representation would be the
following:

@example
@group
# A read access relation
READ
# 4 rows, 11 columns: 4 array dimensions, 3 iterators, 2 parameters
4 11 4 3 0 2
# e/i Arr [1] [2] [3]  i   j   k   M   N   1
   0  -1   0   0   0   0   0   0   0   0  42   # A
   0   0  -1   0   0   2   1   0   0   0   0   #  [2*i+j]
   0   0   0  -1   0   0   1   0   0   0   0   #         [j]
   0   0   0   0  -1   1   0   0   0   1   0   #            [i+N]
@end group
@end example

To understand this representation, consider that OpenScop accesses
are general memory accesses and not array accesses. The memory is
seen as a big array @code{Mem} while usual array names correspond to
the first dimension. Hence our example translates to @code{Mem[42][2*i+j][j][i+N]}.

Unions of access relations are allowed. In this case, each union part must
refer at the same array identifier, and the number of dimensions must be
consistent.

@c %/*************************************************************************
@c % *                 CORE PART DATA STRUCTURE SPECIFICATION                *
@c % *************************************************************************/
@node OpenScop Core Part Data Structure Specification
@subsection OpenScop Core Part Data Structure Specification

The OpenScop specification offers a small set of C data structures devoted to
represent a SCoP in memory in a convenient way. Using them in some tool or
library may greatly facilitate its interaction with other tools or libraries
which rely on this representation as well. Every field may not be useful for
a given tool or library. A general rule for all the data structure is
that a @code{NULL} pointer or a -1 integer value means the information is
not present. Contrary to engineering time, memory is cheap today, so it's much
probably not a big deal that some fields are left empty. Every field may not
be enough for a given tool or library. In this case it is much recommended
to provide a new extension which may be reused by other users
(@pxref{Extension Part}).

Each tool or library may have its own implementation of the OpenScop
data structures. The type names should not be the same as those provided
as an example here (they correspond to the OpenScop Library implementation).
The names of the fields, and their ordering, should however be the same. In this
way, the interaction between tools and libraries should be as simple as a cast.

Before reading at the OpenScop data structures, it is much recommended to
read at the OpenScop file format description, as it is quite close to this
representation (@pxref{OpenScop Core Part File Format Specification}).

@menu
* osl_relation_t::
* osl_relation_list_t::
* osl_interface_t::
* osl_generic_t::
* osl_statement_t::
* osl_scop_t::
@end menu

@node osl_relation_t
@subsubsection osl_relation_t

@example
@group
struct osl_relation @{
  int type;                   /* What this relation is encoding */ 
  int precision;              /* Precision of the matrix elements */ 
  int nb_rows;                /* Number of rows */
  int nb_columns;             /* Number of columns */
  int nb_output_dims;         /* Number of output dimensions */
  int nb_input_dims;          /* Number of input dimensions */
  int nb_local_dims;          /* Number of local dimensions */
  int nb_parameters;          /* Number of parameters */
  void ** m;                  /* Matrix of constraints */
  struct osl_relation * next; /* Next relation in the union */
@};
typedef struct osl_relation   osl_relation_t;
typedef struct osl_relation * osl_relation_p;
@end group
@end example

@noindent The @code{osl_relation_t} structure stores a part of an
union of relations. A union of relation is a @code{NULL}-terminated
linked list of union parts (@code{next} field). The @code{type} field
may provide some information about what the relation is encoding:
@itemize @bullet
@item -1: undefined (@code{OSL_UNDEFINED}),
@item 2: context domain (@code{OSL_TYPE_CONTEXT}),
@item 3: iteration domain (@code{OSL_TYPE_DOMAIN}),
@item 4: scattering relation (@code{OSL_TYPE_SCATTERING}),
@item 6: read access relation (@code{OSL_TYPE_READ}),
@item 7: write access relation (@code{OSL_TYPE_WRITE}),
@item 8: may write access relation (@code{OSL_TYPE_MAY_WRITE}),
@end itemize
The various numbers provide the details on the relation itself
(@pxref{Relation Representation}) while the @code{m} field points to
the constraint matrix. The precision of the constraint matrix elements is
provided by the @code{precision} field. It can take the following
values:
@itemize @bullet
@item 32: 32 bits precision, elements are @code{long int}
      (@code{OSL_PRECISION_SP}),
@item 64: 64 bits precision, elements are @code{long long int}
      (@code{OSL_PRECISION_DP}),
@item 0: multiple precision, elements are GNU GMP Library's
      @code{mpz_t} (@code{OSL_PRECISION_MP}).
@end itemize

@node osl_relation_list_t
@subsubsection osl_relation_list_t

@example
@group
struct osl_relation_list @{
  osl_relation_p elt;              /* Element of the list */
  struct osl_relation_list * next; /* Next element of the list */
@};
typedef struct osl_relation_list   osl_relation_list_t;
typedef struct osl_relation_list * osl_relation_list_p;
@end group
@end example

@noindent The @code{osl_relation_list_t} structure is a @code{NULL}-terminated
linked list of @code{osl_relation_t} data structures.
@code{elt} is a relation element of the list and @code{next} is the pointer to
the next element of the list.

@node osl_interface_t
@subsubsection osl_interface_t

@example
@group
typedef void   (*osl_idump_f) (FILE *, void *, int);
typedef char * (*osl_sprint_f)(void *);
typedef void * (*osl_sread_f) (char *);
typedef void * (*osl_malloc_f)();
typedef void   (*osl_free_f)  (void *);
typedef void * (*osl_clone_f) (void *);
typedef int    (*osl_equal_f) (void *, void *);

struct osl_interface @{
  char * URI;                  /* Unique interface identifier string */
  osl_idump_f  idump;          /* Pointer to the idump function */
  osl_sprint_f sprint;         /* Pointer to the sprint function */
  osl_sread_f  sread;          /* Pointer to the sread function */
  osl_malloc_f malloc;         /* Pointer to the malloc function */
  osl_free_f   free;           /* Pointer to the free function */
  osl_clone_f  clone;          /* Pointer to the clone function */
  osl_equal_f  equal;          /* Pointer to the equal function */
  struct osl_interface * next; /* Next interface in the list */
@};
typedef struct osl_interface   osl_interface_t;
typedef struct osl_interface * osl_interface_p;
@end group
@end example

@noindent The @code{osl_interface_t} structure represents a
node in a @code{NULL}-terminated list of interfaces. Each node stores the
@emph{interface} of a generic OpenScop object, i.e., its unique name
(@code{URI}) and the function pointers to all the base functions it has
to provide. Extension providers will find information relative to those
functions in the OpenScop Library description (@pxref{Base Functions})
and the section dedicated to writing extensions
(@pxref{Extension Development}).

@node osl_generic_t
@subsubsection osl_generic_t

@example
@group
struct osl_generic @{
  void * data;               /* Pointer to some data. */
  osl_interface_p interface; /* Interface to work with the data. */
  struct osl_generic * next; /* Pointer to the next generic. */
@};
typedef struct osl_generic   osl_generic_t;
typedef struct osl_generic * osl_generic_p;
@end group
@end example

@noindent The @code{osl_generic_t} structure represents a node in a
@code{NULL}-terminated list of generic elements. It stores some data
and operations with no pre-defined type. The information is accessible
through the @code{data} pointer while the type and operations are
accessible through the @code{interface} pointer. It is used to represent
data that are allowed to differ in implementations, such as symbols and
extensions.

@node osl_statement_t
@subsubsection osl_statement_t

@example
@group
struct osl_statement @{
  osl_relation_p domain;       /* Iteration domain */
  osl_relation_p scattering;   /* Scattering relation */
  osl_relation_list_p access;  /* List of array access relations */
  osl_generic_p iterators;     /* Original iterators */
  osl_generic_p body;          /* Original statement body */
  void * usr;                  /* A user-defined field */
  struct osl_statement * next; /* Next statement in the list */
@};
typedef struct osl_statement   osl_statement_t;
typedef struct osl_statement * osl_statement_p;
@end group
@end example

@noindent The @code{osl_statement_t} structure represents a node
in a @code{NULL}-terminated linked list of statements. Each node contains the
useful information for a given statement to process it within a polyhedral
framework. The order in the list may matter for naming conventions
(e.g. "S1" for the first statement in the list). The iteration domain
and the scattering are represented using an @code{osl_relation_p}
structure while the accesses are using a list of
relations: one for each memory access in the statement.
The @code{body} and @code{iterators} provide information about
the statement body. Since they are generic types, the specification
is not strict about how they are used. The recommendation is that the
@code{body} field should contain the information about the statement
expression in the original program. The @code{iterators}
field should contain the information about the iterators surrounding
the original statement in the original program. The rationale behind this
is the code generation step should replace the original iterators
from the original statement expression with the generated iterators.
It is also possible to use the @code{usr} field, but it has to be
totally managed by the user.

@node osl_scop_t
@subsubsection osl_scop_t
@example
@group
struct osl_scop @{
  int version;                 /* Version of the data structure */
  char * language;             /* Target language */
  osl_relation_p context;      /* Constraints on the parameters */
  osl_generic_p parameters;    /* Information about parameters */
  osl_statement_p statement;   /* Statement list */
  osl_interface_p registry;    /* Registered extension interfaces */
  osl_generic_p extension;     /* Extension list */
  void * usr;                  /* A user-defined field */
  struct osl_scop * next;      /* Next scop in the list */
@};
typedef struct osl_scop   osl_scop_t;
typedef struct osl_scop * osl_scop_p;
@end group
@end example

@noindent @code{osl_scop_t} represents a node in a
@code{NULL}-terminated list of scops. It stores the useful informations
of a static control part of a program to process it within a polyhedral
framework. To prepare OpenScop specification evolution, the @code{version}
field tells the version of the data structure. It should be set to 1 for
now (and hopefully a very, very, long time).
It contains the informations about the context: the target language
in the @code{language} field, the constraints on the
global parameters in the @code{context} field and the parameters
in the @code{parameters} field. The parameter information is generic
and may be manipulated during the code generation step. 
Finally, it contains the list of statements @code{statement}, the list
of registered extension interfaces @code{registry} and the list of
extentions @code{extension}.
It is also possible to use the @code{usr} field, but it has to be
totally managed by the user.

As an example, let us consider again the matrix multiply program
(@pxref{Preliminary Example}).
The next figure gives a possible representation in memory for this
SCoP thanks to the OpenScop data structures (it has been actually printed
by the @code{osl_scop_dump} function), note that symbols like
parameters, original iterators and statement expression are represented
with an @code{osl_strings_t} which does not belong to the
specification but to the OpenScop Library implementation:

@c @smallexample
@example
+-- osl_scop_t
|    |    
|    Version: 1
|    |    
|    Language: C
|    |    
|    +-- osl_relation_t (CONTEXT, 32 bits)
|    |    1 3 0 0 0 1
|    |    [   1   1  -1 ]
|    |    
|    +-- osl_generic_t
|    |    |    
|    |    +-- osl_interface_t: URI = strings
|    |    |    
|    |    +-- osl_strings_t: N
|    |    |    
|    |    
|    +-- osl_statement_t (S1)
|    |    |    
|    |    +-- osl_relation_t (DOMAIN, 32 bits)
|    |    |    4 5 2 0 0 1
|    |    |    [   1   1   0   0   0 ]
|    |    |    [   1  -1   0   1  -1 ]
|    |    |    [   1   0   1   0   0 ]
|    |    |    [   1   0  -1   1  -1 ]
|    |    |    
|    |    +-- osl_relation_t (SCATTERING, 32 bits)
|    |    |    5 10 5 2 0 1
|    |    |    [   0  -1   0   0   0   0   0   0   0   0 ]
|    |    |    [   0   0  -1   0   0   0   1   0   0   0 ]
|    |    |    [   0   0   0  -1   0   0   0   0   0   0 ]
|    |    |    [   0   0   0   0  -1   0   0   1   0   0 ]
|    |    |    [   0   0   0   0   0  -1   0   0   0   0 ]
|    |    |    
|    |    +-- osl_relation_list_t
|    |    |    |    
|    |    |    +-- osl_relation_t (WRITE, 32 bits)
|    |    |    |    3 8 3 2 0 1
|    |    |    |    [   0  -1   0   0   0   0   0   1 ]
|    |    |    |    [   0   0  -1   0   1   0   0   0 ]
|    |    |    |    [   0   0   0  -1   0   1   0   0 ]
|    |    |    |    
|    |    |    
|    |    +-- osl_generic_t
|    |    |    |    
|    |    |    +-- osl_interface_t: URI = strings
|    |    |    |    
|    |    |    +-- osl_strings_t: i j
|    |    |    |    
|    |    |    
|    |    +-- osl_generic_t
|    |    |    |    
|    |    |    +-- osl_interface_t: URI = strings
|    |    |    |    
|    |    |    +-- osl_strings_t: C[i][j] = 0.0;
|    |    |    |    
|    |    |    
|    |    V
|    |  osl_statement_t (S2)
|    |    |    
|    |    +-- osl_relation_t (DOMAIN, 32 bits)
|    |    |    6 6 3 0 0 1
|    |    |    [   1   1   0   0   0   0 ]
|    |    |    [   1  -1   0   0   1  -1 ]
|    |    |    [   1   0   1   0   0   0 ]
|    |    |    [   1   0  -1   0   1  -1 ]
|    |    |    [   1   0   0   1   0   0 ]
|    |    |    [   1   0   0  -1   1  -1 ]
|    |    |    
|    |    +-- osl_relation_t (SCATTERING, 32 bits)
|    |    |    7 13 7 3 0 1
|    |    |    [   0  -1   0   0   0   0   0   0   0   0   0   0   0 ]
|    |    |    [   0   0  -1   0   0   0   0   0   1   0   0   0   0 ]
|    |    |    [   0   0   0  -1   0   0   0   0   0   0   0   0   0 ]
|    |    |    [   0   0   0   0  -1   0   0   0   0   1   0   0   0 ]
|    |    |    [   0   0   0   0   0  -1   0   0   0   0   0   0   1 ]
|    |    |    [   0   0   0   0   0   0  -1   0   0   0   1   0   0 ]
|    |    |    [   0   0   0   0   0   0   0  -1   0   0   0   0   0 ]
|    |    |    
|    |    +-- osl_relation_list_t
|    |    |    |    
|    |    |    +-- osl_relation_t (WRITE, 32 bits)
|    |    |    |    3 9 3 3 0 1
|    |    |    |    [   0  -1   0   0   0   0   0   0   1 ]
|    |    |    |    [   0   0  -1   0   1   0   0   0   0 ]
|    |    |    |    [   0   0   0  -1   0   1   0   0   0 ]
|    |    |    |    
|    |    |    V
|    |    |  osl_relation_list_t
|    |    |    |    
|    |    |    +-- osl_relation_t (READ, 32 bits)
|    |    |    |    3 9 3 3 0 1
|    |    |    |    [   0  -1   0   0   0   0   0   0   1 ]
|    |    |    |    [   0   0  -1   0   1   0   0   0   0 ]
|    |    |    |    [   0   0   0  -1   0   1   0   0   0 ]
|    |    |    |    
|    |    |    V
|    |    |  osl_relation_list_t
|    |    |    |    
|    |    |    +-- osl_relation_t (READ, 32 bits)
|    |    |    |    3 9 3 3 0 1
|    |    |    |    [   0  -1   0   0   0   0   0   0   2 ]
|    |    |    |    [   0   0  -1   0   1   0   0   0   0 ]
|    |    |    |    [   0   0   0  -1   0   0   1   0   0 ]
|    |    |    |    
|    |    |    V
|    |    |  osl_relation_list_t
|    |    |    |    
|    |    |    +-- osl_relation_t (READ, 32 bits)
|    |    |    |    3 9 3 3 0 1
|    |    |    |    [   0  -1   0   0   0   0   0   0   3 ]
|    |    |    |    [   0   0  -1   0   0   0   1   0   0 ]
|    |    |    |    [   0   0   0  -1   0   1   0   0   0 ]
|    |    |    |    
|    |    |    
|    |    +-- osl_generic_t
|    |    |    |    
|    |    |    +-- osl_interface_t: URI = strings
|    |    |    |    
|    |    |    +-- osl_strings_t: i j k
|    |    |    |    
|    |    |    
|    |    +-- osl_generic_t
|    |    |    |    
|    |    |    +-- osl_interface_t: URI = strings
|    |    |    |    
|    |    |    +-- osl_strings_t: C[i][j] = C[i][j] + A[i][k]*B[k][j];
|    |    |    |    
|    |    |    
|    |    
|    +-- NULL interface
|    |    
|    +-- NULL generic
|    |    
|    
@end example
@c @end smallexample


@c %/*************************************************************************
@c % *                           EXTENSION PART                              *
@c % *************************************************************************/

@node Extension Part
@section Extension Part

The core part of the OpenScop representation embeds what is strictly
necessary to build a complete source-to-source polyhedral framework.
However it may not be enough. Hence, OpenScop offers a very flexible
extension part. Actually, the only constraint to build an extension is
to request the OpenScop maintainer for a unique extension name: its URI
(ask the maintainer through the OpenScop mailing list
@email{openscop-development@@googlegroups.com}).

The policy to support extensions is the following and is pretty simple: an
OpenScop implementation is not required to support any extension. If it
is processing an OpenScop file or data structure which contains an
extension which is not supported, it must (1) warn the user with the 
mention of the URI of the non-supported extension
and (2) ignore this extension.

Extensions in an OpenScop file are provided after the core part, without
any specific order. Each extension is delimited using
XML-like tags corresponding to its URI (e.g., if the extension has the URI
@code{foo}, the begin tag is @code{<foo>} and the end tag is @code{</foo>}).
There is no specification or preferred way to write the extension body.
Extensions in an OpenScop data structure must be accessible through one
pointer. This pointer will be stored in the @code{data}
field of an @code{osl_generic_t} container. There must be only
one extension with the same URI in an OpenScop file or data structure.

Extension writers may write a short documentation about their extension to
be added to this document. For consistency reason, this
documentation should comply to the documentation of the
@code{comment} option (@pxref{Comment Extension}). To describe the
file format, it is allowed to reuse the existing rules and terminals
present in the OpenScop core part file format without defining them
(@pxref{OpenScop Core Part File Format Specification}). By sending a
documentation, you accept it to be added to this document. In
particular, the sender fully accepts the license and copyright notice.

@menu
* Comment Extension::
* Arrays Extension::
* Lines Extension::
* Irregular Extension::
@end menu

@c ---------------------------------------------------------------------------

@node Comment Extension
@subsection Comment Extension

@itemize @bullet
@item URI: @code{comment}.
@item Author: C@'edric Bastoul <cedric.bastoul@@u-psud.fr>.
@item Purpose: the @code{comment} extension stores a textual string.
@end itemize

@menu
* Comment Extension File Format::
* Comment Extension Data Structure Format::
@end menu

@node Comment Extension File Format
@subsubsection Comment Extension File Format

The @code{comment} extension file format respects the following
grammar:
@example
Comment             ::= Begin_tag Body End_tag
Body                ::= _Text
Begin_tag           ::= "<comment>"
End_tag             ::= "</comment>"
@end example

@noindent An example of textual @code{comment} extension is the following:
@example
@group
<comment>
This is a comment string.
</comment>
@end group
@end example

@node Comment Extension Data Structure Format
@subsubsection Comment Extension Data Structure Format

The @code{comment} extension data structure is the following:
@example
@group
struct osl_comment @{
  char * comment;  /* Comment message as a 0-terminated string */
@};
typedef struct osl_comment   osl_comment_t;
typedef struct osl_comment * osl_comment_p;
@end group
@end example

@c ---------------------------------------------------------------------------


@node Arrays Extension
@subsection Arrays Extension

@itemize @bullet
@item URI: @code{arrays}.
@item Author: C@'edric Bastoul <cedric.bastoul@@u-psud.fr>.
@item Purpose: the @code{arrays} extension provides a set of textual array
names corresponding to the array identifiers used in the access relations.
@end itemize

@menu
* Arrays Extension File Format::
* Arrays Extension Data Structure Format::
@end menu

@node Arrays Extension File Format
@subsubsection Arrays Extension File Format

The @code{arrays} extension file format respects the following
grammar:
@example
Arrays              ::= Begin_tag Body End_tag
Body                ::= Nb_items Item_list
Item_List           ::= Item Item_list | (void)
Item                ::= Identifier Name
Nb_items            ::= _Integer
Identifier          ::= _Integer
Name                ::= _String
Begin_tag           ::= "<arrays>"
End_tag             ::= "</arrays>"
@end example

@noindent The number of array names is provided on the first line,
then each following line contains a pair identifier-name.
For instance, the following example is a correct textual @code{arrays}
extension. It corresponds to the array names of the preliminary example
(@pxref{Preliminary Example}):

@example
@group
<arrays>
# Number of array names:
3
1 C # Identifier 1 corresponds to array name "C" 
3 B # Identifier 3 corresponds to array name "B" 
2 A # Identifier 2 corresponds to array name "A" 
</arrays>
@end group
@end example

@node Arrays Extension Data Structure Format
@subsubsection Arrays Extension Data Structure Format

The @code{arrays} extension data structure is the following:

@example
@group
struct osl_arrays @{
  int nb_names;      /* Number of names */
  int  *  id;        /* Array of nb_names identifiers */
  char ** names;     /* Array of nb_names names */
@};
typedef struct osl_arrays   osl_arrays_t;
typedef struct osl_arrays * osl_arrays_p;
@end group
@end example

@noindent Each name has a name string and an identifier: the ith name has name
string @code{names[i]} and identifier @code{id[i]}.


@c ---------------------------------------------------------------------------

@node Lines Extension
@subsection Lines Extension

@menu
* Lines Extension File Format::
* Lines Extension Data Structure Format::
@end menu

@node Lines Extension File Format
@subsubsection Lines Extension File Format

@node Lines Extension Data Structure Format
@subsubsection Lines Extension Data Structure Format

@c ---------------------------------------------------------------------------

@node Irregular Extension
@subsection Irregular Extension

@menu
* Irregular Extension File Format::
* Irregular Extension Data Structure Format::
@end menu


@node Irregular Extension File Format
@subsubsection Irregular Extension File Format

@node Irregular Extension Data Structure Format
@subsubsection Irregular Extension Data Structure Format

@c ---------------------------------------------------------------------------

@node History
@section History

OpenScop is a follow-up of Louis-No@"el Pouchet et al.'s ScopLib effort which
was itself based on C@'edric Bastoul et al.'s Clan tool. People involved in
OpenScop's genesis are:
@itemize @bullet
@item C@'edric Bastoul
@item Uday Bondhugula
@item Tobias Grosser
@item Louis-No@"el Pouchet
@item Sven Verdoolaege
@end itemize

@c %/*************************************************************************
@c % *                          OpenScop LIBRARY                             *
@c % *************************************************************************/

@node OpenScop Library
@chapter OpenScop Library

The OpenScop Library is an example implementation of the OpenScop specification.
Its API is not part of the OpenScop specification. 
It offers basic functionalities to manipulate the OpenScop data structures
(allocate, free, copy, dump, etc.) and file format (read, print, etc.).
The OpenScop Library is @emph{not} a polyhedral library. OpenScop is an
exchange format, and the OpenScop Library reflects this. 

It is a Free Software using the 3-clause BSD License.
Programmers should feel free to use
it or copy/paste its code in any project, Open Source or not@footnote{Closed
source projects should consider to provide some OpenScop file input
and output, so they can be incorporated to any OpenScop-based tool chain.}.

@menu
* Precision::
* Base Functions::
* Example of OpenScop Library Utilization::
* Installation::
* Documentation::
* Development::
@end menu

@node Precision
@section Precision

The OpenScop specification does not impose a specific type for the
constraint matrix elements. For a maximum flexibility, the OpenScop Library
offers an hybrid precision implementation. It supports 32 bits, 64 bits and
multiple precision (relying on GNU GMP) relations transparently. At relation
allocation time, users have two ways to set the precision. The first way is
to call an allocation function with a precision parameter. The second way is
to rely on the environment variable @code{OSL_PRECISION}.
The accepted values for this variable are @code{32} for 32 bits precision,
@code{64} for 64 bits precision and @code{0} for multiple precision. When this
variable is set, its value becomes the default precision for relation elements.
For instance, to ensure the OpenScop Library will use 64 bits precision
by default, the user may set: 
@example
export OSL_PRECISION=64
@end example
@noindent if his shell is, e.g., bash or
@example
setenv OSL_PRECISION 64
@end example
@noindent if his shell is, e.g., tcsh. The user should ad this line to
his .bashrc or .tcshrc (or whatever convenient file) to make this
setting permanent. 

@node Base Functions
@section Base Functions

The OpenScop Library provides, for each OpenScop data structure,
a set of functions devoted to basic manipulation, conversion
from file format to data structures and from data structures to
file format. The naming convention is consistent for all data
structures. Hence, the function prototypes differ only with the
name of the data structure. In the following, we will use the
generic term of @emph{structure} to refer at any OpenScop
data structure. For instance the
@code{osl_}@emph{structure}@code{_malloc()} function is a
generic name can be instantiated to
@code{osl_relation_malloc()} or
@code{osl_statement_malloc()} etc.

We present in this documentation only
the main functions. Many other utility functions are provided
to ease OpenScop format manipulation. The reader is invited to
refer at the technical documentation to learn everything about the
OpenScop Library.

@menu
* Dumping::
* Printing::
* Reading::
* Allocating::
* Deallocating::
* Cloning::
* Testing::
@end menu


@node Dumping
@subsection Dumping: osl_@emph{structure}_dump and idump 

@example
@group
void osl_@emph{structure}_dump(FILE * output, osl_@emph{structure}_p s);
void osl_@emph{structure}_idump(FILE * output, osl_@emph{structure}_p s, int i);
@end group
@end example

@noindent Each OpenScop data structure has a dumping functions
as shown above. Dumping means writing down the content of the data
structure pointed by @code{s} (and its fields recursively)
in a textual form to the
@code{output} file (the file, possibly @code{stdout}, has to be open
for writing). The textual form is not the OpenScop file format but
another representation closer to the internal representation in
memory and mainly intended for debugging purpose. The @code{idump}
function has an additional integer parameter which corresponds to
an indentation level.

@node Printing
@subsection Printing: osl_@emph{structure}_print

@example
@group
void osl_@emph{structure}_print(FILE * output, osl_@emph{structure}_p s);
@end group
@end example

@noindent Each OpenScop data structure has a pretty printing function
as shown above. It prints the content of the data
structure pointed by @code{s} (and its fields recursively)
according to the OpenScop file format
(@pxref{OpenScop Core Part File Format Specification}) to the
@code{output} file (the file, possibly @code{stdout}, has to be open
for writing).

@node Reading
@subsection Reading: osl_@emph{structure}_read

@example
@group
osl_@emph{structure}_p osl_@emph{structure}_read(FILE * input);
@end group
@end example

@noindent Each OpenScop data structure has a reading function
as shown above. It reads the content of an OpenScop
data structure written according to the OpenScop file format 
(@pxref{OpenScop Core Part File Format Specification}) from 
the @code{input} file (the file, possibly @code{stdin}, has to be open
for reading). It returns a pointer to a freshly allocated 
@code{osl_@emph{structure}_t} structure containing the
information.

@node Allocating
@subsection Allocating: osl_@emph{structure}_malloc

@example
@group
osl_@emph{structure}_p osl_@emph{structure}_malloc();
@end group
@end example

@noindent Each OpenScop data structure has a memory allocation function
as shown above (except one see below). It allocates the memory to store
the corresponding data structure, it initializes the pointer fields to
@code{NULL} and the integer fields to @code{OSL_UNDEFINED}
(@code{-1}) and it returns a pointer to the allocated space.

An exception to this base description is the
@code{osl_relation_malloc()} function which requires two
parameters: the number of rows and columns of the constraint
matrix (@pxref{Relation Representation}):

@example
@group
osl_relation_p osl_relation_malloc(int nb_rows, int nb_columns);
@end group
@end example

@noindent The precision of the relation elements will depend on the
@code{OSL_PRECISION} environment variable (@pxref{Precision}) if it is set,
or the maximum available precision if it is not set. Another allocation
function is provided to explicitly set a given precision:

@example
@group
osl_relation_p osl_relation_pmalloc(int precision,
                                    int nb_rows, int nb_columns);
@end group
@end example

@noindent The @code{precision} field may take the following values:
@itemize @bullet
@item @code{OSL_PRECISION_SP} for 32 bits precision,
@item @code{OSL_PRECISION_DP} for 64 bits precision,
@item @code{OSL_PRECISION_MP} for multiple precision,
@end itemize

@node Deallocating
@subsection Deallocating: osl_@emph{structure}_free

@example
@group
void osl_@emph{structure}_free(osl_@emph{structure}_p s);
@end group
@end example

@noindent Each OpenScop data structure has a memory deallocation function
as shown above. It recursively frees the memory allocated for the
structure pointed by @code{s}, i.e., internal structures are also freed.

@node Cloning
@subsection Cloning: osl_@emph{structure}_clone

@example
@group
osl_@emph{structure}_p osl_@emph{structure}_clone(osl_@emph{structure}_p s);
@end group
@end example

@noindent Each OpenScop data structure has a clone function
as shown above. It recursively copies the content of the
structure pointed by @code{s}, i.e., internal structures are also copied.
It returns a pointer to the clone of the structure pointed by @code{s}.

@node Testing
@subsection Testing: osl_@emph{structure}_equal

@example
@group
int osl_@emph{structure}_equal(osl_@emph{structure}_p s1, osl_@emph{structure}_p s2);
@end group
@end example

@noindent Each OpenScop data structure has a testing function
as shown above. It checks whether two pointers are referring to equivalent
structures (either by pointing to the same structure or to different
structures which contain the same information). It returns 1 if the
pointed structures are equivalent, 0 otherwise. This test is
@emph{content-based} and is intended for debugging purpose. It is not
(and will never be) able to state, e.g., that two relations with
different constraint matrices are actually representing the same relation.


@node Example of OpenScop Library Utilization
@section Example of OpenScop Library Utilization
Here is a basic example showing how it is possible to use the
OpenScop Library, assuming that a standard installation has been done.
The following C program reads an OpenScop file from the standard
input and dumps the content of the data structures to the standard output.

@example
/* example.c */
# include <stdio.h>
# include <osl/osl.h>

int main() @{
  osl_scop_p scop;

  // Read the OpenScop file.
  scop = osl_scop_read(stdin);

  // Dump the content of the scop data structure.
  osl_scop_dump(stdout, scop);

  // Save the planet.
  osl_scop_free(scop);

  return 0;
@}
@end example

@noindent The compilation command could be:
@example
gcc example.c -losl -o example
@end example
@noindent A calling command with the input file test.scop could be:
@example
more test.scop | ./example
@end example


@c %  ****************************** INSTALLING ********************************
@node Installation
@section Installation

@menu
* License::
* Requirements::
* Installation Instructions::
* Optional Features::
* Uninstallation::
@end menu

@node License
@subsection License
First of all, it would be very kind to refer the present document in any
publication that results from the use of the OpenScop specification or library,
@pxref{Bas11} (a bibtex entry is provided behind the title page of this
manual, along with the copyright notice).
The OpenScop Library is provided under the 3-clause BSD license:

Copyright (C) 2011 University Paris-Sud 11 and INRIA

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
@enumerate
@item Redistributions of source code must retain the above copyright notice,
      this list of conditions and the following disclaimer.
@item Redistributions in binary form must reproduce the above copyrigh
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
@item The name of the author may not be used to endorse or promote products
      derived from this software without specific prior written permission
@end enumerate

THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

@node Requirements
@subsection Requirements

The OpenScop Library is a stand-alone library. For a basic use,
it does not need any additional tool or library. Anyway, to be able to
work in conjunction with other tools that manipulate multiple precision
numbers, the GNU GMP library can be used as an option.

@menu
* GMP Library::
@end menu


@node GMP Library
@subsubsection GMP Library (optional)

To be able to deal with insanely large coefficient, the user will need to
install the GNU Multiple Precision Library (GMP for short) version 4.2.2
or above@footnote{@code{http://www.swox.com/gmp}}.
The user can compile it by typing the following commands on the GMP root
directory:

@itemize @bullet
@item @code{./configure}
@item @code{make}
@item And as root: @code{make install}
@end itemize

The GMP default installation is @code{/usr/local}. This directory may
not be inside the user's library path. To fix the problem, the user should set
@example
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib
@end example
@noindent if your shell is, e.g., bash or
@example
setenv LD_LIBRARY_PATH $LD_LIBRARY_PATH:/usr/local/lib
@end example
@noindent if your shell is, e.g., tcsh. Add the line to your .bashrc or .tcshrc (or
whatever convenient file) to make this change permanent. Another solution
is to ask GMP to install in the standard path by using the prefix
option of the configure script:
@samp{./configure --prefix=/usr}.

The OpenScop Library has to be built using the GMP library by specifying
the convenient configure script options to buid the GMP version
(@pxref{Optional Features}).


@node Installation Instructions
@subsection Installation Instructions

Once downloaded and unpacked
(e.g. using the @samp{tar -zxvf openscop-@value{LIB_VERSION}.tar.gz} command),
you can compile the OpenScop Library by typing the following commands
on the OpenScop Library's root directory:

@itemize @bullet
@item @code{./autogen.sh}
@item @code{./configure}
@item @code{make}
@item And as root: @code{make install}
@end itemize

The program binaries and object files can be removed from the
source code directory by typing @code{make clean}. To also remove the
files that the @code{configure} script created (so you can compile the
package for a different kind of computer) type @code{make distclean}.

@node Optional Features
@subsection Optional Features
The @code{configure} shell script attempts to guess correct values for
various system-dependent variables and user options used during compilation.
It uses those values to create the @code{Makefile}. Various user options
are provided by the OpenScop Library's configure script. They are summarized in the
following list and may be printed by typing @code{./configure --help} in the
OpenScop Library top-level directory.

@itemize @bullet
@item By default, the installation directory is @code{/usr/local}:
@code{make install} will install the package's files in
@code{/usr/local/bin}, @code{/usr/local/lib} and @code{/usr/local/include}.
The user can specify an installation prefix other than @code{/usr/local} by
giving @code{configure} the option @code{--prefix=PATH}.

@item By default, The OpenScop Library is built in 64bits version.
If the user gives to @code{configure} the option
@code{--enable-int-version}, the 32bits version of the OpenScop Library
will be compiled. In the same way, the option @code{--enable-mp-version}
has to be used to build the multiple precision version.

@item By default, @code{configure} will look for the GMP library
(necessary to build the multiple precision version) in standard
locations. If necessary, the user can specify the GMP path by giving
@code{configure} the option @code{--with-gmp=PATH}.
@end itemize

@node Uninstallation
@subsection Uninstallation
The user can easily remove the OpenScop Library from his system
by typing (as root if necessary) from the OpenScop Library top-level
directory
@code{make uninstall}.

@c %  **************************** DOCUMENTATION ******************************
@node Documentation
@section Documentation
The OpenScop Library distribution provides several sources of documentation.
First, the source code itself is as documented as much as possible.
The code comments use the Doxygen technical documentation system.
The user may install
Doxygen@footnote{@code{http://www.stack.nl/~dimitri/doxygen}} to automatically
generate a technical documentation by typing @code{make doc} or
@code{doxygen ./autoconf/Doxyfile} at the OpenScop Library
top-level directory after running the configure script
(@pxref{Installation Instructions}). Doxygen will generate
documentation sources (in HTML, LaTeX and man) in the @code{doc/source}
directory of the OpenScop Library distribution.

The Texinfo source of the present document is also provided in the @code{doc}
directory. The user can build it in either PDF format
(by typing @code{texi2pdf openscop.texi}) or HTML format
(by typing @code{makeinfo --html openscop.texi}, using @code{--no-split}
option to generate a single HTML file) or info format
(by typing @code{makeinfo openscop.texi}).

@c %  **************************** DEVELOPPING ********************************
@node Development
@section Development

@menu
* Copyright Issue::
* Repository::
* Coding Style::
* Extension Development::
@end menu

@node Copyright Issue 
@subsection Copyright Issue

The OpenScop Library is an Open Source project and you should feel free to
contribute by adding functionalities (in particular extensions), correcting
bugs or improving documentation. However, for painful administrative reasons,
the copyright of the core part (everything except extensions) should not be
impacted by your work. Hence, if you are doing a significant contribution to
the main part, the OpenScop Library maintainer may ask you for an agreement
about this copyright. If you plan to do such a significant contribution, it
may be wise to discuss this issue with the maintainer first. Extensions
may include developer's own copyright.

@node Repository 
@subsection Repository

The main repository of the OpenScop Library is
@url{http://repo.or.cz/w/openscop.git}. Developers may ask the OpenScop Library
maintainer to open them a write access to this repository. Only the maintainer
should ever change the @code{master} branch. Developers should work on their
own branches. To avoid any problem developers should use the @emph{fork}
functionality of the repository.

@node Coding Style 
@subsection Coding Style  

The OpenScop Library is written in C using an object oriented style. Each
important data structure (e.g., @code{struct foo}) has its own header file
(@code{include/osl/foo.h}) where lies the definition of
the data structure, the two typedefs for the data structure (one for the
structure, @code{osl_foo_t}, and one for a pointer
to the structure, @code{osl_foo_p}), the prototypes of the various
functions related to this data structure, all named using the
prefix "@code{osl_foo_}". The source code of the functions is provided in a
separated C file (@code{source/foo.c}).
  
Utility functions independent from the main data structures may be placed in
separate source files (e.g., definition in @code{include/osl/util.h}
and code in @code{source/util.c}). Tool-wide preprocessor directives are
placed in @code{include/osl/macros.h}, macros are prefixed with
"@code{OSL_}".

The core code itself has to be written according to the Google C++ Coding Style:
@url{http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml} (for
what can apply to C), plus the naming conventions discussed above.
The extension parts must only respect the naming convention, but a consistent
coding style is much appreciated.

@node Extension Development
@subsection Extension Development

It's fairly easy to integrate a new extension to OpenScop and the OpenScop
Library. Developing a new extension is very much like adding a new "object":
it requires writing a data structure for the extension data and the base
functions to manage this extension. Here is how developers should proceed
to add an extension called @code{foo} (beware that the naming convention is
strict):

@enumerate
@item Send the name @code{foo} to the maintainer to ensure it is unique and
      hence can be used as an URI. The name (one single
      word, or words separated with underscores "_") should be
      suggested by the extension developers to the OpenScop development
      mailing list @email{openscop-development@@googlegroups.com}). It
      should not correspond to an existing extension
      (see @code{include/osl/scop.h} for the list).The
      maintainer will update @code{include/osl/scop.h} in the development
      version accordingly.
@item Look at the @code{comment} extension. The @code{comment} extension
      (@pxref{Comment Extension}) has been written to be used as a basic
      example for extension developers. Having a look at
      @code{include/osl/extensions/comment.h} and
      @code{source/extensions/comment.c} will be a great help to do it right.
@item Create the extension data structure: it is necessary that the
      extension data can be accessible through only one pointer.
@item Code the base functions for the extension. Any extension must provide
      a small set of functions (naming convention apply only if the
      extension is planed to be integrated to the OpenScop Library
      default extensions):
      @itemize @bullet
      @item @code{osl_foo_idump} (@pxref{Dumping}) 
      @item @code{osl_foo_sprint} has the following prototype:
@example
@group
char * osl_@emph{structure}_sprint(osl_@emph{structure}_p s);
@end group
@end example
           It corresponds to the pretty printing functions of the core
           data structures (@pxref{Printing}) with the
           difference that the OpenScop textual representation is written
           to a string (returned by the function) instead of a file.
      @item @code{osl_foo_sread} has the following prototype:
@example
@group
osl_@emph{structure}_p osl_@emph{structure}_sread(char * string);
@end group
@end example
           It corresponds to the reading functions of the core
           data structures (@pxref{Reading}) with the
           difference that the OpenScop textual representation is read
           from a string (provided as a parameter) instead of a file.
      @item @code{osl_foo_malloc} (@pxref{Allocating}) 
      @item @code{osl_foo_free} (@pxref{Deallocating}) 
      @item @code{osl_foo_clone} (@pxref{Cloning}) 
      @item @code{osl_foo_equal} (@pxref{Testing}) 
      @end itemize
@item Code the other functions you need!
@end enumerate

Now let us consider two scenarios.

First scenario, the extension is external and is
not planned to be integrated to the OpenScop Library. In this case you are
all set. Simply generate an @code{osl_interface_t} for your
extension and have a look at the function
@code{osl_scop_register_extension()} which is devoted to register
a new extension interface to an existing @code{osl_scop_t}.

Second scenario, the extension will integrate the set of default
OpenScop Library extensions (this would be cool so it will be easier
for users to use it). In this case, a few additional
things have to be done:
@enumerate
@item Create the extension header
      @code{include/osl/extensions/foo.h} to store the extension
      structure and function prototypes and the
      extension source file @code{source/extensions/foo.c} for the code
      of the functions.
@item Add the documentation for the extension to the texinfo source of
      this document (in @code{doc/openscop.texi}), following the example
      of the @code{comment} documentation (@pxref{Comment Extension}).
@item Integrate the extension by adding the @code{extensions/foo.c} entry
      to the @code{libosl_la_SOURCES} in the @code{source/Makefile.am}
      file, the @code{osl/foo.h} entry to the
      @code{nobase_pkginclude_HEADERS} and add the corresponding
      @code{#include <osl/extensions/foo.h>} in the
      @code{include/scop.h.in} file.
@item Add the new extension in the
      @code{osl_scop_register_default_extensions()} function.
@item You are done! Prepare a single commit or patch corresponding to the
      integration of the new extension and ask the maintainer to merge it
      to the master branch.
@end enumerate


@c %  ****************************** REFERENCES ********************************
@node References
@chapter References

@itemize
@item
@anchor{Bas03a}[Bas03a] C. Bastoul, P. Feautrier. Improving data locality
by chunking. CC'12 International Conference on Compiler Construction,
LNCS 2622, pages 320-335, Warsaw, April 2003.

@item
@anchor{Bas11}[Bas11] C. Bastoul.
OpenScop: A Specification and a Library for Data Exchange in Polyhedral
Compilation Tools. Technical Report, Paris-Sud University, France, June 2011.

@item
@anchor{Fea92}[Fea92] P. Feautrier. Some efficient solutions to the affine
scheduling problem, part II: multidimensional time.
International Journal of Parallel Programming, 21(6):389--420, December 1992.

@item
@anchor{Gri04}[Gri04] M. Griebl. Automatic parallelization of loop programs
for distributed memory architectures. Habilitation Thesis. Facult@"at f@"ur
Mathematik und Informatik, Universit@"at Passau, 2004.
@emph{http://www.infosun.fmi.uni-passau.de/cl/loopo/}

@item
@anchor{Wil93}[Wil93] Doran K. Wilde.
A library for doing polyhedral operations.
Technical Report 785, IRISA, Rennes, France, 1993.

@end itemize




@c % /*************************************************************************
@c %  *                       PART VI: END OF THE DOCUMENT                    *
@c %  *************************************************************************/
@c @unnumbered Index

@c @printindex cp

@bye