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1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- L A Y O U T --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 2001-2008, Free Software Foundation, Inc. --
10 -- --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING3. If not, go to --
19 -- http://www.gnu.org/licenses for a complete copy of the license. --
20 -- --
21 -- GNAT was originally developed by the GNAT team at New York University. --
22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
23 -- --
24 ------------------------------------------------------------------------------
52 ------------------------
53 -- Local Declarations --
54 ------------------------
57 -- Short hand for System_Storage_Unit
60 -- Formal parameter name used for functions generated for size offset
61 -- values that depend on the discriminant. All such functions have the
62 -- following form:
63 --
64 -- function xxx (V : vtyp) return Unsigned is
65 -- begin
66 -- return ... expression involving V.discrim
67 -- end xxx;
69 -----------------------
70 -- Local Subprograms --
71 -----------------------
73 function Assoc_Add
77 -- This is like Make_Op_Add except that it optimizes some cases knowing
78 -- that associative rearrangement is allowed for constant folding if one
79 -- of the operands is a compile time known value.
81 function Assoc_Multiply
85 -- This is like Make_Op_Multiply except that it optimizes some cases
86 -- knowing that associative rearrangement is allowed for constant
87 -- folding if one of the operands is a compile time known value
89 function Assoc_Subtract
93 -- This is like Make_Op_Subtract except that it optimizes some cases
94 -- knowing that associative rearrangement is allowed for constant
95 -- folding if one of the operands is a compile time known value
98 -- This is used when we cross the boundary from static sizes in bits to
99 -- dynamic sizes in storage units. If the argument N is anything other
100 -- than an integer literal, it is returned unchanged, but if it is an
101 -- integer literal, then it is taken as a size in bits, and is replaced
102 -- by the corresponding size in storage units.
105 -- Given expressions for the low bound (Lo) and the high bound (Hi),
106 -- Build an expression for the value hi-lo+1, converted to type
107 -- Standard.Unsigned. Takes care of the case where the operands
108 -- are of an enumeration type (so that the subtraction cannot be
109 -- done directly) by applying the Pos operator to Hi/Lo first.
111 function Expr_From_SO_Ref
115 -- Given a value D from a size or offset field, return an expression
116 -- representing the value stored. If the value is known at compile time,
117 -- then an N_Integer_Literal is returned with the appropriate value. If
118 -- the value references a constant entity, then an N_Identifier node
119 -- referencing this entity is returned. If the value denotes a size
120 -- function, then returns a call node denoting the given function, with
121 -- a single actual parameter that either refers to the parameter V of
122 -- an enclosing size function (if Comp is Empty or its type doesn't match
123 -- the function's formal), or else is a selected component V.c when Comp
124 -- denotes a component c whose type matches that of the function formal.
125 -- The Loc value is used for the Sloc value of constructed notes.
127 function SO_Ref_From_Expr
132 -- This routine is used in the case where a size/offset value is dynamic
133 -- and is represented by the expression Expr. SO_Ref_From_Expr checks if
134 -- the Expr contains a reference to the identifier V, and if so builds
135 -- a function depending on discriminants of the formal parameter V which
136 -- is of type Vtype. Otherwise, if the parameter Make_Func is True, then
137 -- Expr will be encapsulated in a parameterless function; if Make_Func is
138 -- False, then a constant entity with the value Expr is built. The result
139 -- is a Dynamic_SO_Ref to the created entity. Note that Vtype can be
140 -- omitted if Expr does not contain any reference to V, the created entity.
141 -- The declaration created is inserted in the freeze actions of Ins_Type,
142 -- which also supplies the Sloc for created nodes. This function also takes
143 -- care of making sure that the expression is properly analyzed and
144 -- resolved (which may not be the case yet if we build the expression
145 -- in this unit).
148 -- E is an array type or subtype that has at least one index bound that
149 -- is the value of a record discriminant. For such an array, the function
150 -- computes an expression that yields the maximum possible size of the
151 -- array in storage units. The result is not defined for any other type,
152 -- or for arrays that do not depend on discriminants, and it is a fatal
153 -- error to call this unless Size_Depends_On_Discriminant (E) is True.
156 -- Front-end layout of non-bit-packed array type or subtype
159 -- Front-end layout of record type
162 -- Rewrite node N with an integer literal whose value is V. The Sloc
163 -- for the new node is taken from N, and the type of the literal is
164 -- set to a copy of the type of N on entry.
166 procedure Set_And_Check_Static_Size
170 -- This procedure is called to check explicit given sizes (possibly
171 -- stored in the Esize and RM_Size fields of E) against computed
172 -- Object_Size (Esiz) and Value_Size (RM_Siz) values. Appropriate
173 -- errors and warnings are posted if specified sizes are inconsistent
174 -- with specified sizes. On return, the Esize and RM_Size fields of
175 -- E are set (either from previously given values, or from the newly
176 -- computed values, as appropriate).
179 -- This procedure is called for record types and subtypes, and also for
180 -- atomic array types and subtypes. If no alignment is set, and the size
181 -- is 2 or 4 (or 8 if the word size is 8), then the alignment is set to
182 -- match the size.
184 ----------------------------
185 -- Adjust_Esize_Alignment --
186 ----------------------------
192 begin
193 -- Nothing to do if size unknown
199 -- Determine if size is constrained by an attribute definition clause
200 -- which must be obeyed. If so, we cannot increase the size in this
201 -- routine.
203 -- For a type, the issue is whether an object size clause has been
204 -- set. A normal size clause constrains only the value size (RM_Size)
209 -- For an object, the issue is whether a size clause is present
211 else
215 -- If size is known it must be a multiple of the storage unit size
219 -- If not, and size specified, then give error
222 Error_Msg_NE
227 -- Otherwise bump up size to a storage unit boundary
229 else
234 -- Now we have the size set, it must be a multiple of the alignment
235 -- nothing more we can do here if the alignment is unknown here.
241 -- At this point both the Esize and Alignment are known, so we need
242 -- to make sure they are consistent.
250 -- Here we have a situation where the Esize is not a multiple of
251 -- the alignment. We must either increase Esize or reduce the
252 -- alignment to correct this situation.
254 -- The case in which we can decrease the alignment is where the
255 -- alignment was not set by an alignment clause, and the type in
256 -- question is a discrete type, where it is definitely safe to
257 -- reduce the alignment. For example:
259 -- t : integer range 1 .. 2;
260 -- for t'size use 8;
262 -- In this situation, the initial alignment of t is 4, copied from
263 -- the Integer base type, but it is safe to reduce it to 1 at this
264 -- stage, since we will only be loading a single storage unit.
268 then
269 loop
278 -- Now the only possible approach left is to increase the Esize
279 -- but we can't do that if the size was set by a specific clause.
282 Error_Msg_NE
286 -- Otherwise we can indeed increase the size to a multiple of alignment
288 else
293 ---------------
294 -- Assoc_Add --
295 ---------------
297 function Assoc_Add
301 is
305 begin
306 -- Case of right operand is a constant
312 -- Case of left operand is a constant
318 -- Neither operand is a constant, do the addition with no optimization
320 else
324 -- Case of left operand is an addition
328 -- (C1 + E) + C2 = (C1 + C2) + E
331 Rewrite_Integer
336 -- (E + C1) + C2 = E + (C1 + C2)
339 Rewrite_Integer
345 -- Case of left operand is a subtraction
349 -- (C1 - E) + C2 = (C1 + C2) + E
352 Rewrite_Integer
357 -- (E - C1) + C2 = E - (C1 - C2)
360 Rewrite_Integer
367 -- Not optimizable, do the addition
372 --------------------
373 -- Assoc_Multiply --
374 --------------------
376 function Assoc_Multiply
380 is
384 begin
385 -- Case of right operand is a constant
391 -- Case of left operand is a constant
397 -- Neither operand is a constant, do the multiply with no optimization
399 else
403 -- Case of left operand is an multiplication
407 -- (C1 * E) * C2 = (C1 * C2) + E
410 Rewrite_Integer
415 -- (E * C1) * C2 = E * (C1 * C2)
418 Rewrite_Integer
425 -- Not optimizable, do the multiplication
430 --------------------
431 -- Assoc_Subtract --
432 --------------------
434 function Assoc_Subtract
438 is
442 begin
443 -- Case of right operand is a constant
449 -- Right operand is a constant, do the subtract with no optimization
451 else
455 -- Case of left operand is an addition
459 -- (C1 + E) - C2 = (C1 - C2) + E
462 Rewrite_Integer
467 -- (E + C1) - C2 = E + (C1 - C2)
470 Rewrite_Integer
476 -- Case of left operand is a subtraction
480 -- (C1 - E) - C2 = (C1 - C2) + E
483 Rewrite_Integer
488 -- (E - C1) - C2 = E - (C1 + C2)
491 Rewrite_Integer
498 -- Not optimizable, do the subtraction
503 ----------------
504 -- Bits_To_SU --
505 ----------------
508 begin
516 --------------------
517 -- Compute_Length --
518 --------------------
528 begin
529 -- If the bounds are First and Last attributes for the same dimension
530 -- and both have prefixes that denotes the same entity, then we create
531 -- and return a Length attribute. This may allow the back end to
532 -- generate better code in cases where it already has the length.
541 then
554 return
556 Prefix => New_Occurrence_Of
559 Expressions => New_List
567 -- If type is enumeration type, then use Pos attribute to convert
568 -- to integer type for which subtraction is a permitted operation.
571 Lo_Op :=
577 Hi_Op :=
584 return
586 Left_Opnd =>
593 ----------------------
594 -- Expr_From_SO_Ref --
595 ----------------------
597 function Expr_From_SO_Ref
601 is
604 begin
609 -- If a component is passed in whose type matches the type
610 -- of the function formal, then select that component from
611 -- the "V" parameter rather than passing "V" directly.
616 then
617 return
625 else
626 return
633 else
637 else
642 ---------------------
643 -- Get_Max_SU_Size --
644 ---------------------
658 record
664 -- Shows the status of the value so far. Const means that the value
665 -- is constant, and Val is the current constant value. Dynamic means
666 -- that the value is dynamic, and in this case Nod is the Node_Id of
667 -- the expression to compute the value.
670 -- Calculated value so far if Size.Status = Const,
671 -- or expression value so far if Size.Status = Dynamic.
674 -- This is set to True if the final result must be converted from
675 -- bits to storage units (rounding up to a storage unit boundary).
677 -----------------------
678 -- Local Subprograms --
679 -----------------------
682 -- If the node N represents a discriminant, replace it by the maximum
683 -- value of the discriminant.
686 -- If the node N represents a discriminant, replace it by the minimum
687 -- value of the discriminant.
689 -----------------
690 -- Max_Discrim --
691 -----------------
694 begin
697 then
702 -----------------
703 -- Min_Discrim --
704 -----------------
707 begin
710 then
715 -- Start of processing for Get_Max_SU_Size
717 begin
720 -- Initialize status from component size
725 else
729 -- Loop through indices
740 -- Value of the current subscript range is statically known
744 then
747 -- If known flat bound, entire size of array is zero!
753 -- Current value is constant, evolve value
758 -- Current value is dynamic
760 else
761 -- An interesting little optimization, if we have a pending
762 -- conversion from bits to storage units, and the current
763 -- length is a multiple of the storage unit size, then we
764 -- can take the factor out here statically, avoiding some
765 -- extra dynamic computations at the end.
775 Right_Opnd =>
779 -- Value of the current subscript range is dynamic
781 else
782 -- If the current size value is constant, then here is where we
783 -- make a transition to dynamic values, which are always stored
784 -- in storage units, However, we do not want to convert to SU's
785 -- too soon, consider the case of a packed array of single bits,
786 -- we want to do the SU conversion after computing the size in
787 -- this case.
791 -- If the current value is a multiple of the storage unit,
792 -- then most certainly we can do the conversion now, simply
793 -- by dividing the current value by the storage unit value.
794 -- If this works, we set SU_Convert_Required to False.
798 Size :=
802 -- Otherwise, we go ahead and convert the value in bits,
803 -- and set SU_Convert_Required to True to ensure that the
804 -- final value is indeed properly converted.
806 else
812 -- Length is hi-lo+1
816 -- Check possible range of Len
818 declare
824 begin
830 -- If we cannot verify that range cannot be super-flat,
831 -- we need a max with zero, since length must be non-neg.
834 Len :=
836 Prefix =>
841 Len));
849 -- Here after processing all bounds to set sizes. If the value is
850 -- a constant, then it is bits, so we convert to storage units.
855 -- Case where the value is dynamic
857 else
858 -- Do convert from bits to SU's if needed
862 -- The expression required is (Size.Nod + SU - 1) / SU
866 Left_Opnd =>
877 -----------------------
878 -- Layout_Array_Type --
879 -----------------------
892 -- This is the type with which any generated constants or functions
893 -- will be associated (i.e. inserted into the freeze actions). This
894 -- is normally the type being laid out. The exception occurs when
895 -- we are laying out Itype's which are local to a record type, and
896 -- whose scope is this record type. Such types do not have freeze
897 -- nodes (because we have no place to put them).
899 ------------------------------------
900 -- How An Array Type is Laid Out --
901 ------------------------------------
903 -- Here is what goes on. We need to multiply the component size of
904 -- the array (which has already been set) by the length of each of
905 -- the indexes. If all these values are known at compile time, then
906 -- the resulting size of the array is the appropriate constant value.
908 -- If the component size or at least one bound is dynamic (but no
909 -- discriminants are present), then the size will be computed as an
910 -- expression that calculates the proper size.
912 -- If there is at least one discriminant bound, then the size is also
913 -- computed as an expression, but this expression contains discriminant
914 -- values which are obtained by selecting from a function parameter, and
915 -- the size is given by a function that is passed the variant record in
916 -- question, and whose body is the expression.
921 record
925 -- Calculated value so far if Val_Status = Const
929 -- Expression value so far if Val_Status /= Const
933 -- Records the value or expression computed so far. Const means that
934 -- the value is constant, and Val is the current constant value.
935 -- Dynamic means that the value is dynamic, and in this case Nod is
936 -- the Node_Id of the expression to compute the value, and Discrim
937 -- means that at least one bound is a discriminant, in which case Nod
938 -- is the expression so far (which will be the body of the function).
941 -- Value of size computed so far. See comments above
944 -- Variant record type for the formal parameter of the
945 -- discriminant function V if Status = Discrim.
948 -- This is set to True if the final result must be converted from
949 -- bits to storage units (rounding up to a storage unit boundary).
952 -- This is the amount that a nonstatic computed size will be divided
953 -- by to convert it from bits to storage units. This is normally
954 -- equal to SSU, but can be reduced in the case of packed components
955 -- that fit evenly into a storage unit.
958 -- Indicates whether to request that SO_Ref_From_Expr should
959 -- encapsulate the array size expression in a function.
962 -- If N represents a discriminant, then the Size.Status is set to
963 -- Discrim, and Vtyp is set. The parameter N is replaced with the
964 -- proper expression to extract the discriminant value from V.
966 ----------------
967 -- Discrimify --
968 ----------------
974 begin
977 then
988 N :=
993 -- Set the Etype attributes of the selected name and its prefix.
994 -- Analyze_And_Resolve can't be called here because the Vname
995 -- entity denoted by the prefix will not yet exist (it's created
996 -- by SO_Ref_From_Expr, called at the end of Layout_Array_Type).
1003 -- Start of processing for Layout_Array_Type
1005 begin
1006 -- Default alignment is component alignment
1012 -- Calculate proper type for insertions
1016 else
1020 -- If the component type is a generic formal type then there's no point
1021 -- in determining a size for the array type.
1027 -- Deal with component size if base type
1031 -- Cannot do anything if Esize of component type unknown
1037 -- Set component size if not set already
1044 -- (RM 13.3 (48)) says that the size of an unconstrained array
1045 -- is implementation defined. We choose to leave it as Unknown
1046 -- here, and the actual behavior is determined by the back end.
1052 -- Initialize status from component size
1057 else
1061 -- Loop to process array indices
1067 -- If an index of the array is a generic formal type then there's
1068 -- no point in determining a size for the array type.
1077 -- Value of the current subscript range is statically known
1081 then
1084 -- If known flat bound, entire size of array is zero!
1092 -- If constant, evolve value
1097 -- Current value is dynamic
1099 else
1100 -- An interesting little optimization, if we have a pending
1101 -- conversion from bits to storage units, and the current
1102 -- length is a multiple of the storage unit size, then we
1103 -- can take the factor out here statically, avoiding some
1104 -- extra dynamic computations at the end.
1111 -- Now go ahead and evolve the expression
1116 Right_Opnd =>
1120 -- Value of the current subscript range is dynamic
1122 else
1123 -- If the current size value is constant, then here is where we
1124 -- make a transition to dynamic values, which are always stored
1125 -- in storage units, However, we do not want to convert to SU's
1126 -- too soon, consider the case of a packed array of single bits,
1127 -- we want to do the SU conversion after computing the size in
1128 -- this case.
1132 -- If the current value is a multiple of the storage unit,
1133 -- then most certainly we can do the conversion now, simply
1134 -- by dividing the current value by the storage unit value.
1135 -- If this works, we set SU_Convert_Required to False.
1138 Size :=
1142 -- If the current value is a factor of the storage unit,
1143 -- then we can use a value of one for the size and reduce
1144 -- the strength of the later division.
1151 -- Otherwise, we go ahead and convert the value in bits,
1152 -- and set SU_Convert_Required to True to ensure that the
1153 -- final value is indeed properly converted.
1155 else
1164 -- Length is hi-lo+1
1168 -- If Len isn't a Length attribute, then its range needs to
1169 -- be checked a possible Max with zero needs to be computed.
1173 then
1174 declare
1179 begin
1180 -- Check possible range of Len
1187 -- If range definitely flat or superflat,
1188 -- result size is zero
1196 -- If we cannot verify that range cannot be super-flat,
1197 -- we need a maximum with zero, since length cannot be
1198 -- negative.
1201 Len :=
1203 Prefix =>
1208 Len));
1213 -- At this stage, Len has the expression for the length
1224 -- Here after processing all bounds to set sizes. If the value is
1225 -- a constant, then it is bits, and the only thing we need to do
1226 -- is to check against explicit given size and do alignment adjust.
1232 -- Case where the value is dynamic
1234 else
1235 -- Do convert from bits to SU's if needed
1239 -- The expression required is:
1240 -- (Size.Nod + Storage_Divisor - 1) / Storage_Divisor
1244 Left_Opnd =>
1247 Right_Opnd => Make_Integer_Literal
1252 -- If the array entity is not declared at the library level and its
1253 -- not nested within a subprogram that is marked for inlining, then
1254 -- we request that the size expression be encapsulated in a function.
1255 -- Since this expression is not needed in most cases, we prefer not
1256 -- to incur the overhead of the computation on calls to the enclosing
1257 -- subprogram except for subprograms that require the size.
1262 declare
1265 begin
1277 -- Now set the dynamic size (the Value_Size is always the same
1278 -- as the Object_Size for arrays whose length is dynamic).
1280 -- ??? If Size.Status = Dynamic, Vtyp will not have been set.
1281 -- The added initialization sets it to Empty now, but is this
1282 -- correct?
1284 Set_Esize
1286 SO_Ref_From_Expr
1292 -------------------
1293 -- Layout_Object --
1294 -------------------
1299 begin
1300 -- Nothing to do if backend does layout
1306 -- Set size if not set for object and known for type. Use the
1307 -- RM_Size if that is known for the type and Esize is not.
1318 -- Set alignment from type if unknown and type alignment known
1324 -- Make sure size and alignment are consistent
1328 -- Final adjustment, if we don't know the alignment, and the Esize
1329 -- was not set by an explicit Object_Size attribute clause, then
1330 -- we reset the Esize to unknown, since we really don't know it.
1334 then
1339 ------------------------
1340 -- Layout_Record_Type --
1341 ------------------------
1348 -- Current component being laid out
1351 -- Previous laid out component
1353 procedure Get_Next_Component_Location
1360 -- Given the previous component in Prev_Comp, which is already laid
1361 -- out, and the alignment of the following component, lays out the
1362 -- following component, and returns its starting position in New_Npos
1363 -- (Normalized_Position value), New_Fbit (Normalized_First_Bit value),
1364 -- and New_NPMax (Normalized_Position_Max value). If Prev_Comp is empty
1365 -- (no previous component is present), then New_Npos, New_Fbit and
1366 -- New_NPMax are all set to zero on return. This procedure is also
1367 -- used to compute the size of a record or variant by giving it the
1368 -- last component, and the record alignment. Force_SU is used to force
1369 -- the new component location to be aligned on a storage unit boundary,
1370 -- even in a packed record, False means that the new position does not
1371 -- need to be bumped to a storage unit boundary, True means a storage
1372 -- unit boundary is always required.
1375 -- Lays out component Comp, given Prev_Comp, the previously laid-out
1376 -- component (Prev_Comp = Empty if no components laid out yet). The
1377 -- alignment of the record itself is also updated if needed. Both
1378 -- Comp and Prev_Comp can be either components or discriminants.
1380 procedure Layout_Components
1385 -- This procedure lays out the components of the given component list
1386 -- which contains the components starting with From and ending with To.
1387 -- The Next_Entity chain is used to traverse the components. On entry,
1388 -- Prev_Comp is set to the component preceding the list, so that the
1389 -- list is laid out after this component. Prev_Comp is set to Empty if
1390 -- the component list is to be laid out starting at the start of the
1391 -- record. On return, the components are all laid out, and Prev_Comp is
1392 -- set to the last laid out component. On return, Esiz is set to the
1393 -- resulting Object_Size value, which is the length of the record up
1394 -- to and including the last laid out entity. For Esiz, the value is
1395 -- adjusted to match the alignment of the record. RM_Siz is similarly
1396 -- set to the resulting Value_Size value, which is the same length, but
1397 -- not adjusted to meet the alignment. Note that in the case of variant
1398 -- records, Esiz represents the maximum size.
1401 -- Procedure called to lay out a non-variant record type or subtype
1404 -- Procedure called to lay out a variant record type. Decl is set to the
1405 -- full type declaration for the variant record.
1407 ---------------------------------
1408 -- Get_Next_Component_Location --
1409 ---------------------------------
1411 procedure Get_Next_Component_Location
1418 is
1419 begin
1420 -- No previous component, return zero position
1429 -- Here we have a previous component
1431 declare
1440 -- Expression representing maximum size of previous component
1442 begin
1443 -- Case where previous field had a dynamic size
1447 -- If the previous field had a dynamic length, then it is
1448 -- required to occupy an integral number of storage units,
1449 -- and start on a storage unit boundary. This means that
1450 -- the Normalized_First_Bit value is zero in the previous
1451 -- component, and the new value is also set to zero.
1455 -- In this case, the new position is given by an expression
1456 -- that is the sum of old normalized position and old size.
1458 New_Npos :=
1459 SO_Ref_From_Expr
1461 Left_Opnd =>
1463 Right_Opnd =>
1468 -- Get maximum size of previous component
1472 else
1476 -- Now we can compute the new max position. If the max size
1477 -- is static and the old position is static, then we can
1478 -- compute the new position statically.
1482 then
1485 -- Otherwise new max position is dynamic
1487 else
1488 New_NPMax :=
1489 SO_Ref_From_Expr
1497 -- Previous field has known static Esize
1499 else
1502 -- Bump New_Fbit to storage unit boundary if required
1508 -- If old normalized position is static, we can go ahead
1509 -- and compute the new normalized position directly.
1519 -- Bump alignment if stricter than prev
1525 -- The max position is always equal to the position if
1526 -- the latter is static, since arrays depending on the
1527 -- values of discriminants never have static sizes.
1532 -- Case of old normalized position is dynamic
1534 else
1535 -- If new bit position is within the current storage unit,
1536 -- we can just copy the old position as the result position
1537 -- (we have already set the new first bit value).
1543 -- If new bit position is past the current storage unit, we
1544 -- need to generate a new dynamic value for the position
1545 -- ??? need to deal with alignment
1547 else
1548 New_Npos :=
1549 SO_Ref_From_Expr
1552 Right_Opnd =>
1558 New_NPMax :=
1559 SO_Ref_From_Expr
1562 Right_Opnd =>
1574 ----------------------
1575 -- Layout_Component --
1576 ----------------------
1586 begin
1587 -- Increase alignment of record if necessary. Note that we do not
1588 -- do this for packed records, which have an alignment of one by
1589 -- default, or for records for which an explicit alignment was
1590 -- specified with an alignment clause.
1595 then
1599 -- If original component set, then use same layout
1610 -- Parent field is always at start of record, this will overlap
1611 -- the actual fields that are part of the parent, and that's fine
1622 -- Check case of type of component has a scope of the record we
1623 -- are laying out. When this happens, the type in question is an
1624 -- Itype that has not yet been laid out (that's because such
1625 -- types do not get frozen in the normal manner, because there
1626 -- is no place for the freeze nodes).
1632 -- If component already laid out, then we are done
1638 -- Set size of component from type. We use the Esize except in a
1639 -- packed record, where we use the RM_Size (since that is exactly
1640 -- what the RM_Size value, as distinct from the Object_Size is
1641 -- useful for!)
1645 else
1649 -- Compute the component position from the previous one. See if
1650 -- current component requires being on a storage unit boundary.
1652 -- If record is not packed, we always go to a storage unit boundary
1657 -- Packed cases
1659 else
1660 -- Elementary types do not need SU boundary in packed record
1665 -- Packed array types with a modular packed array type do not
1666 -- force a storage unit boundary (since the code generation
1667 -- treats these as equivalent to the underlying modular type),
1672 then
1675 -- Record types with known length less than or equal to the length
1676 -- of long long integer can also be unaligned, since they can be
1677 -- treated as scalars.
1682 then
1685 -- All other cases force a storage unit boundary, even when packed
1687 else
1692 -- Now get the next component location
1694 Get_Next_Component_Location
1700 -- Set Component_Bit_Offset in the static case
1704 then
1709 -----------------------
1710 -- Layout_Components --
1711 -----------------------
1713 procedure Layout_Components
1718 is
1723 begin
1724 -- Only lay out components if there are some to lay out!
1728 -- Lay out components with no component clauses
1731 loop
1734 then
1735 -- The compatibility of component clauses with composite
1736 -- types isn't checked in Sem_Ch13, so we check it here.
1741 then
1743 Error_Msg_NE
1746 Comp);
1749 else
1760 -- Set size fields, both are zero if no components
1766 -- If record subtype with non-static discriminants, then we don't
1767 -- know which variant will be the one which gets chosen. We don't
1768 -- just want to set the maximum size from the base, because the
1769 -- size should depend on the particular variant.
1771 -- What we do is to use the RM_Size of the base type, which has
1772 -- the necessary conditional computation of the size, using the
1773 -- size information for the particular variant chosen. Records
1774 -- with default discriminants for example have an Esize that is
1775 -- set to the maximum of all variants, but that's not what we
1776 -- want for a constrained subtype.
1780 then
1781 declare
1783 begin
1789 else
1790 -- First the object size, for which we align past the last field
1791 -- to the alignment of the record (the object size is required to
1792 -- be a multiple of the alignment).
1794 Get_Next_Component_Location
1797 End_Npos,
1798 End_Fbit,
1799 End_NPMax,
1802 -- If the resulting normalized position is a dynamic reference,
1803 -- then the size is dynamic, and is stored in storage units. In
1804 -- this case, we set the RM_Size to the same value, it is simply
1805 -- not worth distinguishing Esize and RM_Size values in the
1806 -- dynamic case, since the RM has nothing to say about them.
1808 -- Note that a size cannot have been given in this case, since
1809 -- size specifications cannot be given for variable length types.
1811 declare
1814 begin
1818 -- Set the Object_Size allowing for the alignment. In the
1819 -- dynamic case, we must do the actual runtime computation.
1820 -- We can skip this in the non-packed record case if the
1821 -- last component has a smaller alignment than the overall
1822 -- record alignment.
1829 then
1830 -- The expression we build is:
1831 -- (expr + align - 1) / align * align
1833 Esiz :=
1834 SO_Ref_From_Expr
1837 Left_Opnd =>
1839 Left_Opnd =>
1841 Left_Opnd =>
1843 Right_Opnd =>
1846 Right_Opnd =>
1848 Right_Opnd =>
1854 -- Here Esiz is static, so we can adjust the alignment
1855 -- directly go give the required aligned value.
1857 else
1861 -- Case where computed size is static
1863 else
1864 -- The ending size was computed in Npos in storage units,
1865 -- but the actual size is stored in bits, so adjust
1866 -- accordingly. We also adjust the size to match the
1867 -- alignment here.
1871 -- Compute the resulting Value_Size (RM_Size). For this
1872 -- purpose we do not force alignment of the record or
1873 -- storage size alignment of the result.
1875 Get_Next_Component_Location
1877 Uint_0,
1878 End_Npos,
1879 End_Fbit,
1880 End_NPMax,
1890 -------------------------------
1891 -- Layout_Non_Variant_Record --
1892 -------------------------------
1897 begin
1903 ---------------------------
1904 -- Layout_Variant_Record --
1905 ---------------------------
1917 -- Expression for the evolving RM_Siz value. This is typically a
1918 -- conditional expression which involves tests of discriminant
1919 -- values that are formed as references to the entity V. At
1920 -- the end of scanning all the components, a suitable function
1921 -- is constructed in which V is the parameter.
1923 -----------------------
1924 -- Local Subprograms --
1925 -----------------------
1927 procedure Layout_Component_List
1931 -- Recursive procedure, called to lay out one component list
1932 -- Esiz and RM_Siz_Expr are set to the Object_Size and Value_Size
1933 -- values respectively representing the record size up to and
1934 -- including the last component in the component list (including
1935 -- any variants in this component list). RM_Siz_Expr is returned
1936 -- as an expression which may in the general case involve some
1937 -- references to the discriminants of the current record value,
1938 -- referenced by selecting from the entity V.
1940 ---------------------------
1941 -- Layout_Component_List --
1942 ---------------------------
1944 procedure Layout_Component_List
1948 is
1956 begin
1958 Layout_Components
1963 else
1967 -- Case where no variants are present in the component list
1971 -- The Esiz value has been correctly set by the call to
1972 -- Layout_Components, so there is nothing more to be done.
1974 -- For RM_Siz, we have an SO_Ref value, which we must convert
1975 -- to an appropriate expression.
1978 RM_Siz_Expr :=
1982 else
1985 -- If the size is represented by a function, then we
1986 -- create an appropriate function call using V as
1987 -- the parameter to the call.
1990 RM_Siz_Expr :=
1996 -- If the size is represented by a constant, then the
1997 -- expression we want is a reference to this constant
1999 else
2004 -- Case where variants are present in this component list
2006 else
2007 declare
2016 begin
2023 Layout_Component_List
2026 -- Set the Object_Size. If this is the first variant,
2027 -- we just set the size of this first variant.
2032 -- Otherwise the Object_Size is formed as a maximum
2033 -- of Esiz so far from previous variants, and the new
2034 -- Esiz value from the variant we just processed.
2036 -- If both values are static, we can just compute the
2037 -- maximum directly to save building junk nodes.
2041 then
2044 -- If either value is dynamic, then we have to generate
2045 -- an appropriate Standard_Unsigned'Max attribute call.
2046 -- If one of the values is static then it needs to be
2047 -- converted from bits to storage units to be compatible
2048 -- with the dynamic value.
2050 else
2059 Esiz :=
2060 SO_Ref_From_Expr
2063 Prefix =>
2072 -- Now deal with Value_Size (RM_Siz). We are aiming at
2073 -- an expression that looks like:
2075 -- if xxDx (V.disc) then rmsiz1
2076 -- else if xxDx (V.disc) then rmsiz2
2077 -- else ...
2079 -- Where rmsiz1, rmsiz2... are the RM_Siz values for the
2080 -- individual variants, and xxDx are the discriminant
2081 -- checking functions generated for the variant type.
2083 -- If this is the first variant, we simply set the
2084 -- result as the expression. Note that this takes
2085 -- care of the others case.
2090 -- Otherwise construct the appropriate test
2092 else
2093 -- The test to be used in general is a call to the
2094 -- discriminant checking function. However, it is
2095 -- definitely worth special casing the very common
2096 -- case where a single value is involved.
2102 then
2103 -- Discriminant to be tested
2105 Discrim :=
2107 Prefix =>
2109 Selector_Name =>
2110 New_Occurrence_Of
2113 Dtest :=
2118 -- Generate a call to the discriminant-checking
2119 -- function for the variant. Note that the result
2120 -- has to be complemented since the function returns
2121 -- False when the passed discriminant value matches.
2123 else
2124 -- The checking function takes all of the type's
2125 -- discriminants as parameters, so a list of all
2126 -- the selected discriminants must be constructed.
2131 Append (
2133 Prefix =>
2135 Selector_Name =>
2136 New_Occurrence_Of
2138 D_List);
2143 Dtest :=
2145 Right_Opnd =>
2147 Name =>
2148 New_Occurrence_Of
2150 Parameter_Associations =>
2151 D_List));
2154 RM_Siz_Expr :=
2156 Expressions =>
2157 New_List
2167 -- Start of processing for Layout_Variant_Record
2169 begin
2170 -- We need the discriminant checking functions, since we generate
2171 -- calls to these functions for the RM_Size expression, so make
2172 -- sure that these functions have been constructed in time.
2176 -- Lay out the discriminants
2184 Layout_Components
2190 -- Lay out the main component list (this will make recursive calls
2191 -- to lay out all component lists nested within variants).
2196 -- If the RM_Size is a literal, set its value
2201 -- Otherwise we construct a dynamic SO_Ref
2203 else
2205 SO_Ref_From_Expr
2212 -- Start of processing for Layout_Record_Type
2214 begin
2215 -- If this is a cloned subtype, just copy the size fields from the
2216 -- original, nothing else needs to be done in this case, since the
2217 -- components themselves are all shared.
2220 or else
2223 then
2228 -- Another special case, class-wide types. The RM says that the size
2229 -- of such types is implementation defined (RM 13.3(48)). What we do
2230 -- here is to leave the fields set as unknown values, and the backend
2231 -- determines the actual behavior.
2236 -- All other cases
2238 else
2239 -- Initialize alignment conservatively to 1. This value will
2240 -- be increased as necessary during processing of the record.
2246 -- Initialize previous component. This is Empty unless there
2247 -- are components which have already been laid out by component
2248 -- clauses. If there are such components, we start our lay out of
2249 -- the remaining components following the last such component.
2257 or else
2260 then
2268 -- We have two separate circuits, one for non-variant records and
2269 -- one for variant records. For non-variant records, we simply go
2270 -- through the list of components. This handles all the non-variant
2271 -- cases including those cases of subtypes where there is no full
2272 -- type declaration, so the tree cannot be used to drive the layout.
2273 -- For variant records, we have to drive the layout from the tree
2274 -- since we need to understand the variant structure in this case.
2278 else
2282 -- Scan all the components
2288 and then
2290 then
2291 Layout_Variant_Record;
2292 else
2293 Layout_Non_Variant_Record;
2298 -----------------
2299 -- Layout_Type --
2300 -----------------
2305 begin
2306 -- For string literal types, for now, kill the size always, this
2307 -- is because gigi does not like or need the size to be set ???
2315 -- For access types, set size/alignment. This is system address
2316 -- size, except for fat pointers (unconstrained array access types),
2317 -- where the size is two times the address size, to accommodate the
2318 -- two pointers that are required for a fat pointer (data and
2319 -- template). Note that E_Access_Protected_Subprogram_Type is not
2320 -- an access type for this purpose since it is not a pointer but is
2321 -- equivalent to a record. For access subtypes, copy the size from
2322 -- the base type since Gigi represents them the same way.
2328 -- If we only have a limited view of the type, see whether the
2329 -- non-limited view is available.
2334 then
2338 -- If Esize already set (e.g. by a size clause), then nothing
2339 -- further to be done here.
2344 -- Access to subprogram is a strange beast, and we let the
2345 -- backend figure out what is needed (it may be some kind
2346 -- of fat pointer, including the static link for example.
2351 -- For access subtypes, copy the size information from base type
2357 -- For other access types, we use either address size, or, if
2358 -- a fat pointer is used (pointer-to-unconstrained array case),
2359 -- twice the address size to accommodate a fat pointer.
2365 and then not Debug_Flag_6
2366 then
2369 -- Check for bad convention set
2371 if Warn_On_Export_Import
2372 and then
2374 or else
2376 then
2377 Error_Msg_N
2381 -- If the designated type is a limited view it is unanalyzed. We
2382 -- can examine the declaration itself to determine whether it will
2383 -- need a fat pointer.
2388 and then
2390 = N_Unconstrained_Array_Definition
2391 then
2394 -- When the target is AAMP, access-to-subprogram types are fat
2395 -- pointers consisting of the subprogram address and a static
2396 -- link (with the exception of library-level access types,
2397 -- where a simple subprogram address is used).
2399 elsif AAMP_On_Target
2400 and then
2404 then
2407 else
2411 -- On VMS, reset size to 32 for convention C access type if no
2412 -- explicit size clause is given and the default size is 64. Really
2413 -- we do not know the size, since depending on options for the VMS
2414 -- compiler, the size of a pointer type can be 32 or 64, but
2415 -- choosing 32 as the default improves compatibility with legacy
2416 -- VMS code.
2418 -- Note: we do not use Has_Size_Clause in the test below, because we
2419 -- want to catch the case of a derived type inheriting a size
2420 -- clause. We want to consider this to be an explicit size clause
2421 -- for this purpose, since it would be weird not to inherit the size
2422 -- in this case.
2424 -- We do NOT do this if we are in -gnatdm mode on a non-VMS target
2425 -- since in that case we want the normal pointer representation.
2429 or else
2433 then
2439 -- Scalar types: set size and alignment
2443 -- For discrete types, the RM_Size and Esize must be set
2444 -- already, since this is part of the earlier processing
2445 -- and the front end is always required to lay out the
2446 -- sizes of such types (since they are available as static
2447 -- attributes). All we do is to check that this rule is
2448 -- indeed obeyed!
2452 -- If the RM_Size is not set, then here is where we set it
2454 -- Note: an RM_Size of zero looks like not set here, but this
2455 -- is a rare case, and we can simply reset it without any harm.
2461 -- If Esize for a discrete type is not set then set it
2464 declare
2467 begin
2468 loop
2469 -- If size is big enough, set it and exit
2475 -- If the RM_Size is greater than 64 (happens only
2476 -- when strange values are specified by the user,
2477 -- then Esize is simply a copy of RM_Size, it will
2478 -- be further refined later on)
2484 -- Otherwise double possible size and keep trying
2486 else
2493 -- For non-discrete scalar types, if the RM_Size is not set,
2494 -- then set it now to a copy of the Esize if the Esize is set.
2496 else
2504 -- Non-elementary (composite) types
2506 else
2507 -- If RM_Size is known, set Esize if not known
2511 -- If the alignment is known, we bump the Esize up to the
2512 -- next alignment boundary if it is not already on one.
2515 declare
2518 begin
2523 -- If Esize is set, and RM_Size is not, RM_Size is copied from
2524 -- Esize at least for now this seems reasonable, and is in any
2525 -- case needed for compatibility with old versions of gigi.
2526 -- look to be unknown.
2532 -- For array base types, set component size if object size of
2533 -- the component type is known and is a small power of 2 (8,
2534 -- 16, 32, 64), since this is what will always be used.
2538 then
2539 declare
2542 begin
2543 -- For some reasons, access types can cause trouble,
2544 -- So let's just do this for discrete types ???
2549 then
2550 declare
2553 begin
2558 then
2567 -- Lay out array and record types if front end layout set
2576 -- Case of backend layout, we still do a little in the front end
2578 else
2579 -- Processing for record types
2583 -- Special remaining processing for record types with a known
2584 -- size of 16, 32, or 64 bits whose alignment is not yet set.
2585 -- For these types, we set a corresponding alignment matching
2586 -- the size if possible, or as large as possible if not.
2589 and then not Debug_Flag_Q
2590 then
2594 -- Processing for array types
2598 -- For arrays that are required to be atomic, we do the same
2599 -- processing as described above for short records, since we
2600 -- really need to have the alignment set for the whole array.
2606 -- For unpacked array types, set an alignment of 1 if we know
2607 -- that the component alignment is not greater than 1. The reason
2608 -- we do this is to avoid unnecessary copying of slices of such
2609 -- arrays when passed to subprogram parameters (see special test
2610 -- in Exp_Ch6.Expand_Actuals).
2614 then
2617 then
2624 -- Final step is to check that Esize and RM_Size are compatible
2629 -- Esize is less than RM_Size. That's not good. First we test
2630 -- whether this was set deliberately with an Object_Size clause
2631 -- and if so, object to the clause.
2635 Error_Msg_F
2637 Expression (Get_Attribute_Definition_Clause
2641 -- Adjust Esize up to RM_Size value
2643 declare
2646 begin
2649 -- For scalar types, increase Object_Size to power of 2,
2650 -- but not less than a storage unit in any case (i.e.,
2651 -- normally this means it will be storage-unit addressable).
2660 else
2664 -- Finally, make sure that alignment is consistent with
2665 -- the newly assigned size.
2669 loop
2678 ---------------------
2679 -- Rewrite_Integer --
2680 ---------------------
2686 begin
2691 -------------------------------
2692 -- Set_And_Check_Static_Size --
2693 -------------------------------
2695 procedure Set_And_Check_Static_Size
2699 is
2703 -- Spec is the number of bit specified in the size clause, and
2704 -- Min is the minimum computed size. An error is given that the
2705 -- specified size is too small if Spec < Min, and in this case
2706 -- both Esize and RM_Size are set to unknown in E. The error
2707 -- message is posted on node SC.
2710 -- Spec is the number of bits specified in the size clause, and
2711 -- Max is the maximum computed size. A warning is given about
2712 -- unused bits if Spec > Max. This warning is posted on node SC.
2714 --------------------------
2715 -- Check_Size_Too_Small --
2716 --------------------------
2719 begin
2722 Error_Msg_NE
2729 -----------------------
2730 -- Check_Unused_Bits --
2731 -----------------------
2734 begin
2741 -- Start of processing for Set_And_Check_Static_Size
2743 begin
2744 -- Case where Object_Size (Esize) is already set by a size clause
2753 -- Perform checks on specified size against computed sizes
2761 -- Case where Value_Size (RM_Size) is set by specific Value_Size
2762 -- clause (we do not need to worry about Value_Size being set by
2763 -- a Size clause, since that will have set Esize as well, and we
2764 -- already took care of that case).
2769 -- Perform checks on specified size against computed sizes
2777 -- Set sizes if unknown
2788 -----------------------------
2789 -- Set_Composite_Alignment --
2790 -----------------------------
2796 begin
2797 -- If alignment is already set, then nothing to do
2803 -- Alignment is not known, see if we can set it, taking into account
2804 -- the setting of the Optimize_Alignment mode.
2806 -- If Optimize_Alignment is set to Space, then packed records always
2807 -- have an alignment of 1. But don't do anything for atomic records
2808 -- since we may need higher alignment for indivisible access.
2814 then
2817 -- Not a record, or not packed
2819 else
2820 -- The only other cases we worry about here are where the size is
2821 -- statically known at compile time.
2828 then
2831 else
2835 -- Size is known, alignment is not set
2837 -- Reset alignment to match size if the known size is exactly 2, 4,
2838 -- or 8 storage units.
2847 -- If Optimize_Alignment is set to Space, then make sure the
2848 -- alignment matches the size, for example, if the size is 17
2849 -- bytes then we want an alignment of 1 for the type.
2858 else
2862 -- If Optimize_Alignment is set to Time, then we reset for odd
2863 -- "in between sizes", for example a 17 bit record is given an
2864 -- alignment of 4. Note that this matches the old VMS behavior
2865 -- in versions of GNAT prior to 6.1.1.
2870 then
2879 -- No special alignment fiddling needed
2881 else
2886 -- Here we have Set Align to the proposed improved value. Make sure the
2887 -- value set does not exceed Maximum_Alignment for the target.
2893 -- Further processing for record types only to reduce the alignment
2894 -- set by the above processing in some specific cases. We do not
2895 -- do this for atomic records, since we need max alignment there,
2899 -- For records, there is generally no point in setting alignment
2900 -- higher than word size since we cannot do better than move by
2901 -- words in any case. Omit this if we are optimizing for time,
2902 -- since conceivably we may be able to do better.
2906 then
2910 -- Check components. If any component requires a higher alignment,
2911 -- then we set that higher alignment in any case. Don't do this if
2912 -- we have Optimize_Alignment set to Space. Note that that covers
2913 -- the case of packed records, where we already set alignment to 1.
2916 declare
2919 begin
2923 declare
2926 begin
2927 -- The cases to process are when the alignment of the
2928 -- component type is larger than the alignment we have
2929 -- so far, and either there is no component clause for
2930 -- the component, or the length set by the component
2931 -- clause matches the length of the component type.
2934 and then
2937 and then
2940 then
2952 -- Set chosen alignment, and increase Esize if necessary to match
2953 -- the chosen alignment.
2959 then
2964 --------------------------
2965 -- Set_Discrete_RM_Size --
2966 --------------------------
2971 begin
2972 -- All discrete types except for the base types in standard
2973 -- are constrained, so indicate this by setting Is_Constrained.
2977 -- We set generic types to have an unknown size, since the
2978 -- representation of a generic type is irrelevant, in view
2979 -- of the fact that they have nothing to do with code.
2984 -- If the subtype statically matches the first subtype, then
2985 -- it is required to have exactly the same layout. This is
2986 -- required by aliasing considerations.
2990 then
2994 -- In all other cases the RM_Size is set to the minimum size.
2995 -- Note that this routine is never called for subtypes for which
2996 -- the RM_Size is set explicitly by an attribute clause.
2998 else
3003 ------------------------
3004 -- Set_Elem_Alignment --
3005 ------------------------
3008 begin
3009 -- Do not set alignment for packed array types, unless we are doing
3010 -- front end layout, because otherwise this is always handled in the
3011 -- backend.
3016 -- If there is an alignment clause, then we respect it
3021 -- If the size is not set, then don't attempt to set the alignment. This
3022 -- happens in the backend layout case for access-to-subprogram types.
3027 -- For access types, do not set the alignment if the size is less than
3028 -- the allowed minimum size. This avoids cascaded error messages.
3032 then
3036 -- Here we calculate the alignment as the largest power of two
3037 -- multiple of System.Storage_Unit that does not exceed either
3038 -- the actual size of the type, or the maximum allowed alignment.
3040 declare
3045 begin
3049 loop
3053 -- Now we think we should set the alignment to A, but we
3054 -- skip this if an alignment is already set to a value
3055 -- greater than A (happens for derived types).
3057 -- However, if the alignment is known and too small it
3058 -- must be increased, this happens in a case like:
3060 -- type R is new Character;
3061 -- for R'Size use 16;
3063 -- Here the alignment inherited from Character is 1, but
3064 -- it must be increased to 2 to reflect the increased size.
3072 ----------------------
3073 -- SO_Ref_From_Expr --
3074 ----------------------
3076 function SO_Ref_From_Expr
3081 is
3093 -- Function used to check one node for reference to V
3096 -- Function used to traverse tree to check for reference to V
3098 ----------------------
3099 -- Check_Node_V_Ref --
3100 ----------------------
3103 begin
3107 else
3111 else
3116 -- Start of processing for SO_Ref_From_Expr
3118 begin
3119 -- Case of expression is an integer literal, in this case we just
3120 -- return the value (which must always be non-negative, since size
3121 -- and offset values can never be negative).
3128 -- Case where there is a reference to V, create function
3134 -- Check whether Vtype is a view of a private type and ensure that
3135 -- we use the primary view of the type (which is denoted by its
3136 -- Etype, whether it's the type's partial or full view entity).
3137 -- This is needed to make sure that we use the same (primary) view
3138 -- of the type for all V formals, whether the current view of the
3139 -- type is the partial or full view, so that types will always
3140 -- match on calls from one size function to another.
3144 else
3150 Decl :=
3153 Specification =>
3158 Defining_Identifier =>
3160 Parameter_Type =>
3162 Result_Definition =>
3167 Handled_Statement_Sequence =>
3173 -- The caller requests that the expression be encapsulated in
3174 -- a parameterless function.
3177 Decl :=
3180 Specification =>
3184 Result_Definition =>
3189 Handled_Statement_Sequence =>
3194 -- No reference to V and function not requested, so create a constant
3196 else
3197 Decl :=
3200 Object_Definition =>