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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) 2001-2005 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 2, 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 COPYING. If not, write --
19 -- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, --
20 -- Boston, MA 02110-1301, USA. --
21 -- --
22 -- GNAT was originally developed by the GNAT team at New York University. --
23 -- Extensive contributions were provided by Ada Core Technologies Inc. --
24 -- --
25 ------------------------------------------------------------------------------
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 -----------------------
74 -- E is the entity for a type or object. This procedure checks that the
75 -- size and alignment are compatible, and if not either gives an error
76 -- message if they cannot be adjusted or else adjusts them appropriately.
78 function Assoc_Add
83 -- This is like Make_Op_Add except that it optimizes some cases knowing
84 -- that associative rearrangement is allowed for constant folding if one
85 -- of the operands is a compile time known value.
87 function Assoc_Multiply
92 -- This is like Make_Op_Multiply except that it optimizes some cases
93 -- knowing that associative rearrangement is allowed for constant
94 -- folding if one of the operands is a compile time known value
96 function Assoc_Subtract
101 -- This is like Make_Op_Subtract except that it optimizes some cases
102 -- knowing that associative rearrangement is allowed for constant
103 -- folding if one of the operands is a compile time known value
106 -- This is used when we cross the boundary from static sizes in bits to
107 -- dynamic sizes in storage units. If the argument N is anything other
108 -- than an integer literal, it is returned unchanged, but if it is an
109 -- integer literal, then it is taken as a size in bits, and is replaced
110 -- by the corresponding size in bytes.
113 -- Given expressions for the low bound (Lo) and the high bound (Hi),
114 -- Build an expression for the value hi-lo+1, converted to type
115 -- Standard.Unsigned. Takes care of the case where the operands
116 -- are of an enumeration type (so that the subtraction cannot be
117 -- done directly) by applying the Pos operator to Hi/Lo first.
119 function Expr_From_SO_Ref
124 -- Given a value D from a size or offset field, return an expression
125 -- representing the value stored. If the value is known at compile time,
126 -- then an N_Integer_Literal is returned with the appropriate value. If
127 -- the value references a constant entity, then an N_Identifier node
128 -- referencing this entity is returned. If the value denotes a size
129 -- function, then returns a call node denoting the given function, with
130 -- a single actual parameter that either refers to the parameter V of
131 -- an enclosing size function (if Comp is Empty or its type doesn't match
132 -- the function's formal), or else is a selected component V.c when Comp
133 -- denotes a component c whose type matches that of the function formal.
134 -- The Loc value is used for the Sloc value of constructed notes.
136 function SO_Ref_From_Expr
142 -- This routine is used in the case where a size/offset value is dynamic
143 -- and is represented by the expression Expr. SO_Ref_From_Expr checks if
144 -- the Expr contains a reference to the identifier V, and if so builds
145 -- a function depending on discriminants of the formal parameter V which
146 -- is of type Vtype. Otherwise, if the parameter Make_Func is True, then
147 -- Expr will be encapsulated in a parameterless function; if Make_Func is
148 -- False, then a constant entity with the value Expr is built. The result
149 -- is a Dynamic_SO_Ref to the created entity. Note that Vtype can be
150 -- omitted if Expr does not contain any reference to V, the created entity.
151 -- The declaration created is inserted in the freeze actions of Ins_Type,
152 -- which also supplies the Sloc for created nodes. This function also takes
153 -- care of making sure that the expression is properly analyzed and
154 -- resolved (which may not be the case yet if we build the expression
155 -- in this unit).
158 -- E is an array type or subtype that has at least one index bound that
159 -- is the value of a record discriminant. For such an array, the function
160 -- computes an expression that yields the maximum possible size of the
161 -- array in storage units. The result is not defined for any other type,
162 -- or for arrays that do not depend on discriminants, and it is a fatal
163 -- error to call this unless Size_Depends_On_Discriminant (E) is True.
166 -- Front-end layout of non-bit-packed array type or subtype
169 -- Front-end layout of record type
172 -- Rewrite node N with an integer literal whose value is V. The Sloc
173 -- for the new node is taken from N, and the type of the literal is
174 -- set to a copy of the type of N on entry.
176 procedure Set_And_Check_Static_Size
180 -- This procedure is called to check explicit given sizes (possibly
181 -- stored in the Esize and RM_Size fields of E) against computed
182 -- Object_Size (Esiz) and Value_Size (RM_Siz) values. Appropriate
183 -- errors and warnings are posted if specified sizes are inconsistent
184 -- with specified sizes. On return, the Esize and RM_Size fields of
185 -- E are set (either from previously given values, or from the newly
186 -- computed values, as appropriate).
189 -- This procedure is called for record types and subtypes, and also for
190 -- atomic array types and subtypes. If no alignment is set, and the size
191 -- is 2 or 4 (or 8 if the word size is 8), then the alignment is set to
192 -- match the size.
194 ----------------------------
195 -- Adjust_Esize_Alignment --
196 ----------------------------
202 begin
203 -- Nothing to do if size unknown
209 -- Determine if size is constrained by an attribute definition clause
210 -- which must be obeyed. If so, we cannot increase the size in this
211 -- routine.
213 -- For a type, the issue is whether an object size clause has been
214 -- set. A normal size clause constrains only the value size (RM_Size)
219 -- For an object, the issue is whether a size clause is present
221 else
225 -- If size is known it must be a multiple of the byte size
229 -- If not, and size specified, then give error
232 Error_Msg_NE
236 -- Otherwise bump up size to a byte boundary
238 else
243 -- Now we have the size set, it must be a multiple of the alignment
244 -- nothing more we can do here if the alignment is unknown here.
250 -- At this point both the Esize and Alignment are known, so we need
251 -- to make sure they are consistent.
259 -- Here we have a situation where the Esize is not a multiple of
260 -- the alignment. We must either increase Esize or reduce the
261 -- alignment to correct this situation.
263 -- The case in which we can decrease the alignment is where the
264 -- alignment was not set by an alignment clause, and the type in
265 -- question is a discrete type, where it is definitely safe to
266 -- reduce the alignment. For example:
268 -- t : integer range 1 .. 2;
269 -- for t'size use 8;
271 -- In this situation, the initial alignment of t is 4, copied from
272 -- the Integer base type, but it is safe to reduce it to 1 at this
273 -- stage, since we will only be loading a single byte.
277 then
278 loop
287 -- Now the only possible approach left is to increase the Esize
288 -- but we can't do that if the size was set by a specific clause.
291 Error_Msg_NE
295 -- Otherwise we can indeed increase the size to a multiple of alignment
297 else
302 ---------------
303 -- Assoc_Add --
304 ---------------
306 function Assoc_Add
310 return Node_Id
311 is
315 begin
316 -- Case of right operand is a constant
322 -- Case of left operand is a constant
328 -- Neither operand is a constant, do the addition with no optimization
330 else
334 -- Case of left operand is an addition
338 -- (C1 + E) + C2 = (C1 + C2) + E
341 Rewrite_Integer
346 -- (E + C1) + C2 = E + (C1 + C2)
349 Rewrite_Integer
355 -- Case of left operand is a subtraction
359 -- (C1 - E) + C2 = (C1 + C2) + E
362 Rewrite_Integer
367 -- (E - C1) + C2 = E - (C1 - C2)
370 Rewrite_Integer
377 -- Not optimizable, do the addition
382 --------------------
383 -- Assoc_Multiply --
384 --------------------
386 function Assoc_Multiply
390 return Node_Id
391 is
395 begin
396 -- Case of right operand is a constant
402 -- Case of left operand is a constant
408 -- Neither operand is a constant, do the multiply with no optimization
410 else
414 -- Case of left operand is an multiplication
418 -- (C1 * E) * C2 = (C1 * C2) + E
421 Rewrite_Integer
426 -- (E * C1) * C2 = E * (C1 * C2)
429 Rewrite_Integer
436 -- Not optimizable, do the multiplication
441 --------------------
442 -- Assoc_Subtract --
443 --------------------
445 function Assoc_Subtract
449 return Node_Id
450 is
454 begin
455 -- Case of right operand is a constant
461 -- Right operand is a constant, do the subtract with no optimization
463 else
467 -- Case of left operand is an addition
471 -- (C1 + E) - C2 = (C1 - C2) + E
474 Rewrite_Integer
479 -- (E + C1) - C2 = E + (C1 - C2)
482 Rewrite_Integer
488 -- Case of left operand is a subtraction
492 -- (C1 - E) - C2 = (C1 - C2) + E
495 Rewrite_Integer
500 -- (E - C1) - C2 = E - (C1 + C2)
503 Rewrite_Integer
510 -- Not optimizable, do the subtraction
515 ----------------
516 -- Bits_To_SU --
517 ----------------
520 begin
528 --------------------
529 -- Compute_Length --
530 --------------------
540 begin
541 -- If the bounds are First and Last attributes for the same dimension
542 -- and both have prefixes that denotes the same entity, then we create
543 -- and return a Length attribute. This may allow the back end to
544 -- generate better code in cases where it already has the length.
553 then
566 return
568 Prefix => New_Occurrence_Of
571 Expressions => New_List
579 -- If type is enumeration type, then use Pos attribute to convert
580 -- to integer type for which subtraction is a permitted operation.
583 Lo_Op :=
589 Hi_Op :=
596 return
598 Left_Opnd =>
605 ----------------------
606 -- Expr_From_SO_Ref --
607 ----------------------
609 function Expr_From_SO_Ref
613 return Node_Id
614 is
617 begin
622 -- If a component is passed in whose type matches the type
623 -- of the function formal, then select that component from
624 -- the "V" parameter rather than passing "V" directly.
629 then
630 return
638 else
639 return
646 else
650 else
655 ------------------
656 -- Get_Max_Size --
657 ------------------
671 record
677 -- Shows the status of the value so far. Const means that the value
678 -- is constant, and Val is the current constant value. Dynamic means
679 -- that the value is dynamic, and in this case Nod is the Node_Id of
680 -- the expression to compute the value.
683 -- Calculated value so far if Size.Status = Const,
684 -- or expression value so far if Size.Status = Dynamic.
687 -- This is set to True if the final result must be converted from
688 -- bits to storage units (rounding up to a storage unit boundary).
690 -----------------------
691 -- Local Subprograms --
692 -----------------------
695 -- If the node N represents a discriminant, replace it by the maximum
696 -- value of the discriminant.
699 -- If the node N represents a discriminant, replace it by the minimum
700 -- value of the discriminant.
702 -----------------
703 -- Max_Discrim --
704 -----------------
707 begin
710 then
715 -----------------
716 -- Min_Discrim --
717 -----------------
720 begin
723 then
728 -- Start of processing for Get_Max_Size
730 begin
733 -- Initialize status from component size
738 else
742 -- Loop through indices
753 -- Value of the current subscript range is statically known
757 then
760 -- If known flat bound, entire size of array is zero!
766 -- Current value is constant, evolve value
771 -- Current value is dynamic
773 else
774 -- An interesting little optimization, if we have a pending
775 -- conversion from bits to storage units, and the current
776 -- length is a multiple of the storage unit size, then we
777 -- can take the factor out here statically, avoiding some
778 -- extra dynamic computations at the end.
788 Right_Opnd =>
792 -- Value of the current subscript range is dynamic
794 else
795 -- If the current size value is constant, then here is where we
796 -- make a transition to dynamic values, which are always stored
797 -- in storage units, However, we do not want to convert to SU's
798 -- too soon, consider the case of a packed array of single bits,
799 -- we want to do the SU conversion after computing the size in
800 -- this case.
804 -- If the current value is a multiple of the storage unit,
805 -- then most certainly we can do the conversion now, simply
806 -- by dividing the current value by the storage unit value.
807 -- If this works, we set SU_Convert_Required to False.
811 Size :=
815 -- Otherwise, we go ahead and convert the value in bits,
816 -- and set SU_Convert_Required to True to ensure that the
817 -- final value is indeed properly converted.
819 else
825 -- Length is hi-lo+1
829 -- Check possible range of Len
831 declare
836 begin
842 -- If we cannot verify that range cannot be super-flat,
843 -- we need a max with zero, since length must be non-neg.
846 Len :=
848 Prefix =>
853 Len));
861 -- Here after processing all bounds to set sizes. If the value is
862 -- a constant, then it is bits, and we just return the value.
867 -- Case where the value is dynamic
869 else
870 -- Do convert from bits to SU's if needed
874 -- The expression required is (Size.Nod + SU - 1) / SU
878 Left_Opnd =>
889 -----------------------
890 -- Layout_Array_Type --
891 -----------------------
904 -- This is the type with which any generated constants or functions
905 -- will be associated (i.e. inserted into the freeze actions). This
906 -- is normally the type being laid out. The exception occurs when
907 -- we are laying out Itype's which are local to a record type, and
908 -- whose scope is this record type. Such types do not have freeze
909 -- nodes (because we have no place to put them).
911 ------------------------------------
912 -- How An Array Type is Laid Out --
913 ------------------------------------
915 -- Here is what goes on. We need to multiply the component size of
916 -- the array (which has already been set) by the length of each of
917 -- the indexes. If all these values are known at compile time, then
918 -- the resulting size of the array is the appropriate constant value.
920 -- If the component size or at least one bound is dynamic (but no
921 -- discriminants are present), then the size will be computed as an
922 -- expression that calculates the proper size.
924 -- If there is at least one discriminant bound, then the size is also
925 -- computed as an expression, but this expression contains discriminant
926 -- values which are obtained by selecting from a function parameter, and
927 -- the size is given by a function that is passed the variant record in
928 -- question, and whose body is the expression.
933 record
937 -- Calculated value so far if Val_Status = Const
941 -- Expression value so far if Val_Status /= Const
945 -- Records the value or expression computed so far. Const means that
946 -- the value is constant, and Val is the current constant value.
947 -- Dynamic means that the value is dynamic, and in this case Nod is
948 -- the Node_Id of the expression to compute the value, and Discrim
949 -- means that at least one bound is a discriminant, in which case Nod
950 -- is the expression so far (which will be the body of the function).
953 -- Value of size computed so far. See comments above
956 -- Variant record type for the formal parameter of the
957 -- discriminant function V if Status = Discrim.
960 -- This is set to True if the final result must be converted from
961 -- bits to storage units (rounding up to a storage unit boundary).
964 -- This is the amount that a nonstatic computed size will be divided
965 -- by to convert it from bits to storage units. This is normally
966 -- equal to SSU, but can be reduced in the case of packed components
967 -- that fit evenly into a storage unit.
970 -- Indicates whether to request that SO_Ref_From_Expr should
971 -- encapsulate the array size expresion in a function.
974 -- If N represents a discriminant, then the Size.Status is set to
975 -- Discrim, and Vtyp is set. The parameter N is replaced with the
976 -- proper expression to extract the discriminant value from V.
978 ----------------
979 -- Discrimify --
980 ----------------
986 begin
989 then
1000 N :=
1005 -- Set the Etype attributes of the selected name and its prefix.
1006 -- Analyze_And_Resolve can't be called here because the Vname
1007 -- entity denoted by the prefix will not yet exist (it's created
1008 -- by SO_Ref_From_Expr, called at the end of Layout_Array_Type).
1015 -- Start of processing for Layout_Array_Type
1017 begin
1018 -- Default alignment is component alignment
1024 -- Calculate proper type for insertions
1028 else
1032 -- If the component type is a generic formal type then there's no point
1033 -- in determining a size for the array type.
1039 -- Deal with component size if base type
1043 -- Cannot do anything if Esize of component type unknown
1049 -- Set component size if not set already
1056 -- (RM 13.3 (48)) says that the size of an unconstrained array
1057 -- is implementation defined. We choose to leave it as Unknown
1058 -- here, and the actual behavior is determined by the back end.
1064 -- Initialize status from component size
1069 else
1073 -- Loop to process array indices
1079 -- If an index of the array is a generic formal type then there's
1080 -- no point in determining a size for the array type.
1089 -- Value of the current subscript range is statically known
1093 then
1096 -- If known flat bound, entire size of array is zero!
1104 -- If constant, evolve value
1109 -- Current value is dynamic
1111 else
1112 -- An interesting little optimization, if we have a pending
1113 -- conversion from bits to storage units, and the current
1114 -- length is a multiple of the storage unit size, then we
1115 -- can take the factor out here statically, avoiding some
1116 -- extra dynamic computations at the end.
1123 -- Now go ahead and evolve the expression
1128 Right_Opnd =>
1132 -- Value of the current subscript range is dynamic
1134 else
1135 -- If the current size value is constant, then here is where we
1136 -- make a transition to dynamic values, which are always stored
1137 -- in storage units, However, we do not want to convert to SU's
1138 -- too soon, consider the case of a packed array of single bits,
1139 -- we want to do the SU conversion after computing the size in
1140 -- this case.
1144 -- If the current value is a multiple of the storage unit,
1145 -- then most certainly we can do the conversion now, simply
1146 -- by dividing the current value by the storage unit value.
1147 -- If this works, we set SU_Convert_Required to False.
1150 Size :=
1154 -- If the current value is a factor of the storage unit,
1155 -- then we can use a value of one for the size and reduce
1156 -- the strength of the later division.
1163 -- Otherwise, we go ahead and convert the value in bits,
1164 -- and set SU_Convert_Required to True to ensure that the
1165 -- final value is indeed properly converted.
1167 else
1176 -- Length is hi-lo+1
1180 -- If Len isn't a Length attribute, then its range needs to
1181 -- be checked a possible Max with zero needs to be computed.
1185 then
1186 declare
1191 begin
1192 -- Check possible range of Len
1199 -- If range definitely flat or superflat,
1200 -- result size is zero
1208 -- If we cannot verify that range cannot be super-flat,
1209 -- we need a maximum with zero, since length cannot be
1210 -- negative.
1213 Len :=
1215 Prefix =>
1220 Len));
1225 -- At this stage, Len has the expression for the length
1236 -- Here after processing all bounds to set sizes. If the value is
1237 -- a constant, then it is bits, and the only thing we need to do
1238 -- is to check against explicit given size and do alignment adjust.
1244 -- Case where the value is dynamic
1246 else
1247 -- Do convert from bits to SU's if needed
1251 -- The expression required is:
1252 -- (Size.Nod + Storage_Divisor - 1) / Storage_Divisor
1256 Left_Opnd =>
1259 Right_Opnd => Make_Integer_Literal
1264 -- If the array entity is not declared at the library level and its
1265 -- not nested within a subprogram that is marked for inlining, then
1266 -- we request that the size expression be encapsulated in a function.
1267 -- Since this expression is not needed in most cases, we prefer not
1268 -- to incur the overhead of the computation on calls to the enclosing
1269 -- subprogram except for subprograms that require the size.
1274 declare
1277 begin
1289 -- Now set the dynamic size (the Value_Size is always the same
1290 -- as the Object_Size for arrays whose length is dynamic).
1292 -- ??? If Size.Status = Dynamic, Vtyp will not have been set.
1293 -- The added initialization sets it to Empty now, but is this
1294 -- correct?
1296 Set_Esize
1298 SO_Ref_From_Expr
1304 -------------------
1305 -- Layout_Object --
1306 -------------------
1311 begin
1312 -- Nothing to do if backend does layout
1318 -- Set size if not set for object and known for type. Use the
1319 -- RM_Size if that is known for the type and Esize is not.
1330 -- Set alignment from type if unknown and type alignment known
1336 -- Make sure size and alignment are consistent
1340 -- Final adjustment, if we don't know the alignment, and the Esize
1341 -- was not set by an explicit Object_Size attribute clause, then
1342 -- we reset the Esize to unknown, since we really don't know it.
1346 then
1351 ------------------------
1352 -- Layout_Record_Type --
1353 ------------------------
1360 -- Current component being laid out
1363 -- Previous laid out component
1365 procedure Get_Next_Component_Location
1372 -- Given the previous component in Prev_Comp, which is already laid
1373 -- out, and the alignment of the following component, lays out the
1374 -- following component, and returns its starting position in New_Npos
1375 -- (Normalized_Position value), New_Fbit (Normalized_First_Bit value),
1376 -- and New_NPMax (Normalized_Position_Max value). If Prev_Comp is empty
1377 -- (no previous component is present), then New_Npos, New_Fbit and
1378 -- New_NPMax are all set to zero on return. This procedure is also
1379 -- used to compute the size of a record or variant by giving it the
1380 -- last component, and the record alignment. Force_SU is used to force
1381 -- the new component location to be aligned on a storage unit boundary,
1382 -- even in a packed record, False means that the new position does not
1383 -- need to be bumped to a storage unit boundary, True means a storage
1384 -- unit boundary is always required.
1387 -- Lays out component Comp, given Prev_Comp, the previously laid-out
1388 -- component (Prev_Comp = Empty if no components laid out yet). The
1389 -- alignment of the record itself is also updated if needed. Both
1390 -- Comp and Prev_Comp can be either components or discriminants.
1392 procedure Layout_Components
1397 -- This procedure lays out the components of the given component list
1398 -- which contains the components starting with From and ending with To.
1399 -- The Next_Entity chain is used to traverse the components. On entry,
1400 -- Prev_Comp is set to the component preceding the list, so that the
1401 -- list is laid out after this component. Prev_Comp is set to Empty if
1402 -- the component list is to be laid out starting at the start of the
1403 -- record. On return, the components are all laid out, and Prev_Comp is
1404 -- set to the last laid out component. On return, Esiz is set to the
1405 -- resulting Object_Size value, which is the length of the record up
1406 -- to and including the last laid out entity. For Esiz, the value is
1407 -- adjusted to match the alignment of the record. RM_Siz is similarly
1408 -- set to the resulting Value_Size value, which is the same length, but
1409 -- not adjusted to meet the alignment. Note that in the case of variant
1410 -- records, Esiz represents the maximum size.
1413 -- Procedure called to lay out a non-variant record type or subtype
1416 -- Procedure called to lay out a variant record type. Decl is set to the
1417 -- full type declaration for the variant record.
1419 ---------------------------------
1420 -- Get_Next_Component_Location --
1421 ---------------------------------
1423 procedure Get_Next_Component_Location
1430 is
1431 begin
1432 -- No previous component, return zero position
1441 -- Here we have a previous component
1443 declare
1452 -- Expression representing maximum size of previous component
1454 begin
1455 -- Case where previous field had a dynamic size
1459 -- If the previous field had a dynamic length, then it is
1460 -- required to occupy an integral number of storage units,
1461 -- and start on a storage unit boundary. This means that
1462 -- the Normalized_First_Bit value is zero in the previous
1463 -- component, and the new value is also set to zero.
1467 -- In this case, the new position is given by an expression
1468 -- that is the sum of old normalized position and old size.
1470 New_Npos :=
1471 SO_Ref_From_Expr
1473 Left_Opnd =>
1475 Right_Opnd =>
1480 -- Get maximum size of previous component
1484 else
1488 -- Now we can compute the new max position. If the max size
1489 -- is static and the old position is static, then we can
1490 -- compute the new position statically.
1494 then
1497 -- Otherwise new max position is dynamic
1499 else
1500 New_NPMax :=
1501 SO_Ref_From_Expr
1509 -- Previous field has known static Esize
1511 else
1514 -- Bump New_Fbit to storage unit boundary if required
1520 -- If old normalized position is static, we can go ahead
1521 -- and compute the new normalized position directly.
1531 -- Bump alignment if stricter than prev
1537 -- The max position is always equal to the position if
1538 -- the latter is static, since arrays depending on the
1539 -- values of discriminants never have static sizes.
1544 -- Case of old normalized position is dynamic
1546 else
1547 -- If new bit position is within the current storage unit,
1548 -- we can just copy the old position as the result position
1549 -- (we have already set the new first bit value).
1555 -- If new bit position is past the current storage unit, we
1556 -- need to generate a new dynamic value for the position
1557 -- ??? need to deal with alignment
1559 else
1560 New_Npos :=
1561 SO_Ref_From_Expr
1564 Right_Opnd =>
1570 New_NPMax :=
1571 SO_Ref_From_Expr
1574 Right_Opnd =>
1586 ----------------------
1587 -- Layout_Component --
1588 ----------------------
1597 begin
1598 -- Parent field is always at start of record, this will overlap
1599 -- the actual fields that are part of the parent, and that's fine
1610 -- Check case of type of component has a scope of the record we
1611 -- are laying out. When this happens, the type in question is an
1612 -- Itype that has not yet been laid out (that's because such
1613 -- types do not get frozen in the normal manner, because there
1614 -- is no place for the freeze nodes).
1620 -- Increase alignment of record if necessary. Note that we do not
1621 -- do this for packed records, which have an alignment of one by
1622 -- default, or for records for which an explicit alignment was
1623 -- specified with an alignment clause.
1628 then
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 else
1767 -- First the object size, for which we align past the last
1768 -- field to the alignment of the record (the object size
1769 -- is required to be a multiple of the alignment).
1771 Get_Next_Component_Location
1774 End_Npos,
1775 End_Fbit,
1776 End_NPMax,
1779 -- If the resulting normalized position is a dynamic reference,
1780 -- then the size is dynamic, and is stored in storage units.
1781 -- In this case, we set the RM_Size to the same value, it is
1782 -- simply not worth distinguishing Esize and RM_Size values in
1783 -- the dynamic case, since the RM has nothing to say about them.
1785 -- Note that a size cannot have been given in this case, since
1786 -- size specifications cannot be given for variable length types.
1788 declare
1791 begin
1795 -- Set the Object_Size allowing for alignment. In the
1796 -- dynamic case, we have to actually do the runtime
1797 -- computation. We can skip this in the non-packed
1798 -- record case if the last component has a smaller
1799 -- alignment than the overall record alignment.
1806 then
1807 -- The expression we build is
1808 -- (expr + align - 1) / align * align
1810 Esiz :=
1811 SO_Ref_From_Expr
1814 Left_Opnd =>
1816 Left_Opnd =>
1818 Left_Opnd =>
1820 Right_Opnd =>
1823 Right_Opnd =>
1825 Right_Opnd =>
1831 -- Here Esiz is static, so we can adjust the alignment
1832 -- directly go give the required aligned value.
1834 else
1838 -- Case where computed size is static
1840 else
1841 -- The ending size was computed in Npos in storage units,
1842 -- but the actual size is stored in bits, so adjust
1843 -- accordingly. We also adjust the size to match the
1844 -- alignment here.
1848 -- Compute the resulting Value_Size (RM_Size). For this
1849 -- purpose we do not force alignment of the record or
1850 -- storage size alignment of the result.
1852 Get_Next_Component_Location
1854 Uint_0,
1855 End_Npos,
1856 End_Fbit,
1857 End_NPMax,
1867 -------------------------------
1868 -- Layout_Non_Variant_Record --
1869 -------------------------------
1875 begin
1881 ---------------------------
1882 -- Layout_Variant_Record --
1883 ---------------------------
1892 -- Expression for the evolving RM_Siz value. This is typically a
1893 -- conditional expression which involves tests of discriminant
1894 -- values that are formed as references to the entity V. At
1895 -- the end of scanning all the components, a suitable function
1896 -- is constructed in which V is the parameter.
1898 -----------------------
1899 -- Local Subprograms --
1900 -----------------------
1902 procedure Layout_Component_List
1906 -- Recursive procedure, called to lay out one component list
1907 -- Esiz and RM_Siz_Expr are set to the Object_Size and Value_Size
1908 -- values respectively representing the record size up to and
1909 -- including the last component in the component list (including
1910 -- any variants in this component list). RM_Siz_Expr is returned
1911 -- as an expression which may in the general case involve some
1912 -- references to the discriminants of the current record value,
1913 -- referenced by selecting from the entity V.
1915 ---------------------------
1916 -- Layout_Component_List --
1917 ---------------------------
1919 procedure Layout_Component_List
1923 is
1931 begin
1933 Layout_Components
1938 else
1942 -- Case where no variants are present in the component list
1946 -- The Esiz value has been correctly set by the call to
1947 -- Layout_Components, so there is nothing more to be done.
1949 -- For RM_Siz, we have an SO_Ref value, which we must convert
1950 -- to an appropriate expression.
1953 RM_Siz_Expr :=
1957 else
1960 -- If the size is represented by a function, then we
1961 -- create an appropriate function call using V as
1962 -- the parameter to the call.
1965 RM_Siz_Expr :=
1971 -- If the size is represented by a constant, then the
1972 -- expression we want is a reference to this constant
1974 else
1979 -- Case where variants are present in this component list
1981 else
1982 declare
1991 begin
1998 Layout_Component_List
2001 -- Set the Object_Size. If this is the first variant,
2002 -- we just set the size of this first variant.
2007 -- Otherwise the Object_Size is formed as a maximum
2008 -- of Esiz so far from previous variants, and the new
2009 -- Esiz value from the variant we just processed.
2011 -- If both values are static, we can just compute the
2012 -- maximum directly to save building junk nodes.
2016 then
2019 -- If either value is dynamic, then we have to generate
2020 -- an appropriate Standard_Unsigned'Max attribute call.
2022 else
2023 Esiz :=
2024 SO_Ref_From_Expr
2027 Prefix =>
2036 -- Now deal with Value_Size (RM_Siz). We are aiming at
2037 -- an expression that looks like:
2039 -- if xxDx (V.disc) then rmsiz1
2040 -- else if xxDx (V.disc) then rmsiz2
2041 -- else ...
2043 -- Where rmsiz1, rmsiz2... are the RM_Siz values for the
2044 -- individual variants, and xxDx are the discriminant
2045 -- checking functions generated for the variant type.
2047 -- If this is the first variant, we simply set the
2048 -- result as the expression. Note that this takes
2049 -- care of the others case.
2054 -- Otherwise construct the appropriate test
2056 else
2057 -- The test to be used in general is a call to the
2058 -- discriminant checking function. However, it is
2059 -- definitely worth special casing the very common
2060 -- case where a single value is involved.
2066 then
2067 -- Discriminant to be tested
2069 Discrim :=
2071 Prefix =>
2073 Selector_Name =>
2074 New_Occurrence_Of
2077 Dtest :=
2082 -- Generate a call to the discriminant-checking
2083 -- function for the variant. Note that the result
2084 -- has to be complemented since the function returns
2085 -- False when the passed discriminant value matches.
2087 else
2088 -- The checking function takes all of the type's
2089 -- discriminants as parameters, so a list of all
2090 -- the selected discriminants must be constructed.
2095 Append (
2097 Prefix =>
2099 Selector_Name =>
2100 New_Occurrence_Of
2102 D_List);
2107 Dtest :=
2109 Right_Opnd =>
2111 Name =>
2112 New_Occurrence_Of
2114 Parameter_Associations =>
2115 D_List));
2118 RM_Siz_Expr :=
2120 Expressions =>
2121 New_List
2131 -- Start of processing for Layout_Variant_Record
2133 begin
2134 -- We need the discriminant checking functions, since we generate
2135 -- calls to these functions for the RM_Size expression, so make
2136 -- sure that these functions have been constructed in time.
2140 -- Lay out the discriminants
2142 Layout_Components
2148 -- Lay out the main component list (this will make recursive calls
2149 -- to lay out all component lists nested within variants).
2154 -- If the RM_Size is a literal, set its value
2159 -- Otherwise we construct a dynamic SO_Ref
2161 else
2163 SO_Ref_From_Expr
2170 -- Start of processing for Layout_Record_Type
2172 begin
2173 -- If this is a cloned subtype, just copy the size fields from the
2174 -- original, nothing else needs to be done in this case, since the
2175 -- components themselves are all shared.
2180 then
2185 -- Another special case, class-wide types. The RM says that the size
2186 -- of such types is implementation defined (RM 13.3(48)). What we do
2187 -- here is to leave the fields set as unknown values, and the backend
2188 -- determines the actual behavior.
2193 -- All other cases
2195 else
2196 -- Initialize alignment conservatively to 1. This value will
2197 -- be increased as necessary during processing of the record.
2203 -- Initialize previous component. This is Empty unless there
2204 -- are components which have already been laid out by component
2205 -- clauses. If there are such components, we start our lay out of
2206 -- the remaining components following the last such component.
2215 then
2217 or else
2220 then
2228 -- We have two separate circuits, one for non-variant records and
2229 -- one for variant records. For non-variant records, we simply go
2230 -- through the list of components. This handles all the non-variant
2231 -- cases including those cases of subtypes where there is no full
2232 -- type declaration, so the tree cannot be used to drive the layout.
2233 -- For variant records, we have to drive the layout from the tree
2234 -- since we need to understand the variant structure in this case.
2238 else
2242 -- Scan all the components
2248 and then
2250 then
2251 Layout_Variant_Record;
2252 else
2253 Layout_Non_Variant_Record;
2258 -----------------
2259 -- Layout_Type --
2260 -----------------
2263 begin
2264 -- For string literal types, for now, kill the size always, this
2265 -- is because gigi does not like or need the size to be set ???
2273 -- For access types, set size/alignment. This is system address
2274 -- size, except for fat pointers (unconstrained array access types),
2275 -- where the size is two times the address size, to accommodate the
2276 -- two pointers that are required for a fat pointer (data and
2277 -- template). Note that E_Access_Protected_Subprogram_Type is not
2278 -- an access type for this purpose since it is not a pointer but is
2279 -- equivalent to a record. For access subtypes, copy the size from
2280 -- the base type since Gigi represents them the same way.
2284 -- If Esize already set (e.g. by a size clause), then nothing
2285 -- further to be done here.
2290 -- Access to subprogram is a strange beast, and we let the
2291 -- backend figure out what is needed (it may be some kind
2292 -- of fat pointer, including the static link for example.
2297 -- For access subtypes, copy the size information from base type
2303 -- For other access types, we use either address size, or, if
2304 -- a fat pointer is used (pointer-to-unconstrained array case),
2305 -- twice the address size to accommodate a fat pointer.
2307 else
2308 declare
2311 begin
2314 then
2321 and then not Debug_Flag_6
2322 then
2325 -- Check for bad convention set
2327 if Warn_On_Export_Import
2328 and then
2330 or else
2332 then
2333 Error_Msg_N
2338 else
2346 -- Scalar types: set size and alignment
2350 -- For discrete types, the RM_Size and Esize must be set
2351 -- already, since this is part of the earlier processing
2352 -- and the front end is always required to lay out the
2353 -- sizes of such types (since they are available as static
2354 -- attributes). All we do is to check that this rule is
2355 -- indeed obeyed!
2359 -- If the RM_Size is not set, then here is where we set it
2361 -- Note: an RM_Size of zero looks like not set here, but this
2362 -- is a rare case, and we can simply reset it without any harm.
2368 -- If Esize for a discrete type is not set then set it
2371 declare
2374 begin
2375 loop
2376 -- If size is big enough, set it and exit
2382 -- If the RM_Size is greater than 64 (happens only
2383 -- when strange values are specified by the user,
2384 -- then Esize is simply a copy of RM_Size, it will
2385 -- be further refined later on)
2391 -- Otherwise double possible size and keep trying
2393 else
2400 -- For non-discrete sclar types, if the RM_Size is not set,
2401 -- then set it now to a copy of the Esize if the Esize is set.
2403 else
2411 -- Non-elementary (composite) types
2413 else
2414 -- If RM_Size is known, set Esize if not known
2418 -- If the alignment is known, we bump the Esize up to the
2419 -- next alignment boundary if it is not already on one.
2422 declare
2426 begin
2431 -- If Esize is set, and RM_Size is not, RM_Size is copied from
2432 -- Esize at least for now this seems reasonable, and is in any
2433 -- case needed for compatibility with old versions of gigi.
2434 -- look to be unknown.
2440 -- For array base types, set component size if object size of
2441 -- the component type is known and is a small power of 2 (8,
2442 -- 16, 32, 64), since this is what will always be used.
2446 then
2447 declare
2450 begin
2451 -- For some reasons, access types can cause trouble,
2452 -- So let's just do this for discrete types ???
2457 then
2458 declare
2461 begin
2466 then
2475 -- Lay out array and record types if front end layout set
2484 -- Case of backend layout, we still do a little in the front end
2486 else
2487 -- Processing for record types
2491 -- Special remaining processing for record types with a known
2492 -- size of 16, 32, or 64 bits whose alignment is not yet set.
2493 -- For these types, we set a corresponding alignment matching
2494 -- the size if possible, or as large as possible if not.
2497 and then not Debug_Flag_Q
2498 then
2502 -- Procressing for array types
2506 -- For arrays that are required to be atomic, we do the same
2507 -- processing as described above for short records, since we
2508 -- really need to have the alignment set for the whole array.
2514 -- For unpacked array types, set an alignment of 1 if we know
2515 -- that the component alignment is not greater than 1. The reason
2516 -- we do this is to avoid unnecessary copying of slices of such
2517 -- arrays when passed to subprogram parameters (see special test
2518 -- in Exp_Ch6.Expand_Actuals).
2522 then
2525 then
2532 -- Final step is to check that Esize and RM_Size are compatible
2537 -- Esize is less than RM_Size. That's not good. First we test
2538 -- whether this was set deliberately with an Object_Size clause
2539 -- and if so, object to the clause.
2543 Error_Msg_F
2545 Expression (Get_Attribute_Definition_Clause
2549 -- Adjust Esize up to RM_Size value
2551 declare
2554 begin
2557 -- For scalar types, increase Object_Size to power of 2,
2558 -- but not less than a storage unit in any case (i.e.,
2559 -- normally this means it will be byte addressable).
2568 else
2572 -- Finally, make sure that alignment is consistent with
2573 -- the newly assigned size.
2577 loop
2586 ---------------------
2587 -- Rewrite_Integer --
2588 ---------------------
2594 begin
2599 -------------------------------
2600 -- Set_And_Check_Static_Size --
2601 -------------------------------
2603 procedure Set_And_Check_Static_Size
2607 is
2611 -- Spec is the number of bit specified in the size clause, and
2612 -- Min is the minimum computed size. An error is given that the
2613 -- specified size is too small if Spec < Min, and in this case
2614 -- both Esize and RM_Size are set to unknown in E. The error
2615 -- message is posted on node SC.
2618 -- Spec is the number of bits specified in the size clause, and
2619 -- Max is the maximum computed size. A warning is given about
2620 -- unused bits if Spec > Max. This warning is posted on node SC.
2622 --------------------------
2623 -- Check_Size_Too_Small --
2624 --------------------------
2627 begin
2630 Error_Msg_NE
2637 -----------------------
2638 -- Check_Unused_Bits --
2639 -----------------------
2642 begin
2649 -- Start of processing for Set_And_Check_Static_Size
2651 begin
2652 -- Case where Object_Size (Esize) is already set by a size clause
2661 -- Perform checks on specified size against computed sizes
2669 -- Case where Value_Size (RM_Size) is set by specific Value_Size
2670 -- clause (we do not need to worry about Value_Size being set by
2671 -- a Size clause, since that will have set Esize as well, and we
2672 -- already took care of that case).
2677 -- Perform checks on specified size against computed sizes
2685 -- Set sizes if unknown
2696 -----------------------------
2697 -- Set_Composite_Alignment --
2698 -----------------------------
2704 begin
2711 then
2714 else
2718 -- Size is known, alignment is not set
2720 -- Reset alignment to match size if size is exactly 2, 4, or 8 bytes
2729 -- On VMS, also reset for odd "in between" sizes, e.g. a 17-bit
2730 -- record is given an alignment of 4. This is more consistent with
2731 -- what DEC Ada does.
2741 else
2745 -- No special alignment fiddling needed
2747 else
2751 -- Here Align is set to the proposed improved alignment
2757 -- Further processing for record types only to reduce the alignment
2758 -- set by the above processing in some specific cases. We do not
2759 -- do this for atomic records, since we need max alignment there.
2763 -- For records, there is generally no point in setting alignment
2764 -- higher than word size since we cannot do better than move by
2765 -- words in any case
2771 -- Check components. If any component requires a higher
2772 -- alignment, then we set that higher alignment in any case.
2774 declare
2777 begin
2781 declare
2784 begin
2785 -- The cases to worry about are when the alignment
2786 -- of the component type is larger than the alignment
2787 -- we have so far, and either there is no component
2788 -- clause for the alignment, or the length set by
2789 -- the component clause matches the alignment set.
2792 and then
2795 and then
2798 then
2809 -- Set chosen alignment
2815 then
2821 --------------------------
2822 -- Set_Discrete_RM_Size --
2823 --------------------------
2828 begin
2829 -- All discrete types except for the base types in standard
2830 -- are constrained, so indicate this by setting Is_Constrained.
2834 -- We set generic types to have an unknown size, since the
2835 -- representation of a generic type is irrelevant, in view
2836 -- of the fact that they have nothing to do with code.
2841 -- If the subtype statically matches the first subtype, then
2842 -- it is required to have exactly the same layout. This is
2843 -- required by aliasing considerations.
2847 then
2851 -- In all other cases the RM_Size is set to the minimum size.
2852 -- Note that this routine is never called for subtypes for which
2853 -- the RM_Size is set explicitly by an attribute clause.
2855 else
2860 ------------------------
2861 -- Set_Elem_Alignment --
2862 ------------------------
2865 begin
2866 -- Do not set alignment for packed array types, unless we are doing
2867 -- front end layout, because otherwise this is always handled in the
2868 -- backend.
2873 -- If there is an alignment clause, then we respect it
2878 -- If the size is not set, then don't attempt to set the alignment. This
2879 -- happens in the backend layout case for access-to-subprogram types.
2884 -- For access types, do not set the alignment if the size is less than
2885 -- the allowed minimum size. This avoids cascaded error messages.
2889 then
2893 -- Here we calculate the alignment as the largest power of two
2894 -- multiple of System.Storage_Unit that does not exceed either
2895 -- the actual size of the type, or the maximum allowed alignment.
2897 declare
2902 begin
2906 loop
2910 -- Now we think we should set the alignment to A, but we
2911 -- skip this if an alignment is already set to a value
2912 -- greater than A (happens for derived types).
2914 -- However, if the alignment is known and too small it
2915 -- must be increased, this happens in a case like:
2917 -- type R is new Character;
2918 -- for R'Size use 16;
2920 -- Here the alignment inherited from Character is 1, but
2921 -- it must be increased to 2 to reflect the increased size.
2929 ----------------------
2930 -- SO_Ref_From_Expr --
2931 ----------------------
2933 function SO_Ref_From_Expr
2938 return Dynamic_SO_Ref
2939 is
2951 -- Function used to check one node for reference to V
2954 -- Function used to traverse tree to check for reference to V
2956 ----------------------
2957 -- Check_Node_V_Ref --
2958 ----------------------
2961 begin
2965 else
2969 else
2974 -- Start of processing for SO_Ref_From_Expr
2976 begin
2977 -- Case of expression is an integer literal, in this case we just
2978 -- return the value (which must always be non-negative, since size
2979 -- and offset values can never be negative).
2986 -- Case where there is a reference to V, create function
2992 -- Check whether Vtype is a view of a private type and ensure that
2993 -- we use the primary view of the type (which is denoted by its
2994 -- Etype, whether it's the type's partial or full view entity).
2995 -- This is needed to make sure that we use the same (primary) view
2996 -- of the type for all V formals, whether the current view of the
2997 -- type is the partial or full view, so that types will always
2998 -- match on calls from one size function to another.
3002 else
3008 Decl :=
3011 Specification =>
3016 Defining_Identifier =>
3018 Parameter_Type =>
3020 Result_Definition =>
3025 Handled_Statement_Sequence =>
3031 -- The caller requests that the expression be encapsulated in
3032 -- a parameterless function.
3035 Decl :=
3038 Specification =>
3042 Result_Definition =>
3047 Handled_Statement_Sequence =>
3052 -- No reference to V and function not requested, so create a constant
3054 else
3055 Decl :=
3058 Object_Definition =>