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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) 2001-2014, 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 ------------------------------------------------------------------------------
54 ------------------------
55 -- Local Declarations --
56 ------------------------
59 -- Short hand for System_Storage_Unit
62 -- Formal parameter name used for functions generated for size offset
63 -- values that depend on the discriminant. All such functions have the
64 -- following form:
65 --
66 -- function xxx (V : vtyp) return Unsigned is
67 -- begin
68 -- return ... expression involving V.discrim
69 -- end xxx;
71 -----------------------
72 -- Local Subprograms --
73 -----------------------
75 function Assoc_Add
79 -- This is like Make_Op_Add except that it optimizes some cases knowing
80 -- that associative rearrangement is allowed for constant folding if one
81 -- of the operands is a compile time known value.
83 function Assoc_Multiply
87 -- This is like Make_Op_Multiply except that it optimizes some cases
88 -- knowing that associative rearrangement is allowed for constant folding
89 -- if one of the operands is a compile time known value
91 function Assoc_Subtract
95 -- This is like Make_Op_Subtract except that it optimizes some cases
96 -- knowing that associative rearrangement is allowed for constant folding
97 -- if one of the operands is a compile time known value
100 -- This is used when we cross the boundary from static sizes in bits to
101 -- dynamic sizes in storage units. If the argument N is anything other
102 -- than an integer literal, it is returned unchanged, but if it is an
103 -- integer literal, then it is taken as a size in bits, and is replaced
104 -- by the corresponding size in storage units.
107 -- Given expressions for the low bound (Lo) and the high bound (Hi),
108 -- Build an expression for the value hi-lo+1, converted to type
109 -- Standard.Unsigned. Takes care of the case where the operands
110 -- are of an enumeration type (so that the subtraction cannot be
111 -- done directly) by applying the Pos operator to Hi/Lo first.
114 -- Given an array type or an array subtype E, compute whether its size
115 -- depends on the value of one or more discriminants and set the flag
116 -- Size_Depends_On_Discriminant accordingly. This need not be called
117 -- in front end layout mode since it does the computation on its own.
119 function Expr_From_SO_Ref
123 -- Given a value D from a size or offset field, return an expression
124 -- representing the value stored. If the value is known at compile time,
125 -- then an N_Integer_Literal is returned with the appropriate value. If
126 -- the value references a constant entity, then an N_Identifier node
127 -- referencing this entity is returned. If the value denotes a size
128 -- function, then returns a call node denoting the given function, with
129 -- a single actual parameter that either refers to the parameter V of
130 -- an enclosing size function (if Comp is Empty or its type doesn't match
131 -- the function's formal), or else is a selected component V.c when Comp
132 -- denotes a component c whose type matches that of the function formal.
133 -- The Loc value is used for the Sloc value of constructed notes.
135 function SO_Ref_From_Expr
140 -- This routine is used in the case where a size/offset value is dynamic
141 -- and is represented by the expression Expr. SO_Ref_From_Expr checks if
142 -- the Expr contains a reference to the identifier V, and if so builds
143 -- a function depending on discriminants of the formal parameter V which
144 -- is of type Vtype. Otherwise, if the parameter Make_Func is True, then
145 -- Expr will be encapsulated in a parameterless function; if Make_Func is
146 -- False, then a constant entity with the value Expr is built. The result
147 -- is a Dynamic_SO_Ref to the created entity. Note that Vtype can be
148 -- omitted if Expr does not contain any reference to V, the created entity.
149 -- The declaration created is inserted in the freeze actions of Ins_Type,
150 -- which also supplies the Sloc for created nodes. This function also takes
151 -- care of making sure that the expression is properly analyzed and
152 -- resolved (which may not be the case yet if we build the expression
153 -- in this unit).
156 -- E is an array type or subtype that has at least one index bound that
157 -- is the value of a record discriminant. For such an array, the function
158 -- computes an expression that yields the maximum possible size of the
159 -- array in storage units. The result is not defined for any other type,
160 -- or for arrays that do not depend on discriminants, and it is a fatal
161 -- error to call this unless Size_Depends_On_Discriminant (E) is True.
164 -- Front-end layout of non-bit-packed array type or subtype
167 -- Front-end layout of record type
170 -- Rewrite node N with an integer literal whose value is V. The Sloc for
171 -- the new node is taken from N, and the type of the literal is set to a
172 -- copy of the type of N on entry.
174 procedure Set_And_Check_Static_Size
178 -- This procedure is called to check explicit given sizes (possibly stored
179 -- in the Esize and RM_Size fields of E) against computed Object_Size
180 -- (Esiz) and Value_Size (RM_Siz) values. Appropriate errors and warnings
181 -- are posted if specified sizes are inconsistent with specified sizes. On
182 -- return, Esize and RM_Size fields of E are set (either from previously
183 -- given values, or from the newly computed values, as appropriate).
186 -- This procedure is called for record types and subtypes, and also for
187 -- atomic array types and subtypes. If no alignment is set, and the size
188 -- is 2 or 4 (or 8 if the word size is 8), then the alignment is set to
189 -- match the size.
191 ----------------------------
192 -- Adjust_Esize_Alignment --
193 ----------------------------
199 begin
200 -- Nothing to do if size unknown
206 -- Determine if size is constrained by an attribute definition clause
207 -- which must be obeyed. If so, we cannot increase the size in this
208 -- routine.
210 -- For a type, the issue is whether an object size clause has been set.
211 -- A normal size clause constrains only the value size (RM_Size)
216 -- For an object, the issue is whether a size clause is present
218 else
222 -- If size is known it must be a multiple of the storage unit size
226 -- If not, and size specified, then give error
229 Error_Msg_NE
234 -- Otherwise bump up size to a storage unit boundary
236 else
241 -- Now we have the size set, it must be a multiple of the alignment
242 -- nothing more we can do here if the alignment is unknown here.
248 -- At this point both the Esize and Alignment are known, so we need
249 -- to make sure they are consistent.
257 -- Here we have a situation where the Esize is not a multiple of the
258 -- alignment. We must either increase Esize or reduce the alignment to
259 -- correct this situation.
261 -- The case in which we can decrease the alignment is where the
262 -- alignment was not set by an alignment clause, and the type in
263 -- question is a discrete type, where it is definitely safe to reduce
264 -- the alignment. For example:
266 -- t : integer range 1 .. 2;
267 -- for t'size use 8;
269 -- In this situation, the initial alignment of t is 4, copied from
270 -- the Integer base type, but it is safe to reduce it to 1 at this
271 -- stage, since we will only be loading a single storage unit.
274 then
275 loop
284 -- Now the only possible approach left is to increase the Esize but we
285 -- can't do that if the size was set by a specific clause.
288 Error_Msg_NE
292 -- Otherwise we can indeed increase the size to a multiple of alignment
294 else
299 ---------------
300 -- Assoc_Add --
301 ---------------
303 function Assoc_Add
307 is
311 begin
312 -- Case of right operand is a constant
318 -- Case of left operand is a constant
324 -- Neither operand is a constant, do the addition with no optimization
326 else
330 -- Case of left operand is an addition
334 -- (C1 + E) + C2 = (C1 + C2) + E
337 Rewrite_Integer
342 -- (E + C1) + C2 = E + (C1 + C2)
345 Rewrite_Integer
351 -- Case of left operand is a subtraction
355 -- (C1 - E) + C2 = (C1 + C2) - E
358 Rewrite_Integer
363 -- (E - C1) + C2 = E - (C1 - C2)
365 -- If the type is unsigned then only do the optimization if C1 >= C2,
366 -- to avoid creating a negative literal that can't be used with the
367 -- unsigned type.
372 then
373 Rewrite_Integer
380 -- Not optimizable, do the addition
385 --------------------
386 -- Assoc_Multiply --
387 --------------------
389 function Assoc_Multiply
393 is
397 begin
398 -- Case of right operand is a constant
404 -- Case of left operand is a constant
410 -- Neither operand is a constant, do the multiply with no optimization
412 else
416 -- Case of left operand is an multiplication
420 -- (C1 * E) * C2 = (C1 * C2) + E
423 Rewrite_Integer
428 -- (E * C1) * C2 = E * (C1 * C2)
431 Rewrite_Integer
438 -- Not optimizable, do the multiplication
443 --------------------
444 -- Assoc_Subtract --
445 --------------------
447 function Assoc_Subtract
451 is
455 begin
456 -- Case of right operand is a constant
462 -- Right operand is a constant, do the subtract with no optimization
464 else
468 -- Case of left operand is an addition
472 -- (C1 + E) - C2 = (C1 - C2) + E
475 Rewrite_Integer
480 -- (E + C1) - C2 = E + (C1 - C2)
483 Rewrite_Integer
489 -- Case of left operand is a subtraction
493 -- (C1 - E) - C2 = (C1 - C2) + E
496 Rewrite_Integer
501 -- (E - C1) - C2 = E - (C1 + C2)
504 Rewrite_Integer
511 -- Not optimizable, do the subtraction
516 ----------------
517 -- Bits_To_SU --
518 ----------------
521 begin
529 --------------------
530 -- Compute_Length --
531 --------------------
541 begin
542 -- If the bounds are First and Last attributes for the same dimension
543 -- and both have prefixes that denotes the same entity, then we create
544 -- and return a Length attribute. This may allow the back end to
545 -- generate better code in cases where it already has the length.
554 then
567 return
569 Prefix => New_Occurrence_Of
572 Expressions => New_List
580 -- If type is enumeration type, then use Pos attribute to convert
581 -- to integer type for which subtraction is a permitted operation.
584 Lo_Op :=
590 Hi_Op :=
597 return
599 Left_Opnd =>
606 ----------------------
607 -- Expr_From_SO_Ref --
608 ----------------------
610 function Expr_From_SO_Ref
614 is
617 begin
623 -- If a component is passed in whose type matches the type of
624 -- the function formal, then select that component from the "V"
625 -- parameter rather than passing "V" directly.
630 then
631 return
639 else
640 return
647 else
651 else
656 ---------------------
657 -- Get_Max_SU_Size --
658 ---------------------
672 record
678 -- Shows the status of the value so far. Const means that the value is
679 -- constant, and Val is the current constant value. Dynamic means that
680 -- the value is dynamic, and in this case Nod is the Node_Id of the
681 -- expression to compute the value.
684 -- Calculated value so far if Size.Status = Const,
685 -- or expression value so far if Size.Status = Dynamic.
688 -- This is set to True if the final result must be converted from bits
689 -- to storage units (rounding up to a storage unit boundary).
691 -----------------------
692 -- Local Subprograms --
693 -----------------------
696 -- If the node N represents a discriminant, replace it by the maximum
697 -- value of the discriminant.
700 -- If the node N represents a discriminant, replace it by the minimum
701 -- value of the discriminant.
703 -----------------
704 -- Max_Discrim --
705 -----------------
708 begin
711 then
716 -----------------
717 -- Min_Discrim --
718 -----------------
721 begin
724 then
729 -- Start of processing for Get_Max_SU_Size
731 begin
734 -- Initialize status from component size
739 else
743 -- Loop through indexes
754 -- Value of the current subscript range is statically known
757 and then
759 then
762 -- If known flat bound, entire size of array is zero
768 -- Current value is constant, evolve value
773 -- Current value is dynamic
775 else
776 -- An interesting little optimization, if we have a pending
777 -- conversion from bits to storage units, and the current
778 -- length is a multiple of the storage unit size, then we
779 -- can take the factor out here statically, avoiding some
780 -- extra dynamic computations at the end.
790 Right_Opnd =>
794 -- Value of the current subscript range is dynamic
796 else
797 -- If the current size value is constant, then here is where we
798 -- make a transition to dynamic values, which are always stored
799 -- in storage units, However, we do not want to convert to SU's
800 -- too soon, consider the case of a packed array of single bits,
801 -- we want to do the SU conversion after computing the size in
802 -- this case.
806 -- If the current value is a multiple of the storage unit,
807 -- then most certainly we can do the conversion now, simply
808 -- by dividing the current value by the storage unit value.
809 -- If this works, we set SU_Convert_Required to False.
813 Size :=
817 -- Otherwise, we go ahead and convert the value in bits, and
818 -- set SU_Convert_Required to True to ensure that the final
819 -- value is indeed properly converted.
821 else
827 -- Length is hi-lo+1
831 -- Check possible range of Len
833 declare
839 begin
845 -- If we cannot verify that range cannot be super-flat, we need
846 -- a max with zero, since length must be non-negative.
849 Len :=
851 Prefix =>
856 Len));
864 -- Here after processing all bounds to set sizes. If the value is a
865 -- constant, then it is bits, so we convert to storage units.
870 -- Case where the value is dynamic
872 else
873 -- Do convert from bits to SU's if needed
877 -- The expression required is (Size.Nod + SU - 1) / SU
881 Left_Opnd =>
892 -----------------------
893 -- Layout_Array_Type --
894 -----------------------
907 -- This is the type with which any generated constants or functions
908 -- will be associated (i.e. inserted into the freeze actions). This
909 -- is normally the type being laid out. The exception occurs when
910 -- we are laying out Itype's which are local to a record type, and
911 -- whose scope is this record type. Such types do not have freeze
912 -- nodes (because we have no place to put them).
914 ------------------------------------
915 -- How An Array Type is Laid Out --
916 ------------------------------------
918 -- Here is what goes on. We need to multiply the component size of the
919 -- array (which has already been set) by the length of each of the
920 -- indexes. If all these values are known at compile time, then the
921 -- resulting size of the array is the appropriate constant value.
923 -- If the component size or at least one bound is dynamic (but no
924 -- discriminants are present), then the size will be computed as an
925 -- expression that calculates the proper size.
927 -- If there is at least one discriminant bound, then the size is also
928 -- computed as an expression, but this expression contains discriminant
929 -- values which are obtained by selecting from a function parameter, and
930 -- the size is given by a function that is passed the variant record in
931 -- question, and whose body is the expression.
936 record
940 -- Calculated value so far if Val_Status = Const
944 -- Expression value so far if Val_Status /= Const
948 -- Records the value or expression computed so far. Const means that
949 -- the value is constant, and Val is the current constant value.
950 -- Dynamic means that the value is dynamic, and in this case Nod is
951 -- the Node_Id of the expression to compute the value, and Discrim
952 -- means that at least one bound is a discriminant, in which case Nod
953 -- is the expression so far (which will be the body of the function).
956 -- Value of size computed so far. See comments above
959 -- Variant record type for the formal parameter of the discriminant
960 -- function V if Status = Discrim.
963 -- This is set to True if the final result must be converted from
964 -- bits to storage units (rounding up to a storage unit boundary).
967 -- This is the amount that a nonstatic computed size will be divided
968 -- by to convert it from bits to storage units. This is normally
969 -- equal to SSU, but can be reduced in the case of packed components
970 -- that fit evenly into a storage unit.
973 -- Indicates whether to request that SO_Ref_From_Expr should
974 -- encapsulate the array size expression in a function.
977 -- If N represents a discriminant, then the Size.Status is set to
978 -- Discrim, and Vtyp is set. The parameter N is replaced with the
979 -- proper expression to extract the discriminant value from V.
981 ----------------
982 -- Discrimify --
983 ----------------
989 begin
992 then
1003 N :=
1008 -- Set the Etype attributes of the selected name and its prefix.
1009 -- Analyze_And_Resolve can't be called here because the Vname
1010 -- entity denoted by the prefix will not yet exist (it's created
1011 -- by SO_Ref_From_Expr, called at the end of Layout_Array_Type).
1018 -- Start of processing for Layout_Array_Type
1020 begin
1021 -- Default alignment is component alignment
1027 -- Calculate proper type for insertions
1031 else
1035 -- If the component type is a generic formal type then there's no point
1036 -- in determining a size for the array type.
1042 -- Deal with component size if base type
1046 -- Cannot do anything if Esize of component type unknown
1052 -- Set component size if not set already
1059 -- (RM 13.3 (48)) says that the size of an unconstrained array
1060 -- is implementation defined. We choose to leave it as Unknown
1061 -- here, and the actual behavior is determined by the back end.
1067 -- Initialize status from component size
1072 else
1076 -- Loop to process array indexes
1082 -- If an index of the array is a generic formal type then there is
1083 -- no point in determining a size for the array type.
1092 -- Value of the current subscript range is statically known
1095 and then
1097 then
1100 -- If known flat bound, entire size of array is zero
1108 -- If constant, evolve value
1113 -- Current value is dynamic
1115 else
1116 -- An interesting little optimization, if we have a pending
1117 -- conversion from bits to storage units, and the current
1118 -- length is a multiple of the storage unit size, then we
1119 -- can take the factor out here statically, avoiding some
1120 -- extra dynamic computations at the end.
1127 -- Now go ahead and evolve the expression
1132 Right_Opnd =>
1136 -- Value of the current subscript range is dynamic
1138 else
1139 -- If the current size value is constant, then here is where we
1140 -- make a transition to dynamic values, which are always stored
1141 -- in storage units, However, we do not want to convert to SU's
1142 -- too soon, consider the case of a packed array of single bits,
1143 -- we want to do the SU conversion after computing the size in
1144 -- this case.
1148 -- If the current value is a multiple of the storage unit,
1149 -- then most certainly we can do the conversion now, simply
1150 -- by dividing the current value by the storage unit value.
1151 -- If this works, we set SU_Convert_Required to False.
1154 Size :=
1158 -- If the current value is a factor of the storage unit, then
1159 -- we can use a value of one for the size and reduce the
1160 -- strength of the later division.
1167 -- Otherwise, we go ahead and convert the value in bits, and
1168 -- set SU_Convert_Required to True to ensure that the final
1169 -- value is indeed properly converted.
1171 else
1180 -- Length is hi-lo+1
1184 -- If Len isn't a Length attribute, then its range needs to be
1185 -- checked a possible Max with zero needs to be computed.
1189 then
1190 declare
1195 begin
1196 -- Check possible range of Len
1203 -- If range definitely flat or superflat, result size is 0
1211 -- If we cannot verify that range cannot be super-flat, we
1212 -- need a max with zero, since length cannot be negative.
1215 Len :=
1217 Prefix =>
1222 Len));
1227 -- At this stage, Len has the expression for the length
1238 -- Here after processing all bounds to set sizes. If the value is a
1239 -- constant, then it is bits, and the only thing we need to do is to
1240 -- check against explicit given size and do alignment adjust.
1246 -- Case where the value is dynamic
1248 else
1249 -- Do convert from bits to SU's if needed
1253 -- The expression required is:
1254 -- (Size.Nod + Storage_Divisor - 1) / Storage_Divisor
1258 Left_Opnd =>
1261 Right_Opnd => Make_Integer_Literal
1266 -- If the array entity is not declared at the library level and its
1267 -- not nested within a subprogram that is marked for inlining, then
1268 -- we request that the size expression be encapsulated in a function.
1269 -- Since this expression is not needed in most cases, we prefer not
1270 -- to incur the overhead of the computation on calls to the enclosing
1271 -- subprogram except for subprograms that require the size.
1276 declare
1279 begin
1291 -- Now set the dynamic size (the Value_Size is always the same as the
1292 -- Object_Size for arrays whose length is dynamic).
1294 -- ??? If Size.Status = Dynamic, Vtyp will not have been set.
1295 -- The added initialization sets it to Empty now, but is this
1296 -- correct?
1298 Set_Esize
1300 SO_Ref_From_Expr
1306 ------------------------------------------
1307 -- Compute_Size_Depends_On_Discriminant --
1308 ------------------------------------------
1317 begin
1318 -- Loop to process array indexes
1324 -- If an index of the array is a generic formal type then there is
1325 -- no point in determining a size for the array type.
1336 or else
1339 then
1351 -------------------
1352 -- Layout_Object --
1353 -------------------
1358 begin
1359 -- Nothing to do if backend does layout
1365 -- Set size if not set for object and known for type. Use the RM_Size if
1366 -- that is known for the type and Esize is not.
1377 -- Set alignment from type if unknown and type alignment known
1383 -- Make sure size and alignment are consistent
1387 -- Final adjustment, if we don't know the alignment, and the Esize was
1388 -- not set by an explicit Object_Size attribute clause, then we reset
1389 -- the Esize to unknown, since we really don't know it.
1396 ------------------------
1397 -- Layout_Record_Type --
1398 ------------------------
1405 -- Current component being laid out
1408 -- Previous laid out component
1410 procedure Get_Next_Component_Location
1417 -- Given the previous component in Prev_Comp, which is already laid
1418 -- out, and the alignment of the following component, lays out the
1419 -- following component, and returns its starting position in New_Npos
1420 -- (Normalized_Position value), New_Fbit (Normalized_First_Bit value),
1421 -- and New_NPMax (Normalized_Position_Max value). If Prev_Comp is empty
1422 -- (no previous component is present), then New_Npos, New_Fbit and
1423 -- New_NPMax are all set to zero on return. This procedure is also
1424 -- used to compute the size of a record or variant by giving it the
1425 -- last component, and the record alignment. Force_SU is used to force
1426 -- the new component location to be aligned on a storage unit boundary,
1427 -- even in a packed record, False means that the new position does not
1428 -- need to be bumped to a storage unit boundary, True means a storage
1429 -- unit boundary is always required.
1432 -- Lays out component Comp, given Prev_Comp, the previously laid-out
1433 -- component (Prev_Comp = Empty if no components laid out yet). The
1434 -- alignment of the record itself is also updated if needed. Both
1435 -- Comp and Prev_Comp can be either components or discriminants.
1437 procedure Layout_Components
1442 -- This procedure lays out the components of the given component list
1443 -- which contains the components starting with From and ending with To.
1444 -- The Next_Entity chain is used to traverse the components. On entry,
1445 -- Prev_Comp is set to the component preceding the list, so that the
1446 -- list is laid out after this component. Prev_Comp is set to Empty if
1447 -- the component list is to be laid out starting at the start of the
1448 -- record. On return, the components are all laid out, and Prev_Comp is
1449 -- set to the last laid out component. On return, Esiz is set to the
1450 -- resulting Object_Size value, which is the length of the record up
1451 -- to and including the last laid out entity. For Esiz, the value is
1452 -- adjusted to match the alignment of the record. RM_Siz is similarly
1453 -- set to the resulting Value_Size value, which is the same length, but
1454 -- not adjusted to meet the alignment. Note that in the case of variant
1455 -- records, Esiz represents the maximum size.
1458 -- Procedure called to lay out a non-variant record type or subtype
1461 -- Procedure called to lay out a variant record type. Decl is set to the
1462 -- full type declaration for the variant record.
1464 ---------------------------------
1465 -- Get_Next_Component_Location --
1466 ---------------------------------
1468 procedure Get_Next_Component_Location
1475 is
1476 begin
1477 -- No previous component, return zero position
1486 -- Here we have a previous component
1488 declare
1497 -- Expression representing maximum size of previous component
1499 begin
1500 -- Case where previous field had a dynamic size
1504 -- If the previous field had a dynamic length, then it is
1505 -- required to occupy an integral number of storage units,
1506 -- and start on a storage unit boundary. This means that
1507 -- the Normalized_First_Bit value is zero in the previous
1508 -- component, and the new value is also set to zero.
1512 -- In this case, the new position is given by an expression
1513 -- that is the sum of old normalized position and old size.
1515 New_Npos :=
1516 SO_Ref_From_Expr
1518 Left_Opnd =>
1520 Right_Opnd =>
1525 -- Get maximum size of previous component
1529 else
1533 -- Now we can compute the new max position. If the max size
1534 -- is static and the old position is static, then we can
1535 -- compute the new position statically.
1539 then
1542 -- Otherwise new max position is dynamic
1544 else
1545 New_NPMax :=
1546 SO_Ref_From_Expr
1554 -- Previous field has known static Esize
1556 else
1559 -- Bump New_Fbit to storage unit boundary if required
1565 -- If old normalized position is static, we can go ahead and
1566 -- compute the new normalized position directly.
1576 -- Bump alignment if stricter than prev
1582 -- The max position is always equal to the position if
1583 -- the latter is static, since arrays depending on the
1584 -- values of discriminants never have static sizes.
1589 -- Case of old normalized position is dynamic
1591 else
1592 -- If new bit position is within the current storage unit,
1593 -- we can just copy the old position as the result position
1594 -- (we have already set the new first bit value).
1600 -- If new bit position is past the current storage unit, we
1601 -- need to generate a new dynamic value for the position
1602 -- ??? need to deal with alignment
1604 else
1605 New_Npos :=
1606 SO_Ref_From_Expr
1609 Right_Opnd =>
1615 New_NPMax :=
1616 SO_Ref_From_Expr
1619 Right_Opnd =>
1631 ----------------------
1632 -- Layout_Component --
1633 ----------------------
1643 begin
1644 -- Increase alignment of record if necessary. Note that we do not
1645 -- do this for packed records, which have an alignment of one by
1646 -- default, or for records for which an explicit alignment was
1647 -- specified with an alignment clause.
1652 then
1656 -- If original component set, then use same layout
1667 -- Parent field is always at start of record, this will overlap
1668 -- the actual fields that are part of the parent, and that's fine
1679 -- Check case of type of component has a scope of the record we are
1680 -- laying out. When this happens, the type in question is an Itype
1681 -- that has not yet been laid out (that's because such types do not
1682 -- get frozen in the normal manner, because there is no place for
1683 -- the freeze nodes).
1689 -- If component already laid out, then we are done
1695 -- Set size of component from type. We use the Esize except in a
1696 -- packed record, where we use the RM_Size (since that is what the
1697 -- RM_Size value, as distinct from the Object_Size is useful for).
1701 else
1705 -- Compute the component position from the previous one. See if
1706 -- current component requires being on a storage unit boundary.
1708 -- If record is not packed, we always go to a storage unit boundary
1713 -- Packed cases
1715 else
1716 -- Elementary types do not need SU boundary in packed record
1721 -- Packed array types with a modular packed array type do not
1722 -- force a storage unit boundary (since the code generation
1723 -- treats these as equivalent to the underlying modular type),
1728 then
1731 -- Record types with known length less than or equal to the length
1732 -- of long long integer can also be unaligned, since they can be
1733 -- treated as scalars.
1738 then
1741 -- All other cases force a storage unit boundary, even when packed
1743 else
1748 -- Now get the next component location
1750 Get_Next_Component_Location
1756 -- Set Component_Bit_Offset in the static case
1760 then
1765 -----------------------
1766 -- Layout_Components --
1767 -----------------------
1769 procedure Layout_Components
1774 is
1779 begin
1780 -- Only lay out components if there are some to lay out
1784 -- Lay out components with no component clauses
1787 loop
1790 then
1791 -- The compatibility of component clauses with composite
1792 -- types isn't checked in Sem_Ch13, so we check it here.
1797 then
1799 Error_Msg_NE
1802 Comp);
1805 else
1816 -- Set size fields, both are zero if no components
1822 -- If record subtype with non-static discriminants, then we don't
1823 -- know which variant will be the one which gets chosen. We don't
1824 -- just want to set the maximum size from the base, because the
1825 -- size should depend on the particular variant.
1827 -- What we do is to use the RM_Size of the base type, which has
1828 -- the necessary conditional computation of the size, using the
1829 -- size information for the particular variant chosen. Records
1830 -- with default discriminants for example have an Esize that is
1831 -- set to the maximum of all variants, but that's not what we
1832 -- want for a constrained subtype.
1836 then
1837 declare
1839 begin
1845 else
1846 -- First the object size, for which we align past the last field
1847 -- to the alignment of the record (the object size is required to
1848 -- be a multiple of the alignment).
1850 Get_Next_Component_Location
1853 End_Npos,
1854 End_Fbit,
1855 End_NPMax,
1858 -- If the resulting normalized position is a dynamic reference,
1859 -- then the size is dynamic, and is stored in storage units. In
1860 -- this case, we set the RM_Size to the same value, it is simply
1861 -- not worth distinguishing Esize and RM_Size values in the
1862 -- dynamic case, since the RM has nothing to say about them.
1864 -- Note that a size cannot have been given in this case, since
1865 -- size specifications cannot be given for variable length types.
1867 declare
1870 begin
1874 -- Set the Object_Size allowing for the alignment. In the
1875 -- dynamic case, we must do the actual runtime computation.
1876 -- We can skip this in the non-packed record case if the
1877 -- last component has a smaller alignment than the overall
1878 -- record alignment.
1885 then
1886 -- The expression we build is:
1887 -- (expr + align - 1) / align * align
1889 Esiz :=
1890 SO_Ref_From_Expr
1893 Left_Opnd =>
1895 Left_Opnd =>
1897 Left_Opnd =>
1899 Right_Opnd =>
1902 Right_Opnd =>
1904 Right_Opnd =>
1910 -- Here Esiz is static, so we can adjust the alignment
1911 -- directly go give the required aligned value.
1913 else
1917 -- Case where computed size is static
1919 else
1920 -- The ending size was computed in Npos in storage units,
1921 -- but the actual size is stored in bits, so adjust
1922 -- accordingly. We also adjust the size to match the
1923 -- alignment here.
1927 -- Compute the resulting Value_Size (RM_Size). For this
1928 -- purpose we do not force alignment of the record or
1929 -- storage size alignment of the result.
1931 Get_Next_Component_Location
1933 Uint_0,
1934 End_Npos,
1935 End_Fbit,
1936 End_NPMax,
1946 -------------------------------
1947 -- Layout_Non_Variant_Record --
1948 -------------------------------
1953 begin
1959 ---------------------------
1960 -- Layout_Variant_Record --
1961 ---------------------------
1973 -- Expression for the evolving RM_Siz value. This is typically an if
1974 -- expression which involves tests of discriminant values that are
1975 -- formed as references to the entity V. At the end of scanning all
1976 -- the components, a suitable function is constructed in which V is
1977 -- the parameter.
1979 -----------------------
1980 -- Local Subprograms --
1981 -----------------------
1983 procedure Layout_Component_List
1987 -- Recursive procedure, called to lay out one component list Esiz
1988 -- and RM_Siz_Expr are set to the Object_Size and Value_Size values
1989 -- respectively representing the record size up to and including the
1990 -- last component in the component list (including any variants in
1991 -- this component list). RM_Siz_Expr is returned as an expression
1992 -- which may in the general case involve some references to the
1993 -- discriminants of the current record value, referenced by selecting
1994 -- from the entity V.
1996 ---------------------------
1997 -- Layout_Component_List --
1998 ---------------------------
2000 procedure Layout_Component_List
2004 is
2012 begin
2014 Layout_Components
2019 else
2023 -- Case where no variants are present in the component list
2027 -- The Esiz value has been correctly set by the call to
2028 -- Layout_Components, so there is nothing more to be done.
2030 -- For RM_Siz, we have an SO_Ref value, which we must convert
2031 -- to an appropriate expression.
2034 RM_Siz_Expr :=
2038 else
2041 -- If the size is represented by a function, then we create
2042 -- an appropriate function call using V as the parameter to
2043 -- the call.
2046 RM_Siz_Expr :=
2052 -- If the size is represented by a constant, then the
2053 -- expression we want is a reference to this constant
2055 else
2060 -- Case where variants are present in this component list
2062 else
2063 declare
2072 begin
2079 Layout_Component_List
2082 -- Set the Object_Size. If this is the first variant,
2083 -- we just set the size of this first variant.
2088 -- Otherwise the Object_Size is formed as a maximum
2089 -- of Esiz so far from previous variants, and the new
2090 -- Esiz value from the variant we just processed.
2092 -- If both values are static, we can just compute the
2093 -- maximum directly to save building junk nodes.
2097 then
2100 -- If either value is dynamic, then we have to generate
2101 -- an appropriate Standard_Unsigned'Max attribute call.
2102 -- If one of the values is static then it needs to be
2103 -- converted from bits to storage units to be compatible
2104 -- with the dynamic value.
2106 else
2115 Esiz :=
2116 SO_Ref_From_Expr
2119 Prefix =>
2128 -- Now deal with Value_Size (RM_Siz). We are aiming at
2129 -- an expression that looks like:
2131 -- if xxDx (V.disc) then rmsiz1
2132 -- else if xxDx (V.disc) then rmsiz2
2133 -- else ...
2135 -- Where rmsiz1, rmsiz2... are the RM_Siz values for the
2136 -- individual variants, and xxDx are the discriminant
2137 -- checking functions generated for the variant type.
2139 -- If this is the first variant, we simply set the result
2140 -- as the expression. Note that this takes care of the
2141 -- others case.
2145 -- If this is the only variant and the size is a
2146 -- literal, then use bit size as is, otherwise convert
2147 -- to storage units and continue to the next variant.
2151 then
2153 else
2157 -- Otherwise construct the appropriate test
2159 else
2160 -- The test to be used in general is a call to the
2161 -- discriminant checking function. However, it is
2162 -- definitely worth special casing the very common
2163 -- case where a single value is involved.
2169 then
2170 -- Discriminant to be tested
2172 Discrim :=
2174 Prefix =>
2176 Selector_Name =>
2177 New_Occurrence_Of
2180 Dtest :=
2185 -- Generate a call to the discriminant-checking
2186 -- function for the variant. Note that the result
2187 -- has to be complemented since the function returns
2188 -- False when the passed discriminant value matches.
2190 else
2191 -- The checking function takes all of the type's
2192 -- discriminants as parameters, so a list of all
2193 -- the selected discriminants must be constructed.
2200 Prefix =>
2202 Selector_Name =>
2208 Dtest :=
2210 Right_Opnd =>
2212 Name =>
2213 New_Occurrence_Of
2215 Parameter_Associations =>
2216 D_List));
2219 RM_Siz_Expr :=
2221 Expressions =>
2222 New_List
2234 -- Indicates others present, not used in this case
2237 -- Error routine invoked by the generic instantiation below when
2238 -- the variant part has a nonstatic choice.
2241 Generic_Check_Choices
2247 -----------------------------
2248 -- Non_Static_Choice_Error --
2249 -----------------------------
2252 begin
2253 Flag_Non_Static_Expr
2257 -- Start of processing for Layout_Variant_Record
2259 begin
2260 -- Call Check_Choices here to ensure that Others_Discrete_Choices
2261 -- gets set on any 'others' choice before the discriminant-checking
2262 -- functions are generated. Otherwise the function for the 'others'
2263 -- alternative will unconditionally return True, causing discriminant
2264 -- checks to fail. However, Check_Choices is now normally delayed
2265 -- until the type's freeze entity is processed, due to requirements
2266 -- coming from subtype predicates, so doing it at this point is
2267 -- probably not right in general, but it's not clear how else to deal
2268 -- with this situation. Perhaps we should only generate declarations
2269 -- for the checking functions here, and somehow delay generation of
2270 -- their bodies, but that would be a nontrivial change. ???
2272 declare
2275 begin
2276 Check_Choices
2280 -- We need the discriminant checking functions, since we generate
2281 -- calls to these functions for the RM_Size expression, so make
2282 -- sure that these functions have been constructed in time.
2286 -- Lay out the discriminants
2294 Layout_Components
2300 -- Lay out the main component list (this will make recursive calls
2301 -- to lay out all component lists nested within variants).
2306 -- If the RM_Size is a literal, set its value
2311 -- Otherwise we construct a dynamic SO_Ref
2313 else
2315 SO_Ref_From_Expr
2322 -- Start of processing for Layout_Record_Type
2324 begin
2325 -- If this is a cloned subtype, just copy the size fields from the
2326 -- original, nothing else needs to be done in this case, since the
2327 -- components themselves are all shared.
2331 then
2336 -- Another special case, class-wide types. The RM says that the size
2337 -- of such types is implementation defined (RM 13.3(48)). What we do
2338 -- here is to leave the fields set as unknown values, and the backend
2339 -- determines the actual behavior.
2344 -- All other cases
2346 else
2347 -- Initialize alignment conservatively to 1. This value will be
2348 -- increased as necessary during processing of the record.
2354 -- Initialize previous component. This is Empty unless there are
2355 -- components which have already been laid out by component clauses.
2356 -- If there are such components, we start our lay out of the
2357 -- remaining components following the last such component.
2365 or else
2368 then
2376 -- We have two separate circuits, one for non-variant records and
2377 -- one for variant records. For non-variant records, we simply go
2378 -- through the list of components. This handles all the non-variant
2379 -- cases including those cases of subtypes where there is no full
2380 -- type declaration, so the tree cannot be used to drive the layout.
2381 -- For variant records, we have to drive the layout from the tree
2382 -- since we need to understand the variant structure in this case.
2386 else
2390 -- Scan all the components
2396 and then
2398 then
2399 Layout_Variant_Record;
2400 else
2401 Layout_Non_Variant_Record;
2406 -----------------
2407 -- Layout_Type --
2408 -----------------
2413 begin
2414 -- For string literal types, for now, kill the size always, this is
2415 -- because gigi does not like or need the size to be set ???
2423 -- For access types, set size/alignment. This is system address size,
2424 -- except for fat pointers (unconstrained array access types), where the
2425 -- size is two times the address size, to accommodate the two pointers
2426 -- that are required for a fat pointer (data and template). Note that
2427 -- E_Access_Protected_Subprogram_Type is not an access type for this
2428 -- purpose since it is not a pointer but is equivalent to a record. For
2429 -- access subtypes, copy the size from the base type since Gigi
2430 -- represents them the same way.
2435 -- If we only have a limited view of the type, see whether the
2436 -- non-limited view is available.
2441 then
2445 -- If Esize already set (e.g. by a size clause), then nothing further
2446 -- to be done here.
2451 -- Access to subprogram is a strange beast, and we let the backend
2452 -- figure out what is needed (it may be some kind of fat pointer,
2453 -- including the static link for example.
2458 -- For access subtypes, copy the size information from base type
2464 -- For other access types, we use either address size, or, if a fat
2465 -- pointer is used (pointer-to-unconstrained array case), twice the
2466 -- address size to accommodate a fat pointer.
2473 -- Debug Flag -gnatd6 says make all pointers to unconstrained thin
2475 and then not Debug_Flag_6
2476 then
2479 -- Check for bad convention set
2481 if Warn_On_Export_Import
2482 and then
2484 or else
2486 then
2487 Error_Msg_N
2491 -- If the designated type is a limited view it is unanalyzed. We can
2492 -- examine the declaration itself to determine whether it will need a
2493 -- fat pointer.
2499 N_Unconstrained_Array_Definition
2500 and then not Debug_Flag_6
2501 then
2504 -- When the target is AAMP, access-to-subprogram types are fat
2505 -- pointers consisting of the subprogram address and a static link,
2506 -- with the exception of library-level access types (including
2507 -- library-level anonymous access types, such as for components),
2508 -- where a simple subprogram address is used.
2510 elsif AAMP_On_Target
2511 and then
2514 or else
2516 and then
2519 then
2522 -- Normal case of thin pointer
2524 else
2530 -- Scalar types: set size and alignment
2534 -- For discrete types, the RM_Size and Esize must be set already,
2535 -- since this is part of the earlier processing and the front end is
2536 -- always required to lay out the sizes of such types (since they are
2537 -- available as static attributes). All we do is to check that this
2538 -- rule is indeed obeyed.
2542 -- If the RM_Size is not set, then here is where we set it
2544 -- Note: an RM_Size of zero looks like not set here, but this
2545 -- is a rare case, and we can simply reset it without any harm.
2551 -- If Esize for a discrete type is not set then set it
2554 declare
2557 begin
2558 loop
2559 -- If size is big enough, set it and exit
2565 -- If the RM_Size is greater than 64 (happens only when
2566 -- strange values are specified by the user, then Esize
2567 -- is simply a copy of RM_Size, it will be further
2568 -- refined later on)
2574 -- Otherwise double possible size and keep trying
2576 else
2583 -- For non-discrete scalar types, if the RM_Size is not set, then set
2584 -- it now to a copy of the Esize if the Esize is set.
2586 else
2594 -- Non-elementary (composite) types
2596 else
2597 -- For packed arrays, take size and alignment values from the packed
2598 -- array type if a packed array type has been created and the fields
2599 -- are not currently set.
2603 then
2604 declare
2607 begin
2622 -- If Esize is set, and RM_Size is not, RM_Size is copied from Esize.
2623 -- At least for now this seems reasonable, and is in any case needed
2624 -- for compatibility with old versions of gigi.
2630 -- For array base types, set component size if object size of the
2631 -- component type is known and is a small power of 2 (8, 16, 32, 64),
2632 -- since this is what will always be used.
2635 declare
2638 begin
2639 -- For some reason, access types can cause trouble, So let's
2640 -- just do this for scalar types ???
2645 then
2646 declare
2648 begin
2658 -- Lay out array and record types if front end layout set
2667 -- Case of backend layout, we still do a little in the front end
2669 else
2670 -- Processing for record types
2674 -- Special remaining processing for record types with a known
2675 -- size of 16, 32, or 64 bits whose alignment is not yet set.
2676 -- For these types, we set a corresponding alignment matching
2677 -- the size if possible, or as large as possible if not.
2683 -- Processing for array types
2687 -- For arrays that are required to be atomic, we do the same
2688 -- processing as described above for short records, since we
2689 -- really need to have the alignment set for the whole array.
2695 -- For unpacked array types, set an alignment of 1 if we know
2696 -- that the component alignment is not greater than 1. The reason
2697 -- we do this is to avoid unnecessary copying of slices of such
2698 -- arrays when passed to subprogram parameters (see special test
2699 -- in Exp_Ch6.Expand_Actuals).
2704 then
2709 -- We need to know whether the size depends on the value of one
2710 -- or more discriminants to select the return mechanism. Skip if
2711 -- errors are present, to prevent cascaded messages.
2720 -- Final step is to check that Esize and RM_Size are compatible
2725 -- Esize is less than RM_Size. That's not good. First we test
2726 -- whether this was set deliberately with an Object_Size clause
2727 -- and if so, object to the clause.
2731 Error_Msg_F
2733 Expression (Get_Attribute_Definition_Clause
2737 -- Adjust Esize up to RM_Size value
2739 declare
2742 begin
2745 -- For scalar types, increase Object_Size to power of 2, but
2746 -- not less than a storage unit in any case (i.e., normally
2747 -- this means it will be storage-unit addressable).
2756 else
2760 -- Finally, make sure that alignment is consistent with
2761 -- the newly assigned size.
2765 loop
2774 ---------------------
2775 -- Rewrite_Integer --
2776 ---------------------
2781 begin
2786 -------------------------------
2787 -- Set_And_Check_Static_Size --
2788 -------------------------------
2790 procedure Set_And_Check_Static_Size
2794 is
2798 -- Spec is the number of bit specified in the size clause, and Min is
2799 -- the minimum computed size. An error is given that the specified size
2800 -- is too small if Spec < Min, and in this case both Esize and RM_Size
2801 -- are set to unknown in E. The error message is posted on node SC.
2804 -- Spec is the number of bits specified in the size clause, and Max is
2805 -- the maximum computed size. A warning is given about unused bits if
2806 -- Spec > Max. This warning is posted on node SC.
2808 --------------------------
2809 -- Check_Size_Too_Small --
2810 --------------------------
2813 begin
2822 -----------------------
2823 -- Check_Unused_Bits --
2824 -----------------------
2827 begin
2834 -- Start of processing for Set_And_Check_Static_Size
2836 begin
2837 -- Case where Object_Size (Esize) is already set by a size clause
2846 -- Perform checks on specified size against computed sizes
2854 -- Case where Value_Size (RM_Size) is set by specific Value_Size clause
2855 -- (we do not need to worry about Value_Size being set by a Size clause,
2856 -- since that will have set Esize as well, and we already took care of
2857 -- that case).
2862 -- Perform checks on specified size against computed sizes
2870 -- Set sizes if unknown
2881 -----------------------------
2882 -- Set_Composite_Alignment --
2883 -----------------------------
2889 begin
2890 -- If alignment is already set, then nothing to do
2896 -- Alignment is not known, see if we can set it, taking into account
2897 -- the setting of the Optimize_Alignment mode.
2899 -- If Optimize_Alignment is set to Space, then we try to give packed
2900 -- records an aligmment of 1, unless there is some reason we can't.
2905 then
2906 -- No effect for record with atomic components
2914 -- No effect if independent components
2918 Error_Msg_N
2923 -- No effect if any component is atomic or is a by reference type
2925 declare
2927 begin
2933 then
2935 Error_Msg_N
2938 else
2944 -- Optimize_Alignment has no effect on variable length record
2952 -- All tests passed, we can set alignment to 1
2956 -- Not a record, or not packed
2958 else
2959 -- The only other cases we worry about here are where the size is
2960 -- statically known at compile time.
2966 else
2970 -- Size is known, alignment is not set
2972 -- Reset alignment to match size if the known size is exactly 2, 4,
2973 -- or 8 storage units.
2982 -- If Optimize_Alignment is set to Space, then make sure the
2983 -- alignment matches the size, for example, if the size is 17
2984 -- bytes then we want an alignment of 1 for the type.
2993 else
2997 -- If Optimize_Alignment is set to Time, then we reset for odd
2998 -- "in between sizes", for example a 17 bit record is given an
2999 -- alignment of 4.
3004 then
3013 -- No special alignment fiddling needed
3015 else
3020 -- Here we have Set Align to the proposed improved value. Make sure the
3021 -- value set does not exceed Maximum_Alignment for the target.
3027 -- Further processing for record types only to reduce the alignment
3028 -- set by the above processing in some specific cases. We do not
3029 -- do this for atomic records, since we need max alignment there,
3033 -- For records, there is generally no point in setting alignment
3034 -- higher than word size since we cannot do better than move by
3035 -- words in any case. Omit this if we are optimizing for time,
3036 -- since conceivably we may be able to do better.
3040 then
3044 -- Check components. If any component requires a higher alignment,
3045 -- then we set that higher alignment in any case. Don't do this if
3046 -- we have Optimize_Alignment set to Space. Note that that covers
3047 -- the case of packed records, where we already set alignment to 1.
3050 declare
3053 begin
3057 declare
3060 begin
3061 -- The cases to process are when the alignment of the
3062 -- component type is larger than the alignment we have
3063 -- so far, and either there is no component clause for
3064 -- the component, or the length set by the component
3065 -- clause matches the length of the component type.
3068 and then
3071 and then
3074 then
3086 -- Set chosen alignment, and increase Esize if necessary to match the
3087 -- chosen alignment.
3093 then
3098 --------------------------
3099 -- Set_Discrete_RM_Size --
3100 --------------------------
3105 begin
3106 -- All discrete types except for the base types in standard are
3107 -- constrained, so indicate this by setting Is_Constrained.
3111 -- Set generic types to have an unknown size, since the representation
3112 -- of a generic type is irrelevant, in view of the fact that they have
3113 -- nothing to do with code.
3118 -- If the subtype statically matches the first subtype, then it is
3119 -- required to have exactly the same layout. This is required by
3120 -- aliasing considerations.
3124 then
3128 -- In all other cases the RM_Size is set to the minimum size. Note that
3129 -- this routine is never called for subtypes for which the RM_Size is
3130 -- set explicitly by an attribute clause.
3132 else
3137 ------------------------
3138 -- Set_Elem_Alignment --
3139 ------------------------
3142 begin
3143 -- Do not set alignment for packed array types, unless we are doing
3144 -- front end layout, because otherwise this is always handled in the
3145 -- backend.
3148 and then not Frontend_Layout_On_Target
3149 then
3152 -- If there is an alignment clause, then we respect it
3157 -- If the size is not set, then don't attempt to set the alignment. This
3158 -- happens in the backend layout case for access-to-subprogram types.
3163 -- For access types, do not set the alignment if the size is less than
3164 -- the allowed minimum size. This avoids cascaded error messages.
3170 -- Here we calculate the alignment as the largest power of two multiple
3171 -- of System.Storage_Unit that does not exceed either the object size of
3172 -- the type, or the maximum allowed alignment.
3174 declare
3180 begin
3181 -- The given Esize may be larger that int'last because of a previous
3182 -- error, and the call to UI_To_Int will fail, so use default.
3187 -- If this is an access type and the target doesn't have strict
3188 -- alignment and we are not doing front end layout, then cap the
3189 -- alignment to that of a regular access type. This will avoid
3190 -- giving fat pointers twice the usual alignment for no practical
3191 -- benefit since the misalignment doesn't really matter.
3194 and then not Target_Strict_Alignment
3195 and then not Frontend_Layout_On_Target
3196 then
3199 else
3203 -- If the default alignment of "double" floating-point types is
3204 -- specifically capped, enforce the cap.
3209 then
3212 -- If the default alignment of "double" or larger scalar types is
3213 -- specifically capped, enforce the cap.
3218 then
3221 -- Otherwise enforce the overall alignment cap
3223 else
3232 -- If alignment is currently not set, then we can safetly set it to
3233 -- this new calculated value.
3238 -- Cases where we have inherited an alignment
3240 -- For constructed types, always reset the alignment, these are
3241 -- Generally invisible to the user anyway, and that way we are
3242 -- sure that no constructed types have weird alignments.
3247 -- If this inherited alignment is the same as the one we computed,
3248 -- then obviously everything is fine, and we do not need to reset it.
3253 -- Now we come to the difficult cases where we have inherited an
3254 -- alignment and size, but overridden the size but not the alignment.
3258 -- This is tricky, it might be thought that we should try to
3259 -- inherit the alignment, since that's what the RM implies, but
3260 -- that leads to complex rules and oddities. Consider for example:
3262 -- type R is new Character;
3263 -- for R'Size use 16;
3265 -- It seems quite bogus in this case to inherit an alignment of 1
3266 -- from the parent type Character. Furthermore, if that's what the
3267 -- programmer really wanted for some odd reason, then they could
3268 -- specify the alignment they wanted.
3270 -- Furthermore we really don't want to inherit the alignment in
3271 -- the case of a specified Object_Size for a subtype, since then
3272 -- there would be no way of overriding to give a reasonable value
3273 -- (we don't have an Object_Subtype attribute). Consider:
3275 -- subtype R is new Character;
3276 -- for R'Object_Size use 16;
3278 -- If we inherit the alignment of 1, then we have an odd
3279 -- inefficient alignment for the subtype, which cannot be fixed.
3281 -- So we make the decision that if Size (or Object_Size) is given
3282 -- (and, in the case of a first subtype, the alignment is not set
3283 -- with a specific alignment clause). We reset the alignment to
3284 -- the appropriate value for the specified size. This is a nice
3285 -- simple rule to implement and document.
3287 -- There is one slight glitch, which is that a confirming size
3288 -- clause can now change the alignment, which, if we really think
3289 -- that confirming rep clauses should have no effect, is a no-no.
3291 -- type R is new Character;
3292 -- for R'Alignment use 2;
3293 -- type S is new R;
3294 -- for S'Size use Character'Size;
3296 -- Now the alignment of S is 1 instead of 2, as a result of
3297 -- applying the above rule to the confirming rep clause for S. Not
3298 -- clear this is worth worrying about. If we recorded whether a
3299 -- size clause was confirming we could avoid this, but right now
3300 -- we have no way of doing that or easily figuring it out, so we
3301 -- don't bother.
3303 -- Historical note. In versions of GNAT prior to Nov 6th, 2010, an
3304 -- odd distinction was made between inherited alignments greater
3305 -- than the computed alignment (where the larger alignment was
3306 -- inherited) and inherited alignments smaller than the computed
3307 -- alignment (where the smaller alignment was overridden). This
3308 -- was a dubious fix to get around an ACATS problem which seems
3309 -- to have disappeared anyway, and in any case, this peculiarity
3310 -- was never documented.
3314 -- If no Size (or Object_Size) was specified, then we inherited the
3315 -- object size, so we should inherit the alignment as well and not
3316 -- modify it. This takes care of cases like:
3318 -- type R is new Integer;
3319 -- for R'Alignment use 1;
3320 -- subtype S is R;
3322 -- Here we have R has a default Object_Size of 32, and a specified
3323 -- alignment of 1, and it seeems right for S to inherit both values.
3325 else
3331 ----------------------
3332 -- SO_Ref_From_Expr --
3333 ----------------------
3335 function SO_Ref_From_Expr
3340 is
3348 -- Function used to check one node for reference to V
3351 -- Function used to traverse tree to check for reference to V
3353 ----------------------
3354 -- Check_Node_V_Ref --
3355 ----------------------
3358 begin
3362 else
3366 else
3371 -- Start of processing for SO_Ref_From_Expr
3373 begin
3374 -- Case of expression is an integer literal, in this case we just
3375 -- return the value (which must always be non-negative, since size
3376 -- and offset values can never be negative).
3383 -- Case where there is a reference to V, create function
3389 -- Check whether Vtype is a view of a private type and ensure that
3390 -- we use the primary view of the type (which is denoted by its
3391 -- Etype, whether it's the type's partial or full view entity).
3392 -- This is needed to make sure that we use the same (primary) view
3393 -- of the type for all V formals, whether the current view of the
3394 -- type is the partial or full view, so that types will always
3395 -- match on calls from one size function to another.
3399 else
3405 Decl :=
3408 Specification =>
3413 Defining_Identifier =>
3415 Parameter_Type =>
3417 Result_Definition =>
3422 Handled_Statement_Sequence =>
3428 -- The caller requests that the expression be encapsulated in a
3429 -- parameterless function.
3432 Decl :=
3435 Specification =>
3439 Result_Definition =>
3444 Handled_Statement_Sequence =>
3449 -- No reference to V and function not requested, so create a constant
3451 else
3452 Decl :=
3455 Object_Definition =>