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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) 2001-2016, 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 ---------------------
677 -- Shows the status of the value so far. Const means that the value is
678 -- constant, and Val is the current constant value. Dynamic means that
679 -- the value is dynamic, and in this case Nod is the Node_Id of the
680 -- 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 bits
688 -- 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_SU_Size
730 begin
733 -- Initialize status from component size
738 else
742 -- Loop through indexes
753 -- Value of the current subscript range is statically known
756 and then
758 then
761 -- If known flat bound, entire size of array is zero
767 -- Current value is constant, evolve value
772 -- Current value is dynamic
774 else
775 -- An interesting little optimization, if we have a pending
776 -- conversion from bits to storage units, and the current
777 -- length is a multiple of the storage unit size, then we
778 -- can take the factor out here statically, avoiding some
779 -- extra dynamic computations at the end.
789 Right_Opnd =>
793 -- Value of the current subscript range is dynamic
795 else
796 -- If the current size value is constant, then here is where we
797 -- make a transition to dynamic values, which are always stored
798 -- in storage units, However, we do not want to convert to SU's
799 -- too soon, consider the case of a packed array of single bits,
800 -- we want to do the SU conversion after computing the size in
801 -- this case.
805 -- If the current value is a multiple of the storage unit,
806 -- then most certainly we can do the conversion now, simply
807 -- by dividing the current value by the storage unit value.
808 -- If this works, we set SU_Convert_Required to False.
812 Size :=
816 -- Otherwise, we go ahead and convert the value in bits, and
817 -- set SU_Convert_Required to True to ensure that the final
818 -- value is indeed properly converted.
820 else
826 -- Length is hi-lo+1
830 -- Check possible range of Len
832 declare
838 begin
844 -- If we cannot verify that range cannot be super-flat, we need
845 -- a max with zero, since length must be non-negative.
848 Len :=
850 Prefix =>
855 Len));
863 -- Here after processing all bounds to set sizes. If the value is a
864 -- constant, then it is bits, so we convert to storage units.
869 -- Case where the value is dynamic
871 else
872 -- Do convert from bits to SU's if needed
876 -- The expression required is (Size.Nod + SU - 1) / SU
880 Left_Opnd =>
891 -----------------------
892 -- Layout_Array_Type --
893 -----------------------
906 -- This is the type with which any generated constants or functions
907 -- will be associated (i.e. inserted into the freeze actions). This
908 -- is normally the type being laid out. The exception occurs when
909 -- we are laying out Itype's which are local to a record type, and
910 -- whose scope is this record type. Such types do not have freeze
911 -- nodes (because we have no place to put them).
913 ------------------------------------
914 -- How An Array Type is Laid Out --
915 ------------------------------------
917 -- Here is what goes on. We need to multiply the component size of the
918 -- array (which has already been set) by the length of each of the
919 -- indexes. If all these values are known at compile time, then the
920 -- resulting size of the array is the appropriate constant value.
922 -- If the component size or at least one bound is dynamic (but no
923 -- discriminants are present), then the size will be computed as an
924 -- expression that calculates the proper size.
926 -- If there is at least one discriminant bound, then the size is also
927 -- computed as an expression, but this expression contains discriminant
928 -- values which are obtained by selecting from a function parameter, and
929 -- the size is given by a function that is passed the variant record in
930 -- question, and whose body is the expression.
938 -- Calculated value so far if Val_Status = Const
940 when Discrim
941 | Dynamic
942 =>
944 -- Expression value so far if Val_Status /= Const
947 -- Records the value or expression computed so far. Const means that
948 -- the value is constant, and Val is the current constant value.
949 -- Dynamic means that the value is dynamic, and in this case Nod is
950 -- the Node_Id of the expression to compute the value, and Discrim
951 -- means that at least one bound is a discriminant, in which case Nod
952 -- is the expression so far (which will be the body of the function).
955 -- Value of size computed so far. See comments above
958 -- Variant record type for the formal parameter of the discriminant
959 -- function V if Status = Discrim.
962 -- This is set to True if the final result must be converted from
963 -- bits to storage units (rounding up to a storage unit boundary).
966 -- This is the amount that a nonstatic computed size will be divided
967 -- by to convert it from bits to storage units. This is normally
968 -- equal to SSU, but can be reduced in the case of packed components
969 -- that fit evenly into a storage unit.
972 -- Indicates whether to request that SO_Ref_From_Expr should
973 -- encapsulate the array size expression in a function.
976 -- If N represents a discriminant, then the Size.Status is set to
977 -- Discrim, and Vtyp is set. The parameter N is replaced with the
978 -- proper expression to extract the discriminant value from V.
980 ----------------
981 -- Discrimify --
982 ----------------
988 begin
991 then
1002 N :=
1007 -- Set the Etype attributes of the selected name and its prefix.
1008 -- Analyze_And_Resolve can't be called here because the Vname
1009 -- entity denoted by the prefix will not yet exist (it's created
1010 -- by SO_Ref_From_Expr, called at the end of Layout_Array_Type).
1017 -- Start of processing for Layout_Array_Type
1019 begin
1020 -- Default alignment is component alignment
1026 -- Calculate proper type for insertions
1030 else
1034 -- If the component type is a generic formal type then there's no point
1035 -- in determining a size for the array type.
1041 -- Deal with component size if base type
1045 -- Cannot do anything if Esize of component type unknown
1051 -- Set component size if not set already
1058 -- (RM 13.3 (48)) says that the size of an unconstrained array
1059 -- is implementation defined. We choose to leave it as Unknown
1060 -- here, and the actual behavior is determined by the back end.
1066 -- Initialize status from component size
1071 else
1075 -- Loop to process array indexes
1081 -- If an index of the array is a generic formal type then there is
1082 -- no point in determining a size for the array type.
1091 -- Value of the current subscript range is statically known
1094 and then
1096 then
1099 -- If known flat bound, entire size of array is zero
1107 -- If constant, evolve value
1112 -- Current value is dynamic
1114 else
1115 -- An interesting little optimization, if we have a pending
1116 -- conversion from bits to storage units, and the current
1117 -- length is a multiple of the storage unit size, then we
1118 -- can take the factor out here statically, avoiding some
1119 -- extra dynamic computations at the end.
1126 -- Now go ahead and evolve the expression
1131 Right_Opnd =>
1135 -- Value of the current subscript range is dynamic
1137 else
1138 -- If the current size value is constant, then here is where we
1139 -- make a transition to dynamic values, which are always stored
1140 -- in storage units, However, we do not want to convert to SU's
1141 -- too soon, consider the case of a packed array of single bits,
1142 -- we want to do the SU conversion after computing the size in
1143 -- this case.
1147 -- If the current value is a multiple of the storage unit,
1148 -- then most certainly we can do the conversion now, simply
1149 -- by dividing the current value by the storage unit value.
1150 -- If this works, we set SU_Convert_Required to False.
1153 Size :=
1157 -- If the current value is a factor of the storage unit, then
1158 -- we can use a value of one for the size and reduce the
1159 -- strength of the later division.
1166 -- Otherwise, we go ahead and convert the value in bits, and
1167 -- set SU_Convert_Required to True to ensure that the final
1168 -- value is indeed properly converted.
1170 else
1179 -- Length is hi-lo+1
1183 -- If Len isn't a Length attribute, then its range needs to be
1184 -- checked a possible Max with zero needs to be computed.
1188 then
1189 declare
1194 begin
1195 -- Check possible range of Len
1202 -- If range definitely flat or superflat, result size is 0
1210 -- If we cannot verify that range cannot be super-flat, we
1211 -- need a max with zero, since length cannot be negative.
1214 Len :=
1216 Prefix =>
1221 Len));
1226 -- At this stage, Len has the expression for the length
1237 -- Here after processing all bounds to set sizes. If the value is a
1238 -- constant, then it is bits, and the only thing we need to do is to
1239 -- check against explicit given size and do alignment adjust.
1245 -- Case where the value is dynamic
1247 else
1248 -- Do convert from bits to SU's if needed
1252 -- The expression required is:
1253 -- (Size.Nod + Storage_Divisor - 1) / Storage_Divisor
1257 Left_Opnd =>
1260 Right_Opnd => Make_Integer_Literal
1265 -- If the array entity is not declared at the library level and its
1266 -- not nested within a subprogram that is marked for inlining, then
1267 -- we request that the size expression be encapsulated in a function.
1268 -- Since this expression is not needed in most cases, we prefer not
1269 -- to incur the overhead of the computation on calls to the enclosing
1270 -- subprogram except for subprograms that require the size.
1275 declare
1278 begin
1290 -- Now set the dynamic size (the Value_Size is always the same as the
1291 -- Object_Size for arrays whose length is dynamic).
1293 -- ??? If Size.Status = Dynamic, Vtyp will not have been set.
1294 -- The added initialization sets it to Empty now, but is this
1295 -- correct?
1297 Set_Esize
1299 SO_Ref_From_Expr
1305 ------------------------------------------
1306 -- Compute_Size_Depends_On_Discriminant --
1307 ------------------------------------------
1316 begin
1317 -- Loop to process array indexes
1323 -- If an index of the array is a generic formal type then there is
1324 -- no point in determining a size for the array type.
1335 or else
1338 then
1350 -------------------
1351 -- Layout_Object --
1352 -------------------
1357 begin
1358 -- Nothing to do if backend does layout
1364 -- Set size if not set for object and known for type. Use the RM_Size if
1365 -- that is known for the type and Esize is not.
1376 -- Set alignment from type if unknown and type alignment known
1382 -- Make sure size and alignment are consistent
1386 -- Final adjustment, if we don't know the alignment, and the Esize was
1387 -- not set by an explicit Object_Size attribute clause, then we reset
1388 -- the Esize to unknown, since we really don't know it.
1395 ------------------------
1396 -- Layout_Record_Type --
1397 ------------------------
1404 -- Current component being laid out
1407 -- Previous laid out component
1409 procedure Get_Next_Component_Location
1416 -- Given the previous component in Prev_Comp, which is already laid
1417 -- out, and the alignment of the following component, lays out the
1418 -- following component, and returns its starting position in New_Npos
1419 -- (Normalized_Position value), New_Fbit (Normalized_First_Bit value),
1420 -- and New_NPMax (Normalized_Position_Max value). If Prev_Comp is empty
1421 -- (no previous component is present), then New_Npos, New_Fbit and
1422 -- New_NPMax are all set to zero on return. This procedure is also
1423 -- used to compute the size of a record or variant by giving it the
1424 -- last component, and the record alignment. Force_SU is used to force
1425 -- the new component location to be aligned on a storage unit boundary,
1426 -- even in a packed record, False means that the new position does not
1427 -- need to be bumped to a storage unit boundary, True means a storage
1428 -- unit boundary is always required.
1431 -- Lays out component Comp, given Prev_Comp, the previously laid-out
1432 -- component (Prev_Comp = Empty if no components laid out yet). The
1433 -- alignment of the record itself is also updated if needed. Both
1434 -- Comp and Prev_Comp can be either components or discriminants.
1436 procedure Layout_Components
1441 -- This procedure lays out the components of the given component list
1442 -- which contains the components starting with From and ending with To.
1443 -- The Next_Entity chain is used to traverse the components. On entry,
1444 -- Prev_Comp is set to the component preceding the list, so that the
1445 -- list is laid out after this component. Prev_Comp is set to Empty if
1446 -- the component list is to be laid out starting at the start of the
1447 -- record. On return, the components are all laid out, and Prev_Comp is
1448 -- set to the last laid out component. On return, Esiz is set to the
1449 -- resulting Object_Size value, which is the length of the record up
1450 -- to and including the last laid out entity. For Esiz, the value is
1451 -- adjusted to match the alignment of the record. RM_Siz is similarly
1452 -- set to the resulting Value_Size value, which is the same length, but
1453 -- not adjusted to meet the alignment. Note that in the case of variant
1454 -- records, Esiz represents the maximum size.
1457 -- Procedure called to lay out a non-variant record type or subtype
1460 -- Procedure called to lay out a variant record type. Decl is set to the
1461 -- full type declaration for the variant record.
1463 ---------------------------------
1464 -- Get_Next_Component_Location --
1465 ---------------------------------
1467 procedure Get_Next_Component_Location
1474 is
1475 begin
1476 -- No previous component, return zero position
1485 -- Here we have a previous component
1487 declare
1496 -- Expression representing maximum size of previous component
1498 begin
1499 -- Case where previous field had a dynamic size
1503 -- If the previous field had a dynamic length, then it is
1504 -- required to occupy an integral number of storage units,
1505 -- and start on a storage unit boundary. This means that
1506 -- the Normalized_First_Bit value is zero in the previous
1507 -- component, and the new value is also set to zero.
1511 -- In this case, the new position is given by an expression
1512 -- that is the sum of old normalized position and old size.
1514 New_Npos :=
1515 SO_Ref_From_Expr
1517 Left_Opnd =>
1519 Right_Opnd =>
1524 -- Get maximum size of previous component
1528 else
1532 -- Now we can compute the new max position. If the max size
1533 -- is static and the old position is static, then we can
1534 -- compute the new position statically.
1538 then
1541 -- Otherwise new max position is dynamic
1543 else
1544 New_NPMax :=
1545 SO_Ref_From_Expr
1553 -- Previous field has known static Esize
1555 else
1558 -- Bump New_Fbit to storage unit boundary if required
1564 -- If old normalized position is static, we can go ahead and
1565 -- compute the new normalized position directly.
1575 -- Bump alignment if stricter than prev
1581 -- The max position is always equal to the position if
1582 -- the latter is static, since arrays depending on the
1583 -- values of discriminants never have static sizes.
1588 -- Case of old normalized position is dynamic
1590 else
1591 -- If new bit position is within the current storage unit,
1592 -- we can just copy the old position as the result position
1593 -- (we have already set the new first bit value).
1599 -- If new bit position is past the current storage unit, we
1600 -- need to generate a new dynamic value for the position
1601 -- ??? need to deal with alignment
1603 else
1604 New_Npos :=
1605 SO_Ref_From_Expr
1608 Right_Opnd =>
1614 New_NPMax :=
1615 SO_Ref_From_Expr
1618 Right_Opnd =>
1630 ----------------------
1631 -- Layout_Component --
1632 ----------------------
1642 begin
1643 -- Increase alignment of record if necessary. Note that we do not
1644 -- do this for packed records, which have an alignment of one by
1645 -- default, or for records for which an explicit alignment was
1646 -- specified with an alignment clause.
1651 then
1655 -- If original component set, then use same layout
1666 -- Parent field is always at start of record, this will overlap
1667 -- the actual fields that are part of the parent, and that's fine
1678 -- Check case of type of component has a scope of the record we are
1679 -- laying out. When this happens, the type in question is an Itype
1680 -- that has not yet been laid out (that's because such types do not
1681 -- get frozen in the normal manner, because there is no place for
1682 -- the freeze nodes).
1688 -- If component already laid out, then we are done
1694 -- Set size of component from type. We use the Esize except in a
1695 -- packed record, where we use the RM_Size (since that is what the
1696 -- RM_Size value, as distinct from the Object_Size is useful for).
1700 else
1704 -- Compute the component position from the previous one. See if
1705 -- current component requires being on a storage unit boundary.
1707 -- If record is not packed, we always go to a storage unit boundary
1712 -- Packed cases
1714 else
1715 -- Elementary types do not need SU boundary in packed record
1720 -- Packed array types with a modular packed array type do not
1721 -- force a storage unit boundary (since the code generation
1722 -- treats these as equivalent to the underlying modular type),
1727 then
1730 -- Record types with known length less than or equal to the length
1731 -- of long long integer can also be unaligned, since they can be
1732 -- treated as scalars.
1737 then
1740 -- All other cases force a storage unit boundary, even when packed
1742 else
1747 -- Now get the next component location
1749 Get_Next_Component_Location
1755 -- Set Component_Bit_Offset in the static case
1759 then
1764 -----------------------
1765 -- Layout_Components --
1766 -----------------------
1768 procedure Layout_Components
1773 is
1778 begin
1779 -- Only lay out components if there are some to lay out
1783 -- Lay out components with no component clauses
1786 loop
1789 then
1790 -- The compatibility of component clauses with composite
1791 -- types isn't checked in Sem_Ch13, so we check it here.
1796 then
1798 Error_Msg_NE
1801 Comp);
1804 else
1815 -- Set size fields, both are zero if no components
1821 -- If record subtype with non-static discriminants, then we don't
1822 -- know which variant will be the one which gets chosen. We don't
1823 -- just want to set the maximum size from the base, because the
1824 -- size should depend on the particular variant.
1826 -- What we do is to use the RM_Size of the base type, which has
1827 -- the necessary conditional computation of the size, using the
1828 -- size information for the particular variant chosen. Records
1829 -- with default discriminants for example have an Esize that is
1830 -- set to the maximum of all variants, but that's not what we
1831 -- want for a constrained subtype.
1835 then
1836 declare
1838 begin
1844 else
1845 -- First the object size, for which we align past the last field
1846 -- to the alignment of the record (the object size is required to
1847 -- be a multiple of the alignment).
1849 Get_Next_Component_Location
1852 End_Npos,
1853 End_Fbit,
1854 End_NPMax,
1857 -- If the resulting normalized position is a dynamic reference,
1858 -- then the size is dynamic, and is stored in storage units. In
1859 -- this case, we set the RM_Size to the same value, it is simply
1860 -- not worth distinguishing Esize and RM_Size values in the
1861 -- dynamic case, since the RM has nothing to say about them.
1863 -- Note that a size cannot have been given in this case, since
1864 -- size specifications cannot be given for variable length types.
1866 declare
1869 begin
1873 -- Set the Object_Size allowing for the alignment. In the
1874 -- dynamic case, we must do the actual runtime computation.
1875 -- We can skip this in the non-packed record case if the
1876 -- last component has a smaller alignment than the overall
1877 -- record alignment.
1884 then
1885 -- The expression we build is:
1886 -- (expr + align - 1) / align * align
1888 Esiz :=
1889 SO_Ref_From_Expr
1892 Left_Opnd =>
1894 Left_Opnd =>
1896 Left_Opnd =>
1898 Right_Opnd =>
1901 Right_Opnd =>
1903 Right_Opnd =>
1909 -- Here Esiz is static, so we can adjust the alignment
1910 -- directly go give the required aligned value.
1912 else
1916 -- Case where computed size is static
1918 else
1919 -- The ending size was computed in Npos in storage units,
1920 -- but the actual size is stored in bits, so adjust
1921 -- accordingly. We also adjust the size to match the
1922 -- alignment here.
1926 -- Compute the resulting Value_Size (RM_Size). For this
1927 -- purpose we do not force alignment of the record or
1928 -- storage size alignment of the result.
1930 Get_Next_Component_Location
1932 Uint_0,
1933 End_Npos,
1934 End_Fbit,
1935 End_NPMax,
1945 -------------------------------
1946 -- Layout_Non_Variant_Record --
1947 -------------------------------
1952 begin
1958 ---------------------------
1959 -- Layout_Variant_Record --
1960 ---------------------------
1972 -- Expression for the evolving RM_Siz value. This is typically an if
1973 -- expression which involves tests of discriminant values that are
1974 -- formed as references to the entity V. At the end of scanning all
1975 -- the components, a suitable function is constructed in which V is
1976 -- the parameter.
1978 -----------------------
1979 -- Local Subprograms --
1980 -----------------------
1982 procedure Layout_Component_List
1986 -- Recursive procedure, called to lay out one component list Esiz
1987 -- and RM_Siz_Expr are set to the Object_Size and Value_Size values
1988 -- respectively representing the record size up to and including the
1989 -- last component in the component list (including any variants in
1990 -- this component list). RM_Siz_Expr is returned as an expression
1991 -- which may in the general case involve some references to the
1992 -- discriminants of the current record value, referenced by selecting
1993 -- from the entity V.
1995 ---------------------------
1996 -- Layout_Component_List --
1997 ---------------------------
1999 procedure Layout_Component_List
2003 is
2011 begin
2013 Layout_Components
2018 else
2022 -- Case where no variants are present in the component list
2026 -- The Esiz value has been correctly set by the call to
2027 -- Layout_Components, so there is nothing more to be done.
2029 -- For RM_Siz, we have an SO_Ref value, which we must convert
2030 -- to an appropriate expression.
2033 RM_Siz_Expr :=
2037 else
2040 -- If the size is represented by a function, then we create
2041 -- an appropriate function call using V as the parameter to
2042 -- the call.
2045 RM_Siz_Expr :=
2051 -- If the size is represented by a constant, then the
2052 -- expression we want is a reference to this constant
2054 else
2059 -- Case where variants are present in this component list
2061 else
2062 declare
2071 begin
2078 Layout_Component_List
2081 -- Set the Object_Size. If this is the first variant,
2082 -- we just set the size of this first variant.
2087 -- Otherwise the Object_Size is formed as a maximum
2088 -- of Esiz so far from previous variants, and the new
2089 -- Esiz value from the variant we just processed.
2091 -- If both values are static, we can just compute the
2092 -- maximum directly to save building junk nodes.
2096 then
2099 -- If either value is dynamic, then we have to generate
2100 -- an appropriate Standard_Unsigned'Max attribute call.
2101 -- If one of the values is static then it needs to be
2102 -- converted from bits to storage units to be compatible
2103 -- with the dynamic value.
2105 else
2114 Esiz :=
2115 SO_Ref_From_Expr
2118 Prefix =>
2127 -- Now deal with Value_Size (RM_Siz). We are aiming at
2128 -- an expression that looks like:
2130 -- if xxDx (V.disc) then rmsiz1
2131 -- else if xxDx (V.disc) then rmsiz2
2132 -- else ...
2134 -- Where rmsiz1, rmsiz2... are the RM_Siz values for the
2135 -- individual variants, and xxDx are the discriminant
2136 -- checking functions generated for the variant type.
2138 -- If this is the first variant, we simply set the result
2139 -- as the expression. Note that this takes care of the
2140 -- others case.
2144 -- If this is the only variant and the size is a
2145 -- literal, then use bit size as is, otherwise convert
2146 -- to storage units and continue to the next variant.
2150 then
2152 else
2156 -- Otherwise construct the appropriate test
2158 else
2159 -- The test to be used in general is a call to the
2160 -- discriminant checking function. However, it is
2161 -- definitely worth special casing the very common
2162 -- case where a single value is involved.
2168 then
2169 -- Discriminant to be tested
2171 Discrim :=
2173 Prefix =>
2175 Selector_Name =>
2176 New_Occurrence_Of
2179 Dtest :=
2184 -- Generate a call to the discriminant-checking
2185 -- function for the variant. Note that the result
2186 -- has to be complemented since the function returns
2187 -- False when the passed discriminant value matches.
2189 else
2190 -- The checking function takes all of the type's
2191 -- discriminants as parameters, so a list of all
2192 -- the selected discriminants must be constructed.
2199 Prefix =>
2201 Selector_Name =>
2207 Dtest :=
2209 Right_Opnd =>
2211 Name =>
2212 New_Occurrence_Of
2214 Parameter_Associations =>
2215 D_List));
2218 RM_Siz_Expr :=
2220 Expressions =>
2221 New_List
2233 -- Indicates others present, not used in this case
2236 -- Error routine invoked by the generic instantiation below when
2237 -- the variant part has a nonstatic choice.
2240 Generic_Check_Choices
2246 -----------------------------
2247 -- Non_Static_Choice_Error --
2248 -----------------------------
2251 begin
2252 Flag_Non_Static_Expr
2256 -- Start of processing for Layout_Variant_Record
2258 begin
2259 -- Call Check_Choices here to ensure that Others_Discrete_Choices
2260 -- gets set on any 'others' choice before the discriminant-checking
2261 -- functions are generated. Otherwise the function for the 'others'
2262 -- alternative will unconditionally return True, causing discriminant
2263 -- checks to fail. However, Check_Choices is now normally delayed
2264 -- until the type's freeze entity is processed, due to requirements
2265 -- coming from subtype predicates, so doing it at this point is
2266 -- probably not right in general, but it's not clear how else to deal
2267 -- with this situation. Perhaps we should only generate declarations
2268 -- for the checking functions here, and somehow delay generation of
2269 -- their bodies, but that would be a nontrivial change. ???
2271 declare
2274 begin
2275 Check_Choices
2279 -- We need the discriminant checking functions, since we generate
2280 -- calls to these functions for the RM_Size expression, so make
2281 -- sure that these functions have been constructed in time.
2285 -- Lay out the discriminants
2293 Layout_Components
2299 -- Lay out the main component list (this will make recursive calls
2300 -- to lay out all component lists nested within variants).
2305 -- If the RM_Size is a literal, set its value
2310 -- Otherwise we construct a dynamic SO_Ref
2312 else
2314 SO_Ref_From_Expr
2321 -- Start of processing for Layout_Record_Type
2323 begin
2324 -- If this is a cloned subtype, just copy the size fields from the
2325 -- original, nothing else needs to be done in this case, since the
2326 -- components themselves are all shared.
2330 then
2335 -- Another special case, class-wide types. The RM says that the size
2336 -- of such types is implementation defined (RM 13.3(48)). What we do
2337 -- here is to leave the fields set as unknown values, and the backend
2338 -- determines the actual behavior.
2343 -- All other cases
2345 else
2346 -- Initialize alignment conservatively to 1. This value will be
2347 -- increased as necessary during processing of the record.
2353 -- Initialize previous component. This is Empty unless there are
2354 -- components which have already been laid out by component clauses.
2355 -- If there are such components, we start our lay out of the
2356 -- remaining components following the last such component.
2364 or else
2367 then
2375 -- We have two separate circuits, one for non-variant records and
2376 -- one for variant records. For non-variant records, we simply go
2377 -- through the list of components. This handles all the non-variant
2378 -- cases including those cases of subtypes where there is no full
2379 -- type declaration, so the tree cannot be used to drive the layout.
2380 -- For variant records, we have to drive the layout from the tree
2381 -- since we need to understand the variant structure in this case.
2385 else
2389 -- Scan all the components
2395 and then
2397 then
2398 Layout_Variant_Record;
2399 else
2400 Layout_Non_Variant_Record;
2405 -----------------
2406 -- Layout_Type --
2407 -----------------
2412 begin
2413 -- For string literal types, for now, kill the size always, this is
2414 -- because gigi does not like or need the size to be set ???
2422 -- For access types, set size/alignment. This is system address size,
2423 -- except for fat pointers (unconstrained array access types), where the
2424 -- size is two times the address size, to accommodate the two pointers
2425 -- that are required for a fat pointer (data and template). Note that
2426 -- E_Access_Protected_Subprogram_Type is not an access type for this
2427 -- purpose since it is not a pointer but is equivalent to a record. For
2428 -- access subtypes, copy the size from the base type since Gigi
2429 -- represents them the same way.
2434 -- If we only have a limited view of the type, see whether the
2435 -- non-limited view is available.
2440 then
2444 -- If Esize already set (e.g. by a size clause), then nothing further
2445 -- to be done here.
2450 -- Access to subprogram is a strange beast, and we let the backend
2451 -- figure out what is needed (it may be some kind of fat pointer,
2452 -- including the static link for example.
2457 -- For access subtypes, copy the size information from base type
2463 -- For other access types, we use either address size, or, if a fat
2464 -- pointer is used (pointer-to-unconstrained array case), twice the
2465 -- address size to accommodate a fat pointer.
2472 -- Debug Flag -gnatd6 says make all pointers to unconstrained thin
2474 and then not Debug_Flag_6
2475 then
2478 -- Check for bad convention set
2480 if Warn_On_Export_Import
2481 and then
2483 or else
2485 then
2486 Error_Msg_N
2490 -- If the designated type is a limited view it is unanalyzed. We can
2491 -- examine the declaration itself to determine whether it will need a
2492 -- fat pointer.
2498 N_Unconstrained_Array_Definition
2499 and then not Debug_Flag_6
2500 then
2503 -- Normal case of thin pointer
2505 else
2511 -- Scalar types: set size and alignment
2515 -- For discrete types, the RM_Size and Esize must be set already,
2516 -- since this is part of the earlier processing and the front end is
2517 -- always required to lay out the sizes of such types (since they are
2518 -- available as static attributes). All we do is to check that this
2519 -- rule is indeed obeyed.
2523 -- If the RM_Size is not set, then here is where we set it
2525 -- Note: an RM_Size of zero looks like not set here, but this
2526 -- is a rare case, and we can simply reset it without any harm.
2532 -- If Esize for a discrete type is not set then set it
2535 declare
2538 begin
2539 loop
2540 -- If size is big enough, set it and exit
2546 -- If the RM_Size is greater than 64 (happens only when
2547 -- strange values are specified by the user, then Esize
2548 -- is simply a copy of RM_Size, it will be further
2549 -- refined later on)
2555 -- Otherwise double possible size and keep trying
2557 else
2564 -- For non-discrete scalar types, if the RM_Size is not set, then set
2565 -- it now to a copy of the Esize if the Esize is set.
2567 else
2575 -- Non-elementary (composite) types
2577 else
2578 -- For packed arrays, take size and alignment values from the packed
2579 -- array type if a packed array type has been created and the fields
2580 -- are not currently set.
2584 then
2585 declare
2588 begin
2603 -- If Esize is set, and RM_Size is not, RM_Size is copied from Esize.
2604 -- At least for now this seems reasonable, and is in any case needed
2605 -- for compatibility with old versions of gigi.
2611 -- For array base types, set component size if object size of the
2612 -- component type is known and is a small power of 2 (8, 16, 32, 64),
2613 -- since this is what will always be used.
2616 declare
2619 begin
2620 -- For some reason, access types can cause trouble, So let's
2621 -- just do this for scalar types ???
2626 then
2627 declare
2629 begin
2639 -- Lay out array and record types if front end layout set
2648 -- Case of backend layout, we still do a little in the front end
2650 else
2651 -- Processing for record types
2655 -- Special remaining processing for record types with a known
2656 -- size of 16, 32, or 64 bits whose alignment is not yet set.
2657 -- For these types, we set a corresponding alignment matching
2658 -- the size if possible, or as large as possible if not.
2664 -- Processing for array types
2668 -- For arrays that are required to be atomic/VFA, we do the same
2669 -- processing as described above for short records, since we
2670 -- really need to have the alignment set for the whole array.
2676 -- For unpacked array types, set an alignment of 1 if we know
2677 -- that the component alignment is not greater than 1. The reason
2678 -- we do this is to avoid unnecessary copying of slices of such
2679 -- arrays when passed to subprogram parameters (see special test
2680 -- in Exp_Ch6.Expand_Actuals).
2685 then
2690 -- We need to know whether the size depends on the value of one
2691 -- or more discriminants to select the return mechanism. Skip if
2692 -- errors are present, to prevent cascaded messages.
2701 -- Final step is to check that Esize and RM_Size are compatible
2706 -- Esize is less than RM_Size. That's not good. First we test
2707 -- whether this was set deliberately with an Object_Size clause
2708 -- and if so, object to the clause.
2712 Error_Msg_F
2714 Expression (Get_Attribute_Definition_Clause
2718 -- Adjust Esize up to RM_Size value
2720 declare
2723 begin
2726 -- For scalar types, increase Object_Size to power of 2, but
2727 -- not less than a storage unit in any case (i.e., normally
2728 -- this means it will be storage-unit addressable).
2737 else
2741 -- Finally, make sure that alignment is consistent with
2742 -- the newly assigned size.
2746 loop
2755 ---------------------
2756 -- Rewrite_Integer --
2757 ---------------------
2762 begin
2767 -------------------------------
2768 -- Set_And_Check_Static_Size --
2769 -------------------------------
2771 procedure Set_And_Check_Static_Size
2775 is
2779 -- Spec is the number of bit specified in the size clause, and Min is
2780 -- the minimum computed size. An error is given that the specified size
2781 -- is too small if Spec < Min, and in this case both Esize and RM_Size
2782 -- are set to unknown in E. The error message is posted on node SC.
2785 -- Spec is the number of bits specified in the size clause, and Max is
2786 -- the maximum computed size. A warning is given about unused bits if
2787 -- Spec > Max. This warning is posted on node SC.
2789 --------------------------
2790 -- Check_Size_Too_Small --
2791 --------------------------
2794 begin
2803 -----------------------
2804 -- Check_Unused_Bits --
2805 -----------------------
2808 begin
2815 -- Start of processing for Set_And_Check_Static_Size
2817 begin
2818 -- Case where Object_Size (Esize) is already set by a size clause
2827 -- Perform checks on specified size against computed sizes
2835 -- Case where Value_Size (RM_Size) is set by specific Value_Size clause
2836 -- (we do not need to worry about Value_Size being set by a Size clause,
2837 -- since that will have set Esize as well, and we already took care of
2838 -- that case).
2843 -- Perform checks on specified size against computed sizes
2851 -- Set sizes if unknown
2862 -----------------------------
2863 -- Set_Composite_Alignment --
2864 -----------------------------
2870 begin
2871 -- If alignment is already set, then nothing to do
2877 -- Alignment is not known, see if we can set it, taking into account
2878 -- the setting of the Optimize_Alignment mode.
2880 -- If Optimize_Alignment is set to Space, then we try to give packed
2881 -- records an aligmment of 1, unless there is some reason we can't.
2886 then
2887 -- No effect for record with atomic/VFA components
2893 Error_Msg_N
2895 else
2896 Error_Msg_N
2903 -- No effect if independent components
2907 Error_Msg_N
2912 -- No effect if any component is atomic/VFA or is a by-reference type
2914 declare
2917 begin
2923 then
2927 Error_Msg_N
2930 else
2931 Error_Msg_N
2937 else
2943 -- Optimize_Alignment has no effect on variable length record
2951 -- All tests passed, we can set alignment to 1
2955 -- Not a record, or not packed
2957 else
2958 -- The only other cases we worry about here are where the size is
2959 -- statically known at compile time.
2965 else
2969 -- Size is known, alignment is not set
2971 -- Reset alignment to match size if the known size is exactly 2, 4,
2972 -- or 8 storage units.
2981 -- If Optimize_Alignment is set to Space, then make sure the
2982 -- alignment matches the size, for example, if the size is 17
2983 -- bytes then we want an alignment of 1 for the type.
2992 else
2996 -- If Optimize_Alignment is set to Time, then we reset for odd
2997 -- "in between sizes", for example a 17 bit record is given an
2998 -- alignment of 4.
3003 then
3012 -- No special alignment fiddling needed
3014 else
3019 -- Here we have Set Align to the proposed improved value. Make sure the
3020 -- value set does not exceed Maximum_Alignment for the target.
3026 -- Further processing for record types only to reduce the alignment
3027 -- set by the above processing in some specific cases. We do not
3028 -- do this for atomic/VFA records, since we need max alignment there,
3032 -- For records, there is generally no point in setting alignment
3033 -- higher than word size since we cannot do better than move by
3034 -- words in any case. Omit this if we are optimizing for time,
3035 -- since conceivably we may be able to do better.
3039 then
3043 -- Check components. If any component requires a higher alignment,
3044 -- then we set that higher alignment in any case. Don't do this if
3045 -- we have Optimize_Alignment set to Space. Note that that covers
3046 -- the case of packed records, where we already set alignment to 1.
3049 declare
3052 begin
3056 declare
3059 begin
3060 -- The cases to process are when the alignment of the
3061 -- component type is larger than the alignment we have
3062 -- so far, and either there is no component clause for
3063 -- the component, or the length set by the component
3064 -- clause matches the length of the component type.
3067 and then
3070 and then
3073 then
3085 -- Set chosen alignment, and increase Esize if necessary to match the
3086 -- chosen alignment.
3092 then
3097 --------------------------
3098 -- Set_Discrete_RM_Size --
3099 --------------------------
3104 begin
3105 -- All discrete types except for the base types in standard are
3106 -- constrained, so indicate this by setting Is_Constrained.
3110 -- Set generic types to have an unknown size, since the representation
3111 -- of a generic type is irrelevant, in view of the fact that they have
3112 -- nothing to do with code.
3117 -- If the subtype statically matches the first subtype, then it is
3118 -- required to have exactly the same layout. This is required by
3119 -- aliasing considerations.
3123 then
3127 -- In all other cases the RM_Size is set to the minimum size. Note that
3128 -- this routine is never called for subtypes for which the RM_Size is
3129 -- set explicitly by an attribute clause.
3131 else
3136 ------------------------
3137 -- Set_Elem_Alignment --
3138 ------------------------
3141 begin
3142 -- Do not set alignment for packed array types, unless we are doing
3143 -- front end layout, because otherwise this is always handled in the
3144 -- backend.
3147 and then not Frontend_Layout_On_Target
3148 then
3151 -- If there is an alignment clause, then we respect it
3156 -- If the size is not set, then don't attempt to set the alignment. This
3157 -- happens in the backend layout case for access-to-subprogram types.
3162 -- For access types, do not set the alignment if the size is less than
3163 -- the allowed minimum size. This avoids cascaded error messages.
3169 -- Here we calculate the alignment as the largest power of two multiple
3170 -- of System.Storage_Unit that does not exceed either the object size of
3171 -- the type, or the maximum allowed alignment.
3173 declare
3179 begin
3180 -- The given Esize may be larger that int'last because of a previous
3181 -- error, and the call to UI_To_Int will fail, so use default.
3186 -- If this is an access type and the target doesn't have strict
3187 -- alignment and we are not doing front end layout, then cap the
3188 -- alignment to that of a regular access type. This will avoid
3189 -- giving fat pointers twice the usual alignment for no practical
3190 -- benefit since the misalignment doesn't really matter.
3193 and then not Target_Strict_Alignment
3194 and then not Frontend_Layout_On_Target
3195 then
3198 else
3202 -- If the default alignment of "double" floating-point types is
3203 -- specifically capped, enforce the cap.
3208 then
3211 -- If the default alignment of "double" or larger scalar types is
3212 -- specifically capped, enforce the cap.
3217 then
3220 -- Otherwise enforce the overall alignment cap
3222 else
3231 -- If alignment is currently not set, then we can safely set it to
3232 -- this new calculated value.
3237 -- Cases where we have inherited an alignment
3239 -- For constructed types, always reset the alignment, these are
3240 -- generally invisible to the user anyway, and that way we are
3241 -- sure that no constructed types have weird alignments.
3246 -- If this inherited alignment is the same as the one we computed,
3247 -- then obviously everything is fine, and we do not need to reset it.
3252 else
3253 -- Now we come to the difficult cases of subtypes for which we
3254 -- have inherited an alignment different from the computed one.
3255 -- We resort to the presence of alignment and size clauses to
3256 -- guide our choices. Note that they can generally be present
3257 -- only on the first subtype (except for Object_Size) and that
3258 -- we need to look at the Rep_Item chain to correctly handle
3259 -- derived types.
3261 declare
3264 function Has_Attribute_Clause
3267 -- Wrapper around Get_Attribute_Definition_Clause which tests
3268 -- for the presence of the specified attribute clause.
3270 --------------------------
3271 -- Has_Attribute_Clause --
3272 --------------------------
3274 function Has_Attribute_Clause
3277 begin
3281 begin
3282 -- If the alignment comes from a clause, then we respect it.
3283 -- Consider for example:
3285 -- type R is new Character;
3286 -- for R'Alignment use 1;
3287 -- for R'Size use 16;
3288 -- subtype S is R;
3290 -- Here R has a specified size of 16 and a specified alignment
3291 -- of 1, and it seems right for S to inherit both values.
3296 -- Now we come to the cases where we have inherited alignment
3297 -- and size, and overridden the size but not the alignment.
3302 then
3303 -- This is tricky, it might be thought that we should try to
3304 -- inherit the alignment, since that's what the RM implies,
3305 -- but that leads to complex rules and oddities. Consider
3306 -- for example:
3308 -- type R is new Character;
3309 -- for R'Size use 16;
3311 -- It seems quite bogus in this case to inherit an alignment
3312 -- of 1 from the parent type Character. Furthermore, if that
3313 -- is what the programmer really wanted for some odd reason,
3314 -- then he could specify the alignment directly.
3316 -- Moreover we really don't want to inherit the alignment in
3317 -- the case of a specified Object_Size for a subtype, since
3318 -- there would be no way of overriding to give a reasonable
3319 -- value (as we don't have an Object_Alignment attribute).
3320 -- Consider for example:
3322 -- subtype R is Character;
3323 -- for R'Object_Size use 16;
3325 -- If we inherit the alignment of 1, then it will be very
3326 -- inefficient for the subtype and this cannot be fixed.
3328 -- So we make the decision that if Size (or Object_Size) is
3329 -- given and the alignment is not specified with a clause,
3330 -- we reset the alignment to the appropriate value for the
3331 -- specified size. This is a nice simple rule to implement
3332 -- and document.
3334 -- There is a theoretical glitch, which is that a confirming
3335 -- size clause could now change the alignment, which, if we
3336 -- really think that confirming rep clauses should have no
3337 -- effect, could be seen as a no-no. However that's already
3338 -- implemented by Alignment_Check_For_Size_Change so we do
3339 -- not change the philosophy here.
3341 -- Historical note: in versions prior to Nov 6th, 2011, an
3342 -- odd distinction was made between inherited alignments
3343 -- larger than the computed alignment (where the larger
3344 -- alignment was inherited) and inherited alignments smaller
3345 -- than the computed alignment (where the smaller alignment
3346 -- was overridden). This was a dubious fix to get around an
3347 -- ACATS problem which seems to have disappeared anyway, and
3348 -- in any case, this peculiarity was never documented.
3352 -- If no Size (or Object_Size) was specified, then we have
3353 -- inherited the object size, so we should also inherit the
3354 -- alignment and not modify it.
3356 else
3364 ----------------------
3365 -- SO_Ref_From_Expr --
3366 ----------------------
3368 function SO_Ref_From_Expr
3373 is
3381 -- Function used to check one node for reference to V
3384 -- Function used to traverse tree to check for reference to V
3386 ----------------------
3387 -- Check_Node_V_Ref --
3388 ----------------------
3391 begin
3395 else
3399 else
3404 -- Start of processing for SO_Ref_From_Expr
3406 begin
3407 -- Case of expression is an integer literal, in this case we just
3408 -- return the value (which must always be non-negative, since size
3409 -- and offset values can never be negative).
3416 -- Case where there is a reference to V, create function
3422 -- Check whether Vtype is a view of a private type and ensure that
3423 -- we use the primary view of the type (which is denoted by its
3424 -- Etype, whether it's the type's partial or full view entity).
3425 -- This is needed to make sure that we use the same (primary) view
3426 -- of the type for all V formals, whether the current view of the
3427 -- type is the partial or full view, so that types will always
3428 -- match on calls from one size function to another.
3432 else
3438 Decl :=
3441 Specification =>
3446 Defining_Identifier =>
3448 Parameter_Type =>
3450 Result_Definition =>
3455 Handled_Statement_Sequence =>
3461 -- The caller requests that the expression be encapsulated in a
3462 -- parameterless function.
3465 Decl :=
3468 Specification =>
3472 Result_Definition =>
3477 Handled_Statement_Sequence =>
3482 -- No reference to V and function not requested, so create a constant
3484 else
3485 Decl :=
3488 Object_Definition =>