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1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- L A Y O U T --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 2001-2005, Free Software Foundation, Inc. --
10 -- --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 2, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, --
20 -- Boston, MA 02110-1301, USA. --
21 -- --
22 -- GNAT was originally developed by the GNAT team at New York University. --
23 -- Extensive contributions were provided by Ada Core Technologies Inc. --
24 -- --
25 ------------------------------------------------------------------------------
52 ------------------------
53 -- Local Declarations --
54 ------------------------
57 -- Short hand for System_Storage_Unit
60 -- Formal parameter name used for functions generated for size offset
61 -- values that depend on the discriminant. All such functions have the
62 -- following form:
63 --
64 -- function xxx (V : vtyp) return Unsigned is
65 -- begin
66 -- return ... expression involving V.discrim
67 -- end xxx;
69 -----------------------
70 -- Local Subprograms --
71 -----------------------
74 -- E is the entity for a type or object. This procedure checks that the
75 -- size and alignment are compatible, and if not either gives an error
76 -- message if they cannot be adjusted or else adjusts them appropriately.
78 function Assoc_Add
83 -- This is like Make_Op_Add except that it optimizes some cases knowing
84 -- that associative rearrangement is allowed for constant folding if one
85 -- of the operands is a compile time known value.
87 function Assoc_Multiply
92 -- This is like Make_Op_Multiply except that it optimizes some cases
93 -- knowing that associative rearrangement is allowed for constant
94 -- folding if one of the operands is a compile time known value
96 function Assoc_Subtract
101 -- This is like Make_Op_Subtract except that it optimizes some cases
102 -- knowing that associative rearrangement is allowed for constant
103 -- folding if one of the operands is a compile time known value
106 -- This is used when we cross the boundary from static sizes in bits to
107 -- dynamic sizes in storage units. If the argument N is anything other
108 -- than an integer literal, it is returned unchanged, but if it is an
109 -- integer literal, then it is taken as a size in bits, and is replaced
110 -- by the corresponding size in storage units.
113 -- Given expressions for the low bound (Lo) and the high bound (Hi),
114 -- Build an expression for the value hi-lo+1, converted to type
115 -- Standard.Unsigned. Takes care of the case where the operands
116 -- are of an enumeration type (so that the subtraction cannot be
117 -- done directly) by applying the Pos operator to Hi/Lo first.
119 function Expr_From_SO_Ref
124 -- Given a value D from a size or offset field, return an expression
125 -- representing the value stored. If the value is known at compile time,
126 -- then an N_Integer_Literal is returned with the appropriate value. If
127 -- the value references a constant entity, then an N_Identifier node
128 -- referencing this entity is returned. If the value denotes a size
129 -- function, then returns a call node denoting the given function, with
130 -- a single actual parameter that either refers to the parameter V of
131 -- an enclosing size function (if Comp is Empty or its type doesn't match
132 -- the function's formal), or else is a selected component V.c when Comp
133 -- denotes a component c whose type matches that of the function formal.
134 -- The Loc value is used for the Sloc value of constructed notes.
136 function SO_Ref_From_Expr
142 -- This routine is used in the case where a size/offset value is dynamic
143 -- and is represented by the expression Expr. SO_Ref_From_Expr checks if
144 -- the Expr contains a reference to the identifier V, and if so builds
145 -- a function depending on discriminants of the formal parameter V which
146 -- is of type Vtype. Otherwise, if the parameter Make_Func is True, then
147 -- Expr will be encapsulated in a parameterless function; if Make_Func is
148 -- False, then a constant entity with the value Expr is built. The result
149 -- is a Dynamic_SO_Ref to the created entity. Note that Vtype can be
150 -- omitted if Expr does not contain any reference to V, the created entity.
151 -- The declaration created is inserted in the freeze actions of Ins_Type,
152 -- which also supplies the Sloc for created nodes. This function also takes
153 -- care of making sure that the expression is properly analyzed and
154 -- resolved (which may not be the case yet if we build the expression
155 -- in this unit).
158 -- E is an array type or subtype that has at least one index bound that
159 -- is the value of a record discriminant. For such an array, the function
160 -- computes an expression that yields the maximum possible size of the
161 -- array in storage units. The result is not defined for any other type,
162 -- or for arrays that do not depend on discriminants, and it is a fatal
163 -- error to call this unless Size_Depends_On_Discriminant (E) is True.
166 -- Front-end layout of non-bit-packed array type or subtype
169 -- Front-end layout of record type
172 -- Rewrite node N with an integer literal whose value is V. The Sloc
173 -- for the new node is taken from N, and the type of the literal is
174 -- set to a copy of the type of N on entry.
176 procedure Set_And_Check_Static_Size
180 -- This procedure is called to check explicit given sizes (possibly
181 -- stored in the Esize and RM_Size fields of E) against computed
182 -- Object_Size (Esiz) and Value_Size (RM_Siz) values. Appropriate
183 -- errors and warnings are posted if specified sizes are inconsistent
184 -- with specified sizes. On return, the Esize and RM_Size fields of
185 -- E are set (either from previously given values, or from the newly
186 -- computed values, as appropriate).
189 -- This procedure is called for record types and subtypes, and also for
190 -- atomic array types and subtypes. If no alignment is set, and the size
191 -- is 2 or 4 (or 8 if the word size is 8), then the alignment is set to
192 -- match the size.
194 ----------------------------
195 -- Adjust_Esize_Alignment --
196 ----------------------------
202 begin
203 -- Nothing to do if size unknown
209 -- Determine if size is constrained by an attribute definition clause
210 -- which must be obeyed. If so, we cannot increase the size in this
211 -- routine.
213 -- For a type, the issue is whether an object size clause has been
214 -- set. A normal size clause constrains only the value size (RM_Size)
219 -- For an object, the issue is whether a size clause is present
221 else
225 -- If size is known it must be a multiple of the storage unit size
229 -- If not, and size specified, then give error
232 Error_Msg_NE
237 -- Otherwise bump up size to a storage unit boundary
239 else
244 -- Now we have the size set, it must be a multiple of the alignment
245 -- nothing more we can do here if the alignment is unknown here.
251 -- At this point both the Esize and Alignment are known, so we need
252 -- to make sure they are consistent.
260 -- Here we have a situation where the Esize is not a multiple of
261 -- the alignment. We must either increase Esize or reduce the
262 -- alignment to correct this situation.
264 -- The case in which we can decrease the alignment is where the
265 -- alignment was not set by an alignment clause, and the type in
266 -- question is a discrete type, where it is definitely safe to
267 -- reduce the alignment. For example:
269 -- t : integer range 1 .. 2;
270 -- for t'size use 8;
272 -- In this situation, the initial alignment of t is 4, copied from
273 -- the Integer base type, but it is safe to reduce it to 1 at this
274 -- stage, since we will only be loading a single storage unit.
278 then
279 loop
288 -- Now the only possible approach left is to increase the Esize
289 -- but we can't do that if the size was set by a specific clause.
292 Error_Msg_NE
296 -- Otherwise we can indeed increase the size to a multiple of alignment
298 else
303 ---------------
304 -- Assoc_Add --
305 ---------------
307 function Assoc_Add
311 return Node_Id
312 is
316 begin
317 -- Case of right operand is a constant
323 -- Case of left operand is a constant
329 -- Neither operand is a constant, do the addition with no optimization
331 else
335 -- Case of left operand is an addition
339 -- (C1 + E) + C2 = (C1 + C2) + E
342 Rewrite_Integer
347 -- (E + C1) + C2 = E + (C1 + C2)
350 Rewrite_Integer
356 -- Case of left operand is a subtraction
360 -- (C1 - E) + C2 = (C1 + C2) + E
363 Rewrite_Integer
368 -- (E - C1) + C2 = E - (C1 - C2)
371 Rewrite_Integer
378 -- Not optimizable, do the addition
383 --------------------
384 -- Assoc_Multiply --
385 --------------------
387 function Assoc_Multiply
391 return Node_Id
392 is
396 begin
397 -- Case of right operand is a constant
403 -- Case of left operand is a constant
409 -- Neither operand is a constant, do the multiply with no optimization
411 else
415 -- Case of left operand is an multiplication
419 -- (C1 * E) * C2 = (C1 * C2) + E
422 Rewrite_Integer
427 -- (E * C1) * C2 = E * (C1 * C2)
430 Rewrite_Integer
437 -- Not optimizable, do the multiplication
442 --------------------
443 -- Assoc_Subtract --
444 --------------------
446 function Assoc_Subtract
450 return Node_Id
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 return Node_Id
615 is
618 begin
623 -- If a component is passed in whose type matches the type
624 -- of the function formal, then select that component from
625 -- the "V" 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
679 -- is constant, and Val is the current constant value. Dynamic means
680 -- that the value is dynamic, and in this case Nod is the Node_Id of
681 -- the 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
689 -- bits 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 indices
754 -- Value of the current subscript range is statically known
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,
817 -- and set SU_Convert_Required to True to ensure that the
818 -- final value is indeed properly converted.
820 else
826 -- Length is hi-lo+1
830 -- Check possible range of Len
832 declare
837 begin
843 -- If we cannot verify that range cannot be super-flat,
844 -- we need a max with zero, since length must be non-neg.
847 Len :=
849 Prefix =>
854 Len));
862 -- Here after processing all bounds to set sizes. If the value is
863 -- a constant, then it is bits, so we convert to storage units.
868 -- Case where the value is dynamic
870 else
871 -- Do convert from bits to SU's if needed
875 -- The expression required is (Size.Nod + SU - 1) / SU
879 Left_Opnd =>
890 -----------------------
891 -- Layout_Array_Type --
892 -----------------------
905 -- This is the type with which any generated constants or functions
906 -- will be associated (i.e. inserted into the freeze actions). This
907 -- is normally the type being laid out. The exception occurs when
908 -- we are laying out Itype's which are local to a record type, and
909 -- whose scope is this record type. Such types do not have freeze
910 -- nodes (because we have no place to put them).
912 ------------------------------------
913 -- How An Array Type is Laid Out --
914 ------------------------------------
916 -- Here is what goes on. We need to multiply the component size of
917 -- the array (which has already been set) by the length of each of
918 -- the indexes. If all these values are known at compile time, then
919 -- the resulting size of the array is the appropriate constant value.
921 -- If the component size or at least one bound is dynamic (but no
922 -- discriminants are present), then the size will be computed as an
923 -- expression that calculates the proper size.
925 -- If there is at least one discriminant bound, then the size is also
926 -- computed as an expression, but this expression contains discriminant
927 -- values which are obtained by selecting from a function parameter, and
928 -- the size is given by a function that is passed the variant record in
929 -- question, and whose body is the expression.
934 record
938 -- Calculated value so far if Val_Status = Const
942 -- Expression value so far if Val_Status /= Const
946 -- Records the value or expression computed so far. Const means that
947 -- the value is constant, and Val is the current constant value.
948 -- Dynamic means that the value is dynamic, and in this case Nod is
949 -- the Node_Id of the expression to compute the value, and Discrim
950 -- means that at least one bound is a discriminant, in which case Nod
951 -- is the expression so far (which will be the body of the function).
954 -- Value of size computed so far. See comments above
957 -- Variant record type for the formal parameter of the
958 -- discriminant function V if Status = Discrim.
961 -- This is set to True if the final result must be converted from
962 -- bits to storage units (rounding up to a storage unit boundary).
965 -- This is the amount that a nonstatic computed size will be divided
966 -- by to convert it from bits to storage units. This is normally
967 -- equal to SSU, but can be reduced in the case of packed components
968 -- that fit evenly into a storage unit.
971 -- Indicates whether to request that SO_Ref_From_Expr should
972 -- encapsulate the array size expresion in a function.
975 -- If N represents a discriminant, then the Size.Status is set to
976 -- Discrim, and Vtyp is set. The parameter N is replaced with the
977 -- proper expression to extract the discriminant value from V.
979 ----------------
980 -- Discrimify --
981 ----------------
987 begin
990 then
1001 N :=
1006 -- Set the Etype attributes of the selected name and its prefix.
1007 -- Analyze_And_Resolve can't be called here because the Vname
1008 -- entity denoted by the prefix will not yet exist (it's created
1009 -- by SO_Ref_From_Expr, called at the end of Layout_Array_Type).
1016 -- Start of processing for Layout_Array_Type
1018 begin
1019 -- Default alignment is component alignment
1025 -- Calculate proper type for insertions
1029 else
1033 -- If the component type is a generic formal type then there's no point
1034 -- in determining a size for the array type.
1040 -- Deal with component size if base type
1044 -- Cannot do anything if Esize of component type unknown
1050 -- Set component size if not set already
1057 -- (RM 13.3 (48)) says that the size of an unconstrained array
1058 -- is implementation defined. We choose to leave it as Unknown
1059 -- here, and the actual behavior is determined by the back end.
1065 -- Initialize status from component size
1070 else
1074 -- Loop to process array indices
1080 -- If an index of the array is a generic formal type then there's
1081 -- no point in determining a size for the array type.
1090 -- Value of the current subscript range is statically known
1094 then
1097 -- If known flat bound, entire size of array is zero!
1105 -- If constant, evolve value
1110 -- Current value is dynamic
1112 else
1113 -- An interesting little optimization, if we have a pending
1114 -- conversion from bits to storage units, and the current
1115 -- length is a multiple of the storage unit size, then we
1116 -- can take the factor out here statically, avoiding some
1117 -- extra dynamic computations at the end.
1124 -- Now go ahead and evolve the expression
1129 Right_Opnd =>
1133 -- Value of the current subscript range is dynamic
1135 else
1136 -- If the current size value is constant, then here is where we
1137 -- make a transition to dynamic values, which are always stored
1138 -- in storage units, However, we do not want to convert to SU's
1139 -- too soon, consider the case of a packed array of single bits,
1140 -- we want to do the SU conversion after computing the size in
1141 -- this case.
1145 -- If the current value is a multiple of the storage unit,
1146 -- then most certainly we can do the conversion now, simply
1147 -- by dividing the current value by the storage unit value.
1148 -- If this works, we set SU_Convert_Required to False.
1151 Size :=
1155 -- If the current value is a factor of the storage unit,
1156 -- then we can use a value of one for the size and reduce
1157 -- the strength of the later division.
1164 -- Otherwise, we go ahead and convert the value in bits,
1165 -- and set SU_Convert_Required to True to ensure that the
1166 -- final value is indeed properly converted.
1168 else
1177 -- Length is hi-lo+1
1181 -- If Len isn't a Length attribute, then its range needs to
1182 -- be checked a possible Max with zero needs to be computed.
1186 then
1187 declare
1192 begin
1193 -- Check possible range of Len
1200 -- If range definitely flat or superflat,
1201 -- result size is zero
1209 -- If we cannot verify that range cannot be super-flat,
1210 -- we need a maximum with zero, since length cannot be
1211 -- 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
1238 -- a constant, then it is bits, and the only thing we need to do
1239 -- is to 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
1291 -- as the 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 -- Layout_Object --
1307 -------------------
1312 begin
1313 -- Nothing to do if backend does layout
1319 -- Set size if not set for object and known for type. Use the
1320 -- RM_Size if that is known for the type and Esize is not.
1331 -- Set alignment from type if unknown and type alignment known
1337 -- Make sure size and alignment are consistent
1341 -- Final adjustment, if we don't know the alignment, and the Esize
1342 -- was not set by an explicit Object_Size attribute clause, then
1343 -- we reset the Esize to unknown, since we really don't know it.
1347 then
1352 ------------------------
1353 -- Layout_Record_Type --
1354 ------------------------
1361 -- Current component being laid out
1364 -- Previous laid out component
1366 procedure Get_Next_Component_Location
1373 -- Given the previous component in Prev_Comp, which is already laid
1374 -- out, and the alignment of the following component, lays out the
1375 -- following component, and returns its starting position in New_Npos
1376 -- (Normalized_Position value), New_Fbit (Normalized_First_Bit value),
1377 -- and New_NPMax (Normalized_Position_Max value). If Prev_Comp is empty
1378 -- (no previous component is present), then New_Npos, New_Fbit and
1379 -- New_NPMax are all set to zero on return. This procedure is also
1380 -- used to compute the size of a record or variant by giving it the
1381 -- last component, and the record alignment. Force_SU is used to force
1382 -- the new component location to be aligned on a storage unit boundary,
1383 -- even in a packed record, False means that the new position does not
1384 -- need to be bumped to a storage unit boundary, True means a storage
1385 -- unit boundary is always required.
1388 -- Lays out component Comp, given Prev_Comp, the previously laid-out
1389 -- component (Prev_Comp = Empty if no components laid out yet). The
1390 -- alignment of the record itself is also updated if needed. Both
1391 -- Comp and Prev_Comp can be either components or discriminants.
1393 procedure Layout_Components
1398 -- This procedure lays out the components of the given component list
1399 -- which contains the components starting with From and ending with To.
1400 -- The Next_Entity chain is used to traverse the components. On entry,
1401 -- Prev_Comp is set to the component preceding the list, so that the
1402 -- list is laid out after this component. Prev_Comp is set to Empty if
1403 -- the component list is to be laid out starting at the start of the
1404 -- record. On return, the components are all laid out, and Prev_Comp is
1405 -- set to the last laid out component. On return, Esiz is set to the
1406 -- resulting Object_Size value, which is the length of the record up
1407 -- to and including the last laid out entity. For Esiz, the value is
1408 -- adjusted to match the alignment of the record. RM_Siz is similarly
1409 -- set to the resulting Value_Size value, which is the same length, but
1410 -- not adjusted to meet the alignment. Note that in the case of variant
1411 -- records, Esiz represents the maximum size.
1414 -- Procedure called to lay out a non-variant record type or subtype
1417 -- Procedure called to lay out a variant record type. Decl is set to the
1418 -- full type declaration for the variant record.
1420 ---------------------------------
1421 -- Get_Next_Component_Location --
1422 ---------------------------------
1424 procedure Get_Next_Component_Location
1431 is
1432 begin
1433 -- No previous component, return zero position
1442 -- Here we have a previous component
1444 declare
1453 -- Expression representing maximum size of previous component
1455 begin
1456 -- Case where previous field had a dynamic size
1460 -- If the previous field had a dynamic length, then it is
1461 -- required to occupy an integral number of storage units,
1462 -- and start on a storage unit boundary. This means that
1463 -- the Normalized_First_Bit value is zero in the previous
1464 -- component, and the new value is also set to zero.
1468 -- In this case, the new position is given by an expression
1469 -- that is the sum of old normalized position and old size.
1471 New_Npos :=
1472 SO_Ref_From_Expr
1474 Left_Opnd =>
1476 Right_Opnd =>
1481 -- Get maximum size of previous component
1485 else
1489 -- Now we can compute the new max position. If the max size
1490 -- is static and the old position is static, then we can
1491 -- compute the new position statically.
1495 then
1498 -- Otherwise new max position is dynamic
1500 else
1501 New_NPMax :=
1502 SO_Ref_From_Expr
1510 -- Previous field has known static Esize
1512 else
1515 -- Bump New_Fbit to storage unit boundary if required
1521 -- If old normalized position is static, we can go ahead
1522 -- and compute the new normalized position directly.
1532 -- Bump alignment if stricter than prev
1538 -- The max position is always equal to the position if
1539 -- the latter is static, since arrays depending on the
1540 -- values of discriminants never have static sizes.
1545 -- Case of old normalized position is dynamic
1547 else
1548 -- If new bit position is within the current storage unit,
1549 -- we can just copy the old position as the result position
1550 -- (we have already set the new first bit value).
1556 -- If new bit position is past the current storage unit, we
1557 -- need to generate a new dynamic value for the position
1558 -- ??? need to deal with alignment
1560 else
1561 New_Npos :=
1562 SO_Ref_From_Expr
1565 Right_Opnd =>
1571 New_NPMax :=
1572 SO_Ref_From_Expr
1575 Right_Opnd =>
1587 ----------------------
1588 -- Layout_Component --
1589 ----------------------
1598 begin
1599 -- Parent field is always at start of record, this will overlap
1600 -- the actual fields that are part of the parent, and that's fine
1611 -- Check case of type of component has a scope of the record we
1612 -- are laying out. When this happens, the type in question is an
1613 -- Itype that has not yet been laid out (that's because such
1614 -- types do not get frozen in the normal manner, because there
1615 -- is no place for the freeze nodes).
1621 -- Increase alignment of record if necessary. Note that we do not
1622 -- do this for packed records, which have an alignment of one by
1623 -- default, or for records for which an explicit alignment was
1624 -- specified with an alignment clause.
1629 then
1633 -- If component already laid out, then we are done
1639 -- Set size of component from type. We use the Esize except in a
1640 -- packed record, where we use the RM_Size (since that is exactly
1641 -- what the RM_Size value, as distinct from the Object_Size is
1642 -- useful for!)
1646 else
1650 -- Compute the component position from the previous one. See if
1651 -- current component requires being on a storage unit boundary.
1653 -- If record is not packed, we always go to a storage unit boundary
1658 -- Packed cases
1660 else
1661 -- Elementary types do not need SU boundary in packed record
1666 -- Packed array types with a modular packed array type do not
1667 -- force a storage unit boundary (since the code generation
1668 -- treats these as equivalent to the underlying modular type),
1673 then
1676 -- Record types with known length less than or equal to the length
1677 -- of long long integer can also be unaligned, since they can be
1678 -- treated as scalars.
1683 then
1686 -- All other cases force a storage unit boundary, even when packed
1688 else
1693 -- Now get the next component location
1695 Get_Next_Component_Location
1701 -- Set Component_Bit_Offset in the static case
1705 then
1710 -----------------------
1711 -- Layout_Components --
1712 -----------------------
1714 procedure Layout_Components
1719 is
1724 begin
1725 -- Only lay out components if there are some to lay out!
1729 -- Lay out components with no component clauses
1732 loop
1735 then
1736 -- The compatibility of component clauses with composite
1737 -- types isn't checked in Sem_Ch13, so we check it here.
1742 then
1744 Error_Msg_NE
1747 Comp);
1750 else
1761 -- Set size fields, both are zero if no components
1767 else
1768 -- First the object size, for which we align past the last
1769 -- field to the alignment of the record (the object size
1770 -- is required to be a multiple of the alignment).
1772 Get_Next_Component_Location
1775 End_Npos,
1776 End_Fbit,
1777 End_NPMax,
1780 -- If the resulting normalized position is a dynamic reference,
1781 -- then the size is dynamic, and is stored in storage units.
1782 -- In this case, we set the RM_Size to the same value, it is
1783 -- simply not worth distinguishing Esize and RM_Size values in
1784 -- the dynamic case, since the RM has nothing to say about them.
1786 -- Note that a size cannot have been given in this case, since
1787 -- size specifications cannot be given for variable length types.
1789 declare
1792 begin
1796 -- Set the Object_Size allowing for alignment. In the
1797 -- dynamic case, we have to actually do the runtime
1798 -- computation. We can skip this in the non-packed
1799 -- record case if the last component has a smaller
1800 -- alignment than the overall record alignment.
1807 then
1808 -- The expression we build is
1809 -- (expr + align - 1) / align * align
1811 Esiz :=
1812 SO_Ref_From_Expr
1815 Left_Opnd =>
1817 Left_Opnd =>
1819 Left_Opnd =>
1821 Right_Opnd =>
1824 Right_Opnd =>
1826 Right_Opnd =>
1832 -- Here Esiz is static, so we can adjust the alignment
1833 -- directly go give the required aligned value.
1835 else
1839 -- Case where computed size is static
1841 else
1842 -- The ending size was computed in Npos in storage units,
1843 -- but the actual size is stored in bits, so adjust
1844 -- accordingly. We also adjust the size to match the
1845 -- alignment here.
1849 -- Compute the resulting Value_Size (RM_Size). For this
1850 -- purpose we do not force alignment of the record or
1851 -- storage size alignment of the result.
1853 Get_Next_Component_Location
1855 Uint_0,
1856 End_Npos,
1857 End_Fbit,
1858 End_NPMax,
1868 -------------------------------
1869 -- Layout_Non_Variant_Record --
1870 -------------------------------
1876 begin
1882 ---------------------------
1883 -- Layout_Variant_Record --
1884 ---------------------------
1893 -- Expression for the evolving RM_Siz value. This is typically a
1894 -- conditional expression which involves tests of discriminant
1895 -- values that are formed as references to the entity V. At
1896 -- the end of scanning all the components, a suitable function
1897 -- is constructed in which V is the parameter.
1899 -----------------------
1900 -- Local Subprograms --
1901 -----------------------
1903 procedure Layout_Component_List
1907 -- Recursive procedure, called to lay out one component list
1908 -- Esiz and RM_Siz_Expr are set to the Object_Size and Value_Size
1909 -- values respectively representing the record size up to and
1910 -- including the last component in the component list (including
1911 -- any variants in this component list). RM_Siz_Expr is returned
1912 -- as an expression which may in the general case involve some
1913 -- references to the discriminants of the current record value,
1914 -- referenced by selecting from the entity V.
1916 ---------------------------
1917 -- Layout_Component_List --
1918 ---------------------------
1920 procedure Layout_Component_List
1924 is
1932 begin
1934 Layout_Components
1939 else
1943 -- Case where no variants are present in the component list
1947 -- The Esiz value has been correctly set by the call to
1948 -- Layout_Components, so there is nothing more to be done.
1950 -- For RM_Siz, we have an SO_Ref value, which we must convert
1951 -- to an appropriate expression.
1954 RM_Siz_Expr :=
1958 else
1961 -- If the size is represented by a function, then we
1962 -- create an appropriate function call using V as
1963 -- the parameter to the call.
1966 RM_Siz_Expr :=
1972 -- If the size is represented by a constant, then the
1973 -- expression we want is a reference to this constant
1975 else
1980 -- Case where variants are present in this component list
1982 else
1983 declare
1992 begin
1999 Layout_Component_List
2002 -- Set the Object_Size. If this is the first variant,
2003 -- we just set the size of this first variant.
2008 -- Otherwise the Object_Size is formed as a maximum
2009 -- of Esiz so far from previous variants, and the new
2010 -- Esiz value from the variant we just processed.
2012 -- If both values are static, we can just compute the
2013 -- maximum directly to save building junk nodes.
2017 then
2020 -- If either value is dynamic, then we have to generate
2021 -- an appropriate Standard_Unsigned'Max attribute call.
2023 else
2024 Esiz :=
2025 SO_Ref_From_Expr
2028 Prefix =>
2037 -- Now deal with Value_Size (RM_Siz). We are aiming at
2038 -- an expression that looks like:
2040 -- if xxDx (V.disc) then rmsiz1
2041 -- else if xxDx (V.disc) then rmsiz2
2042 -- else ...
2044 -- Where rmsiz1, rmsiz2... are the RM_Siz values for the
2045 -- individual variants, and xxDx are the discriminant
2046 -- checking functions generated for the variant type.
2048 -- If this is the first variant, we simply set the
2049 -- result as the expression. Note that this takes
2050 -- care of the others case.
2055 -- Otherwise construct the appropriate test
2057 else
2058 -- The test to be used in general is a call to the
2059 -- discriminant checking function. However, it is
2060 -- definitely worth special casing the very common
2061 -- case where a single value is involved.
2067 then
2068 -- Discriminant to be tested
2070 Discrim :=
2072 Prefix =>
2074 Selector_Name =>
2075 New_Occurrence_Of
2078 Dtest :=
2083 -- Generate a call to the discriminant-checking
2084 -- function for the variant. Note that the result
2085 -- has to be complemented since the function returns
2086 -- False when the passed discriminant value matches.
2088 else
2089 -- The checking function takes all of the type's
2090 -- discriminants as parameters, so a list of all
2091 -- the selected discriminants must be constructed.
2096 Append (
2098 Prefix =>
2100 Selector_Name =>
2101 New_Occurrence_Of
2103 D_List);
2108 Dtest :=
2110 Right_Opnd =>
2112 Name =>
2113 New_Occurrence_Of
2115 Parameter_Associations =>
2116 D_List));
2119 RM_Siz_Expr :=
2121 Expressions =>
2122 New_List
2132 -- Start of processing for Layout_Variant_Record
2134 begin
2135 -- We need the discriminant checking functions, since we generate
2136 -- calls to these functions for the RM_Size expression, so make
2137 -- sure that these functions have been constructed in time.
2141 -- Lay out the discriminants
2143 Layout_Components
2149 -- Lay out the main component list (this will make recursive calls
2150 -- to lay out all component lists nested within variants).
2155 -- If the RM_Size is a literal, set its value
2160 -- Otherwise we construct a dynamic SO_Ref
2162 else
2164 SO_Ref_From_Expr
2171 -- Start of processing for Layout_Record_Type
2173 begin
2174 -- If this is a cloned subtype, just copy the size fields from the
2175 -- original, nothing else needs to be done in this case, since the
2176 -- components themselves are all shared.
2181 then
2186 -- Another special case, class-wide types. The RM says that the size
2187 -- of such types is implementation defined (RM 13.3(48)). What we do
2188 -- here is to leave the fields set as unknown values, and the backend
2189 -- determines the actual behavior.
2194 -- All other cases
2196 else
2197 -- Initialize alignment conservatively to 1. This value will
2198 -- be increased as necessary during processing of the record.
2204 -- Initialize previous component. This is Empty unless there
2205 -- are components which have already been laid out by component
2206 -- clauses. If there are such components, we start our lay out of
2207 -- the remaining components following the last such component.
2216 then
2218 or else
2221 then
2229 -- We have two separate circuits, one for non-variant records and
2230 -- one for variant records. For non-variant records, we simply go
2231 -- through the list of components. This handles all the non-variant
2232 -- cases including those cases of subtypes where there is no full
2233 -- type declaration, so the tree cannot be used to drive the layout.
2234 -- For variant records, we have to drive the layout from the tree
2235 -- since we need to understand the variant structure in this case.
2239 else
2243 -- Scan all the components
2249 and then
2251 then
2252 Layout_Variant_Record;
2253 else
2254 Layout_Non_Variant_Record;
2259 -----------------
2260 -- Layout_Type --
2261 -----------------
2264 begin
2265 -- For string literal types, for now, kill the size always, this
2266 -- is because gigi does not like or need the size to be set ???
2274 -- For access types, set size/alignment. This is system address
2275 -- size, except for fat pointers (unconstrained array access types),
2276 -- where the size is two times the address size, to accommodate the
2277 -- two pointers that are required for a fat pointer (data and
2278 -- template). Note that E_Access_Protected_Subprogram_Type is not
2279 -- an access type for this purpose since it is not a pointer but is
2280 -- equivalent to a record. For access subtypes, copy the size from
2281 -- the base type since Gigi represents them the same way.
2285 -- If Esize already set (e.g. by a size clause), then nothing
2286 -- further to be done here.
2291 -- Access to subprogram is a strange beast, and we let the
2292 -- backend figure out what is needed (it may be some kind
2293 -- of fat pointer, including the static link for example.
2298 -- For access subtypes, copy the size information from base type
2304 -- For other access types, we use either address size, or, if
2305 -- a fat pointer is used (pointer-to-unconstrained array case),
2306 -- twice the address size to accommodate a fat pointer.
2308 else
2309 declare
2312 begin
2315 then
2322 and then not Debug_Flag_6
2323 then
2326 -- Check for bad convention set
2328 if Warn_On_Export_Import
2329 and then
2331 or else
2333 then
2334 Error_Msg_N
2339 else
2347 -- Scalar types: set size and alignment
2351 -- For discrete types, the RM_Size and Esize must be set
2352 -- already, since this is part of the earlier processing
2353 -- and the front end is always required to lay out the
2354 -- sizes of such types (since they are available as static
2355 -- attributes). All we do is to check that this rule is
2356 -- indeed obeyed!
2360 -- If the RM_Size is not set, then here is where we set it
2362 -- Note: an RM_Size of zero looks like not set here, but this
2363 -- is a rare case, and we can simply reset it without any harm.
2369 -- If Esize for a discrete type is not set then set it
2372 declare
2375 begin
2376 loop
2377 -- If size is big enough, set it and exit
2383 -- If the RM_Size is greater than 64 (happens only
2384 -- when strange values are specified by the user,
2385 -- then Esize is simply a copy of RM_Size, it will
2386 -- be further refined later on)
2392 -- Otherwise double possible size and keep trying
2394 else
2401 -- For non-discrete sclar types, if the RM_Size is not set,
2402 -- then set it now to a copy of the Esize if the Esize is set.
2404 else
2412 -- Non-elementary (composite) types
2414 else
2415 -- If RM_Size is known, set Esize if not known
2419 -- If the alignment is known, we bump the Esize up to the
2420 -- next alignment boundary if it is not already on one.
2423 declare
2427 begin
2432 -- If Esize is set, and RM_Size is not, RM_Size is copied from
2433 -- Esize at least for now this seems reasonable, and is in any
2434 -- case needed for compatibility with old versions of gigi.
2435 -- look to be unknown.
2441 -- For array base types, set component size if object size of
2442 -- the component type is known and is a small power of 2 (8,
2443 -- 16, 32, 64), since this is what will always be used.
2447 then
2448 declare
2451 begin
2452 -- For some reasons, access types can cause trouble,
2453 -- So let's just do this for discrete types ???
2458 then
2459 declare
2462 begin
2467 then
2476 -- Lay out array and record types if front end layout set
2485 -- Case of backend layout, we still do a little in the front end
2487 else
2488 -- Processing for record types
2492 -- Special remaining processing for record types with a known
2493 -- size of 16, 32, or 64 bits whose alignment is not yet set.
2494 -- For these types, we set a corresponding alignment matching
2495 -- the size if possible, or as large as possible if not.
2498 and then not Debug_Flag_Q
2499 then
2503 -- Procressing for array types
2507 -- For arrays that are required to be atomic, we do the same
2508 -- processing as described above for short records, since we
2509 -- really need to have the alignment set for the whole array.
2515 -- For unpacked array types, set an alignment of 1 if we know
2516 -- that the component alignment is not greater than 1. The reason
2517 -- we do this is to avoid unnecessary copying of slices of such
2518 -- arrays when passed to subprogram parameters (see special test
2519 -- in Exp_Ch6.Expand_Actuals).
2523 then
2526 then
2533 -- Final step is to check that Esize and RM_Size are compatible
2538 -- Esize is less than RM_Size. That's not good. First we test
2539 -- whether this was set deliberately with an Object_Size clause
2540 -- and if so, object to the clause.
2544 Error_Msg_F
2546 Expression (Get_Attribute_Definition_Clause
2550 -- Adjust Esize up to RM_Size value
2552 declare
2555 begin
2558 -- For scalar types, increase Object_Size to power of 2,
2559 -- but not less than a storage unit in any case (i.e.,
2560 -- normally this means it will be storage-unit addressable).
2569 else
2573 -- Finally, make sure that alignment is consistent with
2574 -- the newly assigned size.
2578 loop
2587 ---------------------
2588 -- Rewrite_Integer --
2589 ---------------------
2595 begin
2600 -------------------------------
2601 -- Set_And_Check_Static_Size --
2602 -------------------------------
2604 procedure Set_And_Check_Static_Size
2608 is
2612 -- Spec is the number of bit specified in the size clause, and
2613 -- Min is the minimum computed size. An error is given that the
2614 -- specified size is too small if Spec < Min, and in this case
2615 -- both Esize and RM_Size are set to unknown in E. The error
2616 -- message is posted on node SC.
2619 -- Spec is the number of bits specified in the size clause, and
2620 -- Max is the maximum computed size. A warning is given about
2621 -- unused bits if Spec > Max. This warning is posted on node SC.
2623 --------------------------
2624 -- Check_Size_Too_Small --
2625 --------------------------
2628 begin
2631 Error_Msg_NE
2638 -----------------------
2639 -- Check_Unused_Bits --
2640 -----------------------
2643 begin
2650 -- Start of processing for Set_And_Check_Static_Size
2652 begin
2653 -- Case where Object_Size (Esize) is already set by a size clause
2662 -- Perform checks on specified size against computed sizes
2670 -- Case where Value_Size (RM_Size) is set by specific Value_Size
2671 -- clause (we do not need to worry about Value_Size being set by
2672 -- a Size clause, since that will have set Esize as well, and we
2673 -- already took care of that case).
2678 -- Perform checks on specified size against computed sizes
2686 -- Set sizes if unknown
2697 -----------------------------
2698 -- Set_Composite_Alignment --
2699 -----------------------------
2705 begin
2712 then
2715 else
2719 -- Size is known, alignment is not set
2721 -- Reset alignment to match size if size is exactly 2, 4, or 8
2722 -- storage units.
2731 -- On VMS, also reset for odd "in between" sizes, e.g. a 17-bit
2732 -- record is given an alignment of 4. This is more consistent with
2733 -- what DEC Ada does.
2743 else
2747 -- No special alignment fiddling needed
2749 else
2753 -- Here Align is set to the proposed improved alignment
2759 -- Further processing for record types only to reduce the alignment
2760 -- set by the above processing in some specific cases. We do not
2761 -- do this for atomic records, since we need max alignment there.
2765 -- For records, there is generally no point in setting alignment
2766 -- higher than word size since we cannot do better than move by
2767 -- words in any case
2773 -- Check components. If any component requires a higher
2774 -- alignment, then we set that higher alignment in any case.
2776 declare
2779 begin
2783 declare
2786 begin
2787 -- The cases to worry about are when the alignment
2788 -- of the component type is larger than the alignment
2789 -- we have so far, and either there is no component
2790 -- clause for the alignment, or the length set by
2791 -- the component clause matches the alignment set.
2794 and then
2797 and then
2800 then
2811 -- Set chosen alignment
2817 then
2823 --------------------------
2824 -- Set_Discrete_RM_Size --
2825 --------------------------
2830 begin
2831 -- All discrete types except for the base types in standard
2832 -- are constrained, so indicate this by setting Is_Constrained.
2836 -- We set generic types to have an unknown size, since the
2837 -- representation of a generic type is irrelevant, in view
2838 -- of the fact that they have nothing to do with code.
2843 -- If the subtype statically matches the first subtype, then
2844 -- it is required to have exactly the same layout. This is
2845 -- required by aliasing considerations.
2849 then
2853 -- In all other cases the RM_Size is set to the minimum size.
2854 -- Note that this routine is never called for subtypes for which
2855 -- the RM_Size is set explicitly by an attribute clause.
2857 else
2862 ------------------------
2863 -- Set_Elem_Alignment --
2864 ------------------------
2867 begin
2868 -- Do not set alignment for packed array types, unless we are doing
2869 -- front end layout, because otherwise this is always handled in the
2870 -- backend.
2875 -- If there is an alignment clause, then we respect it
2880 -- If the size is not set, then don't attempt to set the alignment. This
2881 -- happens in the backend layout case for access-to-subprogram types.
2886 -- For access types, do not set the alignment if the size is less than
2887 -- the allowed minimum size. This avoids cascaded error messages.
2891 then
2895 -- Here we calculate the alignment as the largest power of two
2896 -- multiple of System.Storage_Unit that does not exceed either
2897 -- the actual size of the type, or the maximum allowed alignment.
2899 declare
2904 begin
2908 loop
2912 -- Now we think we should set the alignment to A, but we
2913 -- skip this if an alignment is already set to a value
2914 -- greater than A (happens for derived types).
2916 -- However, if the alignment is known and too small it
2917 -- must be increased, this happens in a case like:
2919 -- type R is new Character;
2920 -- for R'Size use 16;
2922 -- Here the alignment inherited from Character is 1, but
2923 -- it must be increased to 2 to reflect the increased size.
2931 ----------------------
2932 -- SO_Ref_From_Expr --
2933 ----------------------
2935 function SO_Ref_From_Expr
2940 return Dynamic_SO_Ref
2941 is
2953 -- Function used to check one node for reference to V
2956 -- Function used to traverse tree to check for reference to V
2958 ----------------------
2959 -- Check_Node_V_Ref --
2960 ----------------------
2963 begin
2967 else
2971 else
2976 -- Start of processing for SO_Ref_From_Expr
2978 begin
2979 -- Case of expression is an integer literal, in this case we just
2980 -- return the value (which must always be non-negative, since size
2981 -- and offset values can never be negative).
2988 -- Case where there is a reference to V, create function
2994 -- Check whether Vtype is a view of a private type and ensure that
2995 -- we use the primary view of the type (which is denoted by its
2996 -- Etype, whether it's the type's partial or full view entity).
2997 -- This is needed to make sure that we use the same (primary) view
2998 -- of the type for all V formals, whether the current view of the
2999 -- type is the partial or full view, so that types will always
3000 -- match on calls from one size function to another.
3004 else
3010 Decl :=
3013 Specification =>
3018 Defining_Identifier =>
3020 Parameter_Type =>
3022 Result_Definition =>
3027 Handled_Statement_Sequence =>
3033 -- The caller requests that the expression be encapsulated in
3034 -- a parameterless function.
3037 Decl :=
3040 Specification =>
3044 Result_Definition =>
3049 Handled_Statement_Sequence =>
3054 -- No reference to V and function not requested, so create a constant
3056 else
3057 Decl :=
3060 Object_Definition =>