| blob | c3908a54538dbe6108d62a20b276052d3e003eca |
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- E X P _ P A K D --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 1992-2023, 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 ------------------------------------------------------------------------------
60 ---------------------------
61 -- Endian Considerations --
62 ---------------------------
64 -- As described in the specification, bit numbering in a packed array
65 -- is consistent with bit numbering in a record representation clause,
66 -- and hence dependent on the endianness of the machine:
68 -- For little-endian machines, element zero is at the right hand end
69 -- (low order end) of a bit field.
71 -- For big-endian machines, element zero is at the left hand end
72 -- (high order end) of a bit field.
74 -- The shifts that are used to right justify a field therefore differ in
75 -- the two cases. For the little-endian case, we can simply use the bit
76 -- number (i.e. the element number * element size) as the count for a right
77 -- shift. For the big-endian case, we have to subtract the shift count from
78 -- an appropriate constant to use in the right shift. We use rotates
79 -- instead of shifts (which is necessary in the store case to preserve
80 -- other fields), and we expect that the backend will be able to change the
81 -- right rotate into a left rotate, avoiding the subtract, if the machine
82 -- architecture provides such an instruction.
84 -----------------------
85 -- Local Subprograms --
86 -----------------------
88 procedure Compute_Linear_Subscript
92 -- Given a constrained array type Atyp, and an indexed component node N
93 -- referencing an array object of this type, build an expression of type
94 -- Standard.Integer representing the zero-based linear subscript value.
95 -- This expression includes any required range checks.
97 function Compute_Number_Components
100 -- Build an expression that multiplies the length of the dimensions of the
101 -- array, used to control array equality checks.
104 -- Given an expression of a packed array type, builds a corresponding
105 -- expression whose type is the implementation type used to represent
106 -- the packed array. Aexp is analyzed and resolved on entry and on exit.
108 procedure Get_Base_And_Bit_Offset
112 -- Given a node N for a name which involves a packed array reference,
113 -- return the base object of the reference and build an expression of
114 -- type Standard.Integer representing the zero-based offset in bits
115 -- from Base'Address to the first bit of the reference.
118 -- There are two versions of the Set routines, the ones used when the
119 -- object is known to be sufficiently well aligned given the number of
120 -- bits, and the ones used when the object is not known to be aligned.
121 -- This routine is used to determine which set to use. Obj is a reference
122 -- to the object, and Csiz is the component size of the packed array.
123 -- True is returned if the alignment of object is known to be sufficient,
124 -- defined as 1 for odd bit sizes, 4 for bit sizes divisible by 4, and
125 -- 2 otherwise.
128 -- Build a left shift node, checking for the case of a shift count of zero
131 -- Build a right shift node, checking for the case of a shift count of zero
133 function RJ_Unchecked_Convert_To
136 -- The packed array code does unchecked conversions which in some cases
137 -- may involve non-discrete types with differing sizes. The semantics of
138 -- such conversions is potentially endianness dependent, and the effect
139 -- we want here for such a conversion is to do the conversion in size as
140 -- though numeric items are involved, and we extend or truncate on the
141 -- left side. This happens naturally in the little-endian case, but in
142 -- the big endian case we can get left justification, when what we want
143 -- is right justification. This routine does the unchecked conversion in
144 -- a stepwise manner to ensure that it gives the expected result. Hence
145 -- the name (RJ = Right justified). The parameters Typ and Expr are as
146 -- for the case of a normal Unchecked_Convert_To call.
149 -- This routine is called in the Get and Set case for arrays that are
150 -- packed but not bit-packed, meaning that they have at least one
151 -- subscript that is of an enumeration type with a non-standard
152 -- representation. This routine modifies the given node to properly
153 -- reference the corresponding packed array type.
155 procedure Setup_Inline_Packed_Array_Reference
161 -- This procedure performs common processing on the N_Indexed_Component
162 -- parameter given as N, whose prefix is a reference to a packed array.
163 -- This is used for the get and set when the component size is 1, 2, 4,
164 -- or for other component sizes when the packed array type is a modular
165 -- type (i.e. the cases that are handled with inline code).
166 --
167 -- On entry:
168 --
169 -- N is the N_Indexed_Component node for the packed array reference
170 --
171 -- Atyp is the constrained array type (the actual subtype has been
172 -- computed if necessary to obtain the constraints, but this is still
173 -- the original array type, not the Packed_Array_Impl_Type value).
174 --
175 -- Obj is the object which is to be indexed. It is always of type Atyp.
176 --
177 -- On return:
178 --
179 -- Obj is the object containing the desired bit field. It is of type
180 -- Unsigned, Long_Unsigned, or Long_Long_Unsigned, and is either the
181 -- entire value, for the small static case, or the proper selected byte
182 -- from the array in the large or dynamic case. This node is analyzed
183 -- and resolved on return.
184 --
185 -- Shift is a node representing the shift count to be used in the
186 -- rotate right instruction that positions the field for access.
187 -- This node is analyzed and resolved on return.
188 --
189 -- Cmask is a mask corresponding to the width of the component field.
190 -- Its value is 2 ** Csize - 1 (e.g. 2#1111# for component size of 4).
191 --
192 -- Note: in some cases the call to this routine may generate actions
193 -- (for handling multi-use references and the generation of the packed
194 -- array type on the fly). Such actions are inserted into the tree
195 -- directly using Insert_Action.
198 -- Perform appropriate justification and byte ordering adjustments for N,
199 -- an element of a packed array type, when both the component type and
200 -- the enclosing packed array type have reverse scalar storage order.
201 -- On little-endian targets, the value is left justified before byte
202 -- swapping. The Etype of the returned expression is an integer type of
203 -- an appropriate power-of-2 size.
205 --------------------------
206 -- Revert_Storage_Order --
207 --------------------------
217 -- Swapping function
223 begin
226 -- Array component size is less than a byte: no swapping needed
231 else
232 -- Select byte swapping function depending on array component size
257 Arg :=
264 Adjusted :=
268 else
276 ------------------------------
277 -- Compute_Linear_Subscript --
278 ------------------------------
280 procedure Compute_Linear_Subscript
284 is
291 begin
294 -- Loop through dimensions
303 -- Get expression for the subscript value. First, if Do_Range_Check
304 -- is set on a subscript, then we must do a range check against the
305 -- original bounds (not the bounds of the packed array type). We do
306 -- this by introducing a subtype conversion.
310 then
314 -- Now evolve the expression for the subscript. First convert
315 -- the subscript to be zero based and of an integer type.
317 -- Case of integer type, where we just subtract to get lower bound
321 -- If length of integer type is smaller than standard integer,
322 -- then we convert to integer first, then do the subtract
324 -- Integer (subscript) - Integer (Styp'First)
327 Newsub :=
330 Right_Opnd =>
336 -- For larger integer types, subtract first, then convert to
337 -- integer, this deals with strange long long integer bounds.
339 -- Integer (subscript - Styp'First)
341 else
342 Newsub :=
346 Right_Opnd =>
352 -- For the enumeration case, we have to use 'Pos to get the value
353 -- to work with before subtracting the lower bound.
355 -- Integer (Styp'Pos (subscr)) - Integer (Styp'Pos (Styp'First));
357 -- This is not quite right for bizarre cases where the size of the
358 -- enumeration type is > Integer'Size bits due to rep clause ???
360 else
363 Newsub :=
371 Right_Opnd =>
384 -- For the first subscript, we just copy that subscript value
389 -- Otherwise, we must multiply what we already have by the current
390 -- stride and then add in the new value to the evolving subscript.
392 else
393 Subscr :=
395 Left_Opnd =>
398 Right_Opnd =>
405 -- Move to next subscript
412 -------------------------------
413 -- Compute_Number_Components --
414 -------------------------------
416 function Compute_Number_Components
419 is
423 begin
424 Len_Expr :=
431 Len_Expr :=
434 Right_Opnd =>
444 -------------------------
445 -- Convert_To_PAT_Type --
446 -------------------------
448 -- The PAT is always obtained from the actual subtype
453 begin
458 -- Just replace the etype with the packed array type. This works because
459 -- the expression will not be further analyzed, and Gigi considers the
460 -- two types equivalent in any case.
462 -- This is not strictly the case ??? If the reference is an actual in
463 -- call, the expansion of the prefix is delayed, and must be reanalyzed,
464 -- see Reset_Packed_Prefix. On the other hand, if the prefix is a simple
465 -- array reference, reanalysis can produce spurious type errors when the
466 -- PAT type is replaced again with the original type of the array. Same
467 -- for the case of a dereference. Ditto for function calls: expansion
468 -- may introduce additional actuals which will trigger errors if call is
469 -- reanalyzed. The following is correct and minimal, but the handling of
470 -- more complex packed expressions in actuals is confused. Probably the
471 -- problem only remains for actuals in calls.
476 or else
480 then
485 -----------------------------------
486 -- Create_Packed_Array_Impl_Type --
487 -----------------------------------
507 -- This procedure is called with Decl set to the declaration for the
508 -- packed array type. It creates the type and installs it as required.
511 -- Set PB_Type to [Rev_]Packed_Bytes{1,2,4} as required by the alignment
512 -- and the scalar storage order requirements (see documentation in the
513 -- spec of this package).
515 -----------------
516 -- Install_PAT --
517 -----------------
522 begin
523 -- We do not want to put the declaration we have created in the tree
524 -- since it is often hard, and sometimes impossible to find a proper
525 -- place for it (the impossible case arises for a packed array type
526 -- with bounds depending on the discriminant, a declaration cannot
527 -- be put inside the record, and the reference to the discriminant
528 -- cannot be outside the record).
530 -- The solution is to analyze the declaration while temporarily
531 -- attached to the tree at an appropriate point, and then we install
532 -- the resulting type as an Itype in the packed array type field of
533 -- the original type, so that no explicit declaration is required.
535 -- Note: the packed type is created in the scope of its parent type.
536 -- There are at least some cases where the current scope is deeper,
537 -- and so when this is the case, we temporarily reset the scope
538 -- for the definition. This is clearly safe, since the first use
539 -- of the packed array type will be the implicit reference from
540 -- the corresponding unpacked type when it is elaborated.
544 else
559 Pop_Scope;
562 -- Set Esize and RM_Size to the actual size of the packed object
563 -- Do not reset RM_Size if already set, as happens in the case of
564 -- a modular type.
576 -- In the case of a modular type, make sure the alignment is
577 -- consistent with the Esize.
582 loop
587 -- Then, in all cases, make sure the opposite is also true
591 -- Set remaining fields of packed array type
597 -- Propagate representation aspects
605 -- We definitely do not want to delay freezing for packed array
606 -- types. This is of particular importance for the itypes that are
607 -- generated for record components depending on discriminants where
608 -- there is no place to put the freeze node.
613 -- If we did allocate a freeze node, then clear out the reference
614 -- since it is obsolete (should we delete the freeze node???)
620 -----------------
621 -- Set_PB_Type --
622 -----------------
625 begin
626 -- If the user has specified an explicit alignment for the
627 -- type or component, take it into account.
632 then
635 else
641 then
644 else
648 else
651 else
656 -- The Rev_Packed_Bytes{1,2,4} types cannot be directly declared with
657 -- the reverse scalar storage order in System.Unsigned_Types because
658 -- their component type is aliased and the combination would then be
659 -- flagged as illegal by the compiler. Moreover changing the compiler
660 -- would not address the bootstrap path issue with earlier versions.
665 -- Start of processing for Create_Packed_Array_Impl_Type
667 begin
668 -- If we already have a packed array type, nothing to do
674 -- If our immediate ancestor subtype is constrained, and it already has
675 -- a packed array type, and it has the same size, then just share the
676 -- same type, since the bounds must be the same. If the ancestor is not
677 -- an array type but a private type, as can happen with multiple
678 -- instantiations, create a new packed type, to avoid privacy issues.
690 then
696 -- We preset the result type size from the size of the original array
697 -- type, since this size clearly belongs to the packed array type. The
698 -- size of the conceptual unpacked type is always set to unknown.
704 -- Case of an array where at least one index is of an enumeration
705 -- type with a non-standard representation, but the component size
706 -- is not appropriate for bit packing. This is the case where we
707 -- have Is_Packed set (we would never be in this unit otherwise),
708 -- but Is_Bit_Packed_Array is false.
710 -- Note that if the component size is appropriate for bit packing,
711 -- then the circuit for the computation of the subscript properly
712 -- deals with the non-standard enumeration type case by taking the
713 -- Pos anyway.
717 -- Here we build a declaration:
719 -- type tttP is array (index1, index2, ...) of component_type
721 -- where index1, index2, are the index types. These are the same
722 -- as the index types of the original array, except for the non-
723 -- standard representation enumeration type case, where we have
724 -- two subcases.
726 -- For the unconstrained array case, we use
728 -- Natural range <>
730 -- For the constrained case, we use
732 -- Natural range Enum_Type'Pos (Enum_Type'First) ..
733 -- Enum_Type'Pos (Enum_Type'Last);
735 -- Note that tttP is created even if no index subtype is a non
736 -- standard enumeration, because we still need to remove padding
737 -- normally inserted for component alignment.
739 PAT :=
743 declare
750 begin
759 -- Unconstrained case
768 -- Constrained case
770 else
774 else
777 Subtype_Mark =>
779 Constraint =>
781 Range_Expression =>
783 Low_Bound =>
785 Prefix =>
790 Prefix =>
794 High_Bound =>
796 Prefix =>
801 Prefix =>
812 Typedef :=
815 Component_Definition =>
818 Subtype_Indication =>
821 else
822 Typedef :=
825 Component_Definition =>
828 Subtype_Indication =>
832 Decl :=
838 Install_PAT;
840 -- Propagate the reverse storage order flag to the base type
845 -- Case of bit-packing required for unconstrained array. We create
846 -- a subtype that is equivalent to use Packed_Bytes{1,2,4} as needed.
850 -- When generating standard DWARF (i.e when GNAT_Encodings is not
851 -- DWARF_GNAT_Encodings_All), the ___XP suffix will be stripped
852 -- by the back-end but generate it anyway to ease compiler debugging.
853 -- This will help to distinguish implementation types from original
854 -- packed arrays.
856 PAT :=
860 Set_PB_Type;
862 Decl :=
867 Install_PAT;
870 -- Remaining code is for the case of bit-packing for constrained array
872 -- The name of the packed array subtype is
874 -- ttt___XPsss
876 -- where sss is the component size in bits and ttt is the name of
877 -- the parent packed type.
879 else
880 PAT :=
884 -- Build an expression for the length of the array in bits.
885 -- This is the product of the length of each of the dimensions
889 -- Temporarily attach the length expression to the tree and analyze
890 -- and resolve it, so that we can test its value. We assume that the
891 -- total length fits in type Integer. This expression may involve
892 -- discriminants, so we treat it as a default/per-object expression.
897 -- Use a modular type if possible. We can do this if we have
898 -- static bounds, and the length is small enough, and the length
899 -- is not zero. We exclude the zero length case because the size
900 -- of things is always at least one, and the zero length object
901 -- would have an anomalous size.
906 -- Check for size known to be too large
910 then
912 Error_Msg_N
915 else
916 Error_Msg_N
921 -- Reset length to arbitrary not too high value to continue
927 -- We normally consider small enough to mean no larger than the
928 -- value of System_Max_Binary_Modulus_Power, checking that in the
929 -- case of values longer than word size, we have long shifts.
932 and then
936 then
937 -- We can use the modular type, it has the form:
939 -- subtype tttPn is btyp
940 -- range 0 .. 2 ** ((Typ'Length (1)
941 -- * ... * Typ'Length (n)) * Csize) - 1;
943 -- The bounds are statically known, and btyp is one of the
944 -- unsigned types, depending on the length.
950 Decl :=
953 Subtype_Indication =>
957 Constraint =>
959 Range_Expression =>
961 Low_Bound =>
969 Install_PAT;
971 -- Propagate a given alignment to the modular type. This can
972 -- cause it to be under-aligned, but that's OK.
982 -- Could not use a modular type, for all other cases, we build
983 -- a packed array subtype:
985 -- subtype tttPn is
986 -- System.Packed_Bytes{1,2,4} (0 .. (Bits + 7) / 8 - 1);
988 -- Bits is the length of the array in bits
990 Set_PB_Type;
992 Bits_U1 :=
994 Left_Opnd =>
996 Left_Opnd =>
1000 Right_Opnd =>
1005 PAT_High :=
1007 Left_Opnd =>
1013 Decl :=
1016 Subtype_Indication =>
1019 Constraint =>
1023 Low_Bound =>
1025 High_Bound =>
1028 Install_PAT;
1030 -- Currently the code in this unit requires that packed arrays
1031 -- represented by non-modular arrays of bytes be on a byte
1032 -- boundary for bit sizes handled by System.Pack_nn units.
1033 -- That's because these units assume the array being accessed
1034 -- starts on a byte boundary.
1042 -----------------------------------
1043 -- Expand_Bit_Packed_Element_Set --
1044 -----------------------------------
1051 -- Used to preserve assignment OK status when assignment is rewritten
1056 -- Initially Rhs is the right hand side value, it will be replaced
1057 -- later by an appropriate unchecked conversion for the assignment.
1067 -- The expression for the shift value that is required
1070 -- Set True if Shift has been used in the generated code at least once,
1071 -- so that it must be duplicated if used again.
1078 -- If the value of the right hand side as an integer constant is
1079 -- known at compile time, Rhs_Val_Known is set True, and Rhs_Val
1080 -- contains the value. Otherwise Rhs_Val_Known is set False, and
1081 -- the Rhs_Val is undefined.
1084 -- Function used to get the value of Shift, making sure that it
1085 -- gets duplicated if the function is called more than once.
1087 ---------------
1088 -- Get_Shift --
1089 ---------------
1092 begin
1093 -- If we used the shift value already, then duplicate it. We
1094 -- set a temporary parent in case actions have to be inserted.
1100 -- If first time, use Shift unchanged, and set flag for first use
1102 else
1108 -- Start of processing for Expand_Bit_Packed_Element_Set
1110 begin
1120 -- We remove side effects, in case the rhs modifies the lhs, because we
1121 -- are about to transform the rhs into an expression that first READS
1122 -- the lhs, so we can do the necessary shifting and masking. Example:
1123 -- "X(2) := F(...);" where F modifies X(3). Otherwise, the side effect
1124 -- will be lost.
1128 -- We convert the right hand side to the proper subtype to ensure
1129 -- that an appropriate range check is made (since the normal range
1130 -- check from assignment will be lost in the transformations). This
1131 -- conversion is analyzed immediately so that subsequent processing
1132 -- can work with an analyzed Rhs (and e.g. look at its Etype)
1134 -- If the right-hand side is a string literal, create a temporary for
1135 -- it, constant-folding is not ready to wrap the bit representation
1136 -- of a string literal.
1139 declare
1141 begin
1142 Decl :=
1156 -- If we are building the initialization procedure for a packed array,
1157 -- and Initialize_Scalars is enabled, each component assignment is an
1158 -- out-of-range value by design. Compile this value without checks,
1159 -- because a call to the array init_proc must not raise an exception.
1161 -- Condition is not consistent with description above, Within_Init_Proc
1162 -- is True also when we are building the IP for a record or protected
1163 -- type that has a packed array component???
1165 if Within_Init_Proc
1166 and then Initialize_Scalars
1167 then
1169 else
1173 -- If any of the indices has a nonstandard representation, introduce
1174 -- the proper Rep_To_Pos conversion, which in turn will generate index
1175 -- checks when needed. We do this on a copy of the index expression,
1176 -- rather that rewriting the LHS altogether.
1180 declare
1186 begin
1189 then
1190 Expr_Copy :=
1203 -- Case of component size 1,2,4 or any component size for the modular
1204 -- case. These are the cases for which we can inline the code.
1208 then
1211 -- The statement to be generated is:
1213 -- Obj := atyp!((Obj and Mask1) or (shift_left (rhs, Shift)))
1215 -- or in the case of a freestanding Reverse_Storage_Order object,
1217 -- Obj := Swap (atyp!((Swap (Obj) and Mask1)
1218 -- or (shift_left (rhs, Shift))))
1220 -- where Mask1 is obtained by shifting Cmask left Shift bits
1221 -- and then complementing the result.
1223 -- the "and Mask1" is omitted if rhs is constant and all 1 bits
1225 -- the "or ..." is omitted if rhs is constant and all 0 bits
1227 -- rhs is converted to the appropriate type
1229 -- The result is converted back to the array type, since
1230 -- otherwise we lose knowledge of the packed nature.
1232 -- Determine if right side is all 0 bits or all 1 bits
1238 -- The following test catches the case of an unchecked conversion of
1239 -- an integer literal. This results from optimizing aggregates of
1240 -- packed types.
1244 then
1248 else
1253 -- Some special checks for the case where the right hand value is
1254 -- known at compile time. Basically we have to take care of the
1255 -- implicit conversion to the subtype of the component object.
1259 -- If we have a biased component type then we must manually do the
1260 -- biasing, since we are taking responsibility in this case for
1261 -- constructing the exact bit pattern to be used.
1267 -- For a negative value, we manually convert the two's complement
1268 -- value to a corresponding unsigned value, so that the proper
1269 -- field width is maintained. If we did not do this, we would
1270 -- get too many leading sign bits later on.
1277 -- Now create copies removing side effects. Note that in some complex
1278 -- cases, this may cause the fact that we have already set a packed
1279 -- array type on Obj to get lost. So we save the type of Obj, and
1280 -- make sure it is reset properly.
1282 declare
1284 begin
1292 -- First we deal with the "and"
1295 declare
1299 begin
1301 Mask1 :=
1307 else
1310 Mask1 :=
1315 New_Rhs :=
1322 -- Then deal with the "or"
1325 declare
1329 -- Adjust Rhs by bias if biased representation for components
1330 -- or remove extraneous high order sign bits if signed.
1335 begin
1336 -- For biased case, do the required biasing by simply
1337 -- converting to the biased subtype (the conversion
1338 -- will generate the required bias).
1343 -- For a signed integer type that is not biased, generate
1344 -- a conversion to unsigned to strip high order sign bits.
1350 -- Set Etype, since it can be referenced before the node is
1351 -- completely analyzed.
1355 -- We now need to do an unchecked conversion of the
1356 -- result to the target type, but it is important that
1357 -- this conversion be a right justified conversion and
1358 -- not a left justified conversion.
1363 begin
1364 if Rhs_Val_Known
1366 then
1367 Or_Rhs :=
1372 else
1373 -- We have to convert the right hand side to Etype (Obj).
1374 -- A special case arises if what we have now is a Val
1375 -- attribute reference whose expression type is Etype (Obj).
1376 -- This happens for assignments of fields from the same
1377 -- array. In this case we get the required right hand side
1378 -- by simply removing the inner attribute reference.
1383 then
1385 Fixup_Rhs;
1387 -- If the value of the right hand side is a known integer
1388 -- value, then just replace it by an untyped constant,
1389 -- which will be properly retyped when we analyze and
1390 -- resolve the expression.
1394 -- Note that Rhs_Val has already been normalized to
1395 -- be an unsigned value with the proper number of bits.
1399 -- Otherwise we need an unchecked conversion
1401 else
1402 Fixup_Rhs;
1413 New_Rhs :=
1420 -- Now do the rewrite
1425 Expression =>
1429 -- All other component sizes for non-modular case
1431 else
1432 -- We generate
1434 -- Set_nn (Arr'address, Subscr, Bits_nn!(Rhs))
1436 -- where Subscr is the computed linear subscript
1438 declare
1445 begin
1448 -- Error, most likely High_Integrity_Mode restriction
1453 -- Acquire proper Set entity. We use the aligned or unaligned
1454 -- case as appropriate.
1458 else
1462 -- Now generate the set reference
1469 -- Set indication of whether the packed array has reverse SSO
1471 Rev_SSO :=
1472 New_Occurrence_Of
1475 -- Below we must make the assumption that Obj is
1476 -- at least byte aligned, since otherwise its address
1477 -- cannot be taken. The assumption holds since the
1478 -- only arrays that can be misaligned are small packed
1479 -- arrays which are implemented as a modular type, and
1480 -- that is not the case here.
1489 Subscr,
1491 Rev_SSO)));
1499 -------------------------------------
1500 -- Expand_Packed_Address_Reference --
1501 -------------------------------------
1508 begin
1509 -- We build an expression that has the form
1511 -- outer_object'Address
1512 -- + (linear-subscript * component_size for each array reference
1513 -- + field'Bit_Position for each record field
1514 -- + ...
1515 -- + ...) / Storage_Unit;
1522 Left_Opnd =>
1528 Right_Opnd =>
1532 Right_Opnd =>
1538 ---------------------------------
1539 -- Expand_Packed_Bit_Reference --
1540 ---------------------------------
1547 begin
1548 -- We build an expression that has the form
1550 -- (linear-subscript * component_size for each array reference
1551 -- + field'Bit_Position for each record field
1552 -- + ...
1553 -- + ...) mod Storage_Unit;
1566 ------------------------------------
1567 -- Expand_Packed_Boolean_Operator --
1568 ------------------------------------
1570 -- This routine expands "a op b" for the packed cases
1582 begin
1594 -- Deal with silly case of XOR where the subcomponent has a range
1595 -- True .. True where an exception must be raised.
1602 -- Now that silliness is taken care of, get packed array type
1609 -- For the modular case, we expand a op b into
1611 -- rtyp!(pat!(a) op pat!(b))
1613 -- where rtyp is the Etype of the left operand. Note that we do not
1614 -- convert to the base type, since this would be unconstrained, and
1615 -- hence not have a corresponding packed array type set.
1617 -- Note that both operands must be modular for this code to be used
1620 and then
1622 then
1623 declare
1626 begin
1640 -- For the array case, we insert the actions
1642 -- Result : Ltype;
1644 -- System.Bit_Ops.Bit_And/Or/Xor
1645 -- (Left'Address,
1646 -- Ltype'Length * Ltype'Component_Size;
1647 -- Right'Address,
1648 -- Rtype'Length * Rtype'Component_Size
1649 -- Result'Address);
1651 -- where Left and Right are the Packed_Bytes{1,2,4} operands and
1652 -- the second argument and fourth arguments are the lengths of the
1653 -- operands in bits. Then we replace the expression by a reference
1654 -- to Result.
1656 -- Note that if we are mixing a modular and array operand, everything
1657 -- works fine, since we ensure that the modular representation has the
1658 -- same physical layout as the array representation (that's what the
1659 -- left justified modular stuff in the big-endian case is about).
1661 else
1662 declare
1666 begin
1692 Left_Opnd =>
1694 Prefix =>
1695 New_Occurrence_Of
1699 Right_Opnd =>
1707 Left_Opnd =>
1709 Prefix =>
1710 New_Occurrence_Of
1714 Right_Opnd =>
1729 -------------------------------------
1730 -- Expand_Packed_Element_Reference --
1731 -------------------------------------
1745 begin
1746 -- If the node is an actual in a call, the prefix has not been fully
1747 -- expanded, to account for the additional expansion for in-out actuals
1748 -- (see expand_actuals for details). If the prefix itself is a packed
1749 -- reference as well, we have to recurse to complete the transformation
1750 -- of the prefix.
1755 then
1759 -- The prefix may be rewritten below as a conversion. If it is a source
1760 -- entity generate reference to it now, to prevent spurious warnings
1761 -- about unused entities.
1765 then
1769 -- If not bit packed, we have the enumeration case, which is easily
1770 -- dealt with (just adjust the subscripts of the indexed component)
1772 -- Note: this leaves the result as an indexed component, which is
1773 -- still a variable, so can be used in the assignment case, as is
1774 -- required in the enumeration case.
1781 -- Remaining processing is for the bit-packed case
1790 -- Case of component size 1,2,4 or any component size for the modular
1791 -- case. These are the cases for which we can inline the code.
1795 then
1800 -- We generate a shift right to position the field, followed by a
1801 -- masking operation to extract the bit field, and we finally do an
1802 -- unchecked conversion to convert the result to the required target.
1804 -- Note that the unchecked conversion automatically deals with the
1805 -- bias if we are dealing with a biased representation. What will
1806 -- happen is that we temporarily generate the biased representation,
1807 -- but almost immediately that will be converted to the original
1808 -- unbiased component type, and the bias will disappear.
1810 Arg :=
1816 -- Component extraction is performed on a native endianness scalar
1817 -- value: if Atyp has reverse storage order, then it has been byte
1818 -- swapped, and if the component being extracted is itself of a
1819 -- composite type with reverse storage order, then we need to swap
1820 -- it back to its expected endianness after extraction.
1825 then
1829 -- We needed to analyze this before we do the unchecked convert
1830 -- below, but we need it temporarily attached to the tree for
1831 -- this analysis (hence the temporary Set_Parent call).
1838 -- All other component sizes for non-modular case
1840 else
1841 -- We generate
1843 -- Component_Type!(Get_nn (Arr'address, Subscr))
1845 -- where Subscr is the computed linear subscript
1847 declare
1851 New_Occurrence_Of
1854 begin
1855 -- Acquire proper Get entity. We use the aligned or unaligned
1856 -- case as appropriate.
1860 else
1864 -- Now generate the get reference
1868 -- Below we make the assumption that Obj is at least byte
1869 -- aligned, since otherwise its address cannot be taken.
1870 -- The assumption holds since the only arrays that can be
1871 -- misaligned are small packed arrays which are implemented
1872 -- as a modular type, and that is not the case here.
1882 Subscr,
1883 Rev_SSO))));
1890 ----------------------
1891 -- Expand_Packed_Eq --
1892 ----------------------
1894 -- Handles expansion of "=" on packed array types
1908 begin
1918 LLexpr :=
1923 RLexpr :=
1928 -- For the modular case, we transform the comparison to:
1930 -- Ltyp'Length = Rtyp'Length and then PAT!(L) = PAT!(R)
1932 -- where PAT is the packed array type. This works fine, since in the
1933 -- modular case we guarantee that the unused bits are always zeroes.
1934 -- We do have to compare the lengths because we could be comparing
1935 -- two different subtypes of the same base type. We can only do this
1936 -- if the PATs on both sides are modular (in which case they are
1937 -- necessarily structurally the same -- same Modulus and so on);
1938 -- otherwise, we have a case where the right operand is not of
1939 -- compile time known size.
1943 then
1949 Left_Opnd =>
1954 Right_Opnd =>
1959 -- For the non-modular case, we call a runtime routine
1961 -- System.Bit_Ops.Bit_Eq
1962 -- (L'Address, L_Length, R'Address, R_Length)
1964 -- where PAT is the packed array type, and the lengths are the lengths
1965 -- in bits of the original packed arrays. This routine takes care of
1966 -- not comparing the unused bits in the last byte.
1968 else
1977 LLexpr,
1983 RLexpr)));
1989 -----------------------
1990 -- Expand_Packed_Not --
1991 -----------------------
1993 -- Handles expansion of "not" on packed array types
2005 begin
2009 -- Deal with silly False..False and True..True subtype case
2013 -- Now that the silliness is taken care of, get packed array type
2018 -- For the case where the packed array type is a modular type, "not A"
2019 -- expands simply into:
2021 -- Rtyp!(PAT!(A) xor Mask)
2023 -- where PAT is the packed array type, Mask is a mask of all 1 bits of
2024 -- length equal to the size of this packed type, and Rtyp is the actual
2025 -- actual subtype of the operand. Preserve old behavior in case size is
2026 -- not set.
2030 else
2043 -- For the array case, we insert the actions
2045 -- Result : Typ;
2047 -- System.Bit_Ops.Bit_Not
2048 -- (Opnd'Address,
2049 -- Typ'Length * Typ'Component_Size,
2050 -- Result'Address);
2052 -- where Opnd is the Packed_Bytes{1,2,4} operand and the second argument
2053 -- is the length of the operand in bits. We then replace the expression
2054 -- with a reference to Result.
2056 else
2057 declare
2060 begin
2074 Left_Opnd =>
2076 Prefix =>
2077 New_Occurrence_Of
2081 Right_Opnd =>
2095 -----------------------------
2096 -- Get_Base_And_Bit_Offset --
2097 -----------------------------
2099 procedure Get_Base_And_Bit_Offset
2103 is
2109 begin
2113 -- We build up an expression serially that has the form
2115 -- linear-subscript * component_size for each array reference
2116 -- + field'Bit_Position for each record field
2117 -- + ...
2119 loop
2127 Term :=
2130 Right_Opnd =>
2136 Term :=
2141 else
2148 else
2149 Offset :=
2159 -------------------------------------
2160 -- Involves_Packed_Array_Reference --
2161 -------------------------------------
2164 begin
2167 then
2173 else
2178 --------------------------
2179 -- Known_Aligned_Enough --
2180 --------------------------
2186 -- If the component is in a record that contains previous packed
2187 -- components, consider it unaligned because the back-end might
2188 -- choose to pack the rest of the record. Lead to less efficient code,
2189 -- but safer vis-a-vis of back-end choices.
2191 --------------------------------
2192 -- In_Partially_Packed_Record --
2193 --------------------------------
2199 begin
2215 -- Start of processing for Known_Aligned_Enough
2217 begin
2218 -- Odd bit sizes don't need alignment anyway
2223 -- If we have a specified alignment, see if it is sufficient, if not
2224 -- then we can't possibly be aligned enough in any case.
2227 -- Alignment required is 4 if size is a multiple of 4, and
2228 -- 2 otherwise (e.g. 12 bits requires 4, 10 bits requires 2)
2235 -- OK, alignment should be sufficient, if object is aligned
2237 -- If object is strictly aligned, then it is definitely aligned
2242 -- Case of subscripted array reference
2246 -- If we have a pointer to an array, then this is definitely
2247 -- aligned, because pointers always point to aligned versions.
2252 -- Otherwise, go look at the prefix
2254 else
2258 -- Case of record field
2262 -- What is significant here is whether the record type is packed
2266 then
2269 -- Or the component has a component clause which might cause
2270 -- the component to become unaligned (we can't tell if the
2271 -- backend is doing alignment computations).
2279 -- In all other cases, go look at prefix
2281 else
2288 -- For a formal parameter, it is safer to assume that it is not
2289 -- aligned, because the formal may be unconstrained while the actual
2290 -- is constrained. In this situation, a small constrained packed
2291 -- array, represented in modular form, may be unaligned.
2295 else
2297 -- If none of the above, must be aligned
2302 ---------------------
2303 -- Make_Shift_Left --
2304 ---------------------
2309 begin
2312 else
2313 Nod :=
2322 ----------------------
2323 -- Make_Shift_Right --
2324 ----------------------
2329 begin
2332 else
2333 Nod :=
2342 -----------------------------
2343 -- RJ_Unchecked_Convert_To --
2344 -----------------------------
2346 function RJ_Unchecked_Convert_To
2349 is
2358 begin
2362 -- For a little-endian target type stored byte-swapped on a
2363 -- big-endian machine, do not mask to Target_Siz bits.
2365 if Bytes_Big_Endian
2367 or else
2370 then
2374 -- First step, if the source type is not a discrete type, then we first
2375 -- convert to a modular type of the source length, since otherwise, on
2376 -- a big-endian machine, we get left-justification. We do it for little-
2377 -- endian machines as well, because there might be junk bits that are
2378 -- not cleared if the type is not numeric. This can be done only if the
2379 -- source siz is different from 0 (i.e. known), otherwise we must trust
2380 -- the type declarations (case of non-discrete components).
2385 then
2389 -- In the big endian case, if the lengths of the two types differ, then
2390 -- we must worry about possible left justification in the conversion,
2391 -- and avoiding that is what this is all about.
2395 -- Next step. If the target is not a discrete type, then we first
2396 -- convert to a modular type of the target length, since otherwise,
2397 -- on a big-endian machine, we get left-justification.
2404 -- And now we can do the final conversion to the target type
2409 ----------------------------------------------
2410 -- Setup_Enumeration_Packed_Array_Reference --
2411 ----------------------------------------------
2413 -- All we have to do here is to find the subscripts that correspond to the
2414 -- index positions that have non-standard enumeration types and insert a
2415 -- Pos attribute to get the proper subscript value.
2417 -- Finally the prefix must be uncheck-converted to the corresponding packed
2418 -- array type.
2420 -- Note that the component type is unchanged, so we do not need to fiddle
2421 -- with the types (Gigi always automatically takes the packed array type if
2422 -- it is set, as it will be in this case).
2430 begin
2431 -- If the array is unconstrained, then we replace the array reference
2432 -- with its actual subtype. This actual subtype will have a packed array
2433 -- type with appropriate bounds.
2441 declare
2445 begin
2448 then
2463 Prefix =>
2470 -----------------------------------------
2471 -- Setup_Inline_Packed_Array_Reference --
2472 -----------------------------------------
2474 procedure Setup_Inline_Packed_Array_Reference
2480 is
2487 begin
2499 else
2502 -- In the case where the PAT is a modular type, we want the actual
2503 -- size in bits of the modular value we use. This is neither the
2504 -- Object_Size nor the Value_Size, either of which may have been
2505 -- reset to strange values, but rather the minimum size. Note that
2506 -- since this is a modular type with full range, the issue of
2507 -- biased representation does not arise.
2514 -- If the component size is not 1, then the subscript must be multiplied
2515 -- by the component size to get the shift count.
2518 Shift :=
2524 -- If we have the array case, then this shift count must be broken down
2525 -- into a byte subscript, and a shift within the byte.
2529 declare
2532 begin
2533 -- We must analyze shift, since we will duplicate it
2536 Analyze_And_Resolve
2539 -- The shift count within the word is
2540 -- shift mod Osiz
2542 New_Shift :=
2547 -- The subscript to be used on the PAT array is
2548 -- shift / Osiz
2550 Obj :=
2561 -- For the modular integer case, the object to be manipulated is the
2562 -- entire array, so Obj is unchanged. Note that we will reset its type
2563 -- to PAT before returning to the caller.
2565 else
2569 -- The one remaining step is to modify the shift count for the
2570 -- big-endian case. Consider the following example in a byte:
2572 -- xxxxxxxx bits of byte
2573 -- vvvvvvvv bits of value
2574 -- 33221100 little-endian numbering
2575 -- 00112233 big-endian numbering
2577 -- Here we have the case of 2-bit fields
2579 -- For the little-endian case, we already have the proper shift count
2580 -- set, e.g. for element 2, the shift count is 2*2 = 4.
2582 -- For the big endian case, we have to adjust the shift count, computing
2583 -- it as (N - F) - Shift, where N is the number of bits in an element of
2584 -- the array used to implement the packed array, F is the number of bits
2585 -- in a source array element, and Shift is the count so far computed.
2587 -- We also have to adjust if the storage order is reversed
2590 Shift :=
2601 -- Make sure final type of object is the appropriate packed type