| blob | d77ec2341fe6107266b8834fc3511ede44507989 |
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- E X P _ C H 5 --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 1992-2007, 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 ------------------------------------------------------------------------------
67 -- Determine if the right hand side of the assignment N is a type
68 -- conversion which requires a change of representation. Called
69 -- only for the array and record cases.
72 -- N is an assignment which assigns an array value. This routine process
73 -- the various special cases and checks required for such assignments,
74 -- including change of representation. Rhs is normally simply the right
75 -- hand side of the assignment, except that if the right hand side is
76 -- a type conversion or a qualified expression, then the Rhs is the
77 -- actual expression inside any such type conversions or qualifications.
79 function Expand_Assign_Array_Loop
87 -- N is an assignment statement which assigns an array value. This routine
88 -- expands the assignment into a loop (or nested loops for the case of a
89 -- multi-dimensional array) to do the assignment component by component.
90 -- Larray and Rarray are the entities of the actual arrays on the left
91 -- hand and right hand sides. L_Type and R_Type are the types of these
92 -- arrays (which may not be the same, due to either sliding, or to a
93 -- change of representation case). Ndim is the number of dimensions and
94 -- the parameter Rev indicates if the loops run normally (Rev = False),
95 -- or reversed (Rev = True). The value returned is the constructed
96 -- loop statement. Auxiliary declarations are inserted before node N
97 -- using the standard Insert_Actions mechanism.
100 -- N is an assignment of a non-tagged record value. This routine handles
101 -- the case where the assignment must be made component by component,
102 -- either because the target is not byte aligned, or there is a change
103 -- of representation.
106 -- Called by Expand_N_Simple_Return_Statement in case we're returning from
107 -- a procedure body, entry body, accept statement, or extended return
108 -- statement. Note that all non-function returns are simple return
109 -- statements.
112 -- Expand simple return from function. Called by
113 -- Expand_N_Simple_Return_Statement in case we're returning from a function
114 -- body.
117 -- Generate the necessary code for controlled and tagged assignment,
118 -- that is to say, finalization of the target before, adjustement of
119 -- the target after and save and restore of the tag and finalization
120 -- pointers which are not 'part of the value' and must not be changed
121 -- upon assignment. N is the original Assignment node.
123 ------------------------------
124 -- Change_Of_Representation --
125 ------------------------------
129 begin
130 return
132 and then
136 -------------------------
137 -- Expand_Assign_Array --
138 -------------------------
140 -- There are two issues here. First, do we let Gigi do a block move, or
141 -- do we expand out into a loop? Second, we need to set the two flags
142 -- Forwards_OK and Backwards_OK which show whether the block move (or
143 -- corresponding loops) can be legitimately done in a forwards (low to
144 -- high) or backwards (high to low) manner.
170 -- This switch is set to True if the array move must be done using
171 -- an explicit front end generated loop.
174 -- If the argument is an access to an array, and the assignment is
175 -- converted into a procedure call, apply explicit dereference.
178 -- Test if Exp is a reference to an array whose declaration has
179 -- an address clause, or it is a slice of such an array.
182 -- Test if Exp is a reference to an array which is either a formal
183 -- parameter or a slice of a formal parameter. These are the cases
184 -- where hidden aliasing can occur.
187 -- Determine if Exp is a reference to an array variable which is other
188 -- than an object defined in the current scope, or a slice of such
189 -- an object. Such objects can be aliased to parameters (unlike local
190 -- array references).
192 -----------------------
193 -- Apply_Dereference --
194 -----------------------
198 begin
206 ------------------------
207 -- Has_Address_Clause --
208 ------------------------
211 begin
212 return
215 or else
219 ---------------------
220 -- Is_Formal_Array --
221 ---------------------
224 begin
225 return
227 or else
231 ------------------------
232 -- Is_Non_Local_Array --
233 ------------------------
236 begin
243 -- Determine if Lhs, Rhs are formal arrays or nonlocal arrays
251 -- Start of processing for Expand_Assign_Array
253 begin
254 -- Deal with length check. Note that the length check is done with
255 -- respect to the right hand side as given, not a possible underlying
256 -- renamed object, since this would generate incorrect extra checks.
260 -- We start by assuming that the move can be done in either direction,
261 -- i.e. that the two sides are completely disjoint.
266 -- Normally it is only the slice case that can lead to overlap, and
267 -- explicit checks for slices are made below. But there is one case
268 -- where the slice can be implicit and invisible to us: when we have a
269 -- one dimensional array, and either both operands are parameters, or
270 -- one is a parameter (which can be a slice passed by reference) and the
271 -- other is a non-local variable. In this case the parameter could be a
272 -- slice that overlaps with the other operand.
274 -- However, if the array subtype is a constrained first subtype in the
275 -- parameter case, then we don't have to worry about overlap, since
276 -- slice assignments aren't possible (other than for a slice denoting
277 -- the whole array).
279 -- Note: No overlap is possible if there is a change of representation,
280 -- so we can exclude this case.
283 and then not Crep
284 and then
286 or else
288 or else
290 and then
294 -- In the case of compiling for the Java or .NET Virtual Machine,
295 -- slices are always passed by making a copy, so we don't have to
296 -- worry about overlap. We also want to prevent generation of "<"
297 -- comparisons for array addresses, since that's a meaningless
298 -- operation on the VM.
301 then
305 -- Note: the bit-packed case is not worrisome here, since if we have
306 -- a slice passed as a parameter, it is always aligned on a byte
307 -- boundary, and if there are no explicit slices, the assignment
308 -- can be performed directly.
311 -- We certainly must use a loop for change of representation and also
312 -- we use the operand of the conversion on the right hand side as the
313 -- effective right hand side (the component types must match in this
314 -- situation).
321 -- We require a loop if the left side is possibly bit unaligned
324 or else
326 then
329 -- Arrays with controlled components are expanded into a loop to force
330 -- calls to Adjust at the component level.
335 -- If object is atomic, we cannot tolerate a loop
338 or else
340 then
343 -- Loop is required if we have atomic components since we have to
344 -- be sure to do any accesses on an element by element basis.
350 then
353 -- Case where no slice is involved
357 -- The following code deals with the case of unconstrained bit packed
358 -- arrays. The problem is that the template for such arrays contains
359 -- the bounds of the actual source level array, but the copy of an
360 -- entire array requires the bounds of the underlying array. It would
361 -- be nice if the back end could take care of this, but right now it
362 -- does not know how, so if we have such a type, then we expand out
363 -- into a loop, which is inefficient but works correctly. If we don't
364 -- do this, we get the wrong length computed for the array to be
365 -- moved. The two cases we need to worry about are:
367 -- Explicit deference of an unconstrained packed array type as in the
368 -- following example:
370 -- procedure C52 is
371 -- type BITS is array(INTEGER range <>) of BOOLEAN;
372 -- pragma PACK(BITS);
373 -- type A is access BITS;
374 -- P1,P2 : A;
375 -- begin
376 -- P1 := new BITS (1 .. 65_535);
377 -- P2 := new BITS (1 .. 65_535);
378 -- P2.ALL := P1.ALL;
379 -- end C52;
381 -- A formal parameter reference with an unconstrained bit array type
382 -- is the other case we need to worry about (here we assume the same
383 -- BITS type declared above):
385 -- procedure Write_All (File : out BITS; Contents : BITS);
386 -- begin
387 -- File.Storage := Contents;
388 -- end Write_All;
390 -- We expand to a loop in either of these two cases
392 -- Question for future thought. Another potentially more efficient
393 -- approach would be to create the actual subtype, and then do an
394 -- unchecked conversion to this actual subtype ???
399 -- Function to perform required test for the first case, above
400 -- (dereference of an unconstrained bit packed array).
402 -----------------------
403 -- Is_UBPA_Reference --
404 -----------------------
411 begin
415 then
424 else
426 return
431 else
436 -- Start of processing for Check_Unconstrained_Bit_Packed_Array
438 begin
440 or else
442 then
445 -- Here if we do not have the case of a reference to a bit packed
446 -- unconstrained array case. In this case gigi can most certainly
447 -- handle the assignment if a forwards move is allowed.
449 -- (could it handle the backwards case also???)
456 -- The back end can always handle the assignment if the right side is a
457 -- string literal (note that overlap is definitely impossible in this
458 -- case). If the type is packed, a string literal is always converted
459 -- into an aggregate, except in the case of a null slice, for which no
460 -- aggregate can be written. In that case, rewrite the assignment as a
461 -- null statement, a length check has already been emitted to verify
462 -- that the range of the left-hand side is empty.
464 -- Note that this code is not executed if we have an assignment of a
465 -- string literal to a non-bit aligned component of a record, a case
466 -- which cannot be handled by the backend.
471 then
478 -- If either operand is bit packed, then we need a loop, since we can't
479 -- be sure that the slice is byte aligned. Similarly, if either operand
480 -- is a possibly unaligned slice, then we need a loop (since the back
481 -- end cannot handle unaligned slices).
487 then
490 -- If we are not bit-packed, and we have only one slice, then no overlap
491 -- is possible except in the parameter case, so we can let the back end
492 -- handle things.
500 -- If the right-hand side is a string literal, introduce a temporary for
501 -- it, for use in the generated loop that will follow.
504 declare
509 begin
510 Decl :=
522 -- Come here to complete the analysis
524 -- Loop_Required: Set to True if we know that a loop is required
525 -- regardless of overlap considerations.
527 -- Forwards_OK: Set to False if we already know that a forwards
528 -- move is not safe, else set to True.
530 -- Backwards_OK: Set to False if we already know that a backwards
531 -- move is not safe, else set to True
533 -- Our task at this stage is to complete the overlap analysis, which can
534 -- result in possibly setting Forwards_OK or Backwards_OK to False, and
535 -- then generating the final code, either by deciding that it is OK
536 -- after all to let Gigi handle it, or by generating appropriate code
537 -- in the front end.
539 declare
557 begin
558 -- Get the expressions for the arrays. If we are dealing with a
559 -- private type, then convert to the underlying type. We can do
560 -- direct assignments to an array that is a private type, but we
561 -- cannot assign to elements of the array without this extra
562 -- unchecked conversion.
566 else
570 Larray :=
571 Unchecked_Convert_To
578 else
582 Rarray :=
583 Unchecked_Convert_To
588 -- If both sides are slices, we must figure out whether it is safe
589 -- to do the move in one direction or the other. It is always safe
590 -- if there is a change of representation since obviously two arrays
591 -- with different representations cannot possibly overlap.
597 -- If both left and right hand arrays are entity names, and refer
598 -- to different entities, then we know that the move is safe (the
599 -- two storage areas are completely disjoint).
604 then
607 -- Otherwise, we assume the worst, which is that the two arrays
608 -- are the same array. There is no need to check if we know that
609 -- is the case, because if we don't know it, we still have to
610 -- assume it!
612 -- Generally if the same array is involved, then we have an
613 -- overlapping case. We will have to really assume the worst (i.e.
614 -- set neither of the OK flags) unless we can determine the lower
615 -- or upper bounds at compile time and compare them.
617 else
633 -- If after that analysis, Forwards_OK is still True, and
634 -- Loop_Required is False, meaning that we have not discovered some
635 -- non-overlap reason for requiring a loop, then we can still let
636 -- gigi handle it.
640 -- Assume gigi can handle it if Forwards_OK is set
645 -- If Forwards_OK is not set, the back end will need something
646 -- like memmove to handle the move. For now, this processing is
647 -- activated using the .s debug flag (-gnatd.s).
654 -- At this stage we have to generate an explicit loop, and we have
655 -- the following cases:
657 -- Forwards_OK = True
659 -- Rnn : right_index := right_index'First;
660 -- for Lnn in left-index loop
661 -- left (Lnn) := right (Rnn);
662 -- Rnn := right_index'Succ (Rnn);
663 -- end loop;
665 -- Note: the above code MUST be analyzed with checks off, because
666 -- otherwise the Succ could overflow. But in any case this is more
667 -- efficient!
669 -- Forwards_OK = False, Backwards_OK = True
671 -- Rnn : right_index := right_index'Last;
672 -- for Lnn in reverse left-index loop
673 -- left (Lnn) := right (Rnn);
674 -- Rnn := right_index'Pred (Rnn);
675 -- end loop;
677 -- Note: the above code MUST be analyzed with checks off, because
678 -- otherwise the Pred could overflow. But in any case this is more
679 -- efficient!
681 -- Forwards_OK = Backwards_OK = False
683 -- This only happens if we have the same array on each side. It is
684 -- possible to create situations using overlays that violate this,
685 -- but we simply do not promise to get this "right" in this case.
687 -- There are two possible subcases. If the No_Implicit_Conditionals
688 -- restriction is set, then we generate the following code:
690 -- declare
691 -- T : constant <operand-type> := rhs;
692 -- begin
693 -- lhs := T;
694 -- end;
696 -- If implicit conditionals are permitted, then we generate:
698 -- if Left_Lo <= Right_Lo then
699 -- <code for Forwards_OK = True above>
700 -- else
701 -- <code for Backwards_OK = True above>
702 -- end if;
704 -- In order to detect possible aliasing, we examine the renamed
705 -- expression when the source or target is a renaming. However,
706 -- the renaming may be intended to capture an address that may be
707 -- affected by subsequent code, and therefore we must recover
708 -- the actual entity for the expansion that follows, not the
709 -- object it renames. In particular, if source or target designate
710 -- a portion of a dynamically allocated object, the pointer to it
711 -- may be reassigned but the renaming preserves the proper location.
714 and then
717 then
722 and then
725 then
729 -- Cases where either Forwards_OK or Backwards_OK is true
736 then
737 declare
742 begin
754 New_Occurrence_Of (
763 else
765 Expand_Assign_Array_Loop
770 -- Case of both are false with No_Implicit_Conditionals
773 declare
777 begin
784 Object_Definition =>
788 Handled_Statement_Sequence =>
796 -- Case of both are false with implicit conditionals allowed
798 else
799 -- Before we generate this code, we must ensure that the left and
800 -- right side array types are defined. They may be itypes, and we
801 -- cannot let them be defined inside the if, since the first use
802 -- in the then may not be executed.
807 -- We normally compare addresses to find out which way round to
808 -- do the loop, since this is realiable, and handles the cases of
809 -- parameters, conversions etc. But we can't do that in the bit
810 -- packed case or the VM case, because addresses don't work there.
813 Condition :=
815 Left_Opnd =>
818 Prefix =>
820 Prefix =>
824 Prefix =>
825 New_Reference_To
830 Right_Opnd =>
833 Prefix =>
835 Prefix =>
839 Prefix =>
840 New_Reference_To
845 -- For the bit packed and VM cases we use the bounds. That's OK,
846 -- because we don't have to worry about parameters, since they
847 -- cannot cause overlap. Perhaps we should worry about weird slice
848 -- conversions ???
850 else
851 -- Copy the bounds and reset the Analyzed flag, because the
852 -- bounds of the index type itself may be universal, and must
853 -- must be reaanalyzed to acquire the proper type for Gigi.
860 Condition :=
870 then
872 -- Call TSS procedure for array assignment, passing the the
873 -- explicit bounds of right and left hand sides.
875 declare
880 begin
901 else
907 Expand_Assign_Array_Loop
912 Expand_Assign_Array_Loop
921 exception
926 ------------------------------
927 -- Expand_Assign_Array_Loop --
928 ------------------------------
930 -- The following is an example of the loop generated for the case of a
931 -- two-dimensional array:
933 -- declare
934 -- R2b : Tm1X1 := 1;
935 -- begin
936 -- for L1b in 1 .. 100 loop
937 -- declare
938 -- R4b : Tm1X2 := 1;
939 -- begin
940 -- for L3b in 1 .. 100 loop
941 -- vm1 (L1b, L3b) := vm2 (R2b, R4b);
942 -- R4b := Tm1X2'succ(R4b);
943 -- end loop;
944 -- end;
945 -- R2b := Tm1X1'succ(R2b);
946 -- end loop;
947 -- end;
949 -- Here Rev is False, and Tm1Xn are the subscript types for the right hand
950 -- side. The declarations of R2b and R4b are inserted before the original
951 -- assignment statement.
953 function Expand_Assign_Array_Loop
961 is
966 -- Entities used as subscripts on left and right sides
970 -- Left and right index types
977 begin
981 else
986 -- Setup index types and subscript entities
988 declare
992 begin
1013 -- Now construct the assignment statement
1015 declare
1019 begin
1025 Assign :=
1027 Name =>
1031 Expression =>
1036 -- We set assignment OK, since there are some cases, e.g. in object
1037 -- declarations, where we are actually assigning into a constant.
1038 -- If there really is an illegality, it was caught long before now,
1039 -- and was flagged when the original assignment was analyzed.
1043 -- Propagate the No_Ctrl_Actions flag to individual assignments
1048 -- Now construct the loop from the inside out, with the last subscript
1049 -- varying most rapidly. Note that Assign is first the raw assignment
1050 -- statement, and then subsequently the loop that wraps it up.
1053 Assign :=
1058 Object_Definition =>
1060 Expression =>
1065 Handled_Statement_Sequence =>
1069 Iteration_Scheme =>
1071 Loop_Parameter_Specification =>
1075 Discrete_Subtype_Definition =>
1079 Assign,
1083 Expression =>
1085 Prefix =>
1095 --------------------------
1096 -- Expand_Assign_Record --
1097 --------------------------
1099 -- The only processing required is in the change of representation case,
1100 -- where we must expand the assignment to a series of field by field
1101 -- assignments.
1107 begin
1108 -- If change of representation, then extract the real right hand side
1109 -- from the type conversion, and proceed with component-wise assignment,
1110 -- since the two types are not the same as far as the back end is
1111 -- concerned.
1116 -- If this may be a case of a large bit aligned component, then proceed
1117 -- with component-wise assignment, to avoid possible clobbering of other
1118 -- components sharing bits in the first or last byte of the component to
1119 -- be assigned.
1122 or
1124 then
1127 -- If neither condition met, then nothing special to do, the back end
1128 -- can handle assignment of the entire component as a single entity.
1130 else
1134 -- At this stage we know that we must do a component wise assignment
1136 declare
1144 function Find_Component
1147 -- Find the component with the given name in the underlying record
1148 -- declaration for Typ. We need to use the actual entity because the
1149 -- type may be private and resolution by identifier alone would fail.
1151 function Make_Component_List_Assign
1154 -- Returns a sequence of statements to assign the components that
1155 -- are referenced in the given component list. The flag U_U is
1156 -- used to force the usage of the inferred value of the variant
1157 -- part expression as the switch for the generated case statement.
1159 function Make_Field_Assign
1162 -- Given C, the entity for a discriminant or component, build an
1163 -- assignment for the corresponding field values. The flag U_U
1164 -- signals the presence of an Unchecked_Union and forces the usage
1165 -- of the inferred discriminant value of C as the right hand side
1166 -- of the assignment.
1169 -- Given CI, a component items list, construct series of statements
1170 -- for fieldwise assignment of the corresponding components.
1172 --------------------
1173 -- Find_Component --
1174 --------------------
1176 function Find_Component
1179 is
1183 begin
1196 --------------------------------
1197 -- Make_Component_List_Assign --
1198 --------------------------------
1200 function Make_Component_List_Assign
1203 is
1214 begin
1233 Statements =>
1238 -- If we have an Unchecked_Union, use the value of the inferred
1239 -- discriminant of the variant part expression as the switch
1240 -- for the case statement. The case statement may later be
1241 -- folded.
1244 Expr :=
1249 else
1250 Expr :=
1253 Selector_Name =>
1266 -----------------------
1267 -- Make_Field_Assign --
1268 -----------------------
1270 function Make_Field_Assign
1273 is
1277 begin
1278 -- In the case of an Unchecked_Union, use the discriminant
1279 -- constraint value as on the right hand side of the assignment.
1282 Expr :=
1286 else
1287 Expr :=
1293 A :=
1295 Name =>
1298 Selector_Name =>
1302 -- Set Assignment_OK, so discriminants can be assigned
1308 ------------------------
1309 -- Make_Field_Assigns --
1310 ------------------------
1316 begin
1321 Append_To
1331 -- Start of processing for Expand_Assign_Record
1333 begin
1334 -- Note that we use the base types for this processing. This results
1335 -- in some extra work in the constrained case, but the change of
1336 -- representation case is so unusual that it is not worth the effort.
1338 -- First copy the discriminants. This is done unconditionally. It
1339 -- is required in the unconstrained left side case, and also in the
1340 -- case where this assignment was constructed during the expansion
1341 -- of a type conversion (since initialization of discriminants is
1342 -- suppressed in this case). It is unnecessary but harmless in
1343 -- other cases.
1351 else
1359 -- We know the underlying type is a record, but its current view
1360 -- may be private. We must retrieve the usable record declaration.
1364 then
1366 else
1372 then
1377 else
1378 Insert_Actions
1388 -----------------------------------
1389 -- Expand_N_Assignment_Statement --
1390 -----------------------------------
1392 -- This procedure implements various cases where an assignment statement
1393 -- cannot just be passed on to the back end in untransformed state.
1402 begin
1403 -- Ada 2005 (AI-327): Handle assignment to priority of protected object
1405 -- Rewrite an assignment to X'Priority into a run-time call
1407 -- For example: X'Priority := New_Prio_Expr;
1408 -- ...is expanded into Set_Ceiling (X._Object, New_Prio_Expr);
1410 -- Note that although X'Priority is notionally an object, it is quite
1411 -- deliberately not defined as an aliased object in the RM. This means
1412 -- that it works fine to rewrite it as a call, without having to worry
1413 -- about complications that would other arise from X'Priority'Access,
1414 -- which is illegal, because of the lack of aliasing.
1417 declare
1424 begin
1425 -- Handle chains of renamings
1431 loop
1435 -- The attribute Priority applied to protected objects has been
1436 -- previously expanded into a call to the Get_Ceiling run-time
1437 -- subprogram.
1441 or else
1443 then
1444 -- Look for the enclosing concurrent type
1453 -- Generate the first actual of the call
1460 -- Select the appropriate run-time call
1463 RT_Subprg_Name :=
1465 else
1466 RT_Subprg_Name :=
1470 Call :=
1484 -- First deal with generation of range check if required. For now we do
1485 -- this only for discrete types.
1489 then
1494 -- Check for a special case where a high level transformation is
1495 -- required. If we have either of:
1497 -- P.field := rhs;
1498 -- P (sub) := rhs;
1500 -- where P is a reference to a bit packed array, then we have to unwind
1501 -- the assignment. The exact meaning of being a reference to a bit
1502 -- packed array is as follows:
1504 -- An indexed component whose prefix is a bit packed array is a
1505 -- reference to a bit packed array.
1507 -- An indexed component or selected component whose prefix is a
1508 -- reference to a bit packed array is itself a reference ot a
1509 -- bit packed array.
1511 -- The required transformation is
1513 -- Tnn : prefix_type := P;
1514 -- Tnn.field := rhs;
1515 -- P := Tnn;
1517 -- or
1519 -- Tnn : prefix_type := P;
1520 -- Tnn (subscr) := rhs;
1521 -- P := Tnn;
1523 -- Since P is going to be evaluated more than once, any subscripts
1524 -- in P must have their evaluation forced.
1528 then
1529 declare
1536 begin
1537 -- Insert the post assignment first, because we want to copy the
1538 -- BPAR_Expr tree before it gets analyzed in the context of the
1539 -- pre assignment. Note that we do not analyze the post assignment
1540 -- yet (we cannot till we have completed the analysis of the pre
1541 -- assignment). As usual, the analysis of this post assignment
1542 -- will happen on its own when we "run into" it after finishing
1543 -- the current assignment.
1550 -- At this stage BPAR_Expr is a reference to a bit packed array
1551 -- where the reference was not expanded in the original tree,
1552 -- since it was on the left side of an assignment. But in the
1553 -- pre-assignment statement (the object definition), BPAR_Expr
1554 -- will end up on the right hand side, and must be reexpanded. To
1555 -- achieve this, we reset the analyzed flag of all selected and
1556 -- indexed components down to the actual indexed component for
1557 -- the packed array.
1560 loop
1563 if Nkind_In
1565 then
1567 else
1572 -- Now we can insert and analyze the pre-assignment
1574 -- If the right-hand side requires a transient scope, it has
1575 -- already been placed on the stack. However, the declaration is
1576 -- inserted in the tree outside of this scope, and must reflect
1577 -- the proper scope for its variable. This awkward bit is forced
1578 -- by the stricter scope discipline imposed by GCC 2.97.
1580 declare
1582 Scope_Is_Transient
1585 begin
1597 Pop_Scope;
1601 -- Now fix up the original assignment and continue processing
1606 -- We do not need to reanalyze that assignment, and we do not need
1607 -- to worry about references to the temporary, but we do need to
1608 -- make sure that the temporary is not marked as a true constant
1609 -- since we now have a generated assignment to it!
1615 -- When we have the appropriate type of aggregate in the expression (it
1616 -- has been determined during analysis of the aggregate by setting the
1617 -- delay flag), let's perform in place assignment and thus avoid
1618 -- creating a temporary.
1627 -- Apply discriminant check if required. If Lhs is an access type to a
1628 -- designated type with discriminants, we must always check.
1632 -- Skip discriminant check if change of representation. Will be
1633 -- done when the change of representation is expanded out.
1639 -- If the type is private without discriminants, and the full type
1640 -- has discriminants (necessarily with defaults) a check may still be
1641 -- necessary if the Lhs is aliased. The private determinants must be
1642 -- visible to build the discriminant constraints.
1644 -- Only an explicit dereference that comes from source indicates
1645 -- aliasing. Access to formals of protected operations and entries
1646 -- create dereferences but are not semantic aliasings.
1652 then
1653 declare
1655 begin
1662 -- If the Lhs has a private type with unknown discriminants, it
1663 -- may have a full view with discriminants, but those are nameable
1664 -- only in the underlying type, so convert the Rhs to it before
1665 -- potential checking.
1669 then
1673 -- In the access type case, we need the same discriminant check, and
1674 -- also range checks if we have an access to constrained array.
1678 then
1681 -- Skip discriminant check if change of representation. Will be
1682 -- done when the change of representation is expanded out.
1696 declare
1700 begin
1701 C_Es :=
1702 Get_Range_Checks
1704 Target_Typ,
1707 Insert_Range_Checks
1709 N,
1710 Target_Typ,
1712 Lhs);
1717 -- Apply range check for access type case
1722 then
1724 Apply_Range_Check
1728 -- Ada 2005 (AI-231): Generate the run-time check
1733 then
1737 -- Case of assignment to a bit packed array element
1741 then
1745 -- Build-in-place function call case. Note that we're not yet doing
1746 -- build-in-place for user-written assignment statements (the assignment
1747 -- here came from an aggregate.)
1751 then
1756 -- Nothing to do for valuetypes
1757 -- ??? Set_Scope_Is_Transient (False);
1763 then
1768 begin
1769 -- In the controlled case, we need to make sure that function
1770 -- calls are evaluated before finalizing the target. In all cases,
1771 -- it makes the expansion easier if the side-effects are removed
1772 -- first.
1777 -- Avoid recursion in the mechanism
1781 -- If dispatching assignment, we need to dispatch to _assign
1785 -- If the type is tagged, we may as well use the predefined
1786 -- primitive assignment. This avoids inlining a lot of code
1787 -- and in the class-wide case, the assignment is replaced by
1788 -- dispatch call to _assign. Note that this cannot be done when
1789 -- discriminant checks are locally suppressed (as in extension
1790 -- aggregate expansions) because otherwise the discriminant
1791 -- check will be performed within the _assign call. It is also
1792 -- suppressed for assignmments created by the expander that
1793 -- correspond to initializations, where we do want to copy the
1794 -- tag (No_Ctrl_Actions flag set True). by the expander and we
1795 -- do not need to mess with tags ever (Expand_Ctrl_Actions flag
1796 -- is set True in this case).
1801 and then Expand_Ctrl_Actions
1803 then
1804 -- Fetch the primitive op _assign and proper type to call it.
1805 -- Because of possible conflits between private and full view
1806 -- the proper type is fetched directly from the operation
1807 -- profile.
1809 declare
1814 begin
1815 -- If the assignment is dispatching, make sure to use the
1816 -- proper type.
1824 -- In case of assignment to a class-wide tagged type, before
1825 -- the assignment we generate run-time check to ensure that
1826 -- the tags of source and target match.
1831 then
1834 Condition =>
1836 Left_Opnd =>
1839 Selector_Name =>
1842 Right_Opnd =>
1845 Selector_Name =>
1861 else
1864 -- We can't afford to have destructive Finalization Actions in
1865 -- the Self assignment case, so if the target and the source
1866 -- are not obviously different, code is generated to avoid the
1867 -- self assignment case:
1869 -- if lhs'address /= rhs'address then
1870 -- <code for controlled and/or tagged assignment>
1871 -- end if;
1874 and then Expand_Ctrl_Actions
1875 then
1878 Condition =>
1880 Left_Opnd =>
1885 Right_Opnd =>
1893 -- We need to set up an exception handler for implementing
1894 -- 7.6.1(18). The remaining adjustments are tackled by the
1895 -- implementation of adjust for record_controllers (see
1896 -- s-finimp.adb).
1898 -- This is skipped if we have no finalization
1900 if Expand_Ctrl_Actions
1902 then
1905 Handled_Statement_Sequence =>
1915 Handled_Statement_Sequence =>
1918 -- If no restrictions on aborts, protect the whole assignement
1919 -- for controlled objects as per 9.8(11).
1922 and then Expand_Ctrl_Actions
1923 and then Abort_Allowed
1924 then
1925 declare
1927 New_Internal_Entity
1930 begin
1938 Expand_At_End_Handler
1943 -- N has been rewritten to a block statement for which it is
1944 -- known by construction that no checks are necessary: analyze
1945 -- it with all checks suppressed.
1951 -- Array types
1954 declare
1957 begin
1959 N_Qualified_Expression)
1960 loop
1968 -- Record types
1974 -- Scalar types. This is where we perform the processing related to the
1975 -- requirements of (RM 13.9.1(9-11)) concerning the handling of invalid
1976 -- scalar values.
1980 -- Case where right side is known valid
1984 -- Here the right side is valid, so it is fine. The case to deal
1985 -- with is when the left side is a local variable reference whose
1986 -- value is not currently known to be valid. If this is the case,
1987 -- and the assignment appears in an unconditional context, then we
1988 -- can mark the left side as now being valid.
1993 then
1997 -- Case where right side may be invalid in the sense of the RM
1998 -- reference above. The RM does not require that we check for the
1999 -- validity on an assignment, but it does require that the assignment
2000 -- of an invalid value not cause erroneous behavior.
2002 -- The general approach in GNAT is to use the Is_Known_Valid flag
2003 -- to avoid the need for validity checking on assignments. However
2004 -- in some cases, we have to do validity checking in order to make
2005 -- sure that the setting of this flag is correct.
2007 else
2008 -- Validate right side if we are validating copies
2010 if Validity_Checks_On
2011 and then Validity_Check_Copies
2012 then
2013 -- Skip this if left hand side is an array or record component
2014 -- and elementary component validity checks are suppressed.
2017 and then not Validity_Check_Components
2018 then
2020 else
2024 -- We can propagate this to the left side where appropriate
2029 then
2033 -- Otherwise check to see what should be done
2035 -- If left side is a local variable, then we just set its flag to
2036 -- indicate that its value may no longer be valid, since we are
2037 -- copying a potentially invalid value.
2042 -- Check for case of a nonlocal variable on the left side which
2043 -- is currently known to be valid. In this case, we simply ensure
2044 -- that the right side is valid. We only play the game of copying
2045 -- validity status for local variables, since we are doing this
2046 -- statically, not by tracing the full flow graph.
2050 then
2051 -- Note: If Validity_Checking mode is set to none, we ignore
2052 -- the Ensure_Valid call so don't worry about that case here.
2056 -- In all other cases, we can safely copy an invalid value without
2057 -- worrying about the status of the left side. Since it is not a
2058 -- variable reference it will not be considered
2059 -- as being known to be valid in any case.
2061 else
2067 -- Defend against invalid subscripts on left side if we are in standard
2068 -- validity checking mode. No need to do this if we are checking all
2069 -- subscripts.
2071 if Validity_Checks_On
2072 and then Validity_Check_Default
2073 and then not Validity_Check_Subscripts
2074 then
2078 exception
2083 ------------------------------
2084 -- Expand_N_Block_Statement --
2085 ------------------------------
2087 -- Encode entity names defined in block statement
2090 begin
2094 -----------------------------
2095 -- Expand_N_Case_Statement --
2096 -----------------------------
2107 begin
2108 -- Check for the situation where we know at compile time which branch
2109 -- will be taken
2114 -- Move statements from this alternative after the case statement.
2115 -- They are already analyzed, so will be skipped by the analyzer.
2119 -- That leaves the case statement as a shell. So now we can kill all
2120 -- other alternatives in the case statement.
2124 declare
2127 begin
2128 -- Loop through case alternatives, skipping pragmas, and skipping
2129 -- the one alternative that we select (and therefore retain).
2135 then
2147 -- Here if the choice is not determined at compile time
2149 declare
2158 begin
2162 else
2166 -- First step is to worry about possible invalid argument. The RM
2167 -- requires (RM 5.4(13)) that if the result is invalid (e.g. it is
2168 -- outside the base range), then Constraint_Error must be raised.
2170 -- Case of validity check required (validity checks are on, the
2171 -- expression is not known to be valid, and the case statement
2172 -- comes from source -- no need to validity check internally
2173 -- generated case statements).
2179 -- If there is only a single alternative, just replace it with the
2180 -- sequence of statements since obviously that is what is going to
2181 -- be executed in all cases.
2186 -- We still need to evaluate the expression if it has any
2187 -- side effects.
2193 -- That leaves the case statement as a shell. The alternative that
2194 -- will be executed is reset to a null list. So now we can kill
2195 -- the entire case statement.
2202 -- An optimization. If there are only two alternatives, and only
2203 -- a single choice, then rewrite the whole case statement as an
2204 -- if statement, since this can result in susbequent optimizations.
2205 -- This helps not only with case statements in the source of a
2206 -- simple form, but also with generated code (discriminant check
2207 -- functions in particular)
2218 -- For TRUE, generate "expression", not expression = true
2222 then
2225 -- For FALSE, generate "expression" and switch then/else
2229 then
2234 -- For a range, generate "expression in range"
2242 then
2243 Cond :=
2248 -- For any other subexpression "expression = value"
2250 else
2251 Cond :=
2257 -- Now rewrite the case as an IF
2269 -- If the last alternative is not an Others choice, replace it with
2270 -- an N_Others_Choice. Note that we do not bother to call Analyze on
2271 -- the modified case statement, since it's only effect would be to
2272 -- compute the contents of the Others_Discrete_Choices which is not
2273 -- needed by the back end anyway.
2275 -- The reason we do this is that the back end always needs some
2276 -- default for a switch, so if we have not supplied one in the
2277 -- processing above for validity checking, then we need to supply
2278 -- one here.
2282 Set_Others_Discrete_Choices
2289 -----------------------------
2290 -- Expand_N_Exit_Statement --
2291 -----------------------------
2293 -- The only processing required is to deal with a possible C/Fortran
2294 -- boolean value used as the condition for the exit statement.
2297 begin
2301 ----------------------------------------
2302 -- Expand_N_Extended_Return_Statement --
2303 ----------------------------------------
2305 -- If there is a Handled_Statement_Sequence, we rewrite this:
2307 -- return Result : T := <expression> do
2308 -- <handled_seq_of_stms>
2309 -- end return;
2311 -- to be:
2313 -- declare
2314 -- Result : T := <expression>;
2315 -- begin
2316 -- <handled_seq_of_stms>
2317 -- return Result;
2318 -- end;
2320 -- Otherwise (no Handled_Statement_Sequence), we rewrite this:
2322 -- return Result : T := <expression>;
2324 -- to be:
2326 -- return <expression>;
2328 -- unless it's build-in-place or there's no <expression>, in which case
2329 -- we generate:
2331 -- declare
2332 -- Result : T := <expression>;
2333 -- begin
2334 -- return Result;
2335 -- end;
2337 -- Note that this case could have been written by the user as an extended
2338 -- return statement, or could have been transformed to this from a simple
2339 -- return statement.
2341 -- That is, we need to have a reified return object if there are statements
2342 -- (which might refer to it) or if we're doing build-in-place (so we can
2343 -- set its address to the final resting place or if there is no expression
2344 -- (in which case default initial values might need to be set).
2365 -- Construct a call to System.Tasking.Stages.Move_Activation_Chain
2366 -- with parameters:
2367 -- From current activation chain
2368 -- To activation chain passed in by the caller
2369 -- New_Master master passed in by the caller
2372 -- Construct call to System.Finalization_Implementation.Move_Final_List
2373 -- with parameters:
2374 --
2375 -- From finalization list of the return statement
2376 -- To finalization list passed in by the caller
2378 ---------------------------
2379 -- Move_Activation_Chain --
2380 ---------------------------
2384 Build_In_Place_Formal
2387 New_Reference_To
2390 Build_In_Place_Formal
2398 begin
2404 From :=
2408 -- ??? Not clear why "Make_Identifier (Loc, Name_uChain)" doesn't
2409 -- work, instead of "New_Reference_To (Chain_Entity, Loc)" above.
2411 return
2417 ---------------------
2418 -- Move_Final_List --
2419 ---------------------
2428 Build_In_Place_Formal
2433 begin
2434 -- Catch cases where a finalization chain entity has not been
2435 -- associated with the return statement entity.
2439 -- Build required call
2441 return
2443 Condition =>
2447 Then_Statements =>
2448 New_List (
2454 -- Start of processing for Expand_N_Extended_Return_Statement
2456 begin
2459 else
2465 -- Build a simple_return_statement that returns the return object when
2466 -- there is a statement sequence, or no expression, or the result will
2467 -- be built in place. Note however that we currently do this for all
2468 -- composite cases, even though nonlimited composite results are not yet
2469 -- built in place (though we plan to do so eventually).
2474 then
2478 -- If the extended return has a handled statement sequence, then wrap
2479 -- it in a block and use the block as the first statement.
2481 else
2482 Statements :=
2488 -- If control gets past the above Statements, we have successfully
2489 -- completed the return statement. If the result type has controlled
2490 -- parts and the return is for a build-in-place function, then we
2491 -- call Move_Final_List to transfer responsibility for finalization
2492 -- of the return object to the caller. An alternative would be to
2493 -- declare a Success flag in the function, initialize it to False,
2494 -- and set it to True here. Then move the Move_Final_List call into
2495 -- the cleanup code, and check Success. If Success then make a call
2496 -- to Move_Final_List else do finalization. Then we can remove the
2497 -- abort-deferral and the nulling-out of the From parameter from
2498 -- Move_Final_List. Note that the current method is not quite correct
2499 -- in the rather obscure case of a select-then-abort statement whose
2500 -- abortable part contains the return statement.
2502 -- We test the type of the expression as well as the return type
2503 -- of the function, because the latter may be a class-wide type
2504 -- which is always treated as controlled, while the expression itself
2505 -- has to have a definite type. The expression may be absent if a
2506 -- constrained aggregate has been expanded into component assignments
2507 -- so we have to check for this as well.
2509 if Is_Build_In_Place
2511 then
2513 or else
2516 then
2521 -- Similarly to the above Move_Final_List, if the result type
2522 -- contains tasks, we call Move_Activation_Chain. Later, the cleanup
2523 -- code will call Complete_Master, which will terminate any
2524 -- unactivated tasks belonging to the return statement master. But
2525 -- Move_Activation_Chain updates their master to be that of the
2526 -- caller, so they will not be terminated unless the return statement
2527 -- completes unsuccessfully due to exception, abort, goto, or exit.
2528 -- As a formality, we test whether the function requires the result
2529 -- to be built in place, though that's necessarily true for the case
2530 -- of result types with task parts.
2536 -- Build a simple_return_statement that returns the return object
2538 Return_Stm :=
2543 Handled_Stm_Seq :=
2547 -- Case where we build a block
2550 Result :=
2555 -- We set the entity of the new block statement to be that of the
2556 -- return statement. This is necessary so that various fields, such
2557 -- as Finalization_Chain_Entity carry over from the return statement
2558 -- to the block. Note that this block is unusual, in that its entity
2559 -- is an E_Return_Statement rather than an E_Block.
2561 Set_Identifier
2564 -- If the object decl was already rewritten as a renaming, then
2565 -- we don't want to do the object allocation and transformation of
2566 -- of the return object declaration to a renaming. This case occurs
2567 -- when the return object is initialized by a call to another
2568 -- build-in-place function, and that function is responsible for the
2569 -- allocation of the return object.
2571 if Is_Build_In_Place
2572 and then
2574 then
2579 -- Locate the implicit access parameter associated with the
2580 -- caller-supplied return object and convert the return
2581 -- statement's return object declaration to a renaming of a
2582 -- dereference of the access parameter. If the return object's
2583 -- declaration includes an expression that has not already been
2584 -- expanded as separate assignments, then add an assignment
2585 -- statement to ensure the return object gets initialized.
2587 -- declare
2588 -- Result : T [:= <expression>];
2589 -- begin
2590 -- ...
2592 -- is converted to
2594 -- declare
2595 -- Result : T renames FuncRA.all;
2596 -- [Result := <expression;]
2597 -- begin
2598 -- ...
2600 declare
2615 begin
2616 -- Build-in-place results must be returned by reference
2620 -- Retrieve the implicit access parameter passed by the caller
2622 Object_Access :=
2625 -- If the return object's declaration includes an expression
2626 -- and the declaration isn't marked as No_Initialization, then
2627 -- we need to generate an assignment to the object and insert
2628 -- it after the declaration before rewriting it as a renaming
2629 -- (otherwise we'll lose the initialization).
2633 then
2634 Init_Assignment :=
2648 and then not Is_Class_Wide_Type
2650 then
2653 Subtype_Mark =>
2654 New_Occurrence_Of
2656 Expression =>
2660 -- In the case of functions where the calling context can
2661 -- determine the form of allocation needed, initialization
2662 -- is done with each part of the if statement that handles
2663 -- the different forms of allocation (this is true for
2664 -- unconstrained and tagged result subtypes).
2666 if Constr_Result
2668 then
2673 -- When the function's subtype is unconstrained, a run-time
2674 -- test is needed to determine the form of allocation to use
2675 -- for the return object. The function has an implicit formal
2676 -- parameter indicating this. If the BIP_Alloc_Form formal has
2677 -- the value one, then the caller has passed access to an
2678 -- existing object for use as the return object. If the value
2679 -- is two, then the return object must be allocated on the
2680 -- secondary stack. Otherwise, the object must be allocated in
2681 -- a storage pool (currently only supported for the global
2682 -- heap, user-defined storage pools TBD ???). We generate an
2683 -- if statement to test the implicit allocation formal and
2684 -- initialize a local access value appropriately, creating
2685 -- allocators in the secondary stack and global heap cases.
2686 -- The special formal also exists and must be tested when the
2687 -- function has a tagged result, even when the result subtype
2688 -- is constrained, because in general such functions can be
2689 -- called in dispatching contexts and must be handled similarly
2690 -- to functions with a class-wide result.
2692 if not Constr_Result
2694 then
2695 Obj_Alloc_Formal :=
2698 declare
2707 begin
2708 -- Reuse the itype created for the function's implicit
2709 -- access formal. This avoids the need to create a new
2710 -- access type here, plus it allows assigning the access
2711 -- formal directly without applying a conversion.
2713 -- Ref_Type := Etype (Object_Access);
2715 -- Create an access type designating the function's
2716 -- result subtype.
2718 Ref_Type :=
2721 Ptr_Type_Decl :=
2724 Type_Definition =>
2727 Subtype_Indication =>
2732 -- Create an access object that will be initialized to an
2733 -- access value denoting the return object, either coming
2734 -- from an implicit access value passed in by the caller
2735 -- or from the result of an allocator.
2737 Alloc_Obj_Id :=
2742 Alloc_Obj_Decl :=
2745 Object_Definition => New_Reference_To
2750 -- Create allocators for both the secondary stack and
2751 -- global heap. If there's an initialization expression,
2752 -- then create these as initialized allocators.
2756 then
2757 Heap_Allocator :=
2759 Expression =>
2761 Subtype_Mark =>
2763 Expression =>
2768 else
2769 -- If the function returns a class-wide type we cannot
2770 -- use the return type for the allocator. Instead we
2771 -- use the type of the expression, which must be an
2772 -- aggregate of a definite type.
2775 Heap_Allocator :=
2777 New_Reference_To
2779 else
2780 Heap_Allocator :=
2785 -- If the object requires default initialization then
2786 -- that will happen later following the elaboration of
2787 -- the object renaming. If we don't turn it off here
2788 -- then the object will be default initialized twice.
2795 -- The allocator is returned on the secondary stack. We
2796 -- don't do this on VM targets, since the SS is not used.
2800 Set_Procedure_To_Call
2803 -- The allocator is returned on the secondary stack,
2804 -- so indicate that the function return, as well as
2805 -- the block that encloses the allocator, must not
2806 -- release it. The flags must be set now because the
2807 -- decision to use the secondary stack is done very
2808 -- late in the course of expanding the return
2809 -- statement, past the point where these flags are
2810 -- normally set.
2813 Set_Sec_Stack_Needed_For_Return
2819 -- Create an if statement to test the BIP_Alloc_Form
2820 -- formal and initialize the access object to either the
2821 -- BIP_Object_Access formal (BIP_Alloc_Form = 0), the
2822 -- result of allocating the object in the secondary stack
2823 -- (BIP_Alloc_Form = 1), or else an allocator to create
2824 -- the return object in the heap (BIP_Alloc_Form = 2).
2826 -- ??? An unchecked type conversion must be made in the
2827 -- case of assigning the access object formal to the
2828 -- local access object, because a normal conversion would
2829 -- be illegal in some cases (such as converting access-
2830 -- to-unconstrained to access-to-constrained), but the
2831 -- the unchecked conversion will presumably fail to work
2832 -- right in just such cases. It's not clear at all how to
2833 -- handle this. ???
2835 Alloc_If_Stmt :=
2837 Condition =>
2839 Left_Opnd =>
2841 Right_Opnd =>
2845 Then_Statements =>
2847 Name =>
2848 New_Reference_To
2850 Expression =>
2852 Subtype_Mark =>
2854 Expression =>
2855 New_Reference_To
2857 Elsif_Parts =>
2859 Condition =>
2861 Left_Opnd =>
2862 New_Reference_To
2864 Right_Opnd =>
2866 UI_From_Int (
2867 BIP_Allocation_Form'Pos
2869 Then_Statements =>
2870 New_List
2872 Name =>
2873 New_Reference_To
2875 Expression =>
2876 SS_Allocator)))),
2877 Else_Statements =>
2879 Name =>
2880 New_Reference_To
2882 Expression =>
2883 Heap_Allocator)));
2885 -- If a separate initialization assignment was created
2886 -- earlier, append that following the assignment of the
2887 -- implicit access formal to the access object, to ensure
2888 -- that the return object is initialized in that case.
2889 -- In this situation, the target of the assignment must
2890 -- be rewritten to denote a derference of the access to
2891 -- the return object passed in by the caller.
2897 Set_Etype
2900 Append_To
2902 Init_Assignment);
2907 -- Remember the local access object for use in the
2908 -- dereference of the renaming created below.
2914 -- Replace the return object declaration with a renaming of a
2915 -- dereference of the access value designating the return
2916 -- object.
2918 Obj_Acc_Deref :=
2926 Subtype_Mark => New_Occurrence_Of
2934 -- Case where we do not build a block
2936 else
2937 -- We're about to drop Return_Object_Declarations on the floor, so
2938 -- we need to insert it, in case it got expanded into useful code.
2942 -- Build simple_return_statement that returns the expression directly
2949 -- Set the flag to prevent infinite recursion
2957 -----------------------------
2958 -- Expand_N_Goto_Statement --
2959 -----------------------------
2961 -- Add poll before goto if polling active
2964 begin
2968 ---------------------------
2969 -- Expand_N_If_Statement --
2970 ---------------------------
2972 -- First we deal with the case of C and Fortran convention boolean values,
2973 -- with zero/non-zero semantics.
2975 -- Second, we deal with the obvious rewriting for the cases where the
2976 -- condition of the IF is known at compile time to be True or False.
2978 -- Third, we remove elsif parts which have non-empty Condition_Actions
2979 -- and rewrite as independent if statements. For example:
2981 -- if x then xs
2982 -- elsif y then ys
2983 -- ...
2984 -- end if;
2986 -- becomes
2987 --
2988 -- if x then xs
2989 -- else
2990 -- <<condition actions of y>>
2991 -- if y then ys
2992 -- ...
2993 -- end if;
2994 -- end if;
2996 -- This rewriting is needed if at least one elsif part has a non-empty
2997 -- Condition_Actions list. We also do the same processing if there is a
2998 -- constant condition in an elsif part (in conjunction with the first
2999 -- processing step mentioned above, for the recursive call made to deal
3000 -- with the created inner if, this deals with properly optimizing the
3001 -- cases of constant elsif conditions).
3011 -- Indicates whether we want warnings when we delete branches of the
3012 -- if statement based on constant condition analysis. We never want
3013 -- these warnings for expander generated code.
3015 begin
3018 -- The following loop deals with constant conditions for the IF. We
3019 -- need a loop because as we eliminate False conditions, we grab the
3020 -- first elsif condition and use it as the primary condition.
3024 -- If condition is True, we can simply rewrite the if statement now
3025 -- by replacing it by the series of then statements.
3029 -- All the else parts can be killed
3039 -- If condition is False, then we can delete the condition and
3040 -- the Then statements
3042 else
3043 -- We do not delete the condition if constant condition warnings
3044 -- are enabled, since otherwise we end up deleting the desired
3045 -- warning. Of course the backend will get rid of this True/False
3046 -- test anyway, so nothing is lost here.
3054 -- If there are no elsif statements, then we simply replace the
3055 -- entire if statement by the sequence of else statements.
3060 then
3063 else
3071 -- If there are elsif statements, the first of them becomes the
3072 -- if/then section of the rebuilt if statement This is the case
3073 -- where we loop to reprocess this copied condition.
3075 else
3081 -- Hed might have been captured as the condition determining
3082 -- the current value for an entity. Now it is detached from
3083 -- the tree, so a Current_Value pointer in the condition might
3084 -- need to be updated.
3095 -- Loop through elsif parts, dealing with constant conditions and
3096 -- possible expression actions that are present.
3103 -- If there are condition actions, then rewrite the if statement
3104 -- as indicated above. We also do the same rewrite for a True or
3105 -- False condition. The further processing of this constant
3106 -- condition is then done by the recursive call to expand the
3107 -- newly created if statement
3111 then
3112 -- Note this is not an implicit if statement, since it is part
3113 -- of an explicit if statement in the source (or of an implicit
3114 -- if statement that has already been tested).
3116 New_If :=
3123 -- Elsif parts for new if come from remaining elsif's of parent
3148 -- No special processing for that elsif part, move to next
3150 else
3156 -- Some more optimizations applicable if we still have an IF statement
3162 -- Another optimization, special cases that can be simplified
3164 -- if expression then
3165 -- return true;
3166 -- else
3167 -- return false;
3168 -- end if;
3170 -- can be changed to:
3172 -- return expression;
3174 -- and
3176 -- if expression then
3177 -- return false;
3178 -- else
3179 -- return true;
3180 -- end if;
3182 -- can be changed to:
3184 -- return not (expression);
3191 then
3192 declare
3196 begin
3198 and then
3200 then
3201 declare
3205 begin
3207 and then
3209 then
3212 then
3221 then
3224 Expression =>
3237 -----------------------------
3238 -- Expand_N_Loop_Statement --
3239 -----------------------------
3241 -- 1. Deal with while condition for C/Fortran boolean
3242 -- 2. Deal with loops with a non-standard enumeration type range
3243 -- 3. Deal with while loops where Condition_Actions is set
3244 -- 4. Insert polling call if required
3250 begin
3259 -- Nothing more to do for plain loop with no iteration scheme
3265 -- Note: we do not have to worry about validity chekcing of the for loop
3266 -- range bounds here, since they were frozen with constant declarations
3267 -- and it is during that process that the validity checking is done.
3269 -- Handle the case where we have a for loop with the range type being an
3270 -- enumeration type with non-standard representation. In this case we
3271 -- expand:
3273 -- for x in [reverse] a .. b loop
3274 -- ...
3275 -- end loop;
3277 -- to
3279 -- for xP in [reverse] integer
3280 -- range etype'Pos (a) .. etype'Pos (b) loop
3281 -- declare
3282 -- x : constant etype := Pos_To_Rep (xP);
3283 -- begin
3284 -- ...
3285 -- end;
3286 -- end loop;
3289 declare
3297 begin
3300 then
3304 New_Id :=
3308 -- If the type has a contiguous representation, successive values
3309 -- can be generated as offsets from the first literal.
3312 Expr :=
3315 Left_Opnd =>
3319 else
3320 -- Use the constructed array Enum_Pos_To_Rep
3322 Expr :=
3332 Iteration_Scheme =>
3334 Loop_Parameter_Specification =>
3339 Discrete_Subtype_Definition =>
3342 Subtype_Mark =>
3345 Constraint =>
3347 Range_Expression =>
3350 Low_Bound =>
3352 Prefix =>
3358 Relocate_Node
3361 High_Bound =>
3363 Prefix =>
3369 Relocate_Node
3381 Handled_Statement_Sequence =>
3389 -- Second case, if we have a while loop with Condition_Actions set, then
3390 -- we change it into a plain loop:
3392 -- while C loop
3393 -- ...
3394 -- end loop;
3396 -- changed to:
3398 -- loop
3399 -- <<condition actions>>
3400 -- exit when not C;
3401 -- ...
3402 -- end loop
3406 then
3407 declare
3410 begin
3411 ES :=
3413 Condition =>
3420 -- This is not an implicit loop, since it is generated in response
3421 -- to the loop statement being processed. If this is itself
3422 -- implicit, the restriction has already been checked. If not,
3423 -- it is an explicit loop.
3436 --------------------------------------
3437 -- Expand_N_Simple_Return_Statement --
3438 --------------------------------------
3441 begin
3442 -- Distinguish the function and non-function cases:
3446 when E_Function |
3447 E_Generic_Function =>
3450 when E_Procedure |
3451 E_Generic_Procedure |
3452 E_Entry |
3453 E_Entry_Family |
3454 E_Return_Statement =>
3461 exception
3466 --------------------------------
3467 -- Expand_Non_Function_Return --
3468 --------------------------------
3482 begin
3483 -- If it is a return from a procedure do no extra steps
3488 -- If it is a nested return within an extended one, replace it with a
3489 -- return of the previously declared return object.
3494 Expression =>
3504 -- Look at the enclosing block to see whether the return is from an
3505 -- accept statement or an entry body.
3512 -- If it is a return from accept statement it is expanded as call to
3513 -- RTS Complete_Rendezvous and a goto to the end of the accept body.
3515 -- (cf : Expand_N_Accept_Statement, Expand_N_Selective_Accept,
3516 -- Expand_N_Accept_Alternative in exp_ch9.adb)
3520 Call :=
3522 Name => New_Reference_To
3525 -- why not insert actions here???
3537 Name => New_Occurrence_Of
3545 -- If it is a return from an entry body, put a Complete_Entry_Body call
3546 -- in front of the return.
3549 Call :=
3551 Name => New_Reference_To
3553 Parameter_Associations => New_List
3555 Prefix =>
3556 New_Reference_To
3557 (Object_Ref
3559 Loc),
3567 -----------------------------------
3568 -- Expand_Simple_Function_Return --
3569 -----------------------------------
3571 -- The "simple" comes from the syntax rule simple_return_statement.
3572 -- The semantics are not at all simple!
3579 -- The function we are returning from
3582 -- The result type of the function
3590 -- The type of the expression (not necessarily the same as R_Type)
3592 begin
3593 -- We rewrite "return <expression>;" to be:
3595 -- return _anon_ : <return_subtype> := <expression>
3597 -- The expansion produced by Expand_N_Extended_Return_Statement will
3598 -- contain simple return statements (for example, a block containing
3599 -- simple return of the return object), which brings us back here with
3600 -- Comes_From_Extended_Return_Statement set. To avoid infinite
3601 -- recursion, we do not transform into an extended return if
3602 -- Comes_From_Extended_Return_Statement is True.
3604 -- The reason for this design is that for Ada 2005 limited returns, we
3605 -- need to reify the return object, so we can build it "in place", and
3606 -- we need a block statement to hang finalization and tasking stuff.
3608 -- ??? In order to avoid disruption, we avoid translating to extended
3609 -- return except in the cases where we really need to (Ada 2005
3610 -- inherently limited). We would prefer eventually to do this
3611 -- translation in all cases except perhaps for the case of Ada 95
3612 -- inherently limited, in order to fully exercise the code in
3613 -- Expand_N_Extended_Return_Statement, and in order to do
3614 -- build-in-place for efficiency when it is not required.
3616 -- As before, we check the type of the return expression rather than the
3617 -- return type of the function, because the latter may be a limited
3618 -- class-wide interface type, which is not a limited type, even though
3619 -- the type of the expression may be.
3624 and then not Debug_Flag_Dot_L
3625 then
3626 declare
3642 begin
3649 -- Here we have a simple return statement that is part of the expansion
3650 -- of an extended return statement (either written by the user, or
3651 -- generated by the above code).
3653 -- Always normalize C/Fortran boolean result. This is not always needed,
3654 -- but it seems a good idea to minimize the passing around of non-
3655 -- normalized values, and in any case this handles the processing of
3656 -- barrier functions for protected types, which turn the condition into
3657 -- a return statement.
3661 then
3666 -- Do validity check if enabled for returns
3668 if Validity_Checks_On
3669 and then Validity_Check_Returns
3670 then
3674 -- Check the result expression of a scalar function against the subtype
3675 -- of the function by inserting a conversion. This conversion must
3676 -- eventually be performed for other classes of types, but for now it's
3677 -- only done for scalars.
3678 -- ???
3685 -- Deal with returning variable length objects and controlled types
3687 -- Nothing to do if we are returning by reference, or this is not a
3688 -- type that requires special processing (indicated by the fact that
3689 -- it requires a cleanup scope for the secondary stack case).
3693 then
3698 -- Mutable records with no variable length components are not
3699 -- returned on the sec-stack, so we need to make sure that the
3700 -- backend will only copy back the size of the actual value, and not
3701 -- the maximum size. We create an actual subtype for this purpose.
3703 declare
3707 begin
3711 then
3720 -- Here if secondary stack is used
3722 else
3723 -- Make sure that no surrounding block will reclaim the secondary
3724 -- stack on which we are going to put the result. Not only may this
3725 -- introduce secondary stack leaks but worse, if the reclamation is
3726 -- done too early, then the result we are returning may get
3727 -- clobbered.
3729 declare
3731 begin
3739 -- Optimize the case where the result is a function call. In this
3740 -- case either the result is already on the secondary stack, or is
3741 -- already being returned with the stack pointer depressed and no
3742 -- further processing is required except to set the By_Ref flag to
3743 -- ensure that gigi does not attempt an extra unnecessary copy.
3744 -- (actually not just unnecessary but harmfully wrong in the case
3745 -- of a controlled type, where gigi does not know how to do a copy).
3746 -- To make up for a gcc 2.8.1 deficiency (???), we perform
3747 -- the copy for array types if the constrained status of the
3748 -- target type is different from that of the expression.
3751 and then
3756 then
3759 -- Remove side effects from the expression now so that other parts
3760 -- of the expander do not have to reanalyze this node without this
3761 -- optimization
3765 -- For controlled types, do the allocation on the secondary stack
3766 -- manually in order to call adjust at the right time:
3768 -- type Anon1 is access R_Type;
3769 -- for Anon1'Storage_pool use ss_pool;
3770 -- Anon2 : anon1 := new R_Type'(expr);
3771 -- return Anon2.all;
3773 -- We do the same for classwide types that are not potentially
3774 -- controlled (by the virtue of restriction No_Finalization) because
3775 -- gigi is not able to properly allocate class-wide types.
3778 declare
3788 begin
3793 Alloc_Node :=
3795 Expression =>
3803 Type_Definition =>
3805 Subtype_Indication =>
3820 -- Otherwise use the gigi mechanism to allocate result on the
3821 -- secondary stack.
3823 else
3826 -- If we are generating code for the VM do not use
3827 -- SS_Allocate since everything is heap-allocated anyway.
3835 -- Implement the rules of 6.5(8-10), which require a tag check in the
3836 -- case of a limited tagged return type, and tag reassignment for
3837 -- nonlimited tagged results. These actions are needed when the return
3838 -- type is a specific tagged type and the result expression is a
3839 -- conversion or a formal parameter, because in that case the tag of the
3840 -- expression might differ from the tag of the specific result type.
3845 N_Unchecked_Type_Conversion)
3848 then
3849 -- When the return type is limited, perform a check that the
3850 -- tag of the result is the same as the tag of the return type.
3855 Condition =>
3857 Left_Opnd =>
3860 Selector_Name =>
3862 Right_Opnd =>
3864 New_Reference_To
3867 Loc))),
3870 -- If the result type is a specific nonlimited tagged type, then we
3871 -- have to ensure that the tag of the result is that of the result
3872 -- type. This is handled by making a copy of the expression in the
3873 -- case where it might have a different tag, namely when the
3874 -- expression is a conversion or a formal parameter. We create a new
3875 -- object of the result type and initialize it from the expression,
3876 -- which will implicitly force the tag to be set appropriately.
3878 else
3879 declare
3888 Object_Definition =>
3893 begin
3902 -- Ada 2005 (AI-344): If the result type is class-wide, then insert
3903 -- a check that the level of the return expression's underlying type
3904 -- is not deeper than the level of the master enclosing the function.
3905 -- Always generate the check when the type of the return expression
3906 -- is class-wide, when it's a type conversion, or when it's a formal
3907 -- parameter. Otherwise, suppress the check in the case where the
3908 -- return expression has a specific type whose level is known not to
3909 -- be statically deeper than the function's result type.
3911 -- Note: accessibility check is skipped in the VM case, since there
3912 -- does not seem to be any practical way to implement this check.
3918 and then
3921 N_Unchecked_Type_Conversion)
3926 then
3927 declare
3930 begin
3931 -- Ada 2005 (AI-251): In class-wide interface objects we displace
3932 -- "this" to reference the base of the object --- required to get
3933 -- access to the TSD of the object.
3938 then
3939 Tag_Node :=
3947 else
3948 Tag_Node :=
3956 Condition =>
3958 Left_Opnd =>
3960 Right_Opnd =>
3968 ------------------------------
3969 -- Make_Tag_Ctrl_Assignment --
3970 ------------------------------
3983 -- Tags are not saved and restored when VM_Target because VM tags are
3984 -- represented implicitly in objects.
3993 begin
3996 -- Finalize the target of the assignment when controlled.
3997 -- We have two exceptions here:
3999 -- 1. If we are in an init proc since it is an initialization
4000 -- more than an assignment
4002 -- 2. If the left-hand side is a temporary that was not initialized
4003 -- (or the parent part of a temporary since it is the case in
4004 -- extension aggregates). Such a temporary does not come from
4005 -- source. We must examine the original node for the prefix, because
4006 -- it may be a component of an entry formal, in which case it has
4007 -- been rewritten and does not appear to come from source either.
4009 -- Case of init proc
4014 -- The left hand side is an uninitialized temporary
4019 then
4021 else
4023 Make_Final_Call (
4029 -- Save the Tag in a local variable Tag_Tmp
4032 Tag_Tmp :=
4039 Expression =>
4043 Loc))));
4045 -- Otherwise Tag_Tmp not used
4047 else
4054 -- Cannot assign part of the object in a VM context, so instead
4055 -- fallback to the previous mechanism, even though it is not
4056 -- completely correct ???
4058 -- Save the Finalization Pointers in local variables Prev_Tmp and
4059 -- Next_Tmp. For objects with Has_Controlled_Component set, these
4060 -- pointers are in the Record_Controller
4065 Ctrl_Ref :=
4068 Selector_Name =>
4072 Prev_Tmp :=
4079 Object_Definition =>
4082 Expression =>
4084 Prefix =>
4088 Next_Tmp :=
4096 Object_Definition =>
4099 Expression =>
4101 Prefix =>
4106 -- Do the Assignment
4110 else
4111 -- Regular (non VM) processing for controlled types and types with
4112 -- controlled components
4114 -- Variables of such types contain pointers used to chain them in
4115 -- finalization lists, in addition to user data. These pointers
4116 -- are specific to each object of the type, not to the value being
4117 -- assigned.
4119 -- Thus they need to be left intact during the assignment. We
4120 -- achieve this by constructing a Storage_Array subtype, and by
4121 -- overlaying objects of this type on the source and target of the
4122 -- assignment. The assignment is then rewritten to assignments of
4123 -- slices of these arrays, copying the user data, and leaving the
4124 -- pointers untouched.
4128 -- A reference to the Prev component of the record controller
4131 -- Index of first byte to be copied (used to skip
4132 -- Root_Controlled in controlled objects).
4135 -- Index of last byte to be copied before outermost record
4136 -- controller data.
4139 -- Length of record controller data (Prev and Next pointers)
4142 -- Index of first byte to be copied after outermost record
4143 -- controller data.
4147 -- Used for computation of the size of the data to be copied
4152 function Build_Slice
4156 -- Build and return a slice of an array of type S overlaid on
4157 -- object Rec, with bounds specified by Lo and Hi. If either
4158 -- bound is empty, a default of S'First (respectively S'Last)
4159 -- is used.
4161 -----------------
4162 -- Build_Slice --
4163 -----------------
4165 function Build_Slice
4169 is
4178 -- Access value designating an opaque storage array of type
4179 -- S overlaid on record Rec.
4181 begin
4182 -- Compute slice bounds using S'First (1) and S'Last as
4183 -- default values when not specified by the caller.
4187 else
4195 else
4200 Prefix =>
4201 Opaque,
4206 -- Start of processing for Controlled_Actions
4208 begin
4209 -- Create a constrained subtype of Storage_Array whose size
4210 -- corresponds to the value being assigned.
4212 -- subtype G is Storage_Offset range
4213 -- 1 .. (Expr'Size + Storage_Unit - 1) / Storage_Unit
4225 then
4231 Source_Size :=
4233 Left_Opnd =>
4235 Prefix =>
4238 Right_Opnd =>
4242 Source_Size :=
4245 Right_Opnd =>
4249 Range_Type :=
4256 Subtype_Indication =>
4258 Subtype_Mark =>
4261 Range_Expression =>
4266 -- subtype S is Storage_Array (G)
4270 Defining_Identifier =>
4273 Subtype_Indication =>
4275 Subtype_Mark =>
4277 Constraint =>
4279 Constraints =>
4282 -- type A is access S
4284 Opaque_Type :=
4291 Type_Definition =>
4293 Subtype_Indication =>
4294 New_Occurrence_Of (
4297 -- Generate appropriate slice assignments
4301 -- For the case of a controlled object, skip the
4302 -- Root_Controlled part.
4305 First_After_Root :=
4307 First_After_Root,
4310 Prefix =>
4316 -- For the case of a record with controlled components, skip
4317 -- the Prev and Next components of the record controller.
4318 -- These components constitute a 'hole' in the middle of the
4319 -- data to be copied.
4322 Prev_Ref :=
4324 Prefix =>
4327 Selector_Name =>
4331 -- Last index before hole: determined by position of
4332 -- the _Controller.Prev component.
4334 Last_Before_Hole :=
4352 -- Hole length: size of the Prev and Next components
4354 Hole_Length :=
4357 Right_Opnd =>
4359 Left_Opnd =>
4363 Right_Opnd =>
4367 -- First index after hole
4369 First_After_Hole :=
4379 Expression =>
4381 Left_Opnd =>
4383 Left_Opnd =>
4388 Last_Before_Hole :=
4390 First_After_Hole :=
4394 -- Assign the first slice (possibly skipping Root_Controlled,
4395 -- up to the beginning of the record controller if present,
4396 -- up to the end of the object if not).
4411 -- If a record controller is present, copy the second slice,
4412 -- from right after the _Controller.Next component up to the
4413 -- end of the object.
4428 else
4432 -- Restore the tag
4437 Name =>
4441 Loc)),
4447 -- Restore the finalization pointers
4451 Name =>
4453 Prefix =>
4461 Name =>
4463 Prefix =>
4470 -- Adjust the target after the assignment when controlled (not in the
4471 -- init proc since it is an initialization more than an assignment).
4474 Make_Adjust_Call (
4483 exception
4484 -- Could use comment here ???