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1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- E X P _ C H 5 --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 1992-2018, 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 procedure Build_Formal_Container_Iteration
74 -- Utility to create declarations and loop statement for both forms
75 -- of formal container iterators.
77 function Convert_To_Iterable_Type
80 -- Returns New_Occurrence_Of (Container), possibly converted to an ancestor
81 -- type, if the type of Container inherited the Iterable aspect from that
82 -- ancestor.
85 -- Determine if the right-hand side of assignment N is a type conversion
86 -- which requires a change of representation. Called only for the array
87 -- and record cases.
90 -- N is an assignment which assigns an array value. This routine process
91 -- the various special cases and checks required for such assignments,
92 -- including change of representation. Rhs is normally simply the right-
93 -- hand side of the assignment, except that if the right-hand side is a
94 -- type conversion or a qualified expression, then the RHS is the actual
95 -- expression inside any such type conversions or qualifications.
97 function Expand_Assign_Array_Loop
105 -- N is an assignment statement which assigns an array value. This routine
106 -- expands the assignment into a loop (or nested loops for the case of a
107 -- multi-dimensional array) to do the assignment component by component.
108 -- Larray and Rarray are the entities of the actual arrays on the left-hand
109 -- and right-hand sides. L_Type and R_Type are the types of these arrays
110 -- (which may not be the same, due to either sliding, or to a change of
111 -- representation case). Ndim is the number of dimensions and the parameter
112 -- Rev indicates if the loops run normally (Rev = False), or reversed
113 -- (Rev = True). The value returned is the constructed loop statement.
114 -- Auxiliary declarations are inserted before node N using the standard
115 -- Insert_Actions mechanism.
118 -- N is an assignment of an untagged record value. This routine handles
119 -- the case where the assignment must be made component by component,
120 -- either because the target is not byte aligned, or there is a change
121 -- of representation, or when we have a tagged type with a representation
122 -- clause (this last case is required because holes in the tagged type
123 -- might be filled with components from child types).
126 -- (AI12-0125): N is an assignment statement whose RHS contains occurrences
127 -- of @ that designate the value of the LHS of the assignment. If the LHS
128 -- is side-effect free the target names can be replaced with a copy of the
129 -- LHS; otherwise the semantics of the assignment is described in terms of
130 -- a procedure with an in-out parameter, and expanded as such.
133 -- Use the primitives specified in an Iterable aspect to expand a loop
134 -- over a so-called formal container, primarily for SPARK usage.
137 -- Same, for an iterator of the form " For E of C". In this case the
138 -- iterator provides the name of the element, and the cursor is generated
139 -- internally.
142 -- Expand loop over arrays and containers that uses the form "for X of C"
143 -- with an optional subtype mark, or "for Y in C".
145 procedure Expand_Iterator_Loop_Over_Container
151 -- Expand loop over containers that uses the form "for X of C" with an
152 -- optional subtype mark, or "for Y in C". Isc is the iteration scheme.
153 -- I_Spec is the iterator specification and Container is either the
154 -- Container (for OF) or the iterator (for IN).
157 -- Expand for loop over predicated subtype
160 -- Generate the necessary code for controlled and tagged assignment, that
161 -- is to say, finalization of the target before, adjustment of the target
162 -- after and save and restore of the tag and finalization pointers which
163 -- are not 'part of the value' and must not be changed upon assignment. N
164 -- is the original Assignment node.
166 --------------------------------------
167 -- Build_Formal_Container_Iteration --
168 --------------------------------------
170 procedure Build_Formal_Container_Iteration
177 is
188 begin
189 -- Use the proper set of primitives depending on the direction of
190 -- iteration. The legality of a reverse iteration has been checked
191 -- during analysis.
197 else
202 -- Declaration for Cursor
204 Init :=
208 Expression =>
214 -- Statement that advances (in the right direction) cursor in loop
216 Advance :=
219 Expression =>
226 -- Iterator is rewritten as a while_loop
228 New_Loop :=
230 Iteration_Scheme =>
232 Condition =>
241 -- If the contruct has a specified loop name, preserve it in the new
242 -- loop, for possible use in exit statements.
246 then
251 ------------------------------
252 -- Change_Of_Representation --
253 ------------------------------
257 begin
258 return
260 and then
264 ------------------------------
265 -- Convert_To_Iterable_Type --
266 ------------------------------
268 function Convert_To_Iterable_Type
271 is
276 begin
280 Result :=
289 -------------------------
290 -- Expand_Assign_Array --
291 -------------------------
293 -- There are two issues here. First, do we let Gigi do a block move, or
294 -- do we expand out into a loop? Second, we need to set the two flags
295 -- Forwards_OK and Backwards_OK which show whether the block move (or
296 -- corresponding loops) can be legitimately done in a forwards (low to
297 -- high) or backwards (high to low) manner.
323 -- This switch is set to True if the array move must be done using
324 -- an explicit front end generated loop.
327 -- If the argument is an access to an array, and the assignment is
328 -- converted into a procedure call, apply explicit dereference.
331 -- Test if Exp is a reference to an array whose declaration has
332 -- an address clause, or it is a slice of such an array.
335 -- Test if Exp is a reference to an array which is either a formal
336 -- parameter or a slice of a formal parameter. These are the cases
337 -- where hidden aliasing can occur.
340 -- Determine if Exp is a reference to an array variable which is other
341 -- than an object defined in the current scope, or a component or a
342 -- slice of such an object. Such objects can be aliased to parameters
343 -- (unlike local array references).
345 -----------------------
346 -- Apply_Dereference --
347 -----------------------
351 begin
359 ------------------------
360 -- Has_Address_Clause --
361 ------------------------
364 begin
365 return
368 or else
372 ---------------------
373 -- Is_Formal_Array --
374 ---------------------
377 begin
378 return
380 or else
384 ------------------------
385 -- Is_Non_Local_Array --
386 ------------------------
389 begin
391 when N_Indexed_Component
392 | N_Selected_Component
393 | N_Slice
394 =>
398 return
404 -- Determine if Lhs, Rhs are formal arrays or nonlocal arrays
412 -- Start of processing for Expand_Assign_Array
414 begin
415 -- Deal with length check. Note that the length check is done with
416 -- respect to the right-hand side as given, not a possible underlying
417 -- renamed object, since this would generate incorrect extra checks.
421 -- We start by assuming that the move can be done in either direction,
422 -- i.e. that the two sides are completely disjoint.
427 -- Normally it is only the slice case that can lead to overlap, and
428 -- explicit checks for slices are made below. But there is one case
429 -- where the slice can be implicit and invisible to us: when we have a
430 -- one dimensional array, and either both operands are parameters, or
431 -- one is a parameter (which can be a slice passed by reference) and the
432 -- other is a non-local variable. In this case the parameter could be a
433 -- slice that overlaps with the other operand.
435 -- However, if the array subtype is a constrained first subtype in the
436 -- parameter case, then we don't have to worry about overlap, since
437 -- slice assignments aren't possible (other than for a slice denoting
438 -- the whole array).
440 -- Note: No overlap is possible if there is a change of representation,
441 -- so we can exclude this case.
444 and then not Crep
445 and then
447 or else
449 or else
451 and then
454 then
458 -- Note: the bit-packed case is not worrisome here, since if we have
459 -- a slice passed as a parameter, it is always aligned on a byte
460 -- boundary, and if there are no explicit slices, the assignment
461 -- can be performed directly.
464 -- If either operand has an address clause clear Backwards_OK and
465 -- Forwards_OK, since we cannot tell if the operands overlap. We
466 -- exclude this treatment when Rhs is an aggregate, since we know
467 -- that overlap can't occur.
471 then
476 -- We certainly must use a loop for change of representation and also
477 -- we use the operand of the conversion on the right-hand side as the
478 -- effective right-hand side (the component types must match in this
479 -- situation).
486 -- We require a loop if the left side is possibly bit unaligned
489 or else
491 then
494 -- Arrays with controlled components are expanded into a loop to force
495 -- calls to Adjust at the component level.
500 -- If object is atomic/VFA, we cannot tolerate a loop
503 or else
505 then
508 -- Loop is required if we have atomic components since we have to
509 -- be sure to do any accesses on an element by element basis.
515 then
518 -- Case where no slice is involved
522 -- The following code deals with the case of unconstrained bit packed
523 -- arrays. The problem is that the template for such arrays contains
524 -- the bounds of the actual source level array, but the copy of an
525 -- entire array requires the bounds of the underlying array. It would
526 -- be nice if the back end could take care of this, but right now it
527 -- does not know how, so if we have such a type, then we expand out
528 -- into a loop, which is inefficient but works correctly. If we don't
529 -- do this, we get the wrong length computed for the array to be
530 -- moved. The two cases we need to worry about are:
532 -- Explicit dereference of an unconstrained packed array type as in
533 -- the following example:
535 -- procedure C52 is
536 -- type BITS is array(INTEGER range <>) of BOOLEAN;
537 -- pragma PACK(BITS);
538 -- type A is access BITS;
539 -- P1,P2 : A;
540 -- begin
541 -- P1 := new BITS (1 .. 65_535);
542 -- P2 := new BITS (1 .. 65_535);
543 -- P2.ALL := P1.ALL;
544 -- end C52;
546 -- A formal parameter reference with an unconstrained bit array type
547 -- is the other case we need to worry about (here we assume the same
548 -- BITS type declared above):
550 -- procedure Write_All (File : out BITS; Contents : BITS);
551 -- begin
552 -- File.Storage := Contents;
553 -- end Write_All;
555 -- We expand to a loop in either of these two cases
557 -- Question for future thought. Another potentially more efficient
558 -- approach would be to create the actual subtype, and then do an
559 -- unchecked conversion to this actual subtype ???
564 -- Function to perform required test for the first case, above
565 -- (dereference of an unconstrained bit packed array).
567 -----------------------
568 -- Is_UBPA_Reference --
569 -----------------------
576 begin
580 then
589 else
591 return
596 else
601 -- Start of processing for Check_Unconstrained_Bit_Packed_Array
603 begin
605 or else
607 then
610 -- Here if we do not have the case of a reference to a bit packed
611 -- unconstrained array case. In this case gigi can most certainly
612 -- handle the assignment if a forwards move is allowed.
614 -- (could it handle the backwards case also???)
621 -- The back end can always handle the assignment if the right side is a
622 -- string literal (note that overlap is definitely impossible in this
623 -- case). If the type is packed, a string literal is always converted
624 -- into an aggregate, except in the case of a null slice, for which no
625 -- aggregate can be written. In that case, rewrite the assignment as a
626 -- null statement, a length check has already been emitted to verify
627 -- that the range of the left-hand side is empty.
629 -- Note that this code is not executed if we have an assignment of a
630 -- string literal to a non-bit aligned component of a record, a case
631 -- which cannot be handled by the backend.
636 then
643 -- If either operand is bit packed, then we need a loop, since we can't
644 -- be sure that the slice is byte aligned. Similarly, if either operand
645 -- is a possibly unaligned slice, then we need a loop (since the back
646 -- end cannot handle unaligned slices).
652 then
655 -- If we are not bit-packed, and we have only one slice, then no overlap
656 -- is possible except in the parameter case, so we can let the back end
657 -- handle things.
665 -- If the right-hand side is a string literal, introduce a temporary for
666 -- it, for use in the generated loop that will follow.
669 declare
673 begin
674 Decl :=
686 -- Come here to complete the analysis
688 -- Loop_Required: Set to True if we know that a loop is required
689 -- regardless of overlap considerations.
691 -- Forwards_OK: Set to False if we already know that a forwards
692 -- move is not safe, else set to True.
694 -- Backwards_OK: Set to False if we already know that a backwards
695 -- move is not safe, else set to True
697 -- Our task at this stage is to complete the overlap analysis, which can
698 -- result in possibly setting Forwards_OK or Backwards_OK to False, and
699 -- then generating the final code, either by deciding that it is OK
700 -- after all to let Gigi handle it, or by generating appropriate code
701 -- in the front end.
703 declare
721 begin
722 -- Get the expressions for the arrays. If we are dealing with a
723 -- private type, then convert to the underlying type. We can do
724 -- direct assignments to an array that is a private type, but we
725 -- cannot assign to elements of the array without this extra
726 -- unchecked conversion.
728 -- Note: We propagate Parent to the conversion nodes to generate
729 -- a well-formed subtree.
733 else
737 declare
739 begin
740 Larray :=
741 Unchecked_Convert_To
750 else
754 declare
756 begin
757 Rarray :=
758 Unchecked_Convert_To
765 -- If both sides are slices, we must figure out whether it is safe
766 -- to do the move in one direction or the other. It is always safe
767 -- if there is a change of representation since obviously two arrays
768 -- with different representations cannot possibly overlap.
774 -- If both left- and right-hand arrays are entity names, and refer
775 -- to different entities, then we know that the move is safe (the
776 -- two storage areas are completely disjoint).
781 then
784 -- Otherwise, we assume the worst, which is that the two arrays
785 -- are the same array. There is no need to check if we know that
786 -- is the case, because if we don't know it, we still have to
787 -- assume it.
789 -- Generally if the same array is involved, then we have an
790 -- overlapping case. We will have to really assume the worst (i.e.
791 -- set neither of the OK flags) unless we can determine the lower
792 -- or upper bounds at compile time and compare them.
794 else
795 Cresult :=
796 Compile_Time_Compare
800 Cresult :=
801 Compile_Time_Compare
819 -- If after that analysis Loop_Required is False, meaning that we
820 -- have not discovered some non-overlap reason for requiring a loop,
821 -- then the outcome depends on the capabilities of the back end.
824 -- Assume the back end can deal with all cases of overlap by
825 -- falling back to memmove if it cannot use a more efficient
826 -- approach.
831 -- At this stage we have to generate an explicit loop, and we have
832 -- the following cases:
834 -- Forwards_OK = True
836 -- Rnn : right_index := right_index'First;
837 -- for Lnn in left-index loop
838 -- left (Lnn) := right (Rnn);
839 -- Rnn := right_index'Succ (Rnn);
840 -- end loop;
842 -- Note: the above code MUST be analyzed with checks off, because
843 -- otherwise the Succ could overflow. But in any case this is more
844 -- efficient.
846 -- Forwards_OK = False, Backwards_OK = True
848 -- Rnn : right_index := right_index'Last;
849 -- for Lnn in reverse left-index loop
850 -- left (Lnn) := right (Rnn);
851 -- Rnn := right_index'Pred (Rnn);
852 -- end loop;
854 -- Note: the above code MUST be analyzed with checks off, because
855 -- otherwise the Pred could overflow. But in any case this is more
856 -- efficient.
858 -- Forwards_OK = Backwards_OK = False
860 -- This only happens if we have the same array on each side. It is
861 -- possible to create situations using overlays that violate this,
862 -- but we simply do not promise to get this "right" in this case.
864 -- There are two possible subcases. If the No_Implicit_Conditionals
865 -- restriction is set, then we generate the following code:
867 -- declare
868 -- T : constant <operand-type> := rhs;
869 -- begin
870 -- lhs := T;
871 -- end;
873 -- If implicit conditionals are permitted, then we generate:
875 -- if Left_Lo <= Right_Lo then
876 -- <code for Forwards_OK = True above>
877 -- else
878 -- <code for Backwards_OK = True above>
879 -- end if;
881 -- In order to detect possible aliasing, we examine the renamed
882 -- expression when the source or target is a renaming. However,
883 -- the renaming may be intended to capture an address that may be
884 -- affected by subsequent code, and therefore we must recover
885 -- the actual entity for the expansion that follows, not the
886 -- object it renames. In particular, if source or target designate
887 -- a portion of a dynamically allocated object, the pointer to it
888 -- may be reassigned but the renaming preserves the proper location.
891 and then
894 then
899 and then
902 then
906 -- Cases where either Forwards_OK or Backwards_OK is true
913 then
914 declare
919 begin
931 New_Occurrence_Of (
940 else
942 Expand_Assign_Array_Loop
947 -- Case of both are false with No_Implicit_Conditionals
950 declare
954 begin
961 Object_Definition =>
965 Handled_Statement_Sequence =>
973 -- Case of both are false with implicit conditionals allowed
975 else
976 -- Before we generate this code, we must ensure that the left and
977 -- right side array types are defined. They may be itypes, and we
978 -- cannot let them be defined inside the if, since the first use
979 -- in the then may not be executed.
984 -- We normally compare addresses to find out which way round to
985 -- do the loop, since this is reliable, and handles the cases of
986 -- parameters, conversions etc. But we can't do that in the bit
987 -- packed case, because addresses don't work there.
990 Condition :=
992 Left_Opnd =>
995 Prefix =>
997 Prefix =>
1001 Prefix =>
1002 New_Occurrence_Of
1007 Right_Opnd =>
1010 Prefix =>
1012 Prefix =>
1016 Prefix =>
1017 New_Occurrence_Of
1022 -- For the bit packed and VM cases we use the bounds. That's OK,
1023 -- because we don't have to worry about parameters, since they
1024 -- cannot cause overlap. Perhaps we should worry about weird slice
1025 -- conversions ???
1027 else
1028 -- Copy the bounds
1033 -- If the types do not match we add an implicit conversion
1034 -- here to ensure proper match
1037 Cright_Lo :=
1041 -- Reset the Analyzed flag, because the bounds of the index
1042 -- type itself may be universal, and must must be reanalyzed
1043 -- to acquire the proper type for the back end.
1048 Condition :=
1058 then
1060 -- Call TSS procedure for array assignment, passing the
1061 -- explicit bounds of right- and left-hand sides.
1063 declare
1068 begin
1089 else
1095 Expand_Assign_Array_Loop
1100 Expand_Assign_Array_Loop
1109 exception
1114 ------------------------------
1115 -- Expand_Assign_Array_Loop --
1116 ------------------------------
1118 -- The following is an example of the loop generated for the case of a
1119 -- two-dimensional array:
1121 -- declare
1122 -- R2b : Tm1X1 := 1;
1123 -- begin
1124 -- for L1b in 1 .. 100 loop
1125 -- declare
1126 -- R4b : Tm1X2 := 1;
1127 -- begin
1128 -- for L3b in 1 .. 100 loop
1129 -- vm1 (L1b, L3b) := vm2 (R2b, R4b);
1130 -- R4b := Tm1X2'succ(R4b);
1131 -- end loop;
1132 -- end;
1133 -- R2b := Tm1X1'succ(R2b);
1134 -- end loop;
1135 -- end;
1137 -- Here Rev is False, and Tm1Xn are the subscript types for the right-hand
1138 -- side. The declarations of R2b and R4b are inserted before the original
1139 -- assignment statement.
1141 function Expand_Assign_Array_Loop
1149 is
1154 -- Entities used as subscripts on left and right sides
1158 -- Left and right index types
1166 -- The increment step for the index of the right-hand side is written
1167 -- as an attribute reference (Succ or Pred). This function returns
1168 -- the corresponding node, which is placed at the end of the loop body.
1170 ----------------
1171 -- Build_Step --
1172 ----------------
1178 begin
1181 else
1185 Step :=
1188 Expression =>
1190 Prefix =>
1196 -- Note that on the last iteration of the loop, the index is increased
1197 -- (or decreased) past the corresponding bound. This is consistent with
1198 -- the C semantics of the back-end, where such an off-by-one value on a
1199 -- dead index variable is OK. However, in CodePeer mode this leads to
1200 -- spurious warnings, and thus we place a guard around the attribute
1201 -- reference. For obvious reasons we only do this for CodePeer.
1204 Step :=
1206 Condition =>
1209 Right_Opnd =>
1219 -- Start of processing for Expand_Assign_Array_Loop
1221 begin
1225 else
1230 -- Setup index types and subscript entities
1232 declare
1236 begin
1252 -- Now construct the assignment statement
1254 declare
1258 begin
1264 Assign :=
1266 Name =>
1270 Expression =>
1275 -- We set assignment OK, since there are some cases, e.g. in object
1276 -- declarations, where we are actually assigning into a constant.
1277 -- If there really is an illegality, it was caught long before now,
1278 -- and was flagged when the original assignment was analyzed.
1282 -- Propagate the No_Ctrl_Actions flag to individual assignments
1287 -- Now construct the loop from the inside out, with the last subscript
1288 -- varying most rapidly. Note that Assign is first the raw assignment
1289 -- statement, and then subsequently the loop that wraps it up.
1292 Assign :=
1297 Object_Definition =>
1299 Expression =>
1304 Handled_Statement_Sequence =>
1308 Iteration_Scheme =>
1310 Loop_Parameter_Specification =>
1314 Discrete_Subtype_Definition =>
1323 --------------------------
1324 -- Expand_Assign_Record --
1325 --------------------------
1332 begin
1333 -- If change of representation, then extract the real right-hand side
1334 -- from the type conversion, and proceed with component-wise assignment,
1335 -- since the two types are not the same as far as the back end is
1336 -- concerned.
1341 -- If this may be a case of a large bit aligned component, then proceed
1342 -- with component-wise assignment, to avoid possible clobbering of other
1343 -- components sharing bits in the first or last byte of the component to
1344 -- be assigned.
1347 or
1349 then
1352 -- If we have a tagged type that has a complete record representation
1353 -- clause, we must do we must do component-wise assignments, since child
1354 -- types may have used gaps for their components, and we might be
1355 -- dealing with a view conversion.
1360 -- If neither condition met, then nothing special to do, the back end
1361 -- can handle assignment of the entire component as a single entity.
1363 else
1367 -- At this stage we know that we must do a component wise assignment
1369 declare
1376 function Find_Component
1379 -- Find the component with the given name in the underlying record
1380 -- declaration for Typ. We need to use the actual entity because the
1381 -- type may be private and resolution by identifier alone would fail.
1383 function Make_Component_List_Assign
1386 -- Returns a sequence of statements to assign the components that
1387 -- are referenced in the given component list. The flag U_U is
1388 -- used to force the usage of the inferred value of the variant
1389 -- part expression as the switch for the generated case statement.
1391 function Make_Field_Assign
1394 -- Given C, the entity for a discriminant or component, build an
1395 -- assignment for the corresponding field values. The flag U_U
1396 -- signals the presence of an Unchecked_Union and forces the usage
1397 -- of the inferred discriminant value of C as the right-hand side
1398 -- of the assignment.
1401 -- Given CI, a component items list, construct series of statements
1402 -- for fieldwise assignment of the corresponding components.
1404 --------------------
1405 -- Find_Component --
1406 --------------------
1408 function Find_Component
1411 is
1415 begin
1428 --------------------------------
1429 -- Make_Component_List_Assign --
1430 --------------------------------
1432 function Make_Component_List_Assign
1435 is
1446 begin
1463 Statements =>
1468 -- If we have an Unchecked_Union, use the value of the inferred
1469 -- discriminant of the variant part expression as the switch
1470 -- for the case statement. The case statement may later be
1471 -- folded.
1474 Expr :=
1479 else
1480 Expr :=
1483 Selector_Name =>
1496 -----------------------
1497 -- Make_Field_Assign --
1498 -----------------------
1500 function Make_Field_Assign
1503 is
1508 begin
1509 -- The discriminant entity to be used in the retrieval below must
1510 -- be one in the corresponding type, given that the assignment may
1511 -- be between derived and parent types.
1515 else
1519 -- In the case of an Unchecked_Union, use the discriminant
1520 -- constraint value as on the right-hand side of the assignment.
1523 Expr :=
1527 else
1528 Expr :=
1534 A :=
1536 Name =>
1539 Selector_Name =>
1543 -- Set Assignment_OK, so discriminants can be assigned
1550 then
1557 ------------------------
1558 -- Make_Field_Assigns --
1559 ------------------------
1565 begin
1571 -- Look for components, but exclude _tag field assignment if
1572 -- the special Componentwise_Assignment flag is set.
1577 then
1578 Append_To
1588 -- Start of processing for Expand_Assign_Record
1590 begin
1591 -- Note that we use the base types for this processing. This results
1592 -- in some extra work in the constrained case, but the change of
1593 -- representation case is so unusual that it is not worth the effort.
1595 -- First copy the discriminants. This is done unconditionally. It
1596 -- is required in the unconstrained left side case, and also in the
1597 -- case where this assignment was constructed during the expansion
1598 -- of a type conversion (since initialization of discriminants is
1599 -- suppressed in this case). It is unnecessary but harmless in
1600 -- other cases.
1602 -- Special case: no copy if the target has no discriminants
1606 then
1613 -- If we are expanding the initialization of a derived record
1614 -- that constrains or renames discriminants of the parent, we
1615 -- must use the corresponding discriminant in the parent.
1617 declare
1620 begin
1621 if Inside_Init_Proc
1623 then
1625 else
1631 -- Within an initialization procedure this is the
1632 -- assignment to an unchecked union component, in which
1633 -- case there is no discriminant to initialize.
1638 else
1639 -- The assignment is part of a conversion from a
1640 -- derived unchecked union type with an inferable
1641 -- discriminant, to a parent type.
1646 else
1654 -- If the derived type has a stored constraint, assign the value
1655 -- of the corresponding discriminants explicitly, skipping those
1656 -- that are renamed discriminants. We cannot just retrieve them
1657 -- from the Rhs by selected component because they are invisible
1658 -- in the type of the right-hand side.
1661 declare
1665 begin
1672 and then
1675 E_Discriminant)
1676 then
1677 Assign :=
1679 Name =>
1682 Selector_Name =>
1683 New_Occurrence_Of
1698 -- We know the underlying type is a record, but its current view
1699 -- may be private. We must retrieve the usable record declaration.
1702 N_Private_Extension_Declaration)
1704 then
1706 else
1716 then
1720 else
1721 Insert_Actions
1730 -------------------------------------
1731 -- Expand_Assign_With_Target_Names --
1732 -------------------------------------
1741 -- The entity of the left-hand side
1744 -- Replace occurrences of the target name by the proper entity: either
1745 -- the entity of the LHS in simple cases, or the formal of the
1746 -- constructed procedure otherwise.
1748 --------------------
1749 -- Replace_Target --
1750 --------------------
1753 begin
1757 -- The expression will be reanalyzed when the enclosing assignment
1758 -- is reanalyzed, so reset the entity, which may be a temporary
1759 -- created during analysis, e.g. a loop variable for an iterated
1760 -- component association. However, if entity is callable then
1761 -- resolution has established its proper identity (including in
1762 -- rewritten prefixed calls) so we must preserve it.
1767 then
1778 -- Local variables
1783 -- Start of processing for Expand_Assign_With_Target_Names
1785 begin
1788 -- The left-hand side is a direct name
1792 then
1796 -- Generate:
1797 -- LHS := ... LHS ...;
1804 -- The left-hand side is not a direct name, but is side-effect free.
1805 -- Capture its value in a temporary to avoid multiple evaluations.
1811 -- Generate:
1812 -- T : LHS_Typ := LHS;
1820 -- Generate:
1821 -- LHS := ... T ...;
1828 -- Otherwise wrap the whole assignment statement in a procedure with an
1829 -- IN OUT parameter. The original assignment then becomes a call to the
1830 -- procedure with the left-hand side as an actual.
1832 else
1836 -- Generate:
1837 -- procedure P (T : in out LHS_Typ) is
1838 -- begin
1839 -- T := ... T ...;
1840 -- end P;
1846 Specification =>
1854 Parameter_Type =>
1859 Handled_Statement_Sequence =>
1866 -- Generate:
1867 -- P (LHS);
1875 -- Analyze rewritten node, either as assignment or procedure call
1880 -----------------------------------
1881 -- Expand_N_Assignment_Statement --
1882 -----------------------------------
1884 -- This procedure implements various cases where an assignment statement
1885 -- cannot just be passed on to the back end in untransformed state.
1895 begin
1896 -- Special case to check right away, if the Componentwise_Assignment
1897 -- flag is set, this is a reanalysis from the expansion of the primitive
1898 -- assignment procedure for a tagged type, and all we need to do is to
1899 -- expand to assignment of components, because otherwise, we would get
1900 -- infinite recursion (since this looks like a tagged assignment which
1901 -- would normally try to *call* the primitive assignment procedure).
1908 -- Defend against invalid subscripts on left side if we are in standard
1909 -- validity checking mode. No need to do this if we are checking all
1910 -- subscripts.
1912 -- Note that we do this right away, because there are some early return
1913 -- paths in this procedure, and this is required on all paths.
1915 if Validity_Checks_On
1916 and then Validity_Check_Default
1917 and then not Validity_Check_Subscripts
1918 then
1922 -- Separate expansion if RHS contain target names. Note that assignment
1923 -- may already have been expanded if RHS is aggregate.
1930 -- Ada 2005 (AI-327): Handle assignment to priority of protected object
1932 -- Rewrite an assignment to X'Priority into a run-time call
1934 -- For example: X'Priority := New_Prio_Expr;
1935 -- ...is expanded into Set_Ceiling (X._Object, New_Prio_Expr);
1937 -- Note that although X'Priority is notionally an object, it is quite
1938 -- deliberately not defined as an aliased object in the RM. This means
1939 -- that it works fine to rewrite it as a call, without having to worry
1940 -- about complications that would other arise from X'Priority'Access,
1941 -- which is illegal, because of the lack of aliasing.
1944 declare
1951 begin
1952 -- Handle chains of renamings
1958 loop
1962 -- The attribute Priority applied to protected objects has been
1963 -- previously expanded into a call to the Get_Ceiling run-time
1964 -- subprogram. In restricted profiles this is not available.
1968 -- Look for the enclosing concurrent type
1977 -- Generate the first actual of the call
1984 -- Select the appropriate run-time call
1987 RT_Subprg_Name :=
1989 else
1990 RT_Subprg_Name :=
1994 Call :=
2009 -- Deal with assignment checks unless suppressed
2013 -- First deal with generation of range check if required
2019 -- Then generate predicate check if required
2024 -- Check for a special case where a high level transformation is
2025 -- required. If we have either of:
2027 -- P.field := rhs;
2028 -- P (sub) := rhs;
2030 -- where P is a reference to a bit packed array, then we have to unwind
2031 -- the assignment. The exact meaning of being a reference to a bit
2032 -- packed array is as follows:
2034 -- An indexed component whose prefix is a bit packed array is a
2035 -- reference to a bit packed array.
2037 -- An indexed component or selected component whose prefix is a
2038 -- reference to a bit packed array is itself a reference ot a
2039 -- bit packed array.
2041 -- The required transformation is
2043 -- Tnn : prefix_type := P;
2044 -- Tnn.field := rhs;
2045 -- P := Tnn;
2047 -- or
2049 -- Tnn : prefix_type := P;
2050 -- Tnn (subscr) := rhs;
2051 -- P := Tnn;
2053 -- Since P is going to be evaluated more than once, any subscripts
2054 -- in P must have their evaluation forced.
2058 then
2059 declare
2065 begin
2066 -- Insert the post assignment first, because we want to copy the
2067 -- BPAR_Expr tree before it gets analyzed in the context of the
2068 -- pre assignment. Note that we do not analyze the post assignment
2069 -- yet (we cannot till we have completed the analysis of the pre
2070 -- assignment). As usual, the analysis of this post assignment
2071 -- will happen on its own when we "run into" it after finishing
2072 -- the current assignment.
2079 -- At this stage BPAR_Expr is a reference to a bit packed array
2080 -- where the reference was not expanded in the original tree,
2081 -- since it was on the left side of an assignment. But in the
2082 -- pre-assignment statement (the object definition), BPAR_Expr
2083 -- will end up on the right-hand side, and must be reexpanded. To
2084 -- achieve this, we reset the analyzed flag of all selected and
2085 -- indexed components down to the actual indexed component for
2086 -- the packed array.
2089 loop
2093 N_Selected_Component)
2094 then
2096 else
2101 -- Now we can insert and analyze the pre-assignment
2103 -- If the right-hand side requires a transient scope, it has
2104 -- already been placed on the stack. However, the declaration is
2105 -- inserted in the tree outside of this scope, and must reflect
2106 -- the proper scope for its variable. This awkward bit is forced
2107 -- by the stricter scope discipline imposed by GCC 2.97.
2109 declare
2111 Scope_Is_Transient
2114 begin
2126 Pop_Scope;
2130 -- Now fix up the original assignment and continue processing
2135 -- We do not need to reanalyze that assignment, and we do not need
2136 -- to worry about references to the temporary, but we do need to
2137 -- make sure that the temporary is not marked as a true constant
2138 -- since we now have a generated assignment to it.
2144 -- When we have the appropriate type of aggregate in the expression (it
2145 -- has been determined during analysis of the aggregate by setting the
2146 -- delay flag), let's perform in place assignment and thus avoid
2147 -- creating a temporary.
2157 -- Apply discriminant check if required. If Lhs is an access type to a
2158 -- designated type with discriminants, we must always check. If the
2159 -- type has unknown discriminants, more elaborate processing below.
2163 then
2164 -- Skip discriminant check if change of representation. Will be
2165 -- done when the change of representation is expanded out.
2171 -- If the type is private without discriminants, and the full type
2172 -- has discriminants (necessarily with defaults) a check may still be
2173 -- necessary if the Lhs is aliased. The private discriminants must be
2174 -- visible to build the discriminant constraints.
2176 -- Only an explicit dereference that comes from source indicates
2177 -- aliasing. Access to formals of protected operations and entries
2178 -- create dereferences but are not semantic aliasings.
2184 then
2185 declare
2189 begin
2190 -- In the case of an expander-generated record subtype whose base
2191 -- type still appears private, Typ will have been set to that
2192 -- private type rather than the underlying record type (because
2193 -- Underlying type will have returned the record subtype), so it's
2194 -- necessary to apply Underlying_Type again to the base type to
2195 -- get the record type we need for the discriminant check. Such
2196 -- subtypes can be created for assignments in certain cases, such
2197 -- as within an instantiation passed this kind of private type.
2198 -- It would be good to avoid this special test, but making changes
2199 -- to prevent this odd form of record subtype seems difficult. ???
2211 -- If the Lhs has a private type with unknown discriminants, it may
2212 -- have a full view with discriminants, but those are nameable only
2213 -- in the underlying type, so convert the Rhs to it before potential
2214 -- checking. Convert Lhs as well, otherwise the actual subtype might
2215 -- not be constructible. If the discriminants have defaults the type
2216 -- is unconstrained and there is nothing to check.
2221 then
2226 -- In the access type case, we need the same discriminant check, and
2227 -- also range checks if we have an access to constrained array.
2231 then
2234 -- Skip discriminant check if change of representation. Will be
2235 -- done when the change of representation is expanded out.
2249 declare
2253 begin
2254 C_Es :=
2255 Get_Range_Checks
2257 Target_Typ,
2260 Insert_Range_Checks
2262 N,
2263 Target_Typ,
2265 Lhs);
2270 -- Apply range check for access type case
2275 then
2277 Apply_Range_Check
2281 -- Ada 2005 (AI-231): Generate the run-time check
2287 -- If an actual is an out parameter of a null-excluding access
2288 -- type, there is access check on entry, so we set the flag
2289 -- Suppress_Assignment_Checks on the generated statement to
2290 -- assign the actual to the parameter block, and we do not want
2291 -- to generate an additional check at this point.
2294 then
2298 -- Ada 2012 (AI05-148): Update current accessibility level if Rhs is a
2299 -- stand-alone obj of an anonymous access type. Do not install the check
2300 -- when the Lhs denotes a container cursor and the Next function employs
2301 -- an access type, because this can never result in a dangling pointer.
2307 then
2308 declare
2310 -- Look through renames to find the underlying entity.
2311 -- For assignment to a rename, we don't care about the
2312 -- Enclosing_Dynamic_Scope of the rename declaration.
2314 ----------------
2315 -- Lhs_Entity --
2316 ----------------
2321 begin
2324 -- Renamed_Object must return an Entity_Name here
2325 -- because of preceding "Present (E_E_A (...))" test.
2333 -- Local Declarations
2337 Condition =>
2339 Left_Opnd =>
2341 Right_Opnd =>
2343 Intval =>
2344 Scope_Depth
2345 (Enclosing_Dynamic_Scope
2351 Name =>
2352 New_Occurrence_Of
2353 (Effective_Extra_Accessibility
2355 Expression =>
2358 begin
2367 -- Case of assignment to a bit packed array element. If there is a
2368 -- change of representation this must be expanded into components,
2369 -- otherwise this is a bit-field assignment.
2373 then
2374 -- Normal case, no change of representation
2380 -- Change of representation case
2382 else
2383 -- Generate the following, to force component-by-component
2384 -- assignments in an efficient way. Otherwise each component
2385 -- will require a temporary and two bit-field manipulations.
2387 -- T1 : Elmt_Type;
2388 -- T1 := RhS;
2389 -- Lhs := T1;
2391 declare
2395 begin
2396 Stats :=
2397 New_List (
2400 Object_Definition =>
2415 -- Build-in-place function call case. This is for assignment statements
2416 -- that come from aggregate component associations or from init procs.
2417 -- User-written assignment statements with b-i-p calls are handled
2418 -- elsewhere.
2426 then
2431 begin
2432 -- In the controlled case, we ensure that function calls are
2433 -- evaluated before finalizing the target. In all cases, it makes
2434 -- the expansion easier if the side effects are removed first.
2439 -- Avoid recursion in the mechanism
2443 -- If dispatching assignment, we need to dispatch to _assign
2447 -- If the type is tagged, we may as well use the predefined
2448 -- primitive assignment. This avoids inlining a lot of code
2449 -- and in the class-wide case, the assignment is replaced
2450 -- by a dispatching call to _assign. It is suppressed in the
2451 -- case of assignments created by the expander that correspond
2452 -- to initializations, where we do want to copy the tag
2453 -- (Expand_Ctrl_Actions flag is set False in this case). It is
2454 -- also suppressed if restriction No_Dispatching_Calls is in
2455 -- force because in that case predefined primitives are not
2456 -- generated.
2460 and then Expand_Ctrl_Actions
2461 and then
2463 then
2466 -- This can happen in an instance when the formal is an
2467 -- extension of a limited interface, and the actual is
2468 -- limited. This is an error according to AI05-0087, but
2469 -- is not caught at the point of instantiation in earlier
2470 -- versions. We also must verify that the limited type does
2471 -- not come from source as corner cases may exist where
2472 -- an assignment was not intended like the pathological case
2473 -- of a raise expression within a return statement.
2475 -- This is wrong, error messages cannot be issued during
2476 -- expansion, since they would be missed in -gnatc mode ???
2479 Error_Msg_N
2486 -- Fetch the primitive op _assign and proper type to call it.
2487 -- Because of possible conflicts between private and full view,
2488 -- fetch the proper type directly from the operation profile.
2490 declare
2495 begin
2496 -- If the assignment is dispatching, make sure to use the
2497 -- proper type.
2505 -- In case of assignment to a class-wide tagged type, before
2506 -- the assignment we generate run-time check to ensure that
2507 -- the tags of source and target match.
2513 then
2514 declare
2518 begin
2520 Lhs_Tag :=
2523 Selector_Name =>
2525 Rhs_Tag :=
2528 Selector_Name =>
2530 else
2531 -- Displace the pointer to the base of the objects
2532 -- applying 'Address, which is later expanded into
2533 -- a call to RE_Base_Address.
2535 Lhs_Tag :=
2537 Prefix =>
2542 Rhs_Tag :=
2544 Prefix =>
2553 Condition =>
2561 declare
2565 begin
2566 -- In order to dispatch the call to _assign the type of
2567 -- the actuals must match. Add conversion (if required).
2586 else
2589 -- We can't afford to have destructive Finalization Actions in
2590 -- the Self assignment case, so if the target and the source
2591 -- are not obviously different, code is generated to avoid the
2592 -- self assignment case:
2594 -- if lhs'address /= rhs'address then
2595 -- <code for controlled and/or tagged assignment>
2596 -- end if;
2598 -- Skip this if Restriction (No_Finalization) is active
2601 and then Expand_Ctrl_Actions
2603 then
2606 Condition =>
2608 Left_Opnd =>
2613 Right_Opnd =>
2621 -- We need to set up an exception handler for implementing
2622 -- 7.6.1(18). The remaining adjustments are tackled by the
2623 -- implementation of adjust for record_controllers (see
2624 -- s-finimp.adb).
2626 -- This is skipped if we have no finalization
2628 if Expand_Ctrl_Actions
2630 then
2633 Handled_Statement_Sequence =>
2643 Handled_Statement_Sequence =>
2646 -- If no restrictions on aborts, protect the whole assignment
2647 -- for controlled objects as per 9.8(11).
2650 and then Expand_Ctrl_Actions
2651 and then Abort_Allowed
2652 then
2653 declare
2655 New_Internal_Entity
2659 begin
2670 -- Present the Abort_Undefer_Direct function to the backend
2671 -- so that it can inline the call to the function.
2675 Expand_At_End_Handler
2680 -- N has been rewritten to a block statement for which it is
2681 -- known by construction that no checks are necessary: analyze
2682 -- it with all checks suppressed.
2688 -- Array types
2691 declare
2694 begin
2696 N_Qualified_Expression)
2697 loop
2705 -- Record types
2711 -- Scalar types. This is where we perform the processing related to the
2712 -- requirements of (RM 13.9.1(9-11)) concerning the handling of invalid
2713 -- scalar values.
2717 -- Case where right side is known valid
2721 -- Here the right side is valid, so it is fine. The case to deal
2722 -- with is when the left side is a local variable reference whose
2723 -- value is not currently known to be valid. If this is the case,
2724 -- and the assignment appears in an unconditional context, then
2725 -- we can mark the left side as now being valid if one of these
2726 -- conditions holds:
2728 -- The expression of the right side has Do_Range_Check set so
2729 -- that we know a range check will be performed. Note that it
2730 -- can be the case that a range check is omitted because we
2731 -- make the assumption that we can assume validity for operands
2732 -- appearing in the right side in determining whether a range
2733 -- check is required
2735 -- The subtype of the right side matches the subtype of the
2736 -- left side. In this case, even though we have not checked
2737 -- the range of the right side, we know it is in range of its
2738 -- subtype if the expression is valid.
2743 then
2746 then
2751 -- Case where right side may be invalid in the sense of the RM
2752 -- reference above. The RM does not require that we check for the
2753 -- validity on an assignment, but it does require that the assignment
2754 -- of an invalid value not cause erroneous behavior.
2756 -- The general approach in GNAT is to use the Is_Known_Valid flag
2757 -- to avoid the need for validity checking on assignments. However
2758 -- in some cases, we have to do validity checking in order to make
2759 -- sure that the setting of this flag is correct.
2761 else
2762 -- Validate right side if we are validating copies
2764 if Validity_Checks_On
2765 and then Validity_Check_Copies
2766 then
2767 -- Skip this if left-hand side is an array or record component
2768 -- and elementary component validity checks are suppressed.
2771 and then not Validity_Check_Components
2772 then
2774 else
2778 -- We can propagate this to the left side where appropriate
2783 then
2787 -- Otherwise check to see what should be done
2789 -- If left side is a local variable, then we just set its flag to
2790 -- indicate that its value may no longer be valid, since we are
2791 -- copying a potentially invalid value.
2796 -- Check for case of a nonlocal variable on the left side which
2797 -- is currently known to be valid. In this case, we simply ensure
2798 -- that the right side is valid. We only play the game of copying
2799 -- validity status for local variables, since we are doing this
2800 -- statically, not by tracing the full flow graph.
2804 then
2805 -- Note: If Validity_Checking mode is set to none, we ignore
2806 -- the Ensure_Valid call so don't worry about that case here.
2810 -- In all other cases, we can safely copy an invalid value without
2811 -- worrying about the status of the left side. Since it is not a
2812 -- variable reference it will not be considered
2813 -- as being known to be valid in any case.
2815 else
2821 exception
2826 ------------------------------
2827 -- Expand_N_Block_Statement --
2828 ------------------------------
2830 -- Encode entity names defined in block statement
2833 begin
2837 -----------------------------
2838 -- Expand_N_Case_Statement --
2839 -----------------------------
2850 begin
2851 -- Check for the situation where we know at compile time which branch
2852 -- will be taken.
2854 -- If the value is static but its subtype is predicated and the value
2855 -- does not obey the predicate, the value is marked non-static, and
2856 -- there can be no corresponding static alternative. In that case we
2857 -- replace the case statement with an exception, regardless of whether
2858 -- assertions are enabled or not, unless predicates are ignored.
2864 then
2873 then
2876 -- Do not consider controlled objects found in a case statement which
2877 -- actually models a case expression because their early finalization
2878 -- will affect the result of the expression.
2884 -- Move statements from this alternative after the case statement.
2885 -- They are already analyzed, so will be skipped by the analyzer.
2889 -- That leaves the case statement as a shell. So now we can kill all
2890 -- other alternatives in the case statement.
2894 declare
2897 begin
2898 -- Loop through case alternatives, skipping pragmas, and skipping
2899 -- the one alternative that we select (and therefore retain).
2905 then
2917 -- Here if the choice is not determined at compile time
2919 declare
2928 begin
2932 else
2936 -- First step is to worry about possible invalid argument. The RM
2937 -- requires (RM 5.4(13)) that if the result is invalid (e.g. it is
2938 -- outside the base range), then Constraint_Error must be raised.
2940 -- Case of validity check required (validity checks are on, the
2941 -- expression is not known to be valid, and the case statement
2942 -- comes from source -- no need to validity check internally
2943 -- generated case statements).
2945 if Validity_Check_Default
2947 then
2951 -- If there is only a single alternative, just replace it with the
2952 -- sequence of statements since obviously that is what is going to
2953 -- be executed in all cases.
2959 -- We still need to evaluate the expression if it has any side
2960 -- effects.
2965 -- Do not consider controlled objects found in a case statement
2966 -- which actually models a case expression because their early
2967 -- finalization will affect the result of the expression.
2975 -- That leaves the case statement as a shell. The alternative that
2976 -- will be executed is reset to a null list. So now we can kill
2977 -- the entire case statement.
2983 -- An optimization. If there are only two alternatives, and only
2984 -- a single choice, then rewrite the whole case statement as an
2985 -- if statement, since this can result in subsequent optimizations.
2986 -- This helps not only with case statements in the source of a
2987 -- simple form, but also with generated code (discriminant check
2988 -- functions in particular).
2990 -- Note: it is OK to do this before expanding out choices for any
2991 -- static predicates, since the if statement processing will handle
2992 -- the static predicate case fine.
3003 -- For TRUE, generate "expression", not expression = true
3007 then
3010 -- For FALSE, generate "expression" and switch then/else
3014 then
3019 -- For a range, generate "expression in range"
3026 then
3027 Cond :=
3032 -- A subtype indication is not a legal operator in a membership
3033 -- test, so retrieve its range.
3036 Cond :=
3039 Right_Opnd =>
3040 Relocate_Node
3043 -- For any other subexpression "expression = value"
3045 else
3046 Cond :=
3052 -- Now rewrite the case as an IF
3064 -- If the last alternative is not an Others choice, replace it with
3065 -- an N_Others_Choice. Note that we do not bother to call Analyze on
3066 -- the modified case statement, since it's only effect would be to
3067 -- compute the contents of the Others_Discrete_Choices which is not
3068 -- needed by the back end anyway.
3070 -- The reason for this is that the back end always needs some default
3071 -- for a switch, so if we have not supplied one in the processing
3072 -- above for validity checking, then we need to supply one here.
3077 -- If Predicates_Ignored is true the value does not satisfy the
3078 -- predicate, and there is no Others choice, Constraint_Error
3079 -- must be raised (4.5.7 (21/3)).
3082 declare
3092 begin
3097 else
3098 Set_Others_Discrete_Choices
3105 -- Deal with possible declarations of controlled objects, and also
3106 -- with rewriting choice sequences for static predicate references.
3111 -- Do not consider controlled objects found in a case statement
3112 -- which actually models a case expression because their early
3113 -- finalization will affect the result of the expression.
3128 -----------------------------
3129 -- Expand_N_Exit_Statement --
3130 -----------------------------
3132 -- The only processing required is to deal with a possible C/Fortran
3133 -- boolean value used as the condition for the exit statement.
3136 begin
3140 ----------------------------------
3141 -- Expand_Formal_Container_Loop --
3142 ----------------------------------
3157 begin
3158 -- The expansion of a formal container loop resembles the one for Ada
3159 -- containers. The only difference is that the primitives mention the
3160 -- domain of iteration explicitly, and function First applied to the
3161 -- container yields a cursor directly.
3163 -- Cursor : Cursor_type := First (Container);
3164 -- while Has_Element (Cursor, Container) loop
3165 -- <original loop statements>
3166 -- Cursor := Next (Container, Cursor);
3167 -- end loop;
3169 Build_Formal_Container_Iteration
3174 -- Build a block to capture declaration of the cursor
3179 Handled_Statement_Sequence =>
3183 -- The loop parameter is declared by an object declaration, but within
3184 -- the loop we must prevent user assignments to it, so we analyze the
3185 -- declaration and reset the entity kind, before analyzing the rest of
3186 -- the loop.
3192 -- The cursor was marked as a loop parameter to prevent user assignments
3193 -- to it, however this renders the advancement step illegal as it is not
3194 -- possible to change the value of a constant. Flag the advancement step
3195 -- as a legal form of assignment to remedy this side effect.
3200 -- Because we have to analyze the initial declaration of the loop
3201 -- parameter multiple times its scope is incorrectly set at this point
3202 -- to the one surrounding the block statement - so set the scope
3203 -- manually to be the actual block statement, and indicate that it is
3204 -- not visible after the block has been analyzed.
3210 ------------------------------------------
3211 -- Expand_Formal_Container_Element_Loop --
3212 ------------------------------------------
3236 begin
3237 -- For an element iterator, the Element aspect must be present,
3238 -- (this is checked during analysis) and the expansion takes the form:
3240 -- Cursor : Cursor_Type := First (Container);
3241 -- Elmt : Element_Type;
3242 -- while Has_Element (Cursor, Container) loop
3243 -- Elmt := Element (Container, Cursor);
3244 -- <original loop statements>
3245 -- Cursor := Next (Container, Cursor);
3246 -- end loop;
3248 -- However this expansion is not legal if the element is indefinite.
3249 -- In that case we create a block to hold a variable declaration
3250 -- initialized with a call to Element, and generate:
3252 -- Cursor : Cursor_Type := First (Container);
3253 -- while Has_Element (Cursor, Container) loop
3254 -- declare
3255 -- Elmt : Element_Type := Element (Container, Cursor);
3256 -- begin
3257 -- <original loop statements>
3258 -- Cursor := Next (Container, Cursor);
3259 -- end;
3260 -- end loop;
3262 Build_Formal_Container_Iteration
3269 -- The loop parameter is declared by an object declaration, but within
3270 -- the loop we must prevent user assignments to it; the following flag
3271 -- accomplishes that.
3275 -- Declaration for Element
3277 Elmt_Decl :=
3291 New_List
3294 Handled_Statement_Sequence =>
3298 else
3299 Elmt_Ref :=
3302 Expression =>
3311 -- The element is assignable in the expanded code
3315 -- The loop is rewritten as a block, to hold the element declaration
3317 New_Loop :=
3320 Handled_Statement_Sequence =>
3325 -- The element is only modified in expanded code, so it appears as
3326 -- unassigned to the warning machinery. We must suppress this spurious
3327 -- warning explicitly.
3335 -----------------------------
3336 -- Expand_N_Goto_Statement --
3337 -----------------------------
3339 -- Add poll before goto if polling active
3342 begin
3346 ---------------------------
3347 -- Expand_N_If_Statement --
3348 ---------------------------
3350 -- First we deal with the case of C and Fortran convention boolean values,
3351 -- with zero/non-zero semantics.
3353 -- Second, we deal with the obvious rewriting for the cases where the
3354 -- condition of the IF is known at compile time to be True or False.
3356 -- Third, we remove elsif parts which have non-empty Condition_Actions and
3357 -- rewrite as independent if statements. For example:
3359 -- if x then xs
3360 -- elsif y then ys
3361 -- ...
3362 -- end if;
3364 -- becomes
3365 --
3366 -- if x then xs
3367 -- else
3368 -- <<condition actions of y>>
3369 -- if y then ys
3370 -- ...
3371 -- end if;
3372 -- end if;
3374 -- This rewriting is needed if at least one elsif part has a non-empty
3375 -- Condition_Actions list. We also do the same processing if there is a
3376 -- constant condition in an elsif part (in conjunction with the first
3377 -- processing step mentioned above, for the recursive call made to deal
3378 -- with the created inner if, this deals with properly optimizing the
3379 -- cases of constant elsif conditions).
3389 -- Indicates whether we want warnings when we delete branches of the
3390 -- if statement based on constant condition analysis. We never want
3391 -- these warnings for expander generated code.
3393 begin
3394 -- Do not consider controlled objects found in an if statement which
3395 -- actually models an if expression because their early finalization
3396 -- will affect the result of the expression.
3404 -- The following loop deals with constant conditions for the IF. We
3405 -- need a loop because as we eliminate False conditions, we grab the
3406 -- first elsif condition and use it as the primary condition.
3410 -- If condition is True, we can simply rewrite the if statement now
3411 -- by replacing it by the series of then statements.
3415 -- All the else parts can be killed
3425 -- If condition is False, then we can delete the condition and
3426 -- the Then statements
3428 else
3429 -- We do not delete the condition if constant condition warnings
3430 -- are enabled, since otherwise we end up deleting the desired
3431 -- warning. Of course the backend will get rid of this True/False
3432 -- test anyway, so nothing is lost here.
3440 -- If there are no elsif statements, then we simply replace the
3441 -- entire if statement by the sequence of else statements.
3446 then
3449 else
3457 -- If there are elsif statements, the first of them becomes the
3458 -- if/then section of the rebuilt if statement This is the case
3459 -- where we loop to reprocess this copied condition.
3461 else
3467 -- Hed might have been captured as the condition determining
3468 -- the current value for an entity. Now it is detached from
3469 -- the tree, so a Current_Value pointer in the condition might
3470 -- need to be updated.
3481 -- Loop through elsif parts, dealing with constant conditions and
3482 -- possible condition actions that are present.
3488 -- Do not consider controlled objects found in an if statement
3489 -- which actually models an if expression because their early
3490 -- finalization will affect the result of the expression.
3498 -- If there are condition actions, then rewrite the if statement
3499 -- as indicated above. We also do the same rewrite for a True or
3500 -- False condition. The further processing of this constant
3501 -- condition is then done by the recursive call to expand the
3502 -- newly created if statement
3506 then
3507 New_If :=
3514 -- Elsif parts for new if come from remaining elsif's of parent
3538 -- Note this is not an implicit if statement, since it is part
3539 -- of an explicit if statement in the source (or of an implicit
3540 -- if statement that has already been tested). We set the flag
3541 -- after calling Analyze to avoid generating extra warnings
3542 -- specific to pure if statements, however (see
3543 -- Sem_Ch5.Analyze_If_Statement).
3548 -- No special processing for that elsif part, move to next
3550 else
3556 -- Some more optimizations applicable if we still have an IF statement
3562 -- Another optimization, special cases that can be simplified
3564 -- if expression then
3565 -- return true;
3566 -- else
3567 -- return false;
3568 -- end if;
3570 -- can be changed to:
3572 -- return expression;
3574 -- and
3576 -- if expression then
3577 -- return false;
3578 -- else
3579 -- return true;
3580 -- end if;
3582 -- can be changed to:
3584 -- return not (expression);
3586 -- Only do these optimizations if we are at least at -O1 level and
3587 -- do not do them if control flow optimizations are suppressed.
3591 then
3597 then
3598 declare
3602 begin
3604 and then
3606 then
3607 declare
3611 begin
3613 and then
3615 then
3618 then
3627 then
3630 Expression =>
3632 Right_Opnd =>
3645 --------------------------
3646 -- Expand_Iterator_Loop --
3647 --------------------------
3656 begin
3657 -- Processing for arrays
3666 else
3670 -- Processing for containers
3672 else
3673 Expand_Iterator_Loop_Over_Container
3678 -------------------------------------
3679 -- Expand_Iterator_Loop_Over_Array --
3680 -------------------------------------
3696 -- Start of processing for Expand_Iterator_Loop_Over_Array
3698 begin
3699 -- for Element of Array loop
3701 -- It requires an internally generated cursor to iterate over the array
3707 -- Generate:
3708 -- Element : Component_Type renames Array (Iterator);
3709 -- Iterator is the index value, or a list of index values
3710 -- in the case of a multidimensional array.
3712 Ind_Comp :=
3720 Subtype_Mark =>
3724 -- Mark the loop variable as needing debug info, so that expansion
3725 -- of the renaming will result in Materialize_Entity getting set via
3726 -- Debug_Renaming_Declaration. (This setting is needed here because
3727 -- the setting in Freeze_Entity comes after the expansion, which is
3728 -- too late. ???)
3732 -- Generate:
3734 -- for Iterator in [reverse] Array'Range (Array_Dim) loop
3735 -- Element : Component_Type renames Array (Iterator);
3736 -- <original loop statements>
3737 -- end loop;
3739 -- If this is an iteration over a multidimensional array, the
3740 -- innermost loop is over the last dimension in Ada, and over
3741 -- the first dimension in Fortran.
3745 else
3749 Core_Loop :=
3751 Iteration_Scheme =>
3753 Loop_Parameter_Specification =>
3756 Discrete_Subtype_Definition =>
3766 -- Processing for multidimensional array. The body of each loop is
3767 -- a loop over a previous dimension, going in decreasing order in Ada
3768 -- and in increasing order in Fortran.
3774 else
3780 -- Generate the dimension loops starting from the innermost one
3782 -- for Iterator in [reverse] Array'Range (Array_Dim - Dim) loop
3783 -- <core loop>
3784 -- end loop;
3786 Core_Loop :=
3788 Iteration_Scheme =>
3790 Loop_Parameter_Specification =>
3793 Discrete_Subtype_Definition =>
3803 -- Update the previously created object renaming declaration with
3804 -- the new iterator, by adding the index of the next loop to the
3805 -- indexed component, in the order that corresponds to the
3806 -- convention.
3811 else
3818 -- Inherit the loop identifier from the original loop. This ensures that
3819 -- the scope stack is consistent after the rewriting.
3829 -----------------------------------------
3830 -- Expand_Iterator_Loop_Over_Container --
3831 -----------------------------------------
3833 -- For a 'for ... in' loop, such as:
3835 -- for Cursor in Iterator_Function (...) loop
3836 -- ...
3837 -- end loop;
3839 -- we generate:
3841 -- Iter : Iterator_Type := Iterator_Function (...);
3842 -- Cursor : Cursor_type := First (Iter); -- or Last for "reverse"
3843 -- while Has_Element (Cursor) loop
3844 -- ...
3845 --
3846 -- Cursor := Iter.Next (Cursor); -- or Prev for "reverse"
3847 -- end loop;
3849 -- For a 'for ... of' loop, such as:
3851 -- for X of Container loop
3852 -- ...
3853 -- end loop;
3855 -- the RM implies the generation of:
3857 -- Iter : Iterator_Type := Container.Iterate; -- the Default_Iterator
3858 -- Cursor : Cursor_Type := First (Iter); -- or Last for "reverse"
3859 -- while Has_Element (Cursor) loop
3860 -- declare
3861 -- X : Element_Type renames Element (Cursor).Element.all;
3862 -- -- or Constant_Element
3863 -- begin
3864 -- ...
3865 -- end;
3866 -- Cursor := Iter.Next (Cursor); -- or Prev for "reverse"
3867 -- end loop;
3869 -- In the general case, we do what the RM says. However, the operations
3870 -- Element and Iter.Next are slow, which is bad inside a loop, because they
3871 -- involve dispatching via interfaces, secondary stack manipulation,
3872 -- Busy/Lock incr/decr, and adjust/finalization/at-end handling. So for the
3873 -- predefined containers, we use an equivalent but optimized expansion.
3875 -- In the optimized case, we make use of these:
3877 -- procedure Next (Position : in out Cursor); -- instead of Iter.Next
3879 -- function Pseudo_Reference
3880 -- (Container : aliased Vector'Class) return Reference_Control_Type;
3882 -- type Element_Access is access all Element_Type;
3884 -- function Get_Element_Access
3885 -- (Position : Cursor) return not null Element_Access;
3887 -- Next is declared in the visible part of the container packages.
3888 -- The other three are added in the private part. (We're not supposed to
3889 -- pollute the namespace for clients. The compiler has no trouble breaking
3890 -- privacy to call things in the private part of an instance.)
3892 -- Source:
3894 -- for X of My_Vector loop
3895 -- X.Count := X.Count + 1;
3896 -- ...
3897 -- end loop;
3899 -- The compiler will generate:
3901 -- Iter : Reversible_Iterator'Class := Iterate (My_Vector);
3902 -- -- Reversible_Iterator is an interface. Iterate is the
3903 -- -- Default_Iterator aspect of Vector. This increments Lock,
3904 -- -- disallowing tampering with cursors. Unfortunately, it does not
3905 -- -- increment Busy. The result of Iterate is Limited_Controlled;
3906 -- -- finalization will decrement Lock. This is a build-in-place
3907 -- -- dispatching call to Iterate.
3909 -- Cur : Cursor := First (Iter); -- or Last
3910 -- -- Dispatching call via interface.
3912 -- Control : Reference_Control_Type := Pseudo_Reference (My_Vector);
3913 -- -- Pseudo_Reference increments Busy, to detect tampering with
3914 -- -- elements, as required by RM. Also redundantly increment
3915 -- -- Lock. Finalization of Control will decrement both Busy and
3916 -- -- Lock. Pseudo_Reference returns a record containing a pointer to
3917 -- -- My_Vector, used by Finalize.
3918 -- --
3919 -- -- Control is not used below, except to finalize it -- it's purely
3920 -- -- an RAII thing. This is needed because we are eliminating the
3921 -- -- call to Reference within the loop.
3923 -- while Has_Element (Cur) loop
3924 -- declare
3925 -- X : My_Element renames Get_Element_Access (Cur).all;
3926 -- -- Get_Element_Access returns a pointer to the element
3927 -- -- designated by Cur. No dispatching here, and no horsing
3928 -- -- around with access discriminants. This is instead of the
3929 -- -- existing
3930 -- --
3931 -- -- X : My_Element renames Reference (Cur).Element.all;
3932 -- --
3933 -- -- which creates a controlled object.
3934 -- begin
3935 -- -- Any attempt to tamper with My_Vector here in the loop
3936 -- -- will correctly raise Program_Error, because of the
3937 -- -- Control.
3938 --
3939 -- X.Count := X.Count + 1;
3940 -- ...
3941 --
3942 -- Next (Cur); -- or Prev
3943 -- -- This is instead of "Cur := Next (Iter, Cur);"
3944 -- end;
3945 -- -- No finalization here
3946 -- end loop;
3947 -- Finalize Iter and Control here, decrementing Lock twice and Busy
3948 -- once.
3950 -- This optimization makes "for ... of" loops over 30 times faster in cases
3951 -- measured.
3953 procedure Expand_Iterator_Loop_Over_Container
3959 is
3976 -- Only for optimized version of "for ... of"
3979 -- The package in which the iterator interface is instantiated. This is
3980 -- typically an instance within the container package.
3983 -- The package in which the container type is declared
3985 begin
3986 -- Determine the advancement and initialization steps for the cursor.
3987 -- Analysis of the expanded loop will verify that the container has a
3988 -- reverse iterator.
3993 else
3998 -- The type of the iterator is the return type of the Iterate function
3999 -- used. For the "of" form this is the default iterator for the type,
4000 -- otherwise it is the type of the explicit function used in the
4001 -- iterator specification. The most common case will be an Iterate
4002 -- function in the container package.
4004 -- The Iterator type is declared in an instance within the container
4005 -- package itself, for example:
4007 -- package Vector_Iterator_Interfaces is new
4008 -- Ada.Iterator_Interfaces (Cursor, Has_Element);
4010 -- If the container type is a derived type, the cursor type is found in
4011 -- the package of the ultimate ancestor type.
4015 else
4023 function Get_Default_Iterator
4025 -- Return the default iterator for a specific type. If the type is
4026 -- derived, we return the inherited or overridden one if
4027 -- appropriate.
4029 --------------------------
4030 -- Get_Default_Iterator --
4031 --------------------------
4033 function Get_Default_Iterator
4035 is
4041 begin
4044 -- A previous version of GNAT allowed indexing aspects to be
4045 -- redefined on derived container types, while the default
4046 -- iterator was inherited from the parent type. This
4047 -- nonstandard extension is preserved for use by the
4048 -- modeling project under debug flag -gnatd.X.
4053 then
4054 Container_Arg :=
4056 Subtype_Mark =>
4057 New_Occurrence_Of
4066 -- The default iterator must be a primitive operation of the
4067 -- type, at the same dispatch slot position. The DT position
4068 -- may not be established if type is not frozen yet.
4075 or else
4079 then
4086 -- If we didn't find it, then our parent type is not
4087 -- iterable, so we return the Default_Iterator aspect of
4088 -- this type.
4092 -- Otherwise not a derived type
4094 else
4099 -- Local variables
4107 -- Start of processing for Handle_Of
4109 begin
4111 Default_Iter :=
4113 else
4119 -- For a container element iterator, the iterator type is obtained
4120 -- from the corresponding aspect, whose return type is descended
4121 -- from the corresponding interface type in some instance of
4122 -- Ada.Iterator_Interfaces. The actuals of that instantiation
4123 -- are Cursor and Has_Element.
4127 -- The iterator type, which is a class-wide type, may itself be
4128 -- derived locally, so the desired instantiation is the scope of
4129 -- the root type of the iterator type.
4133 -- Find declarations needed for "for ... of" optimization
4142 then
4157 then
4161 Object_Definition =>
4163 Expression =>
4165 Name =>
4167 Parameter_Associations =>
4171 -- Rewrite domain of iteration as a call to the default iterator
4172 -- for the container type. The formal may be an access parameter
4173 -- in which case we must build a reference to the container.
4175 declare
4177 begin
4179 Arg :=
4183 else
4189 Name =>
4196 -- Find cursor type in proper iterator package, which is an
4197 -- instantiation of Iterator_Interfaces.
4210 Decl :=
4213 Subtype_Mark =>
4215 Name =>
4217 Prefix =>
4219 Name =>
4221 Parameter_Associations =>
4224 else
4225 Decl :=
4228 Subtype_Mark =>
4230 Name =>
4233 Expressions =>
4237 -- The defining identifier in the iterator is user-visible and
4238 -- must be visible in the debugger.
4242 -- If the container does not have a variable indexing aspect,
4243 -- the element is a constant in the loop. The container itself
4244 -- may be constant, in which case the element is a constant as
4245 -- well. The container has been rewritten as a call to Iterate,
4246 -- so examine original node.
4251 then
4258 -- X in Iterate (S) : type of iterator is type of explicitly given
4259 -- Iterate function, and the loop variable is the cursor. It will be
4260 -- assigned in the loop and must be a variable.
4262 else
4265 -- The iterator type, which is a class-wide type, may itself be
4266 -- derived locally, so the desired instantiation is the scope of
4267 -- the root type of the iterator type, as in the "of" case.
4275 -- For both iterator forms, add a call to the step operation to advance
4276 -- the cursor. Generate:
4278 -- Cursor := Iterator.Next (Cursor);
4280 -- or else
4282 -- Cursor := Next (Cursor);
4285 declare
4289 begin
4290 Step_Call :=
4292 Name =>
4300 else
4301 declare
4304 begin
4305 Rhs :=
4307 Name =>
4322 -- Generate:
4323 -- while Has_Element (Cursor) loop
4324 -- <Stats>
4325 -- end loop;
4327 -- Has_Element is the second actual in the iterator package
4329 New_Loop :=
4331 Iteration_Scheme =>
4333 Condition =>
4335 Name =>
4336 New_Occurrence_Of
4344 -- If present, preserve identifier of loop, which can be used in an exit
4345 -- statement in the body.
4351 -- Create the declarations for Iterator and cursor and insert them
4352 -- before the source loop. Given that the domain of iteration is already
4353 -- an entity, the iterator is just a renaming of that entity. Possible
4354 -- optimization ???
4362 -- Create declaration for cursor
4364 declare
4368 Object_Definition =>
4370 Expression =>
4372 Prefix =>
4374 Selector_Name =>
4377 begin
4378 -- The cursor is only modified in expanded code, so it appears
4379 -- as unassigned to the warning machinery. We must suppress this
4380 -- spurious warning explicitly. The cursor's kind is that of the
4381 -- original loop parameter (it is a constant if the domain of
4382 -- iteration is constant).
4391 -- If the range of iteration is given by a function call that returns
4392 -- a container, the finalization actions have been saved in the
4393 -- Condition_Actions of the iterator. Insert them now at the head of
4394 -- the loop.
4404 -----------------------------
4405 -- Expand_N_Loop_Statement --
4406 -----------------------------
4408 -- 1. Remove null loop entirely
4409 -- 2. Deal with while condition for C/Fortran boolean
4410 -- 3. Deal with loops with a non-standard enumeration type range
4411 -- 4. Deal with while loops where Condition_Actions is set
4412 -- 5. Deal with loops over predicated subtypes
4413 -- 6. Deal with loops with iterators over arrays and containers
4414 -- 7. Insert polling call if required
4421 begin
4422 -- Delete null loop
4429 -- Deal with condition for C/Fortran Boolean
4435 -- Generate polling call
4441 -- Nothing more to do for plain loop with no iteration scheme
4446 -- Case of for loop (Loop_Parameter_Specification present)
4448 -- Note: we do not have to worry about validity checking of the for loop
4449 -- range bounds here, since they were frozen with constant declarations
4450 -- and it is during that process that the validity checking is done.
4453 declare
4463 begin
4464 -- Deal with loop over predicates
4468 then
4471 -- Handle the case where we have a for loop with the range type
4472 -- being an enumeration type with non-standard representation.
4473 -- In this case we expand:
4475 -- for x in [reverse] a .. b loop
4476 -- ...
4477 -- end loop;
4479 -- to
4481 -- for xP in [reverse] integer
4482 -- range etype'Pos (a) .. etype'Pos (b)
4483 -- loop
4484 -- declare
4485 -- x : constant etype := Pos_To_Rep (xP);
4486 -- begin
4487 -- ...
4488 -- end;
4489 -- end loop;
4493 then
4494 New_Id :=
4498 -- If the type has a contiguous representation, successive
4499 -- values can be generated as offsets from the first literal.
4502 Expr :=
4505 Left_Opnd =>
4509 else
4510 -- Use the constructed array Enum_Pos_To_Rep
4512 Expr :=
4514 Prefix =>
4516 Expressions =>
4520 -- Build declaration for loop identifier
4522 Decls :=
4523 New_List (
4534 Iteration_Scheme =>
4536 Loop_Parameter_Specification =>
4541 Discrete_Subtype_Definition =>
4544 Subtype_Mark =>
4547 Constraint =>
4549 Range_Expression =>
4552 Low_Bound =>
4554 Prefix =>
4560 Relocate_Node
4563 High_Bound =>
4565 Prefix =>
4571 Relocate_Node
4572 (Type_High_Bound
4578 Handled_Statement_Sequence =>
4584 -- The loop parameter's entity must be removed from the loop
4585 -- scope's entity list and rendered invisible, since it will
4586 -- now be located in the new block scope. Any other entities
4587 -- already associated with the loop scope, such as the loop
4588 -- parameter's subtype, will remain there.
4590 -- In an element loop, the loop will contain a declaration for
4591 -- a cursor variable; otherwise the loop id is the first entity
4592 -- in the scope constructed for the loop.
4608 -- Nothing to do with other cases of for loops
4610 else
4615 -- Second case, if we have a while loop with Condition_Actions set, then
4616 -- we change it into a plain loop:
4618 -- while C loop
4619 -- ...
4620 -- end loop;
4622 -- changed to:
4624 -- loop
4625 -- <<condition actions>>
4626 -- exit when not C;
4627 -- ...
4628 -- end loop
4633 then
4634 declare
4637 begin
4638 ES :=
4640 Condition =>
4647 -- This is not an implicit loop, since it is generated in response
4648 -- to the loop statement being processed. If this is itself
4649 -- implicit, the restriction has already been checked. If not,
4650 -- it is an explicit loop.
4661 -- Here to deal with iterator case
4665 then
4668 -- An iterator loop may generate renaming declarations for elements
4669 -- that require debug information. This is the case in particular
4670 -- with element iterators, where debug information must be generated
4671 -- for the temporary that holds the element value. These temporaries
4672 -- are created within a transient block whose local declarations are
4673 -- transferred to the loop, which now has nontrivial local objects.
4677 then
4682 -- When the iteration scheme mentiones attribute 'Loop_Entry, the loop
4683 -- is transformed into a conditional block where the original loop is
4684 -- the sole statement. Inspect the statements of the nested loop for
4685 -- controlled objects.
4696 ----------------------------
4697 -- Expand_Predicated_Loop --
4698 ----------------------------
4700 -- Note: the expander can handle generation of loops over predicated
4701 -- subtypes for both the dynamic and static cases. Depending on what
4702 -- we decide is allowed in Ada 2012 mode and/or extensions allowed
4703 -- mode, the semantic analyzer may disallow one or both forms.
4714 begin
4715 -- Case of iteration over non-static predicate, should not be possible
4716 -- since this is not allowed by the semantics and should have been
4717 -- caught during analysis of the loop statement.
4722 -- If the predicate list is empty, that corresponds to a predicate of
4723 -- False, in which case the loop won't run at all, and we rewrite the
4724 -- entire loop as a null statement.
4730 -- For expansion over a static predicate we generate the following
4732 -- declare
4733 -- J : Ltype := min-val;
4734 -- begin
4735 -- loop
4736 -- body
4737 -- case J is
4738 -- when endpoint => J := startpoint;
4739 -- when endpoint => J := startpoint;
4740 -- ...
4741 -- when max-val => exit;
4742 -- when others => J := Lval'Succ (J);
4743 -- end case;
4744 -- end loop;
4745 -- end;
4747 -- with min-val replaced by max-val and Succ replaced by Pred if the
4748 -- loop parameter specification carries a Reverse indicator.
4750 -- To make this a little clearer, let's take a specific example:
4752 -- type Int is range 1 .. 10;
4753 -- subtype StaticP is Int with
4754 -- predicate => StaticP in 3 | 10 | 5 .. 7;
4755 -- ...
4756 -- for L in StaticP loop
4757 -- Put_Line ("static:" & J'Img);
4758 -- end loop;
4760 -- In this case, the loop is transformed into
4762 -- begin
4763 -- J : L := 3;
4764 -- loop
4765 -- body
4766 -- case J is
4767 -- when 3 => J := 5;
4768 -- when 7 => J := 10;
4769 -- when 10 => exit;
4770 -- when others => J := L'Succ (J);
4771 -- end case;
4772 -- end loop;
4773 -- end;
4775 -- In addition, if the loop specification is given by a subtype
4776 -- indication that constrains a predicated type, the bounds of
4777 -- iteration are given by those of the subtype indication.
4779 else
4787 -- If the domain is an itype, note the bounds of its range.
4793 -- Given static expression or static range, returns an identifier
4794 -- whose value is the low bound of the expression value or range.
4797 -- Given static expression or static range, returns an identifier
4798 -- whose value is the high bound of the expression value or range.
4800 ------------
4801 -- Hi_Val --
4802 ------------
4805 begin
4808 else
4814 ------------
4815 -- Lo_Val --
4816 ------------
4819 begin
4822 else
4828 -- Start of processing for Static_Predicate
4830 begin
4831 -- Convert loop identifier to normal variable and reanalyze it so
4832 -- that this conversion works. We have to use the same defining
4833 -- identifier, since there may be references in the loop body.
4838 -- In most loops the loop variable is assigned in various
4839 -- alternatives in the body. However, in the rare case when
4840 -- the range specifies a single element, the loop variable
4841 -- may trigger a spurious warning that is could be constant.
4842 -- This warning might as well be suppressed.
4851 -- Loop to create branches of case statement
4857 -- Initial value is largest value in predicate.
4860 D :=
4866 else
4867 D :=
4878 else
4879 S :=
4896 and then
4898 then
4905 else
4906 -- Initial value is smallest value in predicate
4909 D :=
4914 else
4915 D :=
4926 else
4927 S :=
4944 and then
4946 then
4954 -- Add others choice
4956 declare
4959 begin
4962 else
4966 S :=
4969 Expression =>
4983 -- Construct case statement and append to body statements
4985 Cstm :=
4991 -- Rewrite the loop
4998 Handled_Statement_Sequence =>
5010 ------------------------------
5011 -- Make_Tag_Ctrl_Assignment --
5012 ------------------------------
5025 and then not Comp_Asn
5032 begin
5033 -- Finalize the target of the assignment when controlled
5035 -- We have two exceptions here:
5037 -- 1. If we are in an init proc since it is an initialization more
5038 -- than an assignment.
5040 -- 2. If the left-hand side is a temporary that was not initialized
5041 -- (or the parent part of a temporary since it is the case in
5042 -- extension aggregates). Such a temporary does not come from
5043 -- source. We must examine the original node for the prefix, because
5044 -- it may be a component of an entry formal, in which case it has
5045 -- been rewritten and does not appear to come from source either.
5047 -- Case of init proc
5052 -- The left-hand side is an uninitialized temporary object
5057 N_Object_Declaration
5059 then
5062 else
5063 Fin_Call :=
5064 Make_Final_Call
5073 -- Save the Tag in a local variable Tag_Id
5082 Expression =>
5085 Selector_Name =>
5088 -- Otherwise Tag_Id is not used
5090 else
5094 -- If the tagged type has a full rep clause, expand the assignment into
5095 -- component-wise assignments. Mark the node as unanalyzed in order to
5096 -- generate the proper code and propagate this scenario by setting a
5097 -- flag to avoid infinite recursion.
5106 -- Restore the tag
5111 Name =>
5114 Selector_Name =>
5119 -- Adjust the target after the assignment when controlled (not in the
5120 -- init proc since it is an initialization more than an assignment).
5123 Adj_Call :=
5124 Make_Adjust_Call
5135 exception
5137 -- Could use comment here ???