1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2002 Free Software Foundation, Inc. --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 2, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
22 -- GNAT was originally developed by the GNAT team at New York University. --
23 -- Extensive contributions were provided by Ada Core Technologies Inc. --
25 ------------------------------------------------------------------------------
27 -- Package containing routines used to deal with runtime checks. These
28 -- routines are used both by the semantics and by the expander. In some
29 -- cases, checks are enabled simply by setting flags for gigi, and in
30 -- other cases the code for the check is expanded.
32 -- The approach used for range and length checks, in regards to suppressed
33 -- checks, is to attempt to detect at compilation time that a constraint
34 -- error will occur. If this is detected a warning or error is issued and the
35 -- offending expression or statement replaced with a constraint error node.
36 -- This always occurs whether checks are suppressed or not. Dynamic range
37 -- checks are, of course, not inserted if checks are suppressed.
39 with Types; use Types;
40 with Uintp; use Uintp;
45 -- Called for each new main source program, to initialize internal
46 -- variables used in the package body of the Checks unit.
48 function Access_Checks_Suppressed (E : Entity_Id) return Boolean;
49 function Accessibility_Checks_Suppressed (E : Entity_Id) return Boolean;
50 function Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean;
51 function Division_Checks_Suppressed (E : Entity_Id) return Boolean;
52 function Elaboration_Checks_Suppressed (E : Entity_Id) return Boolean;
53 function Index_Checks_Suppressed (E : Entity_Id) return Boolean;
54 function Length_Checks_Suppressed (E : Entity_Id) return Boolean;
55 function Overflow_Checks_Suppressed (E : Entity_Id) return Boolean;
56 function Range_Checks_Suppressed (E : Entity_Id) return Boolean;
57 function Storage_Checks_Suppressed (E : Entity_Id) return Boolean;
58 function Tag_Checks_Suppressed (E : Entity_Id) return Boolean;
59 -- These functions check to see if the named check is suppressed,
60 -- either by an active scope suppress setting, or because the check
61 -- has been specifically suppressed for the given entity. If no entity
62 -- is relevant for the current check, then Empty is used as an argument.
63 -- Note: the reason we insist on specifying Empty is to force the
64 -- caller to think about whether there is any relevant entity that
67 -- General note on following checks. These checks are always active if
68 -- Expander_Active and not Inside_A_Generic. They are inactive and have
69 -- no effect Inside_A_Generic. In the case where not Expander_Active
70 -- and not Inside_A_Generic, most of them are inactive, but some of them
71 -- operate anyway since they may generate useful compile time warnings.
73 procedure Apply_Access_Check (N : Node_Id);
74 -- Determines whether an expression node requires a runtime access
75 -- check and if so inserts the appropriate run-time check.
77 procedure Apply_Accessibility_Check (N : Node_Id; Typ : Entity_Id);
78 -- Given a name N denoting an access parameter, emits a run-time
79 -- accessibility check (if necessary), checking that the level of
80 -- the object denoted by the access parameter is not deeper than the
81 -- level of the type Typ. Program_Error is raised if the check fails.
83 procedure Apply_Alignment_Check (E : Entity_Id; N : Node_Id);
84 -- E is the entity for an object. If there is an address clause for
85 -- this entity, and checks are enabled, then this procedure generates
86 -- a check that the specified address has an alignment consistent with
87 -- the alignment of the object, raising PE if this is not the case. The
88 -- resulting check (if one is generated) is inserted before node N.
90 procedure Apply_Array_Size_Check (N : Node_Id; Typ : Entity_Id);
91 -- N is the node for an object declaration that declares an object of
92 -- array type Typ. This routine generates, if necessary, a check that
93 -- the size of the array is not too large, raising Storage_Error if so.
95 procedure Apply_Arithmetic_Overflow_Check (N : Node_Id);
96 -- Given a binary arithmetic operator (+ - *) expand a software integer
97 -- overflow check using range checks on a larger checking type or a call
98 -- to an appropriate runtime routine. This is used for all three operators
99 -- for the signed integer case, and for +/- in the fixed-point case. The
100 -- check is expanded only if Software_Overflow_Checking is enabled and
101 -- Do_Overflow_Check is set on node N. Note that divide is handled
102 -- separately using Apply_Arithmetic_Divide_Overflow_Check.
104 procedure Apply_Constraint_Check
107 No_Sliding : Boolean := False);
108 -- Top-level procedure, calls all the others depending on the class of Typ.
109 -- Checks that expression N verifies the constraint of type Typ. No_Sliding
110 -- is only relevant for constrained array types, id set to true, it
111 -- checks that indexes are in range.
113 procedure Apply_Discriminant_Check
116 Lhs : Node_Id := Empty);
117 -- Given an expression N of a discriminated type, or of an access type
118 -- whose designated type is a discriminanted type, generates a check to
119 -- ensure that the expression can be converted to the subtype given as
120 -- the second parameter. Lhs is empty except in the case of assignments,
121 -- where the target object may be needed to determine the subtype to
122 -- check against (such as the cases of unconstrained formal parameters
123 -- and unconstrained aliased objects). For the case of unconstrained
124 -- formals, the check is peformed only if the corresponding actual is
125 -- constrained, i.e., whether Lhs'Constrained is True.
127 function Build_Discriminant_Checks
131 -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression
132 -- that compares discriminants of the expression with discriminants of the
133 -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In).
135 procedure Apply_Divide_Check (N : Node_Id);
136 -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem. An appropriate
137 -- check is generated to ensure that the right operand is non-zero. In
138 -- the divide case, we also check that we do not have the annoying case
139 -- of the largest negative number divided by minus one.
141 procedure Apply_Type_Conversion_Checks (N : Node_Id);
142 -- N is an N_Type_Conversion node. A type conversion actually involves
143 -- two sorts of checks. The first check is the checks that ensures that
144 -- the operand in the type conversion fits onto the base type of the
145 -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second
146 -- check is there to ensure that once the operand has been converted to
147 -- a value of the target type, this converted value meets the
148 -- constraints imposed by the target subtype (see RM 4.6 (51)).
150 procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id);
151 -- The argument N is an attribute reference node intended for processing
152 -- by gigi. The attribute is one that returns a universal integer, but
153 -- the attribute reference node is currently typed with the expected
154 -- result type. This routine deals with range and overflow checks needed
155 -- to make sure that the universal result is in range.
157 procedure Determine_Range
162 -- N is a node for a subexpression. If N is of a discrete type with
163 -- no error indications, and no other peculiarities (e.g. missing
164 -- type fields), then OK is True on return, and Lo and Hi are set
165 -- to a conservative estimate of the possible range of values of N.
166 -- Thus if OK is True on return, the value of the subexpression N is
167 -- known to like in the range Lo .. Hi (inclusive). If the expression
168 -- is not of a discrete type, or some kind of error condition is
169 -- detected, then OK is False on exit, and Lo/Hi are set to No_Uint.
170 -- Thus the significance of OK being False on return is that no
171 -- useful information is available on the range of the expression.
173 -------------------------------------------------------
174 -- Control and Optimization of Range/Overflow Checks --
175 -------------------------------------------------------
177 -- Range checks are controlled by the Do_Range_Check flag. The front end
178 -- is responsible for setting this flag in relevant nodes. Originally
179 -- the back end generated all corresponding range checks. But later on
180 -- we decided to generate all range checks in the front end. We are now
181 -- in the transitional phase where some of these checks are still done
182 -- by the back end, but many are done by the front end.
184 -- Overflow checks are similarly controlled by the Do_Overflow_Check
185 -- flag. The difference here is that if Backend_Overflow_Checks is
186 -- is (Backend_Overflow_Checks_On_Target set False), then the actual
187 -- overflow checks are generated by the front end, but if back end
188 -- overflow checks are active (Backend_Overflow_Checks_On_Target
189 -- set True), then the back end does generate the checks.
191 -- The following two routines are used to set these flags, they allow
192 -- for the possibility of eliminating checks. Checks can be eliminated
193 -- if an identical check has already been performed.
195 procedure Enable_Overflow_Check (N : Node_Id);
196 -- First this routine determines if an overflow check is needed by doing
197 -- an appropriate range check. If a check is not needed, then the call
198 -- has no effect. If a check is needed then this routine sets the flag
199 -- Set Do_Overflow_Check in node N to True, unless it can be determined
200 -- that the check is not needed. The only condition under which this is
201 -- the case is if there was an identical check earlier on.
203 procedure Enable_Range_Check (N : Node_Id);
204 -- Set Do_Range_Check flag in node N True, unless it can be determined
205 -- that the check is not needed. The only condition under which this is
206 -- the case is if there was an identical check earlier on. This routine
207 -- is not responsible for doing range analysis to determine whether or
208 -- not such a check is needed -- the caller is expected to do this. The
209 -- one other case in which the request to set the flag is ignored is
210 -- when Kill_Range_Check is set in an N_Unchecked_Conversion node.
212 -- The following routines are used to keep track of processing sequences
213 -- of statements (e.g. the THEN statements of an IF statement). A check
214 -- that appears within such a sequence can eliminate an identical check
215 -- within this sequence of statements. However, after the end of the
216 -- sequence of statements, such a check is no longer of interest, since
217 -- it may not have been executed.
219 procedure Conditional_Statements_Begin;
220 -- This call marks the start of processing of a sequence of statements.
221 -- Every call to this procedure must be followed by a matching call to
222 -- Conditional_Statements_End.
224 procedure Conditional_Statements_End;
225 -- This call removes from consideration all saved checks since the
226 -- corresponding call to Conditional_Statements_Begin. These two
227 -- procedures operate in a stack like manner.
229 -- The mechanism for optimizing checks works by remembering checks
230 -- that have already been made, but certain conditions, for example
231 -- an assignment to a variable involved in a check, may mean that the
232 -- remembered check is no longer valid, in the sense that if the same
233 -- expression appears again, another check is required because the
234 -- value may have changed.
236 -- The following routines are used to note conditions which may render
237 -- some or all of the stored and remembered checks to be invalidated.
239 procedure Kill_Checks (V : Entity_Id);
240 -- This procedure records an assignment or other condition that causes
241 -- the value of the variable to be changed, invalidating any stored
242 -- checks that reference the value. Note that all such checks must
243 -- be discarded, even if they are not in the current statement range.
245 procedure Kill_All_Checks;
246 -- This procedure kills all remembered checks.
248 -----------------------------
249 -- Length and Range Checks --
250 -----------------------------
252 -- In the following procedures, there are three arguments which have
253 -- a common meaning as follows:
255 -- Expr The expression to be checked. If a check is required,
256 -- the appropriate flag will be placed on this node. Whether
257 -- this node is further examined depends on the setting of
258 -- the parameter Source_Typ, as described below.
260 -- Target_Typ The target type on which the check is to be based. For
261 -- example, if we have a scalar range check, then the check
262 -- is that we are in range of this type.
264 -- Source_Typ Normally Empty, but can be set to a type, in which case
265 -- this type is used for the check, see below.
267 -- The checks operate in one of two modes:
269 -- If Source_Typ is Empty, then the node Expr is examined, at the
270 -- very least to get the source subtype. In addition for some of
271 -- the checks, the actual form of the node may be examined. For
272 -- example, a node of type Integer whose actual form is an Integer
273 -- conversion from a type with range 0 .. 3 can be determined to
274 -- have a value in the range 0 .. 3.
276 -- If Source_Typ is given, then nothing can be assumed about the
277 -- Expr, and indeed its contents are not examined. In this case the
278 -- check is based on the assumption that Expr can be an arbitrary
279 -- value of the given Source_Typ.
281 -- Currently, the only case in which a Source_Typ is explicitly supplied
282 -- is for the case of Out and In_Out parameters, where, for the conversion
283 -- on return (the Out direction), the types must be reversed. This is
284 -- handled by the caller.
286 procedure Apply_Length_Check
288 Target_Typ : Entity_Id;
289 Source_Typ : Entity_Id := Empty);
290 -- This procedure builds a sequence of declarations to do a length check
291 -- that checks if the lengths of the two arrays Target_Typ and source type
292 -- are the same. The resulting actions are inserted at Node using a call
293 -- to Insert_Actions.
295 -- For access types, the Directly_Designated_Type is retrieved and
296 -- processing continues as enumerated above, with a guard against
299 -- Note: calls to Apply_Length_Check currently never supply an explicit
300 -- Source_Typ parameter, but Apply_Length_Check takes this parameter and
301 -- processes it as described above for consistency with the other routines
304 procedure Apply_Range_Check
306 Target_Typ : Entity_Id;
307 Source_Typ : Entity_Id := Empty);
308 -- For an Node of kind N_Range, constructs a range check action that
309 -- tests first that the range is not null and then that the range
310 -- is contained in the Target_Typ range.
312 -- For scalar types, constructs a range check action that first tests that
313 -- the expression is contained in the Target_Typ range. The difference
314 -- between this and Apply_Scalar_Range_Check is that the latter generates
315 -- the actual checking code in gigi against the Etype of the expression.
317 -- For constrained array types, construct series of range check actions
318 -- to check that each Expr range is properly contained in the range of
321 -- For a type conversion to an unconstrained array type, constructs
322 -- a range check action to check that the bounds of the source type
323 -- are within the constraints imposed by the Target_Typ.
325 -- For access types, the Directly_Designated_Type is retrieved and
326 -- processing continues as enumerated above, with a guard against
329 -- The source type is used by type conversions to unconstrained array
330 -- types to retrieve the corresponding bounds.
332 procedure Apply_Static_Length_Check
334 Target_Typ : Entity_Id;
335 Source_Typ : Entity_Id := Empty);
336 -- Tries to determine statically whether the two array types source type
337 -- and Target_Typ have the same length. If it can be determined at compile
338 -- time that they do not, then an N_Raise_Constraint_Error node replaces
339 -- Expr, and a warning message is issued.
341 procedure Apply_Scalar_Range_Check
343 Target_Typ : Entity_Id;
344 Source_Typ : Entity_Id := Empty;
345 Fixed_Int : Boolean := False);
346 -- For scalar types, determines whether an expression node should be
347 -- flagged as needing a runtime range check. If the node requires such
348 -- a check, the Do_Range_Check flag is turned on. The Fixed_Int flag
349 -- if set causes any fixed-point values to be treated as though they
350 -- were discrete values (i.e. the underlying integer value is used).
352 type Check_Result is private;
353 -- Type used to return result of Range_Check call, for later use in
354 -- call to Insert_Range_Checks procedure.
356 procedure Append_Range_Checks
357 (Checks : Check_Result;
359 Suppress_Typ : Entity_Id;
360 Static_Sloc : Source_Ptr;
361 Flag_Node : Node_Id);
362 -- Called to append range checks as returned by a call to Range_Check.
363 -- Stmts is a list to which either the dynamic check is appended or
364 -- the raise Constraint_Error statement is appended (for static checks).
365 -- Static_Sloc is the Sloc at which the raise CE node points,
366 -- Flag_Node is used as the node at which to set the Has_Dynamic_Check
367 -- flag. Checks_On is a boolean value that says if range and index checking
370 procedure Insert_Range_Checks
371 (Checks : Check_Result;
373 Suppress_Typ : Entity_Id;
374 Static_Sloc : Source_Ptr := No_Location;
375 Flag_Node : Node_Id := Empty;
376 Do_Before : Boolean := False);
377 -- Called to insert range checks as returned by a call to Range_Check.
378 -- Node is the node after which either the dynamic check is inserted or
379 -- the raise Constraint_Error statement is inserted (for static checks).
380 -- Suppress_Typ is the type to check to determine if checks are suppressed.
381 -- Static_Sloc, if passed, is the Sloc at which the raise CE node points,
382 -- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally
383 -- set at Node. If Flag_Node is present, then this is used instead as the
384 -- node at which to set the Has_Dynamic_Check flag. Normally the check is
385 -- inserted after, if Do_Before is True, the check is inserted before
390 Target_Typ : Entity_Id;
391 Source_Typ : Entity_Id := Empty;
392 Warn_Node : Node_Id := Empty)
394 -- Like Apply_Range_Check, except it does not modify anything. Instead
395 -- it returns an encapsulated result of the check operations for later
396 -- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its
397 -- Sloc is used, in the static case, for the generated warning or error.
398 -- Additionally, it is used rather than Expr (or Low/High_Bound of Expr)
399 -- in constructing the check.
401 -----------------------
402 -- Expander Routines --
403 -----------------------
405 -- Some of the earlier processing for checks results in temporarily
406 -- setting the Do_Range_Check flag rather than actually generating
407 -- checks. Now we are moving the generation of such checks into the
408 -- front end for reasons of efficiency and simplicity (there were
409 -- difficutlies in handling this in the back end when side effects
410 -- were present in the expressions being checked).
412 -- Probably we could eliminate the Do_Range_Check flag entirely and
413 -- generate the checks earlier, but this is a delicate area and it
414 -- seemed safer to implement the following routines, which are called
415 -- late on in the expansion process. They check the Do_Range_Check flag
416 -- and if it is set, generate the actual checks and reset the flag.
418 procedure Generate_Range_Check
420 Target_Type : Entity_Id;
421 Reason : RT_Exception_Code);
422 -- This procedure is called to actually generate and insert a range
423 -- check. A check is generated to ensure that the value of N lies
424 -- within the range of the target type. Note that the base type of
425 -- N may be different from the base type of the target type. This
426 -- happens in the conversion case. The Reason parameter is the
427 -- exception code to be used for the exception if raised.
429 -- Note on the relation of this routine to the Do_Range_Check flag.
430 -- Mostly for historical reasons, we often set the Do_Range_Check
431 -- flag and then later we call Generate_Range_Check if this flag is
432 -- set. Most probably we could eliminate this intermediate setting
433 -- of the flag (historically the back end dealt with range checks,
434 -- using this flag to indicate if a check was required, then we
435 -- moved checks into the front end).
437 procedure Generate_Index_Checks (N : Node_Id);
438 -- This procedure is called to generate index checks on the subscripts
439 -- for the indexed component node N. Each subscript expression is
440 -- examined, and if the Do_Range_Check flag is set, an appropriate
441 -- index check is generated and the flag is reset.
443 -- Similarly, we set the flag Do_Discriminant_Check in the semantic
444 -- analysis to indicate that a discriminant check is required for a
445 -- selected component of a discriminated type. The following routine
446 -- is called from the expander to actually generate the call.
448 procedure Generate_Discriminant_Check (N : Node_Id);
449 -- N is a selected component for which a discriminant check is required
450 -- to make sure that the discriminants have appropriate values for the
451 -- selection. This is done by calling the appropriate discriminant
452 -- checking routine for the selector.
454 -----------------------
455 -- Validity Checking --
456 -----------------------
458 -- In (RM 13.9.1(9-11)) we have the following rules on invalid values
460 -- If the representation of a scalar object does not represent a
461 -- value of the object's subtype (perhaps because the object was not
462 -- initialized), the object is said to have an invalid representation.
463 -- It is a bounded error to evaluate the value of such an object. If
464 -- the error is detected, either Constraint_Error or Program_Error is
465 -- raised. Otherwise, execution continues using the invalid
466 -- representation. The rules of the language outside this subclause
467 -- assume that all objects have valid representations. The semantics
468 -- of operations on invalid representations are as follows:
470 -- 10 If the representation of the object represents a value of the
471 -- object's type, the value of the type is used.
473 -- 11 If the representation of the object does not represent a value
474 -- of the object's type, the semantics of operations on such
475 -- representations is implementation-defined, but does not by
476 -- itself lead to erroneous or unpredictable execution, or to
477 -- other objects becoming abnormal.
479 -- We quote the rules in full here since they are quite delicate. Most
480 -- of the time, we can just compute away with wrong values, and get a
481 -- possibly wrong result, which is well within the range of allowed
482 -- implementation defined behavior. The two tricky cases are subscripted
483 -- array assignments, where we don't want to do wild stores, and case
484 -- statements where we don't want to do wild jumps.
486 -- In GNAT, we control validity checking with a switch -gnatV that
487 -- can take three parameters, n/d/f for None/Default/Full. These
488 -- modes have the following meanings:
490 -- None (no validity checking)
492 -- In this mode, there is no specific checking for invalid values
493 -- and the code generator assumes that all stored values are always
494 -- within the bounds of the object subtype. The consequences are as
497 -- For case statements, an out of range invalid value will cause
498 -- Constraint_Error to be raised, or an arbitrary one of the case
499 -- alternatives will be executed. Wild jumps cannot result even
500 -- in this mode, since we always do a range check
502 -- For subscripted array assignments, wild stores will result in
503 -- the expected manner when addresses are calculated using values
504 -- of subscripts that are out of range.
506 -- It could perhaps be argued that this mode is still conformant with
507 -- the letter of the RM, since implementation defined is a rather
508 -- broad category, but certainly it is not in the spirit of the
509 -- RM requirement, since wild stores certainly seem to be a case of
510 -- erroneous behavior.
512 -- Default (default standard RM-compatible validity checking)
514 -- In this mode, which is the default, minimal validity checking is
515 -- performed to ensure no erroneous behavior as follows:
517 -- For case statements, an out of range invalid value will cause
518 -- Constraint_Error to be raised.
520 -- For subscripted array assignments, invalid out of range
521 -- subscript values will cause Constraint_Error to be raised.
523 -- Full (Full validity checking)
525 -- In this mode, the protections guaranteed by the standard mode are
526 -- in place, and the following additional checks are made:
528 -- For every assignment, the right side is checked for validity
530 -- For every call, IN and IN OUT parameters are checked for validity
532 -- For every subscripted array reference, both for stores and loads,
533 -- all subscripts are checked for validity.
535 -- These checks are not required by the RM, but will in practice
536 -- improve the detection of uninitialized variables, particularly
537 -- if used in conjunction with pragma Normalize_Scalars.
539 -- In the above description, we talk about performing validity checks,
540 -- but we don't actually generate a check in a case where the compiler
541 -- can be sure that the value is valid. Note that this assurance must
542 -- be achieved without assuming that any uninitialized value lies within
543 -- the range of its type. The following are cases in which values are
544 -- known to be valid. The flag Is_Known_Valid is used to keep track of
545 -- some of these cases.
547 -- If all possible stored values are valid, then any uninitialized
548 -- value must be valid.
550 -- Literals, including enumeration literals, are clearly always valid.
552 -- Constants are always assumed valid, with a validity check being
553 -- performed on the initializing value where necessary to ensure that
556 -- For variables, the status is set to known valid if there is an
557 -- initializing expression. Again a check is made on the initializing
558 -- value if necessary to ensure that this assumption is valid. The
559 -- status can change as a result of local assignments to a variable.
560 -- If a known valid value is unconditionally assigned, then we mark
561 -- the left side as known valid. If a value is assigned that is not
562 -- known to be valid, then we mark the left side as invalid. This
563 -- kind of processing does NOT apply to non-local variables since we
564 -- are not following the flow graph (more properly the flow of actual
565 -- processing only corresponds to the flow graph for local assignments).
566 -- For non-local variables, we preserve the current setting, i.e. a
567 -- validity check is performed when assigning to a knonwn valid global.
569 -- Note: no validity checking is required if range checks are suppressed
570 -- regardless of the setting of the validity checking mode.
572 -- The following procedures are used in handling validity checking
574 procedure Apply_Subscript_Validity_Checks (Expr : Node_Id);
575 -- Expr is the node for an indexed component. If validity checking and
576 -- range checking are enabled, all subscripts for this indexed component
577 -- are checked for validity.
579 procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id);
580 -- Expr is a lvalue, i.e. an expression representing the target of
581 -- an assignment. This procedure checks for this expression involving
582 -- an assignment to an array value. We have to be sure that all the
583 -- subscripts in such a case are valid, since according to the rules
584 -- in (RM 13.9.1(9-11)) such assignments are not permitted to result
585 -- in erroneous behavior in the case of invalid subscript values.
587 procedure Ensure_Valid (Expr : Node_Id; Holes_OK : Boolean := False);
588 -- Ensure that Expr represents a valid value of its type. If this type
589 -- is not a scalar type, then the call has no effect, since validity
590 -- is only an issue for scalar types. The effect of this call is to
591 -- check if the value is known valid, if so, nothing needs to be done.
592 -- If this is not known, then either Expr is set to be range checked,
593 -- or specific checking code is inserted so that an exception is raised
594 -- if the value is not valid.
596 -- The optional argument Holes_OK indicates whether it is necessary to
597 -- worry about enumeration types with non-standard representations leading
598 -- to "holes" in the range of possible representations. If Holes_OK is
599 -- True, then such values are assumed valid (this is used when the caller
600 -- will make a separate check for this case anyway). If Holes_OK is False,
601 -- then this case is checked, and code is inserted to ensure that Expr is
602 -- valid, raising Constraint_Error if the value is not valid.
604 function Expr_Known_Valid (Expr : Node_Id) return Boolean;
605 -- This function tests it the value of Expr is known to be valid in
606 -- the sense of RM 13.9.1(9-11). In the case of GNAT, it is only
607 -- discrete types which are a concern, since for non-discrete types
608 -- we simply continue computation with invalid values, which does
609 -- not lead to erroneous behavior. Thus Expr_Known_Valid always
610 -- returns True if the type of Expr is non-discrete. For discrete
611 -- types the value returned is True only if it can be determined
612 -- that the value is Valid. Otherwise False is returned.
614 procedure Insert_Valid_Check (Expr : Node_Id);
615 -- Inserts code that will check for the value of Expr being valid, in
616 -- the sense of the 'Valid attribute returning True. Constraint_Error
617 -- will be raised if the value is not valid.
619 procedure Remove_Checks (Expr : Node_Id);
620 -- Remove all checks from Expr except those that are only executed
621 -- conditionally (on the right side of And Then/Or Else. This call
622 -- removes only embedded checks (Do_Range_Check, Do_Overflow_Check).
626 type Check_Result is array (Positive range 1 .. 2) of Node_Id;
627 -- There are two cases for the result returned by Range_Check:
629 -- For the static case the result is one or two nodes that should cause
630 -- a Constraint_Error. Typically these will include Expr itself or the
631 -- direct descendents of Expr, such as Low/High_Bound (Expr)). It is the
632 -- responsibility of the caller to rewrite and substitute the nodes with
633 -- N_Raise_Constraint_Error nodes.
635 -- For the non-static case a single N_Raise_Constraint_Error node
636 -- with a non-empty Condition field is returned.
638 -- Unused entries in Check_Result, if any, are simply set to Empty
639 -- For external clients, the required processing on this result is
640 -- achieved using the Insert_Range_Checks routine.
642 pragma Inline (Apply_Length_Check);
643 pragma Inline (Apply_Range_Check);
644 pragma Inline (Apply_Static_Length_Check);
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