1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2008, 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 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. --
21 -- GNAT was originally developed by the GNAT team at New York University. --
22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
24 ------------------------------------------------------------------------------
26 -- Package containing routines used to deal with runtime checks. These
27 -- routines are used both by the semantics and by the expander. In some
28 -- cases, checks are enabled simply by setting flags for gigi, and in
29 -- other cases the code for the check is expanded.
31 -- The approach used for range and length checks, in regards to suppressed
32 -- checks, is to attempt to detect at compilation time that a constraint
33 -- error will occur. If this is detected a warning or error is issued and the
34 -- offending expression or statement replaced with a constraint error node.
35 -- This always occurs whether checks are suppressed or not. Dynamic range
36 -- checks are, of course, not inserted if checks are suppressed.
38 with Namet; use Namet;
40 with Types; use Types;
41 with Uintp; use Uintp;
46 -- Called for each new main source program, to initialize internal
47 -- variables used in the package body of the Checks unit.
49 function Access_Checks_Suppressed (E : Entity_Id) return Boolean;
50 function Accessibility_Checks_Suppressed (E : Entity_Id) return Boolean;
51 function Alignment_Checks_Suppressed (E : Entity_Id) return Boolean;
52 function Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean;
53 function Division_Checks_Suppressed (E : Entity_Id) return Boolean;
54 function Elaboration_Checks_Suppressed (E : Entity_Id) return Boolean;
55 function Index_Checks_Suppressed (E : Entity_Id) return Boolean;
56 function Length_Checks_Suppressed (E : Entity_Id) return Boolean;
57 function Overflow_Checks_Suppressed (E : Entity_Id) return Boolean;
58 function Range_Checks_Suppressed (E : Entity_Id) return Boolean;
59 function Storage_Checks_Suppressed (E : Entity_Id) return Boolean;
60 function Tag_Checks_Suppressed (E : Entity_Id) return Boolean;
61 function Validity_Checks_Suppressed (E : Entity_Id) return Boolean;
62 -- These functions check to see if the named check is suppressed, either
63 -- by an active scope suppress setting, or because the check has been
64 -- specifically suppressed for the given entity. If no entity is relevant
65 -- for the current check, then Empty is used as an argument. Note: the
66 -- reason we insist on specifying Empty is to force the caller to think
67 -- about whether there is any relevant entity that should be checked.
69 -------------------------------------------
70 -- Procedures to Activate Checking Flags --
71 -------------------------------------------
73 procedure Activate_Division_Check (N : Node_Id);
74 pragma Inline (Activate_Division_Check);
75 -- Sets Do_Division_Check flag in node N, and handles possible local raise.
76 -- Always call this routine rather than calling Set_Do_Division_Check to
77 -- set an explicit value of True, to ensure handling the local raise case.
79 procedure Activate_Overflow_Check (N : Node_Id);
80 pragma Inline (Activate_Overflow_Check);
81 -- Sets Do_Overflow_Check flag in node N, and handles possible local raise.
82 -- Always call this routine rather than calling Set_Do_Overflow_Check to
83 -- set an explicit value of True, to ensure handling the local raise case.
85 procedure Activate_Range_Check (N : Node_Id);
86 pragma Inline (Activate_Range_Check);
87 -- Sets Do_Range_Check flag in node N, and handles possible local raise
88 -- Always call this routine rather than calling Set_Do_Range_Check to
89 -- set an explicit value of True, to ensure handling the local raise case.
91 --------------------------------
92 -- Procedures to Apply Checks --
93 --------------------------------
95 -- General note on following checks. These checks are always active if
96 -- Expander_Active and not Inside_A_Generic. They are inactive and have
97 -- no effect Inside_A_Generic. In the case where not Expander_Active
98 -- and not Inside_A_Generic, most of them are inactive, but some of them
99 -- operate anyway since they may generate useful compile time warnings.
101 procedure Apply_Access_Check (N : Node_Id);
102 -- Determines whether an expression node requires a runtime access
103 -- check and if so inserts the appropriate run-time check.
105 procedure Apply_Accessibility_Check
108 Insert_Node : Node_Id);
109 -- Given a name N denoting an access parameter, emits a run-time
110 -- accessibility check (if necessary), checking that the level of
111 -- the object denoted by the access parameter is not deeper than the
112 -- level of the type Typ. Program_Error is raised if the check fails.
113 -- Insert_Node indicates the node where the check should be inserted.
115 procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id);
116 -- E is the entity for an object which has an address clause. If checks
117 -- are enabled, then this procedure generates a check that the specified
118 -- address has an alignment consistent with the alignment of the object,
119 -- raising PE if this is not the case. The resulting check (if one is
120 -- generated) is inserted before node N. check is also made for the case of
121 -- a clear overlay situation that the size of the overlaying object is not
122 -- larger than the overlaid object.
124 procedure Apply_Arithmetic_Overflow_Check (N : Node_Id);
125 -- Given a binary arithmetic operator (+ - *) expand a software integer
126 -- overflow check using range checks on a larger checking type or a call
127 -- to an appropriate runtime routine. This is used for all three operators
128 -- for the signed integer case, and for +/- in the fixed-point case. The
129 -- check is expanded only if Software_Overflow_Checking is enabled and
130 -- Do_Overflow_Check is set on node N. Note that divide is handled
131 -- separately using Apply_Arithmetic_Divide_Overflow_Check.
133 procedure Apply_Constraint_Check
136 No_Sliding : Boolean := False);
137 -- Top-level procedure, calls all the others depending on the class of Typ.
138 -- Checks that expression N satisfies the constraint of type Typ.
139 -- No_Sliding is only relevant for constrained array types, if set to True,
140 -- it checks that indexes are in range.
142 procedure Apply_Discriminant_Check
145 Lhs : Node_Id := Empty);
146 -- Given an expression N of a discriminated type, or of an access type
147 -- whose designated type is a discriminanted type, generates a check to
148 -- ensure that the expression can be converted to the subtype given as
149 -- the second parameter. Lhs is empty except in the case of assignments,
150 -- where the target object may be needed to determine the subtype to
151 -- check against (such as the cases of unconstrained formal parameters
152 -- and unconstrained aliased objects). For the case of unconstrained
153 -- formals, the check is peformed only if the corresponding actual is
154 -- constrained, i.e., whether Lhs'Constrained is True.
156 function Build_Discriminant_Checks
160 -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression
161 -- that compares discriminants of the expression with discriminants of the
162 -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In).
164 procedure Apply_Divide_Check (N : Node_Id);
165 -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem. An appropriate
166 -- check is generated to ensure that the right operand is non-zero. In
167 -- the divide case, we also check that we do not have the annoying case
168 -- of the largest negative number divided by minus one.
170 procedure Apply_Type_Conversion_Checks (N : Node_Id);
171 -- N is an N_Type_Conversion node. A type conversion actually involves
172 -- two sorts of checks. The first check is the checks that ensures that
173 -- the operand in the type conversion fits onto the base type of the
174 -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second
175 -- check is there to ensure that once the operand has been converted to
176 -- a value of the target type, this converted value meets the
177 -- constraints imposed by the target subtype (see RM 4.6 (51)).
179 procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id);
180 -- The argument N is an attribute reference node intended for processing
181 -- by gigi. The attribute is one that returns a universal integer, but
182 -- the attribute reference node is currently typed with the expected
183 -- result type. This routine deals with range and overflow checks needed
184 -- to make sure that the universal result is in range.
186 procedure Determine_Range
191 Assume_Valid : Boolean := False);
192 -- N is a node for a subexpression. If N is of a discrete type with no
193 -- error indications, and no other peculiarities (e.g. missing type
194 -- fields), then OK is True on return, and Lo and Hi are set to a
195 -- conservative estimate of the possible range of values of N. Thus if OK
196 -- is True on return, the value of the subexpression N is known to like in
197 -- the range Lo .. Hi (inclusive). If the expression is not of a discrete
198 -- type, or some kind of error condition is detected, then OK is False on
199 -- exit, and Lo/Hi are set to No_Uint. Thus the significance of OK being
200 -- False on return is that no useful information is available on the range
201 -- of the expression. Assume_Valid determines whether the processing is
202 -- allowed to assume that values are in range of their subtypes. If it is
203 -- set to True, then this assumption is valid, if False, then processing
204 -- is done using base types to allow invalid values.
206 procedure Install_Null_Excluding_Check (N : Node_Id);
207 -- Determines whether an access node requires a runtime access check and
208 -- if so inserts the appropriate run-time check.
210 -------------------------------------------------------
211 -- Control and Optimization of Range/Overflow Checks --
212 -------------------------------------------------------
214 -- Range checks are controlled by the Do_Range_Check flag. The front end
215 -- is responsible for setting this flag in relevant nodes. Originally
216 -- the back end generated all corresponding range checks. But later on
217 -- we decided to generate many range checks in the front end. We are now
218 -- in the transitional phase where some of these checks are still done
219 -- by the back end, but many are done by the front end. It is possible
220 -- that in the future we might move all the checks to the front end. The
221 -- main remaining back end checks are for subscript checking.
223 -- Overflow checks are similarly controlled by the Do_Overflow_Check flag.
224 -- The difference here is that if back end overflow checks are inactive
225 -- (Backend_Overflow_Checks_On_Target set False), then the actual overflow
226 -- checks are generated by the front end, but if back end overflow checks
227 -- are active (Backend_Overflow_Checks_On_Target set True), then the back
228 -- end does generate the checks.
230 -- The following two routines are used to set these flags, they allow
231 -- for the possibility of eliminating checks. Checks can be eliminated
232 -- if an identical check has already been performed.
234 procedure Enable_Overflow_Check (N : Node_Id);
235 -- First this routine determines if an overflow check is needed by doing
236 -- an appropriate range check. If a check is not needed, then the call
237 -- has no effect. If a check is needed then this routine sets the flag
238 -- Do_Overflow_Check in node N to True, unless it can be determined that
239 -- the check is not needed. The only condition under which this is the
240 -- case is if there was an identical check earlier on.
242 procedure Enable_Range_Check (N : Node_Id);
243 -- Set Do_Range_Check flag in node N True, unless it can be determined
244 -- that the check is not needed. The only condition under which this is
245 -- the case is if there was an identical check earlier on. This routine
246 -- is not responsible for doing range analysis to determine whether or
247 -- not such a check is needed -- the caller is expected to do this. The
248 -- one other case in which the request to set the flag is ignored is
249 -- when Kill_Range_Check is set in an N_Unchecked_Conversion node.
251 -- The following routines are used to keep track of processing sequences
252 -- of statements (e.g. the THEN statements of an IF statement). A check
253 -- that appears within such a sequence can eliminate an identical check
254 -- within this sequence of statements. However, after the end of the
255 -- sequence of statements, such a check is no longer of interest, since
256 -- it may not have been executed.
258 procedure Conditional_Statements_Begin;
259 -- This call marks the start of processing of a sequence of statements.
260 -- Every call to this procedure must be followed by a matching call to
261 -- Conditional_Statements_End.
263 procedure Conditional_Statements_End;
264 -- This call removes from consideration all saved checks since the
265 -- corresponding call to Conditional_Statements_Begin. These two
266 -- procedures operate in a stack like manner.
268 -- The mechanism for optimizing checks works by remembering checks
269 -- that have already been made, but certain conditions, for example
270 -- an assignment to a variable involved in a check, may mean that the
271 -- remembered check is no longer valid, in the sense that if the same
272 -- expression appears again, another check is required because the
273 -- value may have changed.
275 -- The following routines are used to note conditions which may render
276 -- some or all of the stored and remembered checks to be invalidated.
278 procedure Kill_Checks (V : Entity_Id);
279 -- This procedure records an assignment or other condition that causes
280 -- the value of the variable to be changed, invalidating any stored
281 -- checks that reference the value. Note that all such checks must
282 -- be discarded, even if they are not in the current statement range.
284 procedure Kill_All_Checks;
285 -- This procedure kills all remembered checks
287 -----------------------------
288 -- Length and Range Checks --
289 -----------------------------
291 -- In the following procedures, there are three arguments which have
292 -- a common meaning as follows:
294 -- Expr The expression to be checked. If a check is required,
295 -- the appropriate flag will be placed on this node. Whether
296 -- this node is further examined depends on the setting of
297 -- the parameter Source_Typ, as described below.
299 -- ??? Apply_Length_Check and Apply_Range_Check do not have an Expr
302 -- ??? Apply_Length_Check and Apply_Range_Check have a Ck_Node formal
303 -- which is undocumented, is it the same as Expr?
305 -- Target_Typ The target type on which the check is to be based. For
306 -- example, if we have a scalar range check, then the check
307 -- is that we are in range of this type.
309 -- Source_Typ Normally Empty, but can be set to a type, in which case
310 -- this type is used for the check, see below.
312 -- The checks operate in one of two modes:
314 -- If Source_Typ is Empty, then the node Expr is examined, at the very
315 -- least to get the source subtype. In addition for some of the checks,
316 -- the actual form of the node may be examined. For example, a node of
317 -- type Integer whose actual form is an Integer conversion from a type
318 -- with range 0 .. 3 can be determined to have a value in range 0 .. 3.
320 -- If Source_Typ is given, then nothing can be assumed about the Expr,
321 -- and indeed its contents are not examined. In this case the check is
322 -- based on the assumption that Expr can be an arbitrary value of the
325 -- Currently, the only case in which a Source_Typ is explicitly supplied
326 -- is for the case of Out and In_Out parameters, where, for the conversion
327 -- on return (the Out direction), the types must be reversed. This is
328 -- handled by the caller.
330 procedure Apply_Length_Check
332 Target_Typ : Entity_Id;
333 Source_Typ : Entity_Id := Empty);
334 -- This procedure builds a sequence of declarations to do a length check
335 -- that checks if the lengths of the two arrays Target_Typ and source type
336 -- are the same. The resulting actions are inserted at Node using a call
337 -- to Insert_Actions.
339 -- For access types, the Directly_Designated_Type is retrieved and
340 -- processing continues as enumerated above, with a guard against null
343 -- Note: calls to Apply_Length_Check currently never supply an explicit
344 -- Source_Typ parameter, but Apply_Length_Check takes this parameter and
345 -- processes it as described above for consistency with the other routines
348 procedure Apply_Range_Check
350 Target_Typ : Entity_Id;
351 Source_Typ : Entity_Id := Empty);
352 -- For a Node of kind N_Range, constructs a range check action that tests
353 -- first that the range is not null and then that the range is contained in
354 -- the Target_Typ range.
356 -- For scalar types, constructs a range check action that first tests that
357 -- the expression is contained in the Target_Typ range. The difference
358 -- between this and Apply_Scalar_Range_Check is that the latter generates
359 -- the actual checking code in gigi against the Etype of the expression.
361 -- For constrained array types, construct series of range check actions
362 -- to check that each Expr range is properly contained in the range of
365 -- For a type conversion to an unconstrained array type, constructs a range
366 -- check action to check that the bounds of the source type are within the
367 -- constraints imposed by the Target_Typ.
369 -- For access types, the Directly_Designated_Type is retrieved and
370 -- processing continues as enumerated above, with a guard against null
373 -- The source type is used by type conversions to unconstrained array
374 -- types to retrieve the corresponding bounds.
376 procedure Apply_Static_Length_Check
378 Target_Typ : Entity_Id;
379 Source_Typ : Entity_Id := Empty);
380 -- Tries to determine statically whether the two array types source type
381 -- and Target_Typ have the same length. If it can be determined at compile
382 -- time that they do not, then an N_Raise_Constraint_Error node replaces
383 -- Expr, and a warning message is issued.
385 procedure Apply_Scalar_Range_Check
387 Target_Typ : Entity_Id;
388 Source_Typ : Entity_Id := Empty;
389 Fixed_Int : Boolean := False);
390 -- For scalar types, determines whether an expression node should be
391 -- flagged as needing a runtime range check. If the node requires such a
392 -- check, the Do_Range_Check flag is turned on. The Fixed_Int flag if set
393 -- causes any fixed-point values to be treated as though they were discrete
394 -- values (i.e. the underlying integer value is used).
396 type Check_Result is private;
397 -- Type used to return result of Get_Range_Checks call, for later use in
398 -- call to Insert_Range_Checks procedure.
400 function Get_Range_Checks
402 Target_Typ : Entity_Id;
403 Source_Typ : Entity_Id := Empty;
404 Warn_Node : Node_Id := Empty) return Check_Result;
405 -- Like Apply_Range_Check, except it does not modify anything. Instead
406 -- it returns an encapsulated result of the check operations for later
407 -- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its
408 -- Sloc is used, in the static case, for the generated warning or error.
409 -- Additionally, it is used rather than Expr (or Low/High_Bound of Expr)
410 -- in constructing the check.
412 procedure Append_Range_Checks
413 (Checks : Check_Result;
415 Suppress_Typ : Entity_Id;
416 Static_Sloc : Source_Ptr;
417 Flag_Node : Node_Id);
418 -- Called to append range checks as returned by a call to Get_Range_Checks.
419 -- Stmts is a list to which either the dynamic check is appended or the
420 -- raise Constraint_Error statement is appended (for static checks).
421 -- Static_Sloc is the Sloc at which the raise CE node points, Flag_Node is
422 -- used as the node at which to set the Has_Dynamic_Check flag. Checks_On
423 -- is a boolean value that says if range and index checking is on or not.
425 procedure Insert_Range_Checks
426 (Checks : Check_Result;
428 Suppress_Typ : Entity_Id;
429 Static_Sloc : Source_Ptr := No_Location;
430 Flag_Node : Node_Id := Empty;
431 Do_Before : Boolean := False);
432 -- Called to insert range checks as returned by a call to Get_Range_Checks.
433 -- Node is the node after which either the dynamic check is inserted or
434 -- the raise Constraint_Error statement is inserted (for static checks).
435 -- Suppress_Typ is the type to check to determine if checks are suppressed.
436 -- Static_Sloc, if passed, is the Sloc at which the raise CE node points,
437 -- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally
438 -- set at Node. If Flag_Node is present, then this is used instead as the
439 -- node at which to set the Has_Dynamic_Check flag. Normally the check is
440 -- inserted after, if Do_Before is True, the check is inserted before
443 -----------------------
444 -- Expander Routines --
445 -----------------------
447 -- Some of the earlier processing for checks results in temporarily setting
448 -- the Do_Range_Check flag rather than actually generating checks. Now we
449 -- are moving the generation of such checks into the front end for reasons
450 -- of efficiency and simplicity (there were difficulties in handling this
451 -- in the back end when side effects were present in the expressions being
454 -- Probably we could eliminate the Do_Range_Check flag entirely and
455 -- generate the checks earlier, but this is a delicate area and it
456 -- seemed safer to implement the following routines, which are called
457 -- late on in the expansion process. They check the Do_Range_Check flag
458 -- and if it is set, generate the actual checks and reset the flag.
460 procedure Generate_Range_Check
462 Target_Type : Entity_Id;
463 Reason : RT_Exception_Code);
464 -- This procedure is called to actually generate and insert a range check.
465 -- A check is generated to ensure that the value of N lies within the range
466 -- of the target type. Note that the base type of N may be different from
467 -- the base type of the target type. This happens in the conversion case.
468 -- The Reason parameter is the exception code to be used for the exception
471 -- Note on the relation of this routine to the Do_Range_Check flag. Mostly
472 -- for historical reasons, we often set the Do_Range_Check flag and then
473 -- later we call Generate_Range_Check if this flag is set. Most probably we
474 -- could eliminate this intermediate setting of the flag (historically the
475 -- back end dealt with range checks, using this flag to indicate if a check
476 -- was required, then we moved checks into the front end).
478 procedure Generate_Index_Checks (N : Node_Id);
479 -- This procedure is called to generate index checks on the subscripts for
480 -- the indexed component node N. Each subscript expression is examined, and
481 -- if the Do_Range_Check flag is set, an appropriate index check is
482 -- generated and the flag is reset.
484 -- Similarly, we set the flag Do_Discriminant_Check in the semantic
485 -- analysis to indicate that a discriminant check is required for selected
486 -- component of a discriminated type. The following routine is called from
487 -- the expander to actually generate the call.
489 procedure Generate_Discriminant_Check (N : Node_Id);
490 -- N is a selected component for which a discriminant check is required to
491 -- make sure that the discriminants have appropriate values for the
492 -- selection. This is done by calling the appropriate discriminant checking
493 -- routine for the selector.
495 -----------------------
496 -- Validity Checking --
497 -----------------------
499 -- In (RM 13.9.1(9-11)) we have the following rules on invalid values
501 -- If the representation of a scalar object does not represent value of
502 -- the object's subtype (perhaps because the object was not initialized),
503 -- the object is said to have an invalid representation. It is a bounded
504 -- error to evaluate the value of such an object. If the error is
505 -- detected, either Constraint_Error or Program_Error is raised.
506 -- Otherwise, execution continues using the invalid representation. The
507 -- rules of the language outside this subclause assume that all objects
508 -- have valid representations. The semantics of operations on invalid
509 -- representations are as follows:
511 -- 10 If the representation of the object represents a value of the
512 -- object's type, the value of the type is used.
514 -- 11 If the representation of the object does not represent a value
515 -- of the object's type, the semantics of operations on such
516 -- representations is implementation-defined, but does not by
517 -- itself lead to erroneous or unpredictable execution, or to
518 -- other objects becoming abnormal.
520 -- We quote the rules in full here since they are quite delicate. Most
521 -- of the time, we can just compute away with wrong values, and get a
522 -- possibly wrong result, which is well within the range of allowed
523 -- implementation defined behavior. The two tricky cases are subscripted
524 -- array assignments, where we don't want to do wild stores, and case
525 -- statements where we don't want to do wild jumps.
527 -- In GNAT, we control validity checking with a switch -gnatV that can take
528 -- three parameters, n/d/f for None/Default/Full. These modes have the
529 -- following meanings:
531 -- None (no validity checking)
533 -- In this mode, there is no specific checking for invalid values
534 -- and the code generator assumes that all stored values are always
535 -- within the bounds of the object subtype. The consequences are as
538 -- For case statements, an out of range invalid value will cause
539 -- Constraint_Error to be raised, or an arbitrary one of the case
540 -- alternatives will be executed. Wild jumps cannot result even
541 -- in this mode, since we always do a range check
543 -- For subscripted array assignments, wild stores will result in
544 -- the expected manner when addresses are calculated using values
545 -- of subscripts that are out of range.
547 -- It could perhaps be argued that this mode is still conformant with
548 -- the letter of the RM, since implementation defined is a rather
549 -- broad category, but certainly it is not in the spirit of the
550 -- RM requirement, since wild stores certainly seem to be a case of
551 -- erroneous behavior.
553 -- Default (default standard RM-compatible validity checking)
555 -- In this mode, which is the default, minimal validity checking is
556 -- performed to ensure no erroneous behavior as follows:
558 -- For case statements, an out of range invalid value will cause
559 -- Constraint_Error to be raised.
561 -- For subscripted array assignments, invalid out of range
562 -- subscript values will cause Constraint_Error to be raised.
564 -- Full (Full validity checking)
566 -- In this mode, the protections guaranteed by the standard mode are
567 -- in place, and the following additional checks are made:
569 -- For every assignment, the right side is checked for validity
571 -- For every call, IN and IN OUT parameters are checked for validity
573 -- For every subscripted array reference, both for stores and loads,
574 -- all subscripts are checked for validity.
576 -- These checks are not required by the RM, but will in practice
577 -- improve the detection of uninitialized variables, particularly
578 -- if used in conjunction with pragma Normalize_Scalars.
580 -- In the above description, we talk about performing validity checks,
581 -- but we don't actually generate a check in a case where the compiler
582 -- can be sure that the value is valid. Note that this assurance must
583 -- be achieved without assuming that any uninitialized value lies within
584 -- the range of its type. The following are cases in which values are
585 -- known to be valid. The flag Is_Known_Valid is used to keep track of
586 -- some of these cases.
588 -- If all possible stored values are valid, then any uninitialized
589 -- value must be valid.
591 -- Literals, including enumeration literals, are clearly always valid
593 -- Constants are always assumed valid, with a validity check being
594 -- performed on the initializing value where necessary to ensure that
597 -- For variables, the status is set to known valid if there is an
598 -- initializing expression. Again a check is made on the initializing
599 -- value if necessary to ensure that this assumption is valid. The
600 -- status can change as a result of local assignments to a variable.
601 -- If a known valid value is unconditionally assigned, then we mark
602 -- the left side as known valid. If a value is assigned that is not
603 -- known to be valid, then we mark the left side as invalid. This
604 -- kind of processing does NOT apply to non-local variables since we
605 -- are not following the flow graph (more properly the flow of actual
606 -- processing only corresponds to the flow graph for local assignments).
607 -- For non-local variables, we preserve the current setting, i.e. a
608 -- validity check is performed when assigning to a knonwn valid global.
610 -- Note: no validity checking is required if range checks are suppressed
611 -- regardless of the setting of the validity checking mode.
613 -- The following procedures are used in handling validity checking
615 procedure Apply_Subscript_Validity_Checks (Expr : Node_Id);
616 -- Expr is the node for an indexed component. If validity checking and
617 -- range checking are enabled, all subscripts for this indexed component
618 -- are checked for validity.
620 procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id);
621 -- Expr is a lvalue, i.e. an expression representing the target of an
622 -- assignment. This procedure checks for this expression involving an
623 -- assignment to an array value. We have to be sure that all the subscripts
624 -- in such a case are valid, since according to the rules in (RM
625 -- 13.9.1(9-11)) such assignments are not permitted to result in erroneous
626 -- behavior in the case of invalid subscript values.
628 procedure Ensure_Valid (Expr : Node_Id; Holes_OK : Boolean := False);
629 -- Ensure that Expr represents a valid value of its type. If this type
630 -- is not a scalar type, then the call has no effect, since validity
631 -- is only an issue for scalar types. The effect of this call is to
632 -- check if the value is known valid, if so, nothing needs to be done.
633 -- If this is not known, then either Expr is set to be range checked,
634 -- or specific checking code is inserted so that an exception is raised
635 -- if the value is not valid.
637 -- The optional argument Holes_OK indicates whether it is necessary to
638 -- worry about enumeration types with non-standard representations leading
639 -- to "holes" in the range of possible representations. If Holes_OK is
640 -- True, then such values are assumed valid (this is used when the caller
641 -- will make a separate check for this case anyway). If Holes_OK is False,
642 -- then this case is checked, and code is inserted to ensure that Expr is
643 -- valid, raising Constraint_Error if the value is not valid.
645 function Expr_Known_Valid (Expr : Node_Id) return Boolean;
646 -- This function tests it the value of Expr is known to be valid in the
647 -- sense of RM 13.9.1(9-11). In the case of GNAT, it is only discrete types
648 -- which are a concern, since for non-discrete types we simply continue
649 -- computation with invalid values, which does not lead to erroneous
650 -- behavior. Thus Expr_Known_Valid always returns True if the type of Expr
651 -- is non-discrete. For discrete types the value returned is True only if
652 -- it can be determined that the value is Valid. Otherwise False is
655 procedure Insert_Valid_Check (Expr : Node_Id);
656 -- Inserts code that will check for the value of Expr being valid, in
657 -- the sense of the 'Valid attribute returning True. Constraint_Error
658 -- will be raised if the value is not valid.
660 procedure Null_Exclusion_Static_Checks (N : Node_Id);
661 -- Ada 2005 (AI-231): Check bad usages of the null-exclusion issue
663 procedure Remove_Checks (Expr : Node_Id);
664 -- Remove all checks from Expr except those that are only executed
665 -- conditionally (on the right side of And Then/Or Else. This call
666 -- removes only embedded checks (Do_Range_Check, Do_Overflow_Check).
668 procedure Validity_Check_Range (N : Node_Id);
669 -- If N is an N_Range node, then Ensure_Valid is called on its bounds,
670 -- if validity checking of operands is enabled.
672 -----------------------------
673 -- Handling of Check Names --
674 -----------------------------
676 -- The following table contains Name_Id's for recognized checks. The first
677 -- entries (corresponding to the values of the subtype Predefined_Check_Id)
678 -- contain the Name_Id values for the checks that are predefined, including
679 -- All_Checks (see Types). Remaining entries are those that are introduced
680 -- by pragma Check_Names.
682 package Check_Names is new Table.Table (
683 Table_Component_Type => Name_Id,
684 Table_Index_Type => Check_Id,
685 Table_Low_Bound => 1,
687 Table_Increment => 200,
688 Table_Name => "Name_Check_Names");
690 function Get_Check_Id (N : Name_Id) return Check_Id;
691 -- Function to search above table for matching name. If found returns the
692 -- corresponding Check_Id value in the range 1 .. Check_Name.Last. If not
693 -- found returns No_Check_Id.
697 type Check_Result is array (Positive range 1 .. 2) of Node_Id;
698 -- There are two cases for the result returned by Range_Check:
700 -- For the static case the result is one or two nodes that should cause
701 -- a Constraint_Error. Typically these will include Expr itself or the
702 -- direct descendents of Expr, such as Low/High_Bound (Expr)). It is the
703 -- responsibility of the caller to rewrite and substitute the nodes with
704 -- N_Raise_Constraint_Error nodes.
706 -- For the non-static case a single N_Raise_Constraint_Error node with a
707 -- non-empty Condition field is returned.
709 -- Unused entries in Check_Result, if any, are simply set to Empty For
710 -- external clients, the required processing on this result is achieved
711 -- using the Insert_Range_Checks routine.
713 pragma Inline (Apply_Length_Check);
714 pragma Inline (Apply_Range_Check);
715 pragma Inline (Apply_Static_Length_Check);
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