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1 | ------------------------------------------------------------------------------ |
2 | -- -- | |
3 | -- GNAT COMPILER COMPONENTS -- | |
4 | -- -- | |
5 | -- C H E C K S -- | |
6 | -- -- | |
7 | -- S p e c -- | |
8 | -- -- | |
11b4899f | 9 | -- Copyright (C) 1992-2007, Free Software Foundation, Inc. -- |
70482933 RK |
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- -- | |
b5c84c3c | 13 | -- ware Foundation; either version 3, or (at your option) any later ver- -- |
70482933 RK |
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 -- | |
b5c84c3c RD |
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. -- | |
70482933 RK |
20 | -- -- |
21 | -- GNAT was originally developed by the GNAT team at New York University. -- | |
71ff80dc | 22 | -- Extensive contributions were provided by Ada Core Technologies Inc. -- |
70482933 RK |
23 | -- -- |
24 | ------------------------------------------------------------------------------ | |
25 | ||
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. | |
30 | ||
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. | |
37 | ||
939c12d2 RD |
38 | with Namet; use Namet; |
39 | with Table; | |
40 | with Types; use Types; | |
41 | with Uintp; use Uintp; | |
70482933 RK |
42 | |
43 | package Checks is | |
44 | ||
45 | procedure Initialize; | |
46 | -- Called for each new main source program, to initialize internal | |
47 | -- variables used in the package body of the Checks unit. | |
48 | ||
49 | function Access_Checks_Suppressed (E : Entity_Id) return Boolean; | |
50 | function Accessibility_Checks_Suppressed (E : Entity_Id) return Boolean; | |
c064e066 | 51 | function Alignment_Checks_Suppressed (E : Entity_Id) return Boolean; |
70482933 RK |
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; | |
c064e066 RD |
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. | |
70482933 | 68 | |
11b4899f JM |
69 | ------------------------------------------- |
70 | -- Procedures to Activate Checking Flags -- | |
71 | ------------------------------------------- | |
72 | ||
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. | |
78 | ||
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. | |
84 | ||
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. | |
90 | ||
91 | -------------------------------- | |
92 | -- Procedures to Apply Checks -- | |
93 | -------------------------------- | |
94 | ||
70482933 RK |
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. | |
100 | ||
101 | procedure Apply_Access_Check (N : Node_Id); | |
fbf5a39b AC |
102 | -- Determines whether an expression node requires a runtime access |
103 | -- check and if so inserts the appropriate run-time check. | |
70482933 RK |
104 | |
105 | procedure Apply_Accessibility_Check (N : Node_Id; Typ : Entity_Id); | |
106 | -- Given a name N denoting an access parameter, emits a run-time | |
107 | -- accessibility check (if necessary), checking that the level of | |
108 | -- the object denoted by the access parameter is not deeper than the | |
109 | -- level of the type Typ. Program_Error is raised if the check fails. | |
110 | ||
c064e066 RD |
111 | procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id); |
112 | -- E is the entity for an object which has an address clause. If checks | |
113 | -- are enabled, then this procedure generates a check that the specified | |
114 | -- address has an alignment consistent with the alignment of the object, | |
115 | -- raising PE if this is not the case. The resulting check (if one is | |
116 | -- generated) is inserted before node N. check is also made for the case of | |
117 | -- a clear overlay situation that the size of the overlaying object is not | |
118 | -- larger than the overlaid object. | |
de76a39c | 119 | |
70482933 RK |
120 | procedure Apply_Arithmetic_Overflow_Check (N : Node_Id); |
121 | -- Given a binary arithmetic operator (+ - *) expand a software integer | |
122 | -- overflow check using range checks on a larger checking type or a call | |
123 | -- to an appropriate runtime routine. This is used for all three operators | |
124 | -- for the signed integer case, and for +/- in the fixed-point case. The | |
125 | -- check is expanded only if Software_Overflow_Checking is enabled and | |
126 | -- Do_Overflow_Check is set on node N. Note that divide is handled | |
127 | -- separately using Apply_Arithmetic_Divide_Overflow_Check. | |
128 | ||
129 | procedure Apply_Constraint_Check | |
130 | (N : Node_Id; | |
131 | Typ : Entity_Id; | |
132 | No_Sliding : Boolean := False); | |
133 | -- Top-level procedure, calls all the others depending on the class of Typ. | |
134 | -- Checks that expression N verifies the constraint of type Typ. No_Sliding | |
135 | -- is only relevant for constrained array types, id set to true, it | |
136 | -- checks that indexes are in range. | |
137 | ||
138 | procedure Apply_Discriminant_Check | |
139 | (N : Node_Id; | |
140 | Typ : Entity_Id; | |
141 | Lhs : Node_Id := Empty); | |
142 | -- Given an expression N of a discriminated type, or of an access type | |
143 | -- whose designated type is a discriminanted type, generates a check to | |
144 | -- ensure that the expression can be converted to the subtype given as | |
145 | -- the second parameter. Lhs is empty except in the case of assignments, | |
146 | -- where the target object may be needed to determine the subtype to | |
147 | -- check against (such as the cases of unconstrained formal parameters | |
148 | -- and unconstrained aliased objects). For the case of unconstrained | |
149 | -- formals, the check is peformed only if the corresponding actual is | |
150 | -- constrained, i.e., whether Lhs'Constrained is True. | |
151 | ||
152 | function Build_Discriminant_Checks | |
153 | (N : Node_Id; | |
154 | T_Typ : Entity_Id) | |
155 | return Node_Id; | |
156 | -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression | |
157 | -- that compares discriminants of the expression with discriminants of the | |
158 | -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In). | |
159 | ||
160 | procedure Apply_Divide_Check (N : Node_Id); | |
161 | -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem. An appropriate | |
162 | -- check is generated to ensure that the right operand is non-zero. In | |
163 | -- the divide case, we also check that we do not have the annoying case | |
164 | -- of the largest negative number divided by minus one. | |
165 | ||
166 | procedure Apply_Type_Conversion_Checks (N : Node_Id); | |
167 | -- N is an N_Type_Conversion node. A type conversion actually involves | |
168 | -- two sorts of checks. The first check is the checks that ensures that | |
169 | -- the operand in the type conversion fits onto the base type of the | |
170 | -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second | |
171 | -- check is there to ensure that once the operand has been converted to | |
172 | -- a value of the target type, this converted value meets the | |
173 | -- constraints imposed by the target subtype (see RM 4.6 (51)). | |
174 | ||
175 | procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id); | |
176 | -- The argument N is an attribute reference node intended for processing | |
177 | -- by gigi. The attribute is one that returns a universal integer, but | |
178 | -- the attribute reference node is currently typed with the expected | |
179 | -- result type. This routine deals with range and overflow checks needed | |
180 | -- to make sure that the universal result is in range. | |
181 | ||
182 | procedure Determine_Range | |
183 | (N : Node_Id; | |
184 | OK : out Boolean; | |
185 | Lo : out Uint; | |
186 | Hi : out Uint); | |
1525324e AC |
187 | -- N is a node for a subexpression. If N is of a discrete type with no |
188 | -- error indications, and no other peculiarities (e.g. missing type | |
189 | -- fields), then OK is True on return, and Lo and Hi are set to a | |
190 | -- conservative estimate of the possible range of values of N. Thus if OK | |
191 | -- is True on return, the value of the subexpression N is known to like in | |
192 | -- the range Lo .. Hi (inclusive). If the expression is not of a discrete | |
193 | -- type, or some kind of error condition is detected, then OK is False on | |
194 | -- exit, and Lo/Hi are set to No_Uint. Thus the significance of OK being | |
195 | -- False on return is that no useful information is available on the range | |
196 | -- of the expression. | |
197 | ||
198 | procedure Install_Null_Excluding_Check (N : Node_Id); | |
199 | -- Determines whether an access node requires a runtime access check and | |
200 | -- if so inserts the appropriate run-time check. | |
70482933 | 201 | |
fbf5a39b AC |
202 | ------------------------------------------------------- |
203 | -- Control and Optimization of Range/Overflow Checks -- | |
204 | ------------------------------------------------------- | |
205 | ||
206 | -- Range checks are controlled by the Do_Range_Check flag. The front end | |
207 | -- is responsible for setting this flag in relevant nodes. Originally | |
208 | -- the back end generated all corresponding range checks. But later on | |
209 | -- we decided to generate all range checks in the front end. We are now | |
210 | -- in the transitional phase where some of these checks are still done | |
211 | -- by the back end, but many are done by the front end. | |
212 | ||
1525324e AC |
213 | -- Overflow checks are similarly controlled by the Do_Overflow_Check flag. |
214 | -- The difference here is that if Backend_Overflow_Checks is is | |
215 | -- (Backend_Overflow_Checks_On_Target set False), then the actual overflow | |
216 | -- checks are generated by the front end, but if back end overflow checks | |
217 | -- are active (Backend_Overflow_Checks_On_Target set True), then the back | |
218 | -- end does generate the checks. | |
fbf5a39b AC |
219 | |
220 | -- The following two routines are used to set these flags, they allow | |
221 | -- for the possibility of eliminating checks. Checks can be eliminated | |
222 | -- if an identical check has already been performed. | |
223 | ||
224 | procedure Enable_Overflow_Check (N : Node_Id); | |
225 | -- First this routine determines if an overflow check is needed by doing | |
226 | -- an appropriate range check. If a check is not needed, then the call | |
227 | -- has no effect. If a check is needed then this routine sets the flag | |
228 | -- Set Do_Overflow_Check in node N to True, unless it can be determined | |
229 | -- that the check is not needed. The only condition under which this is | |
230 | -- the case is if there was an identical check earlier on. | |
231 | ||
232 | procedure Enable_Range_Check (N : Node_Id); | |
233 | -- Set Do_Range_Check flag in node N True, unless it can be determined | |
234 | -- that the check is not needed. The only condition under which this is | |
235 | -- the case is if there was an identical check earlier on. This routine | |
236 | -- is not responsible for doing range analysis to determine whether or | |
237 | -- not such a check is needed -- the caller is expected to do this. The | |
238 | -- one other case in which the request to set the flag is ignored is | |
239 | -- when Kill_Range_Check is set in an N_Unchecked_Conversion node. | |
240 | ||
241 | -- The following routines are used to keep track of processing sequences | |
242 | -- of statements (e.g. the THEN statements of an IF statement). A check | |
243 | -- that appears within such a sequence can eliminate an identical check | |
244 | -- within this sequence of statements. However, after the end of the | |
245 | -- sequence of statements, such a check is no longer of interest, since | |
246 | -- it may not have been executed. | |
247 | ||
248 | procedure Conditional_Statements_Begin; | |
249 | -- This call marks the start of processing of a sequence of statements. | |
250 | -- Every call to this procedure must be followed by a matching call to | |
251 | -- Conditional_Statements_End. | |
252 | ||
253 | procedure Conditional_Statements_End; | |
254 | -- This call removes from consideration all saved checks since the | |
255 | -- corresponding call to Conditional_Statements_Begin. These two | |
256 | -- procedures operate in a stack like manner. | |
257 | ||
258 | -- The mechanism for optimizing checks works by remembering checks | |
259 | -- that have already been made, but certain conditions, for example | |
260 | -- an assignment to a variable involved in a check, may mean that the | |
261 | -- remembered check is no longer valid, in the sense that if the same | |
262 | -- expression appears again, another check is required because the | |
263 | -- value may have changed. | |
264 | ||
265 | -- The following routines are used to note conditions which may render | |
266 | -- some or all of the stored and remembered checks to be invalidated. | |
267 | ||
268 | procedure Kill_Checks (V : Entity_Id); | |
269 | -- This procedure records an assignment or other condition that causes | |
270 | -- the value of the variable to be changed, invalidating any stored | |
271 | -- checks that reference the value. Note that all such checks must | |
272 | -- be discarded, even if they are not in the current statement range. | |
273 | ||
274 | procedure Kill_All_Checks; | |
9de61fcb | 275 | -- This procedure kills all remembered checks |
fbf5a39b | 276 | |
70482933 RK |
277 | ----------------------------- |
278 | -- Length and Range Checks -- | |
279 | ----------------------------- | |
280 | ||
281 | -- In the following procedures, there are three arguments which have | |
282 | -- a common meaning as follows: | |
283 | ||
284 | -- Expr The expression to be checked. If a check is required, | |
285 | -- the appropriate flag will be placed on this node. Whether | |
286 | -- this node is further examined depends on the setting of | |
287 | -- the parameter Source_Typ, as described below. | |
288 | ||
675d6070 TQ |
289 | -- ??? Apply_Length_Check and Apply_Range_Check do not have an Expr |
290 | -- formal | |
291 | ||
292 | -- ??? Apply_Length_Check and Apply_Range_Check have a Ck_Node formal | |
293 | -- which is undocumented, is it the same as Expr? | |
294 | ||
70482933 RK |
295 | -- Target_Typ The target type on which the check is to be based. For |
296 | -- example, if we have a scalar range check, then the check | |
297 | -- is that we are in range of this type. | |
298 | ||
299 | -- Source_Typ Normally Empty, but can be set to a type, in which case | |
300 | -- this type is used for the check, see below. | |
301 | ||
302 | -- The checks operate in one of two modes: | |
303 | ||
1525324e AC |
304 | -- If Source_Typ is Empty, then the node Expr is examined, at the very |
305 | -- least to get the source subtype. In addition for some of the checks, | |
306 | -- the actual form of the node may be examined. For example, a node of | |
307 | -- type Integer whose actual form is an Integer conversion from a type | |
308 | -- with range 0 .. 3 can be determined to have a value in range 0 .. 3. | |
70482933 | 309 | |
1525324e AC |
310 | -- If Source_Typ is given, then nothing can be assumed about the Expr, |
311 | -- and indeed its contents are not examined. In this case the check is | |
312 | -- based on the assumption that Expr can be an arbitrary value of the | |
313 | -- given Source_Typ. | |
70482933 RK |
314 | |
315 | -- Currently, the only case in which a Source_Typ is explicitly supplied | |
316 | -- is for the case of Out and In_Out parameters, where, for the conversion | |
317 | -- on return (the Out direction), the types must be reversed. This is | |
318 | -- handled by the caller. | |
319 | ||
320 | procedure Apply_Length_Check | |
321 | (Ck_Node : Node_Id; | |
322 | Target_Typ : Entity_Id; | |
323 | Source_Typ : Entity_Id := Empty); | |
324 | -- This procedure builds a sequence of declarations to do a length check | |
325 | -- that checks if the lengths of the two arrays Target_Typ and source type | |
326 | -- are the same. The resulting actions are inserted at Node using a call | |
327 | -- to Insert_Actions. | |
328 | -- | |
329 | -- For access types, the Directly_Designated_Type is retrieved and | |
1525324e AC |
330 | -- processing continues as enumerated above, with a guard against null |
331 | -- values. | |
70482933 RK |
332 | -- |
333 | -- Note: calls to Apply_Length_Check currently never supply an explicit | |
334 | -- Source_Typ parameter, but Apply_Length_Check takes this parameter and | |
335 | -- processes it as described above for consistency with the other routines | |
336 | -- in this section. | |
337 | ||
338 | procedure Apply_Range_Check | |
339 | (Ck_Node : Node_Id; | |
340 | Target_Typ : Entity_Id; | |
341 | Source_Typ : Entity_Id := Empty); | |
675d6070 | 342 | -- For a Node of kind N_Range, constructs a range check action that tests |
1525324e AC |
343 | -- first that the range is not null and then that the range is contained in |
344 | -- the Target_Typ range. | |
70482933 RK |
345 | -- |
346 | -- For scalar types, constructs a range check action that first tests that | |
347 | -- the expression is contained in the Target_Typ range. The difference | |
348 | -- between this and Apply_Scalar_Range_Check is that the latter generates | |
349 | -- the actual checking code in gigi against the Etype of the expression. | |
350 | -- | |
351 | -- For constrained array types, construct series of range check actions | |
352 | -- to check that each Expr range is properly contained in the range of | |
353 | -- Target_Typ. | |
354 | -- | |
1525324e AC |
355 | -- For a type conversion to an unconstrained array type, constructs a range |
356 | -- check action to check that the bounds of the source type are within the | |
357 | -- constraints imposed by the Target_Typ. | |
70482933 RK |
358 | -- |
359 | -- For access types, the Directly_Designated_Type is retrieved and | |
1525324e AC |
360 | -- processing continues as enumerated above, with a guard against null |
361 | -- values. | |
70482933 RK |
362 | -- |
363 | -- The source type is used by type conversions to unconstrained array | |
364 | -- types to retrieve the corresponding bounds. | |
365 | ||
366 | procedure Apply_Static_Length_Check | |
367 | (Expr : Node_Id; | |
368 | Target_Typ : Entity_Id; | |
369 | Source_Typ : Entity_Id := Empty); | |
370 | -- Tries to determine statically whether the two array types source type | |
371 | -- and Target_Typ have the same length. If it can be determined at compile | |
372 | -- time that they do not, then an N_Raise_Constraint_Error node replaces | |
373 | -- Expr, and a warning message is issued. | |
374 | ||
375 | procedure Apply_Scalar_Range_Check | |
376 | (Expr : Node_Id; | |
377 | Target_Typ : Entity_Id; | |
378 | Source_Typ : Entity_Id := Empty; | |
379 | Fixed_Int : Boolean := False); | |
380 | -- For scalar types, determines whether an expression node should be | |
1525324e AC |
381 | -- flagged as needing a runtime range check. If the node requires such a |
382 | -- check, the Do_Range_Check flag is turned on. The Fixed_Int flag if set | |
383 | -- causes any fixed-point values to be treated as though they were discrete | |
384 | -- values (i.e. the underlying integer value is used). | |
70482933 RK |
385 | |
386 | type Check_Result is private; | |
939c12d2 | 387 | -- Type used to return result of Get_Range_Checks call, for later use in |
70482933 RK |
388 | -- call to Insert_Range_Checks procedure. |
389 | ||
939c12d2 RD |
390 | function Get_Range_Checks |
391 | (Ck_Node : Node_Id; | |
392 | Target_Typ : Entity_Id; | |
393 | Source_Typ : Entity_Id := Empty; | |
394 | Warn_Node : Node_Id := Empty) return Check_Result; | |
395 | -- Like Apply_Range_Check, except it does not modify anything. Instead | |
396 | -- it returns an encapsulated result of the check operations for later | |
397 | -- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its | |
398 | -- Sloc is used, in the static case, for the generated warning or error. | |
399 | -- Additionally, it is used rather than Expr (or Low/High_Bound of Expr) | |
400 | -- in constructing the check. | |
401 | ||
70482933 RK |
402 | procedure Append_Range_Checks |
403 | (Checks : Check_Result; | |
404 | Stmts : List_Id; | |
405 | Suppress_Typ : Entity_Id; | |
406 | Static_Sloc : Source_Ptr; | |
407 | Flag_Node : Node_Id); | |
939c12d2 | 408 | -- Called to append range checks as returned by a call to Get_Range_Checks. |
1525324e AC |
409 | -- Stmts is a list to which either the dynamic check is appended or the |
410 | -- raise Constraint_Error statement is appended (for static checks). | |
411 | -- Static_Sloc is the Sloc at which the raise CE node points, Flag_Node is | |
412 | -- used as the node at which to set the Has_Dynamic_Check flag. Checks_On | |
413 | -- is a boolean value that says if range and index checking is on or not. | |
70482933 | 414 | |
70482933 RK |
415 | procedure Insert_Range_Checks |
416 | (Checks : Check_Result; | |
417 | Node : Node_Id; | |
418 | Suppress_Typ : Entity_Id; | |
419 | Static_Sloc : Source_Ptr := No_Location; | |
420 | Flag_Node : Node_Id := Empty; | |
421 | Do_Before : Boolean := False); | |
939c12d2 | 422 | -- Called to insert range checks as returned by a call to Get_Range_Checks. |
70482933 RK |
423 | -- Node is the node after which either the dynamic check is inserted or |
424 | -- the raise Constraint_Error statement is inserted (for static checks). | |
425 | -- Suppress_Typ is the type to check to determine if checks are suppressed. | |
426 | -- Static_Sloc, if passed, is the Sloc at which the raise CE node points, | |
427 | -- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally | |
428 | -- set at Node. If Flag_Node is present, then this is used instead as the | |
429 | -- node at which to set the Has_Dynamic_Check flag. Normally the check is | |
430 | -- inserted after, if Do_Before is True, the check is inserted before | |
431 | -- Node. | |
432 | ||
fbf5a39b AC |
433 | ----------------------- |
434 | -- Expander Routines -- | |
435 | ----------------------- | |
436 | ||
1525324e AC |
437 | -- Some of the earlier processing for checks results in temporarily setting |
438 | -- the Do_Range_Check flag rather than actually generating checks. Now we | |
439 | -- are moving the generation of such checks into the front end for reasons | |
440 | -- of efficiency and simplicity (there were difficutlies in handling this | |
441 | -- in the back end when side effects were present in the expressions being | |
442 | -- checked). | |
fbf5a39b AC |
443 | |
444 | -- Probably we could eliminate the Do_Range_Check flag entirely and | |
445 | -- generate the checks earlier, but this is a delicate area and it | |
446 | -- seemed safer to implement the following routines, which are called | |
447 | -- late on in the expansion process. They check the Do_Range_Check flag | |
448 | -- and if it is set, generate the actual checks and reset the flag. | |
449 | ||
450 | procedure Generate_Range_Check | |
451 | (N : Node_Id; | |
452 | Target_Type : Entity_Id; | |
453 | Reason : RT_Exception_Code); | |
1525324e AC |
454 | -- This procedure is called to actually generate and insert a range check. |
455 | -- A check is generated to ensure that the value of N lies within the range | |
456 | -- of the target type. Note that the base type of N may be different from | |
457 | -- the base type of the target type. This happens in the conversion case. | |
458 | -- The Reason parameter is the exception code to be used for the exception | |
459 | -- if raised. | |
fbf5a39b | 460 | -- |
1525324e AC |
461 | -- Note on the relation of this routine to the Do_Range_Check flag. Mostly |
462 | -- for historical reasons, we often set the Do_Range_Check flag and then | |
463 | -- later we call Generate_Range_Check if this flag is set. Most probably we | |
464 | -- could eliminate this intermediate setting of the flag (historically the | |
465 | -- back end dealt with range checks, using this flag to indicate if a check | |
466 | -- was required, then we moved checks into the front end). | |
fbf5a39b AC |
467 | |
468 | procedure Generate_Index_Checks (N : Node_Id); | |
1525324e AC |
469 | -- This procedure is called to generate index checks on the subscripts for |
470 | -- the indexed component node N. Each subscript expression is examined, and | |
471 | -- if the Do_Range_Check flag is set, an appropriate index check is | |
472 | -- generated and the flag is reset. | |
fbf5a39b AC |
473 | |
474 | -- Similarly, we set the flag Do_Discriminant_Check in the semantic | |
1525324e AC |
475 | -- analysis to indicate that a discriminant check is required for selected |
476 | -- component of a discriminated type. The following routine is called from | |
477 | -- the expander to actually generate the call. | |
fbf5a39b AC |
478 | |
479 | procedure Generate_Discriminant_Check (N : Node_Id); | |
1525324e AC |
480 | -- N is a selected component for which a discriminant check is required to |
481 | -- make sure that the discriminants have appropriate values for the | |
482 | -- selection. This is done by calling the appropriate discriminant checking | |
483 | -- routine for the selector. | |
fbf5a39b | 484 | |
70482933 RK |
485 | ----------------------- |
486 | -- Validity Checking -- | |
487 | ----------------------- | |
488 | ||
489 | -- In (RM 13.9.1(9-11)) we have the following rules on invalid values | |
490 | ||
1525324e AC |
491 | -- If the representation of a scalar object does not represent value of |
492 | -- the object's subtype (perhaps because the object was not initialized), | |
493 | -- the object is said to have an invalid representation. It is a bounded | |
494 | -- error to evaluate the value of such an object. If the error is | |
495 | -- detected, either Constraint_Error or Program_Error is raised. | |
496 | -- Otherwise, execution continues using the invalid representation. The | |
497 | -- rules of the language outside this subclause assume that all objects | |
498 | -- have valid representations. The semantics of operations on invalid | |
499 | -- representations are as follows: | |
70482933 RK |
500 | -- |
501 | -- 10 If the representation of the object represents a value of the | |
502 | -- object's type, the value of the type is used. | |
503 | -- | |
504 | -- 11 If the representation of the object does not represent a value | |
505 | -- of the object's type, the semantics of operations on such | |
506 | -- representations is implementation-defined, but does not by | |
507 | -- itself lead to erroneous or unpredictable execution, or to | |
508 | -- other objects becoming abnormal. | |
509 | ||
510 | -- We quote the rules in full here since they are quite delicate. Most | |
511 | -- of the time, we can just compute away with wrong values, and get a | |
512 | -- possibly wrong result, which is well within the range of allowed | |
513 | -- implementation defined behavior. The two tricky cases are subscripted | |
514 | -- array assignments, where we don't want to do wild stores, and case | |
515 | -- statements where we don't want to do wild jumps. | |
516 | ||
1525324e AC |
517 | -- In GNAT, we control validity checking with a switch -gnatV that can take |
518 | -- three parameters, n/d/f for None/Default/Full. These modes have the | |
519 | -- following meanings: | |
70482933 RK |
520 | |
521 | -- None (no validity checking) | |
522 | ||
523 | -- In this mode, there is no specific checking for invalid values | |
524 | -- and the code generator assumes that all stored values are always | |
525 | -- within the bounds of the object subtype. The consequences are as | |
526 | -- follows: | |
527 | ||
528 | -- For case statements, an out of range invalid value will cause | |
529 | -- Constraint_Error to be raised, or an arbitrary one of the case | |
530 | -- alternatives will be executed. Wild jumps cannot result even | |
531 | -- in this mode, since we always do a range check | |
532 | ||
533 | -- For subscripted array assignments, wild stores will result in | |
534 | -- the expected manner when addresses are calculated using values | |
535 | -- of subscripts that are out of range. | |
536 | ||
537 | -- It could perhaps be argued that this mode is still conformant with | |
538 | -- the letter of the RM, since implementation defined is a rather | |
539 | -- broad category, but certainly it is not in the spirit of the | |
540 | -- RM requirement, since wild stores certainly seem to be a case of | |
541 | -- erroneous behavior. | |
542 | ||
543 | -- Default (default standard RM-compatible validity checking) | |
544 | ||
545 | -- In this mode, which is the default, minimal validity checking is | |
546 | -- performed to ensure no erroneous behavior as follows: | |
547 | ||
548 | -- For case statements, an out of range invalid value will cause | |
549 | -- Constraint_Error to be raised. | |
550 | ||
551 | -- For subscripted array assignments, invalid out of range | |
552 | -- subscript values will cause Constraint_Error to be raised. | |
553 | ||
554 | -- Full (Full validity checking) | |
555 | ||
556 | -- In this mode, the protections guaranteed by the standard mode are | |
557 | -- in place, and the following additional checks are made: | |
558 | ||
559 | -- For every assignment, the right side is checked for validity | |
560 | ||
561 | -- For every call, IN and IN OUT parameters are checked for validity | |
562 | ||
563 | -- For every subscripted array reference, both for stores and loads, | |
564 | -- all subscripts are checked for validity. | |
565 | ||
566 | -- These checks are not required by the RM, but will in practice | |
567 | -- improve the detection of uninitialized variables, particularly | |
568 | -- if used in conjunction with pragma Normalize_Scalars. | |
569 | ||
570 | -- In the above description, we talk about performing validity checks, | |
571 | -- but we don't actually generate a check in a case where the compiler | |
572 | -- can be sure that the value is valid. Note that this assurance must | |
573 | -- be achieved without assuming that any uninitialized value lies within | |
574 | -- the range of its type. The following are cases in which values are | |
575 | -- known to be valid. The flag Is_Known_Valid is used to keep track of | |
576 | -- some of these cases. | |
577 | ||
578 | -- If all possible stored values are valid, then any uninitialized | |
579 | -- value must be valid. | |
580 | ||
9de61fcb | 581 | -- Literals, including enumeration literals, are clearly always valid |
70482933 RK |
582 | |
583 | -- Constants are always assumed valid, with a validity check being | |
584 | -- performed on the initializing value where necessary to ensure that | |
585 | -- this is the case. | |
586 | ||
587 | -- For variables, the status is set to known valid if there is an | |
588 | -- initializing expression. Again a check is made on the initializing | |
589 | -- value if necessary to ensure that this assumption is valid. The | |
590 | -- status can change as a result of local assignments to a variable. | |
591 | -- If a known valid value is unconditionally assigned, then we mark | |
592 | -- the left side as known valid. If a value is assigned that is not | |
593 | -- known to be valid, then we mark the left side as invalid. This | |
594 | -- kind of processing does NOT apply to non-local variables since we | |
595 | -- are not following the flow graph (more properly the flow of actual | |
596 | -- processing only corresponds to the flow graph for local assignments). | |
597 | -- For non-local variables, we preserve the current setting, i.e. a | |
598 | -- validity check is performed when assigning to a knonwn valid global. | |
599 | ||
600 | -- Note: no validity checking is required if range checks are suppressed | |
601 | -- regardless of the setting of the validity checking mode. | |
602 | ||
603 | -- The following procedures are used in handling validity checking | |
604 | ||
605 | procedure Apply_Subscript_Validity_Checks (Expr : Node_Id); | |
606 | -- Expr is the node for an indexed component. If validity checking and | |
607 | -- range checking are enabled, all subscripts for this indexed component | |
608 | -- are checked for validity. | |
609 | ||
610 | procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id); | |
1525324e AC |
611 | -- Expr is a lvalue, i.e. an expression representing the target of an |
612 | -- assignment. This procedure checks for this expression involving an | |
613 | -- assignment to an array value. We have to be sure that all the subscripts | |
614 | -- in such a case are valid, since according to the rules in (RM | |
615 | -- 13.9.1(9-11)) such assignments are not permitted to result in erroneous | |
616 | -- behavior in the case of invalid subscript values. | |
70482933 RK |
617 | |
618 | procedure Ensure_Valid (Expr : Node_Id; Holes_OK : Boolean := False); | |
619 | -- Ensure that Expr represents a valid value of its type. If this type | |
620 | -- is not a scalar type, then the call has no effect, since validity | |
621 | -- is only an issue for scalar types. The effect of this call is to | |
622 | -- check if the value is known valid, if so, nothing needs to be done. | |
623 | -- If this is not known, then either Expr is set to be range checked, | |
624 | -- or specific checking code is inserted so that an exception is raised | |
625 | -- if the value is not valid. | |
626 | -- | |
627 | -- The optional argument Holes_OK indicates whether it is necessary to | |
628 | -- worry about enumeration types with non-standard representations leading | |
629 | -- to "holes" in the range of possible representations. If Holes_OK is | |
630 | -- True, then such values are assumed valid (this is used when the caller | |
631 | -- will make a separate check for this case anyway). If Holes_OK is False, | |
632 | -- then this case is checked, and code is inserted to ensure that Expr is | |
633 | -- valid, raising Constraint_Error if the value is not valid. | |
634 | ||
635 | function Expr_Known_Valid (Expr : Node_Id) return Boolean; | |
1525324e AC |
636 | -- This function tests it the value of Expr is known to be valid in the |
637 | -- sense of RM 13.9.1(9-11). In the case of GNAT, it is only discrete types | |
638 | -- which are a concern, since for non-discrete types we simply continue | |
639 | -- computation with invalid values, which does not lead to erroneous | |
640 | -- behavior. Thus Expr_Known_Valid always returns True if the type of Expr | |
641 | -- is non-discrete. For discrete types the value returned is True only if | |
642 | -- it can be determined that the value is Valid. Otherwise False is | |
643 | -- returned. | |
70482933 RK |
644 | |
645 | procedure Insert_Valid_Check (Expr : Node_Id); | |
646 | -- Inserts code that will check for the value of Expr being valid, in | |
647 | -- the sense of the 'Valid attribute returning True. Constraint_Error | |
648 | -- will be raised if the value is not valid. | |
649 | ||
2820d220 | 650 | procedure Null_Exclusion_Static_Checks (N : Node_Id); |
0ab80019 | 651 | -- Ada 2005 (AI-231): Check bad usages of the null-exclusion issue |
2820d220 | 652 | |
8cbb664e MG |
653 | procedure Remove_Checks (Expr : Node_Id); |
654 | -- Remove all checks from Expr except those that are only executed | |
655 | -- conditionally (on the right side of And Then/Or Else. This call | |
656 | -- removes only embedded checks (Do_Range_Check, Do_Overflow_Check). | |
657 | ||
c064e066 RD |
658 | procedure Validity_Check_Range (N : Node_Id); |
659 | -- If N is an N_Range node, then Ensure_Valid is called on its bounds, | |
660 | -- if validity checking of operands is enabled. | |
661 | ||
939c12d2 RD |
662 | ----------------------------- |
663 | -- Handling of Check Names -- | |
664 | ----------------------------- | |
665 | ||
666 | -- The following table contains Name_Id's for recognized checks. The first | |
667 | -- entries (corresponding to the values of the subtype Predefined_Check_Id) | |
668 | -- contain the Name_Id values for the checks that are predefined, including | |
669 | -- All_Checks (see Types). Remaining entries are those that are introduced | |
670 | -- by pragma Check_Names. | |
671 | ||
672 | package Check_Names is new Table.Table ( | |
673 | Table_Component_Type => Name_Id, | |
674 | Table_Index_Type => Check_Id, | |
675 | Table_Low_Bound => 1, | |
676 | Table_Initial => 30, | |
677 | Table_Increment => 200, | |
678 | Table_Name => "Name_Check_Names"); | |
679 | ||
680 | function Get_Check_Id (N : Name_Id) return Check_Id; | |
681 | -- Function to search above table for matching name. If found returns the | |
682 | -- corresponding Check_Id value in the range 1 .. Check_Name.Last. If not | |
683 | -- found returns No_Check_Id. | |
684 | ||
70482933 RK |
685 | private |
686 | ||
687 | type Check_Result is array (Positive range 1 .. 2) of Node_Id; | |
688 | -- There are two cases for the result returned by Range_Check: | |
689 | -- | |
690 | -- For the static case the result is one or two nodes that should cause | |
691 | -- a Constraint_Error. Typically these will include Expr itself or the | |
692 | -- direct descendents of Expr, such as Low/High_Bound (Expr)). It is the | |
693 | -- responsibility of the caller to rewrite and substitute the nodes with | |
694 | -- N_Raise_Constraint_Error nodes. | |
695 | -- | |
1525324e AC |
696 | -- For the non-static case a single N_Raise_Constraint_Error node with a |
697 | -- non-empty Condition field is returned. | |
70482933 | 698 | -- |
1525324e AC |
699 | -- Unused entries in Check_Result, if any, are simply set to Empty For |
700 | -- external clients, the required processing on this result is achieved | |
701 | -- using the Insert_Range_Checks routine. | |
70482933 | 702 | |
70482933 RK |
703 | pragma Inline (Apply_Length_Check); |
704 | pragma Inline (Apply_Range_Check); | |
705 | pragma Inline (Apply_Static_Length_Check); | |
706 | end Checks; |