1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- C H E C K S -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2012, Free Software Foundation, Inc. -- 10-- -- 11-- GNAT is free software; you can redistribute it and/or modify it under -- 12-- terms of the GNU General Public License as published by the Free Soft- -- 13-- ware Foundation; either version 3, or (at your option) any later ver- -- 14-- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- 15-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- 16-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License -- 17-- for more details. You should have received a copy of the GNU General -- 18-- Public License distributed with GNAT; see file COPYING3. If not, go to -- 19-- http://www.gnu.org/licenses for a complete copy of the license. -- 20-- -- 21-- GNAT was originally developed by the GNAT team at New York University. -- 22-- Extensive contributions were provided by Ada Core Technologies Inc. -- 23-- -- 24------------------------------------------------------------------------------ 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 38with Namet; use Namet; 39with Table; 40with Types; use Types; 41with Uintp; use Uintp; 42 43package 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; 51 function Alignment_Checks_Suppressed (E : Entity_Id) return Boolean; 52 function Atomic_Synchronization_Disabled (E : Entity_Id) return Boolean; 53 function Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean; 54 function Division_Checks_Suppressed (E : Entity_Id) return Boolean; 55 function Elaboration_Checks_Suppressed (E : Entity_Id) return Boolean; 56 function Index_Checks_Suppressed (E : Entity_Id) return Boolean; 57 function Length_Checks_Suppressed (E : Entity_Id) return Boolean; 58 function Overflow_Checks_Suppressed (E : Entity_Id) return Boolean; 59 function Range_Checks_Suppressed (E : Entity_Id) return Boolean; 60 function Storage_Checks_Suppressed (E : Entity_Id) return Boolean; 61 function Tag_Checks_Suppressed (E : Entity_Id) return Boolean; 62 function Validity_Checks_Suppressed (E : Entity_Id) return Boolean; 63 -- These functions check to see if the named check is suppressed, either 64 -- by an active scope suppress setting, or because the check has been 65 -- specifically suppressed for the given entity. If no entity is relevant 66 -- for the current check, then Empty is used as an argument. Note: the 67 -- reason we insist on specifying Empty is to force the caller to think 68 -- about whether there is any relevant entity that should be checked. 69 70 function Is_Check_Suppressed (E : Entity_Id; C : Check_Id) return Boolean; 71 -- This function is called if Checks_May_Be_Suppressed (E) is True to 72 -- determine whether check C is suppressed either on the entity E or 73 -- as the result of a scope suppress pragma. If Checks_May_Be_Suppressed 74 -- is False, then the status of the check can be determined simply by 75 -- examining Scope_Suppress, so this routine is not called in that case. 76 77 function Overflow_Check_Mode return Overflow_Mode_Type; 78 -- Returns current overflow checking mode, taking into account whether 79 -- we are inside an assertion expression. 80 81 ------------------------------------------- 82 -- Procedures to Activate Checking Flags -- 83 ------------------------------------------- 84 85 procedure Activate_Division_Check (N : Node_Id); 86 pragma Inline (Activate_Division_Check); 87 -- Sets Do_Division_Check flag in node N, and handles possible local raise. 88 -- Always call this routine rather than calling Set_Do_Division_Check to 89 -- set an explicit value of True, to ensure handling the local raise case. 90 91 procedure Activate_Overflow_Check (N : Node_Id); 92 pragma Inline (Activate_Overflow_Check); 93 -- Sets Do_Overflow_Check flag in node N, and handles possible local raise. 94 -- Always call this routine rather than calling Set_Do_Overflow_Check to 95 -- set an explicit value of True, to ensure handling the local raise case. 96 -- Note that this call has no effect for MOD, REM, and unary "+" for which 97 -- overflow is never possible in any case. 98 99 procedure Activate_Range_Check (N : Node_Id); 100 pragma Inline (Activate_Range_Check); 101 -- Sets Do_Range_Check flag in node N, and handles possible local raise 102 -- Always call this routine rather than calling Set_Do_Range_Check to 103 -- set an explicit value of True, to ensure handling the local raise case. 104 105 -------------------------------- 106 -- Procedures to Apply Checks -- 107 -------------------------------- 108 109 -- General note on following checks. These checks are always active if 110 -- Expander_Active and not Inside_A_Generic. They are inactive and have 111 -- no effect Inside_A_Generic. In the case where not Expander_Active 112 -- and not Inside_A_Generic, most of them are inactive, but some of them 113 -- operate anyway since they may generate useful compile time warnings. 114 115 procedure Apply_Access_Check (N : Node_Id); 116 -- Determines whether an expression node requires a runtime access 117 -- check and if so inserts the appropriate run-time check. 118 119 procedure Apply_Accessibility_Check 120 (N : Node_Id; 121 Typ : Entity_Id; 122 Insert_Node : Node_Id); 123 -- Given a name N denoting an access parameter, emits a run-time 124 -- accessibility check (if necessary), checking that the level of 125 -- the object denoted by the access parameter is not deeper than the 126 -- level of the type Typ. Program_Error is raised if the check fails. 127 -- Insert_Node indicates the node where the check should be inserted. 128 129 procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id); 130 -- E is the entity for an object which has an address clause. If checks 131 -- are enabled, then this procedure generates a check that the specified 132 -- address has an alignment consistent with the alignment of the object, 133 -- raising PE if this is not the case. The resulting check (if one is 134 -- generated) is prepended to the Actions list of N_Freeze_Entity node N. 135 -- Note that the check references E'Alignment, so it cannot be emitted 136 -- before N (its freeze node), otherwise this would cause an illegal 137 -- access before elaboration error in GIGI. For the case of a clear overlay 138 -- situation, we also check that the size of the overlaying object is not 139 -- larger than the overlaid object. 140 141 procedure Apply_Arithmetic_Overflow_Check (N : Node_Id); 142 -- Handle overflow checking for an arithmetic operator. Also handles the 143 -- cases of ELIMINATED and MINIMIZED overflow checking mode. If the mode 144 -- is one of the latter two, then this routine can also be called with 145 -- an if or case expression node to make sure that we properly handle 146 -- overflow checking for dependent expressions. This routine handles 147 -- front end vs back end overflow checks (in the front end case it expands 148 -- the necessary check). Note that divide is handled separately using 149 -- Apply_Divide_Checks. Node N may or may not have Do_Overflow_Check. 150 -- In STRICT mode, there is nothing to do if this flag is off, but in 151 -- MINIMIZED/ELIMINATED mode we still have to deal with possible use 152 -- of doing operations in Long_Long_Integer or Bignum mode. 153 154 procedure Apply_Constraint_Check 155 (N : Node_Id; 156 Typ : Entity_Id; 157 No_Sliding : Boolean := False); 158 -- Top-level procedure, calls all the others depending on the class of 159 -- Typ. Checks that expression N satisfies the constraint of type Typ. 160 -- No_Sliding is only relevant for constrained array types, if set to 161 -- True, it checks that indexes are in range. 162 163 procedure Apply_Discriminant_Check 164 (N : Node_Id; 165 Typ : Entity_Id; 166 Lhs : Node_Id := Empty); 167 -- Given an expression N of a discriminated type, or of an access type 168 -- whose designated type is a discriminanted type, generates a check to 169 -- ensure that the expression can be converted to the subtype given as 170 -- the second parameter. Lhs is empty except in the case of assignments, 171 -- where the target object may be needed to determine the subtype to 172 -- check against (such as the cases of unconstrained formal parameters 173 -- and unconstrained aliased objects). For the case of unconstrained 174 -- formals, the check is performed only if the corresponding actual is 175 -- constrained, i.e., whether Lhs'Constrained is True. 176 177 procedure Apply_Divide_Checks (N : Node_Id); 178 -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem if either of the 179 -- flags Do_Division_Check or Do_Overflow_Check is set, then this routine 180 -- ensures that the appropriate checks are made. Note that overflow can 181 -- occur in the signed case for the case of the largest negative number 182 -- divided by minus one. 183 184 procedure Apply_Parameter_Aliasing_Checks 185 (Call : Node_Id; 186 Subp : Entity_Id); 187 -- Given a subprogram call Call, add a check to verify that none of the 188 -- actuals overlap. Subp denotes the subprogram being called. 189 190 procedure Apply_Parameter_Validity_Checks (Subp : Entity_Id); 191 -- Given a subprogram Subp, add both a pre and post condition pragmas that 192 -- verify the proper initialization of scalars in parameters and function 193 -- results. 194 195 procedure Apply_Predicate_Check (N : Node_Id; Typ : Entity_Id); 196 -- N is an expression to which a predicate check may need to be applied 197 -- for Typ, if Typ has a predicate function. The check is applied only 198 -- if the type of N does not match Typ. 199 200 procedure Apply_Type_Conversion_Checks (N : Node_Id); 201 -- N is an N_Type_Conversion node. A type conversion actually involves 202 -- two sorts of checks. The first check is the checks that ensures that 203 -- the operand in the type conversion fits onto the base type of the 204 -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second 205 -- check is there to ensure that once the operand has been converted to 206 -- a value of the target type, this converted value meets the 207 -- constraints imposed by the target subtype (see RM 4.6 (51)). 208 209 procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id); 210 -- The argument N is an attribute reference node intended for processing 211 -- by gigi. The attribute is one that returns a universal integer, but 212 -- the attribute reference node is currently typed with the expected 213 -- result type. This routine deals with range and overflow checks needed 214 -- to make sure that the universal result is in range. 215 216 function Build_Discriminant_Checks 217 (N : Node_Id; 218 T_Typ : Entity_Id) 219 return Node_Id; 220 -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression 221 -- that compares discriminants of the expression with discriminants of the 222 -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In). 223 224 function Convert_From_Bignum (N : Node_Id) return Node_Id; 225 -- Returns result of converting node N from Bignum. The returned value is 226 -- not analyzed, the caller takes responsibility for this. Node N must be 227 -- a subexpression node of type Bignum. The result is Long_Long_Integer. 228 229 function Convert_To_Bignum (N : Node_Id) return Node_Id; 230 -- Returns result of converting node N to Bignum. The returned value is not 231 -- analyzed, the caller takes responsibility for this. Node N must be a 232 -- subexpression node of a signed integer type or Bignum type (if it is 233 -- already a Bignum, the returned value is Relocate_Node (N)). 234 235 procedure Determine_Range 236 (N : Node_Id; 237 OK : out Boolean; 238 Lo : out Uint; 239 Hi : out Uint; 240 Assume_Valid : Boolean := False); 241 -- N is a node for a subexpression. If N is of a discrete type with no 242 -- error indications, and no other peculiarities (e.g. missing Etype), 243 -- then OK is True on return, and Lo and Hi are set to a conservative 244 -- estimate of the possible range of values of N. Thus if OK is True on 245 -- return, the value of the subexpression N is known to lie in the range 246 -- Lo .. Hi (inclusive). If the expression is not of a discrete type, or 247 -- some kind of error condition is detected, then OK is False on exit, and 248 -- Lo/Hi are set to No_Uint. Thus the significance of OK being False on 249 -- return is that no useful information is available on the range of the 250 -- expression. Assume_Valid determines whether the processing is allowed to 251 -- assume that values are in range of their subtypes. If it is set to True, 252 -- then this assumption is valid, if False, then processing is done using 253 -- base types to allow invalid values. 254 255 procedure Install_Null_Excluding_Check (N : Node_Id); 256 -- Determines whether an access node requires a runtime access check and 257 -- if so inserts the appropriate run-time check. 258 259 function Make_Bignum_Block (Loc : Source_Ptr) return Node_Id; 260 -- This function is used by top level overflow checking routines to do a 261 -- mark/release operation on the secondary stack around bignum operations. 262 -- The block created looks like: 263 -- 264 -- declare 265 -- M : Mark_Id := SS_Mark; 266 -- begin 267 -- SS_Release (M); 268 -- end; 269 -- 270 -- The idea is that the caller will insert any needed extra declarations 271 -- after the declaration of M, and any needed statements (in particular 272 -- the bignum operations) before the call to SS_Release, and then do an 273 -- Insert_Action of the whole block (it is returned unanalyzed). The Loc 274 -- parameter is used to supply Sloc values for the constructed tree. 275 276 procedure Minimize_Eliminate_Overflows 277 (N : Node_Id; 278 Lo : out Uint; 279 Hi : out Uint; 280 Top_Level : Boolean); 281 -- This is the main routine for handling MINIMIZED and ELIMINATED overflow 282 -- processing. On entry N is a node whose result is a signed integer 283 -- subtype. The Do_Overflow_Check flag may or may not be set on N. If the 284 -- node is an arithmetic operation, then a range analysis is carried out, 285 -- and there are three possibilities: 286 -- 287 -- The node is left unchanged (apart from expansion of an exponentiation 288 -- operation). This happens if the routine can determine that the result 289 -- is definitely in range. The Do_Overflow_Check flag is turned off in 290 -- this case. 291 -- 292 -- The node is transformed into an arithmetic operation with a result 293 -- type of Long_Long_Integer. 294 -- 295 -- The node is transformed into a function call that calls an appropriate 296 -- function in the System.Bignums package to compute a Bignum result. 297 -- 298 -- In the first two cases, Lo and Hi are set to the bounds of the possible 299 -- range of results, computed as accurately as possible. In the third case 300 -- Lo and Hi are set to No_Uint (there are some cases where we could get an 301 -- advantage from keeping result ranges for Bignum values, but it could use 302 -- a lot of space and is very unlikely to be valuable). 303 -- 304 -- If the node is not an arithmetic operation, then it is unchanged but 305 -- Lo and Hi are still set (to the bounds of the result subtype if nothing 306 -- better can be determined). 307 -- 308 -- Note: this function is recursive, if called with an arithmetic operator, 309 -- recursive calls are made to process the operands using this procedure. 310 -- So we end up doing things top down. Nothing happens to an arithmetic 311 -- expression until this procedure is called on the top level node and 312 -- then the recursive calls process all the children. We have to do it 313 -- this way. If we try to do it bottom up in natural expansion order, then 314 -- there are two problems. First, where do we stash the bounds, and more 315 -- importantly, semantic processing will be messed up. Consider A+B+C where 316 -- A,B,C are all of type integer, if we processed A+B before doing semantic 317 -- analysis of the addition of this result to C, that addition could end up 318 -- with a Long_Long_Integer left operand and an Integer right operand, and 319 -- we would get a semantic error. 320 -- 321 -- The routine is called in three situations if we are operating in either 322 -- MINIMIZED or ELIMINATED modes. 323 -- 324 -- Overflow processing applied to the top node of an expression tree when 325 -- that node is an arithmetic operator. In this case the result is 326 -- converted to the appropriate result type (there is special processing 327 -- when the parent is a conversion, see body for details). 328 -- 329 -- Overflow processing applied to the operands of a comparison operation. 330 -- In this case, the comparison is done on the result Long_Long_Integer 331 -- or Bignum values, without raising any exceptions. 332 -- 333 -- Overflow processing applied to the left operand of a membership test. 334 -- In this case no exception is raised if a Long_Long_Integer or Bignum 335 -- result is outside the range of the type of that left operand (it is 336 -- just that the result of IN is false in that case). 337 -- 338 -- Note that if Bignum values appear, the caller must take care of doing 339 -- the appropriate mark/release operations on the secondary stack. 340 -- 341 -- Top_Level is used to avoid inefficient unnecessary transitions into the 342 -- Bignum domain. If Top_Level is True, it means that the caller will have 343 -- to convert any Bignum value back to Long_Long_Integer, possibly checking 344 -- that the value is in range. This is the normal case for a top level 345 -- operator in a subexpression. There is no point in going into Bignum mode 346 -- to avoid an overflow just so we can check for overflow the next moment. 347 -- For calls from comparisons and membership tests, and for all recursive 348 -- calls, we do want to transition into the Bignum domain if necessary. 349 -- Note that this setting is only relevant in ELIMINATED mode. 350 351 ------------------------------------------------------- 352 -- Control and Optimization of Range/Overflow Checks -- 353 ------------------------------------------------------- 354 355 -- Range checks are controlled by the Do_Range_Check flag. The front end 356 -- is responsible for setting this flag in relevant nodes. Originally 357 -- the back end generated all corresponding range checks. But later on 358 -- we decided to generate many range checks in the front end. We are now 359 -- in the transitional phase where some of these checks are still done 360 -- by the back end, but many are done by the front end. It is possible 361 -- that in the future we might move all the checks to the front end. The 362 -- main remaining back end checks are for subscript checking. 363 364 -- Overflow checks are similarly controlled by the Do_Overflow_Check flag. 365 -- The difference here is that if back end overflow checks are inactive 366 -- (Backend_Overflow_Checks_On_Target set False), then the actual overflow 367 -- checks are generated by the front end, but if back end overflow checks 368 -- are active (Backend_Overflow_Checks_On_Target set True), then the back 369 -- end does generate the checks. 370 371 -- The following two routines are used to set these flags, they allow 372 -- for the possibility of eliminating checks. Checks can be eliminated 373 -- if an identical check has already been performed. 374 375 procedure Enable_Overflow_Check (N : Node_Id); 376 -- First this routine determines if an overflow check is needed by doing 377 -- an appropriate range check. If a check is not needed, then the call 378 -- has no effect. If a check is needed then this routine sets the flag 379 -- Do_Overflow_Check in node N to True, unless it can be determined that 380 -- the check is not needed. The only condition under which this is the 381 -- case is if there was an identical check earlier on. 382 383 procedure Enable_Range_Check (N : Node_Id); 384 -- Set Do_Range_Check flag in node N True, unless it can be determined 385 -- that the check is not needed. The only condition under which this is 386 -- the case is if there was an identical check earlier on. This routine 387 -- is not responsible for doing range analysis to determine whether or 388 -- not such a check is needed -- the caller is expected to do this. The 389 -- one other case in which the request to set the flag is ignored is 390 -- when Kill_Range_Check is set in an N_Unchecked_Conversion node. 391 392 -- The following routines are used to keep track of processing sequences 393 -- of statements (e.g. the THEN statements of an IF statement). A check 394 -- that appears within such a sequence can eliminate an identical check 395 -- within this sequence of statements. However, after the end of the 396 -- sequence of statements, such a check is no longer of interest, since 397 -- it may not have been executed. 398 399 procedure Conditional_Statements_Begin; 400 -- This call marks the start of processing of a sequence of statements. 401 -- Every call to this procedure must be followed by a matching call to 402 -- Conditional_Statements_End. 403 404 procedure Conditional_Statements_End; 405 -- This call removes from consideration all saved checks since the 406 -- corresponding call to Conditional_Statements_Begin. These two 407 -- procedures operate in a stack like manner. 408 409 -- The mechanism for optimizing checks works by remembering checks 410 -- that have already been made, but certain conditions, for example 411 -- an assignment to a variable involved in a check, may mean that the 412 -- remembered check is no longer valid, in the sense that if the same 413 -- expression appears again, another check is required because the 414 -- value may have changed. 415 416 -- The following routines are used to note conditions which may render 417 -- some or all of the stored and remembered checks to be invalidated. 418 419 procedure Kill_Checks (V : Entity_Id); 420 -- This procedure records an assignment or other condition that causes 421 -- the value of the variable to be changed, invalidating any stored 422 -- checks that reference the value. Note that all such checks must 423 -- be discarded, even if they are not in the current statement range. 424 425 procedure Kill_All_Checks; 426 -- This procedure kills all remembered checks 427 428 ----------------------------- 429 -- Length and Range Checks -- 430 ----------------------------- 431 432 -- In the following procedures, there are three arguments which have 433 -- a common meaning as follows: 434 435 -- Expr The expression to be checked. If a check is required, 436 -- the appropriate flag will be placed on this node. Whether 437 -- this node is further examined depends on the setting of 438 -- the parameter Source_Typ, as described below. 439 440 -- ??? Apply_Length_Check and Apply_Range_Check do not have an Expr 441 -- formal 442 443 -- ??? Apply_Length_Check and Apply_Range_Check have a Ck_Node formal 444 -- which is undocumented, is it the same as Expr? 445 446 -- Target_Typ The target type on which the check is to be based. For 447 -- example, if we have a scalar range check, then the check 448 -- is that we are in range of this type. 449 450 -- Source_Typ Normally Empty, but can be set to a type, in which case 451 -- this type is used for the check, see below. 452 453 -- The checks operate in one of two modes: 454 455 -- If Source_Typ is Empty, then the node Expr is examined, at the very 456 -- least to get the source subtype. In addition for some of the checks, 457 -- the actual form of the node may be examined. For example, a node of 458 -- type Integer whose actual form is an Integer conversion from a type 459 -- with range 0 .. 3 can be determined to have a value in range 0 .. 3. 460 461 -- If Source_Typ is given, then nothing can be assumed about the Expr, 462 -- and indeed its contents are not examined. In this case the check is 463 -- based on the assumption that Expr can be an arbitrary value of the 464 -- given Source_Typ. 465 466 -- Currently, the only case in which a Source_Typ is explicitly supplied 467 -- is for the case of Out and In_Out parameters, where, for the conversion 468 -- on return (the Out direction), the types must be reversed. This is 469 -- handled by the caller. 470 471 procedure Apply_Length_Check 472 (Ck_Node : Node_Id; 473 Target_Typ : Entity_Id; 474 Source_Typ : Entity_Id := Empty); 475 -- This procedure builds a sequence of declarations to do a length check 476 -- that checks if the lengths of the two arrays Target_Typ and source type 477 -- are the same. The resulting actions are inserted at Node using a call 478 -- to Insert_Actions. 479 -- 480 -- For access types, the Directly_Designated_Type is retrieved and 481 -- processing continues as enumerated above, with a guard against null 482 -- values. 483 -- 484 -- Note: calls to Apply_Length_Check currently never supply an explicit 485 -- Source_Typ parameter, but Apply_Length_Check takes this parameter and 486 -- processes it as described above for consistency with the other routines 487 -- in this section. 488 489 procedure Apply_Range_Check 490 (Ck_Node : Node_Id; 491 Target_Typ : Entity_Id; 492 Source_Typ : Entity_Id := Empty); 493 -- For a Node of kind N_Range, constructs a range check action that tests 494 -- first that the range is not null and then that the range is contained in 495 -- the Target_Typ range. 496 -- 497 -- For scalar types, constructs a range check action that first tests that 498 -- the expression is contained in the Target_Typ range. The difference 499 -- between this and Apply_Scalar_Range_Check is that the latter generates 500 -- the actual checking code in gigi against the Etype of the expression. 501 -- 502 -- For constrained array types, construct series of range check actions 503 -- to check that each Expr range is properly contained in the range of 504 -- Target_Typ. 505 -- 506 -- For a type conversion to an unconstrained array type, constructs a range 507 -- check action to check that the bounds of the source type are within the 508 -- constraints imposed by the Target_Typ. 509 -- 510 -- For access types, the Directly_Designated_Type is retrieved and 511 -- processing continues as enumerated above, with a guard against null 512 -- values. 513 -- 514 -- The source type is used by type conversions to unconstrained array 515 -- types to retrieve the corresponding bounds. 516 517 procedure Apply_Static_Length_Check 518 (Expr : Node_Id; 519 Target_Typ : Entity_Id; 520 Source_Typ : Entity_Id := Empty); 521 -- Tries to determine statically whether the two array types source type 522 -- and Target_Typ have the same length. If it can be determined at compile 523 -- time that they do not, then an N_Raise_Constraint_Error node replaces 524 -- Expr, and a warning message is issued. 525 526 procedure Apply_Scalar_Range_Check 527 (Expr : Node_Id; 528 Target_Typ : Entity_Id; 529 Source_Typ : Entity_Id := Empty; 530 Fixed_Int : Boolean := False); 531 -- For scalar types, determines whether an expression node should be 532 -- flagged as needing a runtime range check. If the node requires such a 533 -- check, the Do_Range_Check flag is turned on. The Fixed_Int flag if set 534 -- causes any fixed-point values to be treated as though they were discrete 535 -- values (i.e. the underlying integer value is used). 536 537 type Check_Result is private; 538 -- Type used to return result of Get_Range_Checks call, for later use in 539 -- call to Insert_Range_Checks procedure. 540 541 function Get_Range_Checks 542 (Ck_Node : Node_Id; 543 Target_Typ : Entity_Id; 544 Source_Typ : Entity_Id := Empty; 545 Warn_Node : Node_Id := Empty) return Check_Result; 546 -- Like Apply_Range_Check, except it does not modify anything. Instead 547 -- it returns an encapsulated result of the check operations for later 548 -- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its 549 -- Sloc is used, in the static case, for the generated warning or error. 550 -- Additionally, it is used rather than Expr (or Low/High_Bound of Expr) 551 -- in constructing the check. 552 553 procedure Append_Range_Checks 554 (Checks : Check_Result; 555 Stmts : List_Id; 556 Suppress_Typ : Entity_Id; 557 Static_Sloc : Source_Ptr; 558 Flag_Node : Node_Id); 559 -- Called to append range checks as returned by a call to Get_Range_Checks. 560 -- Stmts is a list to which either the dynamic check is appended or the 561 -- raise Constraint_Error statement is appended (for static checks). 562 -- Static_Sloc is the Sloc at which the raise CE node points, Flag_Node is 563 -- used as the node at which to set the Has_Dynamic_Check flag. Checks_On 564 -- is a boolean value that says if range and index checking is on or not. 565 566 procedure Insert_Range_Checks 567 (Checks : Check_Result; 568 Node : Node_Id; 569 Suppress_Typ : Entity_Id; 570 Static_Sloc : Source_Ptr := No_Location; 571 Flag_Node : Node_Id := Empty; 572 Do_Before : Boolean := False); 573 -- Called to insert range checks as returned by a call to Get_Range_Checks. 574 -- Node is the node after which either the dynamic check is inserted or 575 -- the raise Constraint_Error statement is inserted (for static checks). 576 -- Suppress_Typ is the type to check to determine if checks are suppressed. 577 -- Static_Sloc, if passed, is the Sloc at which the raise CE node points, 578 -- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally 579 -- set at Node. If Flag_Node is present, then this is used instead as the 580 -- node at which to set the Has_Dynamic_Check flag. Normally the check is 581 -- inserted after, if Do_Before is True, the check is inserted before 582 -- Node. 583 584 ----------------------- 585 -- Expander Routines -- 586 ----------------------- 587 588 -- Some of the earlier processing for checks results in temporarily setting 589 -- the Do_Range_Check flag rather than actually generating checks. Now we 590 -- are moving the generation of such checks into the front end for reasons 591 -- of efficiency and simplicity (there were difficulties in handling this 592 -- in the back end when side effects were present in the expressions being 593 -- checked). 594 595 -- Probably we could eliminate the Do_Range_Check flag entirely and 596 -- generate the checks earlier, but this is a delicate area and it 597 -- seemed safer to implement the following routines, which are called 598 -- late on in the expansion process. They check the Do_Range_Check flag 599 -- and if it is set, generate the actual checks and reset the flag. 600 601 procedure Generate_Range_Check 602 (N : Node_Id; 603 Target_Type : Entity_Id; 604 Reason : RT_Exception_Code); 605 -- This procedure is called to actually generate and insert a range check. 606 -- A check is generated to ensure that the value of N lies within the range 607 -- of the target type. Note that the base type of N may be different from 608 -- the base type of the target type. This happens in the conversion case. 609 -- The Reason parameter is the exception code to be used for the exception 610 -- if raised. 611 -- 612 -- Note on the relation of this routine to the Do_Range_Check flag. Mostly 613 -- for historical reasons, we often set the Do_Range_Check flag and then 614 -- later we call Generate_Range_Check if this flag is set. Most probably we 615 -- could eliminate this intermediate setting of the flag (historically the 616 -- back end dealt with range checks, using this flag to indicate if a check 617 -- was required, then we moved checks into the front end). 618 619 procedure Generate_Index_Checks (N : Node_Id); 620 -- This procedure is called to generate index checks on the subscripts for 621 -- the indexed component node N. Each subscript expression is examined, and 622 -- if the Do_Range_Check flag is set, an appropriate index check is 623 -- generated and the flag is reset. 624 625 -- Similarly, we set the flag Do_Discriminant_Check in the semantic 626 -- analysis to indicate that a discriminant check is required for selected 627 -- component of a discriminated type. The following routine is called from 628 -- the expander to actually generate the call. 629 630 procedure Generate_Discriminant_Check (N : Node_Id); 631 -- N is a selected component for which a discriminant check is required to 632 -- make sure that the discriminants have appropriate values for the 633 -- selection. This is done by calling the appropriate discriminant checking 634 -- routine for the selector. 635 636 ----------------------- 637 -- Validity Checking -- 638 ----------------------- 639 640 -- In (RM 13.9.1(9-11)) we have the following rules on invalid values 641 642 -- If the representation of a scalar object does not represent value of 643 -- the object's subtype (perhaps because the object was not initialized), 644 -- the object is said to have an invalid representation. It is a bounded 645 -- error to evaluate the value of such an object. If the error is 646 -- detected, either Constraint_Error or Program_Error is raised. 647 -- Otherwise, execution continues using the invalid representation. The 648 -- rules of the language outside this subclause assume that all objects 649 -- have valid representations. The semantics of operations on invalid 650 -- representations are as follows: 651 -- 652 -- 10 If the representation of the object represents a value of the 653 -- object's type, the value of the type is used. 654 -- 655 -- 11 If the representation of the object does not represent a value 656 -- of the object's type, the semantics of operations on such 657 -- representations is implementation-defined, but does not by 658 -- itself lead to erroneous or unpredictable execution, or to 659 -- other objects becoming abnormal. 660 661 -- We quote the rules in full here since they are quite delicate. Most 662 -- of the time, we can just compute away with wrong values, and get a 663 -- possibly wrong result, which is well within the range of allowed 664 -- implementation defined behavior. The two tricky cases are subscripted 665 -- array assignments, where we don't want to do wild stores, and case 666 -- statements where we don't want to do wild jumps. 667 668 -- In GNAT, we control validity checking with a switch -gnatV that can take 669 -- three parameters, n/d/f for None/Default/Full. These modes have the 670 -- following meanings: 671 672 -- None (no validity checking) 673 674 -- In this mode, there is no specific checking for invalid values 675 -- and the code generator assumes that all stored values are always 676 -- within the bounds of the object subtype. The consequences are as 677 -- follows: 678 679 -- For case statements, an out of range invalid value will cause 680 -- Constraint_Error to be raised, or an arbitrary one of the case 681 -- alternatives will be executed. Wild jumps cannot result even 682 -- in this mode, since we always do a range check 683 684 -- For subscripted array assignments, wild stores will result in 685 -- the expected manner when addresses are calculated using values 686 -- of subscripts that are out of range. 687 688 -- It could perhaps be argued that this mode is still conformant with 689 -- the letter of the RM, since implementation defined is a rather 690 -- broad category, but certainly it is not in the spirit of the 691 -- RM requirement, since wild stores certainly seem to be a case of 692 -- erroneous behavior. 693 694 -- Default (default standard RM-compatible validity checking) 695 696 -- In this mode, which is the default, minimal validity checking is 697 -- performed to ensure no erroneous behavior as follows: 698 699 -- For case statements, an out of range invalid value will cause 700 -- Constraint_Error to be raised. 701 702 -- For subscripted array assignments, invalid out of range 703 -- subscript values will cause Constraint_Error to be raised. 704 705 -- Full (Full validity checking) 706 707 -- In this mode, the protections guaranteed by the standard mode are 708 -- in place, and the following additional checks are made: 709 710 -- For every assignment, the right side is checked for validity 711 712 -- For every call, IN and IN OUT parameters are checked for validity 713 714 -- For every subscripted array reference, both for stores and loads, 715 -- all subscripts are checked for validity. 716 717 -- These checks are not required by the RM, but will in practice 718 -- improve the detection of uninitialized variables, particularly 719 -- if used in conjunction with pragma Normalize_Scalars. 720 721 -- In the above description, we talk about performing validity checks, 722 -- but we don't actually generate a check in a case where the compiler 723 -- can be sure that the value is valid. Note that this assurance must 724 -- be achieved without assuming that any uninitialized value lies within 725 -- the range of its type. The following are cases in which values are 726 -- known to be valid. The flag Is_Known_Valid is used to keep track of 727 -- some of these cases. 728 729 -- If all possible stored values are valid, then any uninitialized 730 -- value must be valid. 731 732 -- Literals, including enumeration literals, are clearly always valid 733 734 -- Constants are always assumed valid, with a validity check being 735 -- performed on the initializing value where necessary to ensure that 736 -- this is the case. 737 738 -- For variables, the status is set to known valid if there is an 739 -- initializing expression. Again a check is made on the initializing 740 -- value if necessary to ensure that this assumption is valid. The 741 -- status can change as a result of local assignments to a variable. 742 -- If a known valid value is unconditionally assigned, then we mark 743 -- the left side as known valid. If a value is assigned that is not 744 -- known to be valid, then we mark the left side as invalid. This 745 -- kind of processing does NOT apply to non-local variables since we 746 -- are not following the flow graph (more properly the flow of actual 747 -- processing only corresponds to the flow graph for local assignments). 748 -- For non-local variables, we preserve the current setting, i.e. a 749 -- validity check is performed when assigning to a knonwn valid global. 750 751 -- Note: no validity checking is required if range checks are suppressed 752 -- regardless of the setting of the validity checking mode. 753 754 -- The following procedures are used in handling validity checking 755 756 procedure Apply_Subscript_Validity_Checks (Expr : Node_Id); 757 -- Expr is the node for an indexed component. If validity checking and 758 -- range checking are enabled, all subscripts for this indexed component 759 -- are checked for validity. 760 761 procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id); 762 -- Expr is a lvalue, i.e. an expression representing the target of an 763 -- assignment. This procedure checks for this expression involving an 764 -- assignment to an array value. We have to be sure that all the subscripts 765 -- in such a case are valid, since according to the rules in (RM 766 -- 13.9.1(9-11)) such assignments are not permitted to result in erroneous 767 -- behavior in the case of invalid subscript values. 768 769 procedure Ensure_Valid (Expr : Node_Id; Holes_OK : Boolean := False); 770 -- Ensure that Expr represents a valid value of its type. If this type 771 -- is not a scalar type, then the call has no effect, since validity 772 -- is only an issue for scalar types. The effect of this call is to 773 -- check if the value is known valid, if so, nothing needs to be done. 774 -- If this is not known, then either Expr is set to be range checked, 775 -- or specific checking code is inserted so that an exception is raised 776 -- if the value is not valid. 777 -- 778 -- The optional argument Holes_OK indicates whether it is necessary to 779 -- worry about enumeration types with non-standard representations leading 780 -- to "holes" in the range of possible representations. If Holes_OK is 781 -- True, then such values are assumed valid (this is used when the caller 782 -- will make a separate check for this case anyway). If Holes_OK is False, 783 -- then this case is checked, and code is inserted to ensure that Expr is 784 -- valid, raising Constraint_Error if the value is not valid. 785 786 function Expr_Known_Valid (Expr : Node_Id) return Boolean; 787 -- This function tests it the value of Expr is known to be valid in the 788 -- sense of RM 13.9.1(9-11). In the case of GNAT, it is only discrete types 789 -- which are a concern, since for non-discrete types we simply continue 790 -- computation with invalid values, which does not lead to erroneous 791 -- behavior. Thus Expr_Known_Valid always returns True if the type of Expr 792 -- is non-discrete. For discrete types the value returned is True only if 793 -- it can be determined that the value is Valid. Otherwise False is 794 -- returned. 795 796 procedure Insert_Valid_Check (Expr : Node_Id); 797 -- Inserts code that will check for the value of Expr being valid, in 798 -- the sense of the 'Valid attribute returning True. Constraint_Error 799 -- will be raised if the value is not valid. 800 801 procedure Null_Exclusion_Static_Checks (N : Node_Id); 802 -- Ada 2005 (AI-231): Check bad usages of the null-exclusion issue 803 804 procedure Remove_Checks (Expr : Node_Id); 805 -- Remove all checks from Expr except those that are only executed 806 -- conditionally (on the right side of And Then/Or Else. This call 807 -- removes only embedded checks (Do_Range_Check, Do_Overflow_Check). 808 809 procedure Validity_Check_Range (N : Node_Id); 810 -- If N is an N_Range node, then Ensure_Valid is called on its bounds, 811 -- if validity checking of operands is enabled. 812 813 ----------------------------- 814 -- Handling of Check Names -- 815 ----------------------------- 816 817 -- The following table contains Name_Id's for recognized checks. The first 818 -- entries (corresponding to the values of the subtype Predefined_Check_Id) 819 -- contain the Name_Id values for the checks that are predefined, including 820 -- All_Checks (see Types). Remaining entries are those that are introduced 821 -- by pragma Check_Names. 822 823 package Check_Names is new Table.Table ( 824 Table_Component_Type => Name_Id, 825 Table_Index_Type => Check_Id, 826 Table_Low_Bound => 1, 827 Table_Initial => 30, 828 Table_Increment => 200, 829 Table_Name => "Name_Check_Names"); 830 831 function Get_Check_Id (N : Name_Id) return Check_Id; 832 -- Function to search above table for matching name. If found returns the 833 -- corresponding Check_Id value in the range 1 .. Check_Name.Last. If not 834 -- found returns No_Check_Id. 835 836private 837 838 type Check_Result is array (Positive range 1 .. 2) of Node_Id; 839 -- There are two cases for the result returned by Range_Check: 840 -- 841 -- For the static case the result is one or two nodes that should cause 842 -- a Constraint_Error. Typically these will include Expr itself or the 843 -- direct descendents of Expr, such as Low/High_Bound (Expr)). It is the 844 -- responsibility of the caller to rewrite and substitute the nodes with 845 -- N_Raise_Constraint_Error nodes. 846 -- 847 -- For the non-static case a single N_Raise_Constraint_Error node with a 848 -- non-empty Condition field is returned. 849 -- 850 -- Unused entries in Check_Result, if any, are simply set to Empty For 851 -- external clients, the required processing on this result is achieved 852 -- using the Insert_Range_Checks routine. 853 854 pragma Inline (Apply_Length_Check); 855 pragma Inline (Apply_Range_Check); 856 pragma Inline (Apply_Static_Length_Check); 857end Checks; 858