1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- C H E C K S -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2013, 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 Predicate_Checks_Suppressed (E : Entity_Id) return Boolean; 60 function Range_Checks_Suppressed (E : Entity_Id) return Boolean; 61 function Storage_Checks_Suppressed (E : Entity_Id) return Boolean; 62 function Tag_Checks_Suppressed (E : Entity_Id) return Boolean; 63 function Validity_Checks_Suppressed (E : Entity_Id) return Boolean; 64 -- These functions check to see if the named check is suppressed, either 65 -- by an active scope suppress setting, or because the check has been 66 -- specifically suppressed for the given entity. If no entity is relevant 67 -- for the current check, then Empty is used as an argument. Note: the 68 -- reason we insist on specifying Empty is to force the caller to think 69 -- about whether there is any relevant entity that should be checked. 70 71 function Is_Check_Suppressed (E : Entity_Id; C : Check_Id) return Boolean; 72 -- This function is called if Checks_May_Be_Suppressed (E) is True to 73 -- determine whether check C is suppressed either on the entity E or 74 -- as the result of a scope suppress pragma. If Checks_May_Be_Suppressed 75 -- is False, then the status of the check can be determined simply by 76 -- examining Scope_Suppress, so this routine is not called in that case. 77 78 function Overflow_Check_Mode return Overflow_Mode_Type; 79 -- Returns current overflow checking mode, taking into account whether 80 -- we are inside an assertion expression. 81 82 ------------------------------------------- 83 -- Procedures to Activate Checking Flags -- 84 ------------------------------------------- 85 86 procedure Activate_Division_Check (N : Node_Id); 87 pragma Inline (Activate_Division_Check); 88 -- Sets Do_Division_Check flag in node N, and handles possible local raise. 89 -- Always call this routine rather than calling Set_Do_Division_Check to 90 -- set an explicit value of True, to ensure handling the local raise case. 91 92 procedure Activate_Overflow_Check (N : Node_Id); 93 pragma Inline (Activate_Overflow_Check); 94 -- Sets Do_Overflow_Check flag in node N, and handles possible local raise. 95 -- Always call this routine rather than calling Set_Do_Overflow_Check to 96 -- set an explicit value of True, to ensure handling the local raise case. 97 -- Note that this call has no effect for MOD, REM, and unary "+" for which 98 -- overflow is never possible in any case. 99 100 procedure Activate_Range_Check (N : Node_Id); 101 pragma Inline (Activate_Range_Check); 102 -- Sets Do_Range_Check flag in node N, and handles possible local raise 103 -- Always call this routine rather than calling Set_Do_Range_Check to 104 -- set an explicit value of True, to ensure handling the local raise case. 105 106 -------------------------------- 107 -- Procedures to Apply Checks -- 108 -------------------------------- 109 110 -- General note on following checks. These checks are always active if 111 -- Expander_Active and not Inside_A_Generic. They are inactive and have 112 -- no effect Inside_A_Generic. In the case where not Expander_Active 113 -- and not Inside_A_Generic, most of them are inactive, but some of them 114 -- operate anyway since they may generate useful compile time warnings. 115 116 procedure Apply_Access_Check (N : Node_Id); 117 -- Determines whether an expression node requires a runtime access 118 -- check and if so inserts the appropriate run-time check. 119 120 procedure Apply_Accessibility_Check 121 (N : Node_Id; 122 Typ : Entity_Id; 123 Insert_Node : Node_Id); 124 -- Given a name N denoting an access parameter, emits a run-time 125 -- accessibility check (if necessary), checking that the level of 126 -- the object denoted by the access parameter is not deeper than the 127 -- level of the type Typ. Program_Error is raised if the check fails. 128 -- Insert_Node indicates the node where the check should be inserted. 129 130 procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id); 131 -- E is the entity for an object which has an address clause. If checks 132 -- are enabled, then this procedure generates a check that the specified 133 -- address has an alignment consistent with the alignment of the object, 134 -- raising PE if this is not the case. The resulting check (if one is 135 -- generated) is prepended to the Actions list of N_Freeze_Entity node N. 136 -- Note that the check references E'Alignment, so it cannot be emitted 137 -- before N (its freeze node), otherwise this would cause an illegal 138 -- access before elaboration error in GIGI. For the case of a clear overlay 139 -- situation, we also check that the size of the overlaying object is not 140 -- larger than the overlaid object. 141 142 procedure Apply_Arithmetic_Overflow_Check (N : Node_Id); 143 -- Handle overflow checking for an arithmetic operator. Also handles the 144 -- cases of ELIMINATED and MINIMIZED overflow checking mode. If the mode 145 -- is one of the latter two, then this routine can also be called with 146 -- an if or case expression node to make sure that we properly handle 147 -- overflow checking for dependent expressions. This routine handles 148 -- front end vs back end overflow checks (in the front end case it expands 149 -- the necessary check). Note that divide is handled separately using 150 -- Apply_Divide_Checks. Node N may or may not have Do_Overflow_Check. 151 -- In STRICT mode, there is nothing to do if this flag is off, but in 152 -- MINIMIZED/ELIMINATED mode we still have to deal with possible use 153 -- of doing operations in Long_Long_Integer or Bignum mode. 154 155 procedure Apply_Constraint_Check 156 (N : Node_Id; 157 Typ : Entity_Id; 158 No_Sliding : Boolean := False); 159 -- Top-level procedure, calls all the others depending on the class of 160 -- Typ. Checks that expression N satisfies the constraint of type Typ. 161 -- No_Sliding is only relevant for constrained array types, if set to 162 -- True, it checks that indexes are in range. 163 164 procedure Apply_Discriminant_Check 165 (N : Node_Id; 166 Typ : Entity_Id; 167 Lhs : Node_Id := Empty); 168 -- Given an expression N of a discriminated type, or of an access type 169 -- whose designated type is a discriminanted type, generates a check to 170 -- ensure that the expression can be converted to the subtype given as 171 -- the second parameter. Lhs is empty except in the case of assignments, 172 -- where the target object may be needed to determine the subtype to 173 -- check against (such as the cases of unconstrained formal parameters 174 -- and unconstrained aliased objects). For the case of unconstrained 175 -- formals, the check is performed only if the corresponding actual is 176 -- constrained, i.e., whether Lhs'Constrained is True. 177 178 procedure Apply_Divide_Checks (N : Node_Id); 179 -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem if either of the 180 -- flags Do_Division_Check or Do_Overflow_Check is set, then this routine 181 -- ensures that the appropriate checks are made. Note that overflow can 182 -- occur in the signed case for the case of the largest negative number 183 -- divided by minus one. 184 185 procedure Apply_Parameter_Aliasing_Checks 186 (Call : Node_Id; 187 Subp : Entity_Id); 188 -- Given a subprogram call Call, add a check to verify that none of the 189 -- actuals overlap. Subp denotes the subprogram being called. 190 191 procedure Apply_Parameter_Validity_Checks (Subp : Entity_Id); 192 -- Given a subprogram Subp, add both a pre and post condition pragmas that 193 -- verify the proper initialization of scalars in parameters and function 194 -- results. 195 196 procedure Apply_Predicate_Check (N : Node_Id; Typ : Entity_Id); 197 -- N is an expression to which a predicate check may need to be applied 198 -- for Typ, if Typ has a predicate function. The check is applied only 199 -- if the type of N does not match Typ. 200 201 procedure Apply_Type_Conversion_Checks (N : Node_Id); 202 -- N is an N_Type_Conversion node. A type conversion actually involves 203 -- two sorts of checks. The first check is the checks that ensures that 204 -- the operand in the type conversion fits onto the base type of the 205 -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second 206 -- check is there to ensure that once the operand has been converted to 207 -- a value of the target type, this converted value meets the 208 -- constraints imposed by the target subtype (see RM 4.6 (51)). 209 210 procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id); 211 -- The argument N is an attribute reference node intended for processing 212 -- by gigi. The attribute is one that returns a universal integer, but 213 -- the attribute reference node is currently typed with the expected 214 -- result type. This routine deals with range and overflow checks needed 215 -- to make sure that the universal result is in range. 216 217 function Build_Discriminant_Checks 218 (N : Node_Id; 219 T_Typ : Entity_Id) 220 return Node_Id; 221 -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression 222 -- that compares discriminants of the expression with discriminants of the 223 -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In). 224 225 function Convert_From_Bignum (N : Node_Id) return Node_Id; 226 -- Returns result of converting node N from Bignum. The returned value is 227 -- not analyzed, the caller takes responsibility for this. Node N must be 228 -- a subexpression node of type Bignum. The result is Long_Long_Integer. 229 230 function Convert_To_Bignum (N : Node_Id) return Node_Id; 231 -- Returns result of converting node N to Bignum. The returned value is not 232 -- analyzed, the caller takes responsibility for this. Node N must be a 233 -- subexpression node of a signed integer type or Bignum type (if it is 234 -- already a Bignum, the returned value is Relocate_Node (N)). 235 236 procedure Determine_Range 237 (N : Node_Id; 238 OK : out Boolean; 239 Lo : out Uint; 240 Hi : out Uint; 241 Assume_Valid : Boolean := False); 242 -- N is a node for a subexpression. If N is of a discrete type with no 243 -- error indications, and no other peculiarities (e.g. missing Etype), 244 -- then OK is True on return, and Lo and Hi are set to a conservative 245 -- estimate of the possible range of values of N. Thus if OK is True on 246 -- return, the value of the subexpression N is known to lie in the range 247 -- Lo .. Hi (inclusive). If the expression is not of a discrete type, or 248 -- some kind of error condition is detected, then OK is False on exit, and 249 -- Lo/Hi are set to No_Uint. Thus the significance of OK being False on 250 -- return is that no useful information is available on the range of the 251 -- expression. Assume_Valid determines whether the processing is allowed to 252 -- assume that values are in range of their subtypes. If it is set to True, 253 -- then this assumption is valid, if False, then processing is done using 254 -- base types to allow invalid values. 255 256 procedure Install_Null_Excluding_Check (N : Node_Id); 257 -- Determines whether an access node requires a runtime access check and 258 -- if so inserts the appropriate run-time check. 259 260 function Make_Bignum_Block (Loc : Source_Ptr) return Node_Id; 261 -- This function is used by top level overflow checking routines to do a 262 -- mark/release operation on the secondary stack around bignum operations. 263 -- The block created looks like: 264 -- 265 -- declare 266 -- M : Mark_Id := SS_Mark; 267 -- begin 268 -- SS_Release (M); 269 -- end; 270 -- 271 -- The idea is that the caller will insert any needed extra declarations 272 -- after the declaration of M, and any needed statements (in particular 273 -- the bignum operations) before the call to SS_Release, and then do an 274 -- Insert_Action of the whole block (it is returned unanalyzed). The Loc 275 -- parameter is used to supply Sloc values for the constructed tree. 276 277 procedure Minimize_Eliminate_Overflows 278 (N : Node_Id; 279 Lo : out Uint; 280 Hi : out Uint; 281 Top_Level : Boolean); 282 -- This is the main routine for handling MINIMIZED and ELIMINATED overflow 283 -- processing. On entry N is a node whose result is a signed integer 284 -- subtype. The Do_Overflow_Check flag may or may not be set on N. If the 285 -- node is an arithmetic operation, then a range analysis is carried out, 286 -- and there are three possibilities: 287 -- 288 -- The node is left unchanged (apart from expansion of an exponentiation 289 -- operation). This happens if the routine can determine that the result 290 -- is definitely in range. The Do_Overflow_Check flag is turned off in 291 -- this case. 292 -- 293 -- The node is transformed into an arithmetic operation with a result 294 -- type of Long_Long_Integer. 295 -- 296 -- The node is transformed into a function call that calls an appropriate 297 -- function in the System.Bignums package to compute a Bignum result. 298 -- 299 -- In the first two cases, Lo and Hi are set to the bounds of the possible 300 -- range of results, computed as accurately as possible. In the third case 301 -- Lo and Hi are set to No_Uint (there are some cases where we could get an 302 -- advantage from keeping result ranges for Bignum values, but it could use 303 -- a lot of space and is very unlikely to be valuable). 304 -- 305 -- If the node is not an arithmetic operation, then it is unchanged but 306 -- Lo and Hi are still set (to the bounds of the result subtype if nothing 307 -- better can be determined). 308 -- 309 -- Note: this function is recursive, if called with an arithmetic operator, 310 -- recursive calls are made to process the operands using this procedure. 311 -- So we end up doing things top down. Nothing happens to an arithmetic 312 -- expression until this procedure is called on the top level node and 313 -- then the recursive calls process all the children. We have to do it 314 -- this way. If we try to do it bottom up in natural expansion order, then 315 -- there are two problems. First, where do we stash the bounds, and more 316 -- importantly, semantic processing will be messed up. Consider A+B+C where 317 -- A,B,C are all of type integer, if we processed A+B before doing semantic 318 -- analysis of the addition of this result to C, that addition could end up 319 -- with a Long_Long_Integer left operand and an Integer right operand, and 320 -- we would get a semantic error. 321 -- 322 -- The routine is called in three situations if we are operating in either 323 -- MINIMIZED or ELIMINATED modes. 324 -- 325 -- Overflow processing applied to the top node of an expression tree when 326 -- that node is an arithmetic operator. In this case the result is 327 -- converted to the appropriate result type (there is special processing 328 -- when the parent is a conversion, see body for details). 329 -- 330 -- Overflow processing applied to the operands of a comparison operation. 331 -- In this case, the comparison is done on the result Long_Long_Integer 332 -- or Bignum values, without raising any exceptions. 333 -- 334 -- Overflow processing applied to the left operand of a membership test. 335 -- In this case no exception is raised if a Long_Long_Integer or Bignum 336 -- result is outside the range of the type of that left operand (it is 337 -- just that the result of IN is false in that case). 338 -- 339 -- Note that if Bignum values appear, the caller must take care of doing 340 -- the appropriate mark/release operations on the secondary stack. 341 -- 342 -- Top_Level is used to avoid inefficient unnecessary transitions into the 343 -- Bignum domain. If Top_Level is True, it means that the caller will have 344 -- to convert any Bignum value back to Long_Long_Integer, possibly checking 345 -- that the value is in range. This is the normal case for a top level 346 -- operator in a subexpression. There is no point in going into Bignum mode 347 -- to avoid an overflow just so we can check for overflow the next moment. 348 -- For calls from comparisons and membership tests, and for all recursive 349 -- calls, we do want to transition into the Bignum domain if necessary. 350 -- Note that this setting is only relevant in ELIMINATED mode. 351 352 ------------------------------------------------------- 353 -- Control and Optimization of Range/Overflow Checks -- 354 ------------------------------------------------------- 355 356 -- Range checks are controlled by the Do_Range_Check flag. The front end 357 -- is responsible for setting this flag in relevant nodes. Originally 358 -- the back end generated all corresponding range checks. But later on 359 -- we decided to generate many range checks in the front end. We are now 360 -- in the transitional phase where some of these checks are still done 361 -- by the back end, but many are done by the front end. It is possible 362 -- that in the future we might move all the checks to the front end. The 363 -- main remaining back end checks are for subscript checking. 364 365 -- Overflow checks are similarly controlled by the Do_Overflow_Check flag. 366 -- The difference here is that if back end overflow checks are inactive 367 -- (Backend_Overflow_Checks_On_Target set False), then the actual overflow 368 -- checks are generated by the front end, but if back end overflow checks 369 -- are active (Backend_Overflow_Checks_On_Target set True), then the back 370 -- end does generate the checks. 371 372 -- The following two routines are used to set these flags, they allow 373 -- for the possibility of eliminating checks. Checks can be eliminated 374 -- if an identical check has already been performed. 375 376 procedure Enable_Overflow_Check (N : Node_Id); 377 -- First this routine determines if an overflow check is needed by doing 378 -- an appropriate range check. If a check is not needed, then the call 379 -- has no effect. If a check is needed then this routine sets the flag 380 -- Do_Overflow_Check in node N to True, unless it can be determined that 381 -- the check is not needed. The only condition under which this is the 382 -- case is if there was an identical check earlier on. 383 384 procedure Enable_Range_Check (N : Node_Id); 385 -- Set Do_Range_Check flag in node N True, unless it can be determined 386 -- that the check is not needed. The only condition under which this is 387 -- the case is if there was an identical check earlier on. This routine 388 -- is not responsible for doing range analysis to determine whether or 389 -- not such a check is needed -- the caller is expected to do this. The 390 -- one other case in which the request to set the flag is ignored is 391 -- when Kill_Range_Check is set in an N_Unchecked_Conversion node. 392 393 -- The following routines are used to keep track of processing sequences 394 -- of statements (e.g. the THEN statements of an IF statement). A check 395 -- that appears within such a sequence can eliminate an identical check 396 -- within this sequence of statements. However, after the end of the 397 -- sequence of statements, such a check is no longer of interest, since 398 -- it may not have been executed. 399 400 procedure Conditional_Statements_Begin; 401 -- This call marks the start of processing of a sequence of statements. 402 -- Every call to this procedure must be followed by a matching call to 403 -- Conditional_Statements_End. 404 405 procedure Conditional_Statements_End; 406 -- This call removes from consideration all saved checks since the 407 -- corresponding call to Conditional_Statements_Begin. These two 408 -- procedures operate in a stack like manner. 409 410 -- The mechanism for optimizing checks works by remembering checks 411 -- that have already been made, but certain conditions, for example 412 -- an assignment to a variable involved in a check, may mean that the 413 -- remembered check is no longer valid, in the sense that if the same 414 -- expression appears again, another check is required because the 415 -- value may have changed. 416 417 -- The following routines are used to note conditions which may render 418 -- some or all of the stored and remembered checks to be invalidated. 419 420 procedure Kill_Checks (V : Entity_Id); 421 -- This procedure records an assignment or other condition that causes 422 -- the value of the variable to be changed, invalidating any stored 423 -- checks that reference the value. Note that all such checks must 424 -- be discarded, even if they are not in the current statement range. 425 426 procedure Kill_All_Checks; 427 -- This procedure kills all remembered checks 428 429 ----------------------------- 430 -- Length and Range Checks -- 431 ----------------------------- 432 433 -- In the following procedures, there are three arguments which have 434 -- a common meaning as follows: 435 436 -- Expr The expression to be checked. If a check is required, 437 -- the appropriate flag will be placed on this node. Whether 438 -- this node is further examined depends on the setting of 439 -- the parameter Source_Typ, as described below. 440 441 -- ??? Apply_Length_Check and Apply_Range_Check do not have an Expr 442 -- formal 443 444 -- ??? Apply_Length_Check and Apply_Range_Check have a Ck_Node formal 445 -- which is undocumented, is it the same as Expr? 446 447 -- Target_Typ The target type on which the check is to be based. For 448 -- example, if we have a scalar range check, then the check 449 -- is that we are in range of this type. 450 451 -- Source_Typ Normally Empty, but can be set to a type, in which case 452 -- this type is used for the check, see below. 453 454 -- The checks operate in one of two modes: 455 456 -- If Source_Typ is Empty, then the node Expr is examined, at the very 457 -- least to get the source subtype. In addition for some of the checks, 458 -- the actual form of the node may be examined. For example, a node of 459 -- type Integer whose actual form is an Integer conversion from a type 460 -- with range 0 .. 3 can be determined to have a value in range 0 .. 3. 461 462 -- If Source_Typ is given, then nothing can be assumed about the Expr, 463 -- and indeed its contents are not examined. In this case the check is 464 -- based on the assumption that Expr can be an arbitrary value of the 465 -- given Source_Typ. 466 467 -- Currently, the only case in which a Source_Typ is explicitly supplied 468 -- is for the case of Out and In_Out parameters, where, for the conversion 469 -- on return (the Out direction), the types must be reversed. This is 470 -- handled by the caller. 471 472 procedure Apply_Length_Check 473 (Ck_Node : Node_Id; 474 Target_Typ : Entity_Id; 475 Source_Typ : Entity_Id := Empty); 476 -- This procedure builds a sequence of declarations to do a length check 477 -- that checks if the lengths of the two arrays Target_Typ and source type 478 -- are the same. The resulting actions are inserted at Node using a call 479 -- to Insert_Actions. 480 -- 481 -- For access types, the Directly_Designated_Type is retrieved and 482 -- processing continues as enumerated above, with a guard against null 483 -- values. 484 -- 485 -- Note: calls to Apply_Length_Check currently never supply an explicit 486 -- Source_Typ parameter, but Apply_Length_Check takes this parameter and 487 -- processes it as described above for consistency with the other routines 488 -- in this section. 489 490 procedure Apply_Range_Check 491 (Ck_Node : Node_Id; 492 Target_Typ : Entity_Id; 493 Source_Typ : Entity_Id := Empty); 494 -- For a Node of kind N_Range, constructs a range check action that tests 495 -- first that the range is not null and then that the range is contained in 496 -- the Target_Typ range. 497 -- 498 -- For scalar types, constructs a range check action that first tests that 499 -- the expression is contained in the Target_Typ range. The difference 500 -- between this and Apply_Scalar_Range_Check is that the latter generates 501 -- the actual checking code in gigi against the Etype of the expression. 502 -- 503 -- For constrained array types, construct series of range check actions 504 -- to check that each Expr range is properly contained in the range of 505 -- Target_Typ. 506 -- 507 -- For a type conversion to an unconstrained array type, constructs a range 508 -- check action to check that the bounds of the source type are within the 509 -- constraints imposed by the Target_Typ. 510 -- 511 -- For access types, the Directly_Designated_Type is retrieved and 512 -- processing continues as enumerated above, with a guard against null 513 -- values. 514 -- 515 -- The source type is used by type conversions to unconstrained array 516 -- types to retrieve the corresponding bounds. 517 518 procedure Apply_Static_Length_Check 519 (Expr : Node_Id; 520 Target_Typ : Entity_Id; 521 Source_Typ : Entity_Id := Empty); 522 -- Tries to determine statically whether the two array types source type 523 -- and Target_Typ have the same length. If it can be determined at compile 524 -- time that they do not, then an N_Raise_Constraint_Error node replaces 525 -- Expr, and a warning message is issued. 526 527 procedure Apply_Scalar_Range_Check 528 (Expr : Node_Id; 529 Target_Typ : Entity_Id; 530 Source_Typ : Entity_Id := Empty; 531 Fixed_Int : Boolean := False); 532 -- For scalar types, determines whether an expression node should be 533 -- flagged as needing a runtime range check. If the node requires such a 534 -- check, the Do_Range_Check flag is turned on. The Fixed_Int flag if set 535 -- causes any fixed-point values to be treated as though they were discrete 536 -- values (i.e. the underlying integer value is used). 537 538 type Check_Result is private; 539 -- Type used to return result of Get_Range_Checks call, for later use in 540 -- call to Insert_Range_Checks procedure. 541 542 function Get_Range_Checks 543 (Ck_Node : Node_Id; 544 Target_Typ : Entity_Id; 545 Source_Typ : Entity_Id := Empty; 546 Warn_Node : Node_Id := Empty) return Check_Result; 547 -- Like Apply_Range_Check, except it does not modify anything. Instead 548 -- it returns an encapsulated result of the check operations for later 549 -- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its 550 -- Sloc is used, in the static case, for the generated warning or error. 551 -- Additionally, it is used rather than Expr (or Low/High_Bound of Expr) 552 -- in constructing the check. 553 554 procedure Append_Range_Checks 555 (Checks : Check_Result; 556 Stmts : List_Id; 557 Suppress_Typ : Entity_Id; 558 Static_Sloc : Source_Ptr; 559 Flag_Node : Node_Id); 560 -- Called to append range checks as returned by a call to Get_Range_Checks. 561 -- Stmts is a list to which either the dynamic check is appended or the 562 -- raise Constraint_Error statement is appended (for static checks). 563 -- Static_Sloc is the Sloc at which the raise CE node points, Flag_Node is 564 -- used as the node at which to set the Has_Dynamic_Check flag. Checks_On 565 -- is a boolean value that says if range and index checking is on or not. 566 567 procedure Insert_Range_Checks 568 (Checks : Check_Result; 569 Node : Node_Id; 570 Suppress_Typ : Entity_Id; 571 Static_Sloc : Source_Ptr := No_Location; 572 Flag_Node : Node_Id := Empty; 573 Do_Before : Boolean := False); 574 -- Called to insert range checks as returned by a call to Get_Range_Checks. 575 -- Node is the node after which either the dynamic check is inserted or 576 -- the raise Constraint_Error statement is inserted (for static checks). 577 -- Suppress_Typ is the type to check to determine if checks are suppressed. 578 -- Static_Sloc, if passed, is the Sloc at which the raise CE node points, 579 -- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally 580 -- set at Node. If Flag_Node is present, then this is used instead as the 581 -- node at which to set the Has_Dynamic_Check flag. Normally the check is 582 -- inserted after, if Do_Before is True, the check is inserted before 583 -- Node. 584 585 ----------------------- 586 -- Expander Routines -- 587 ----------------------- 588 589 -- Some of the earlier processing for checks results in temporarily setting 590 -- the Do_Range_Check flag rather than actually generating checks. Now we 591 -- are moving the generation of such checks into the front end for reasons 592 -- of efficiency and simplicity (there were difficulties in handling this 593 -- in the back end when side effects were present in the expressions being 594 -- checked). 595 596 -- Probably we could eliminate the Do_Range_Check flag entirely and 597 -- generate the checks earlier, but this is a delicate area and it 598 -- seemed safer to implement the following routines, which are called 599 -- late on in the expansion process. They check the Do_Range_Check flag 600 -- and if it is set, generate the actual checks and reset the flag. 601 602 procedure Generate_Range_Check 603 (N : Node_Id; 604 Target_Type : Entity_Id; 605 Reason : RT_Exception_Code); 606 -- This procedure is called to actually generate and insert a range check. 607 -- A check is generated to ensure that the value of N lies within the range 608 -- of the target type. Note that the base type of N may be different from 609 -- the base type of the target type. This happens in the conversion case. 610 -- The Reason parameter is the exception code to be used for the exception 611 -- if raised. 612 -- 613 -- Note on the relation of this routine to the Do_Range_Check flag. Mostly 614 -- for historical reasons, we often set the Do_Range_Check flag and then 615 -- later we call Generate_Range_Check if this flag is set. Most probably we 616 -- could eliminate this intermediate setting of the flag (historically the 617 -- back end dealt with range checks, using this flag to indicate if a check 618 -- was required, then we moved checks into the front end). 619 620 procedure Generate_Index_Checks (N : Node_Id); 621 -- This procedure is called to generate index checks on the subscripts for 622 -- the indexed component node N. Each subscript expression is examined, and 623 -- if the Do_Range_Check flag is set, an appropriate index check is 624 -- generated and the flag is reset. 625 626 -- Similarly, we set the flag Do_Discriminant_Check in the semantic 627 -- analysis to indicate that a discriminant check is required for selected 628 -- component of a discriminated type. The following routine is called from 629 -- the expander to actually generate the call. 630 631 procedure Generate_Discriminant_Check (N : Node_Id); 632 -- N is a selected component for which a discriminant check is required to 633 -- make sure that the discriminants have appropriate values for the 634 -- selection. This is done by calling the appropriate discriminant checking 635 -- routine for the selector. 636 637 ----------------------- 638 -- Validity Checking -- 639 ----------------------- 640 641 -- In (RM 13.9.1(9-11)) we have the following rules on invalid values 642 643 -- If the representation of a scalar object does not represent value of 644 -- the object's subtype (perhaps because the object was not initialized), 645 -- the object is said to have an invalid representation. It is a bounded 646 -- error to evaluate the value of such an object. If the error is 647 -- detected, either Constraint_Error or Program_Error is raised. 648 -- Otherwise, execution continues using the invalid representation. The 649 -- rules of the language outside this subclause assume that all objects 650 -- have valid representations. The semantics of operations on invalid 651 -- representations are as follows: 652 -- 653 -- 10 If the representation of the object represents a value of the 654 -- object's type, the value of the type is used. 655 -- 656 -- 11 If the representation of the object does not represent a value 657 -- of the object's type, the semantics of operations on such 658 -- representations is implementation-defined, but does not by 659 -- itself lead to erroneous or unpredictable execution, or to 660 -- other objects becoming abnormal. 661 662 -- We quote the rules in full here since they are quite delicate. Most 663 -- of the time, we can just compute away with wrong values, and get a 664 -- possibly wrong result, which is well within the range of allowed 665 -- implementation defined behavior. The two tricky cases are subscripted 666 -- array assignments, where we don't want to do wild stores, and case 667 -- statements where we don't want to do wild jumps. 668 669 -- In GNAT, we control validity checking with a switch -gnatV that can take 670 -- three parameters, n/d/f for None/Default/Full. These modes have the 671 -- following meanings: 672 673 -- None (no validity checking) 674 675 -- In this mode, there is no specific checking for invalid values 676 -- and the code generator assumes that all stored values are always 677 -- within the bounds of the object subtype. The consequences are as 678 -- follows: 679 680 -- For case statements, an out of range invalid value will cause 681 -- Constraint_Error to be raised, or an arbitrary one of the case 682 -- alternatives will be executed. Wild jumps cannot result even 683 -- in this mode, since we always do a range check 684 685 -- For subscripted array assignments, wild stores will result in 686 -- the expected manner when addresses are calculated using values 687 -- of subscripts that are out of range. 688 689 -- It could perhaps be argued that this mode is still conformant with 690 -- the letter of the RM, since implementation defined is a rather 691 -- broad category, but certainly it is not in the spirit of the 692 -- RM requirement, since wild stores certainly seem to be a case of 693 -- erroneous behavior. 694 695 -- Default (default standard RM-compatible validity checking) 696 697 -- In this mode, which is the default, minimal validity checking is 698 -- performed to ensure no erroneous behavior as follows: 699 700 -- For case statements, an out of range invalid value will cause 701 -- Constraint_Error to be raised. 702 703 -- For subscripted array assignments, invalid out of range 704 -- subscript values will cause Constraint_Error to be raised. 705 706 -- Full (Full validity checking) 707 708 -- In this mode, the protections guaranteed by the standard mode are 709 -- in place, and the following additional checks are made: 710 711 -- For every assignment, the right side is checked for validity 712 713 -- For every call, IN and IN OUT parameters are checked for validity 714 715 -- For every subscripted array reference, both for stores and loads, 716 -- all subscripts are checked for validity. 717 718 -- These checks are not required by the RM, but will in practice 719 -- improve the detection of uninitialized variables, particularly 720 -- if used in conjunction with pragma Normalize_Scalars. 721 722 -- In the above description, we talk about performing validity checks, 723 -- but we don't actually generate a check in a case where the compiler 724 -- can be sure that the value is valid. Note that this assurance must 725 -- be achieved without assuming that any uninitialized value lies within 726 -- the range of its type. The following are cases in which values are 727 -- known to be valid. The flag Is_Known_Valid is used to keep track of 728 -- some of these cases. 729 730 -- If all possible stored values are valid, then any uninitialized 731 -- value must be valid. 732 733 -- Literals, including enumeration literals, are clearly always valid 734 735 -- Constants are always assumed valid, with a validity check being 736 -- performed on the initializing value where necessary to ensure that 737 -- this is the case. 738 739 -- For variables, the status is set to known valid if there is an 740 -- initializing expression. Again a check is made on the initializing 741 -- value if necessary to ensure that this assumption is valid. The 742 -- status can change as a result of local assignments to a variable. 743 -- If a known valid value is unconditionally assigned, then we mark 744 -- the left side as known valid. If a value is assigned that is not 745 -- known to be valid, then we mark the left side as invalid. This 746 -- kind of processing does NOT apply to non-local variables since we 747 -- are not following the flow graph (more properly the flow of actual 748 -- processing only corresponds to the flow graph for local assignments). 749 -- For non-local variables, we preserve the current setting, i.e. a 750 -- validity check is performed when assigning to a knonwn valid global. 751 752 -- Note: no validity checking is required if range checks are suppressed 753 -- regardless of the setting of the validity checking mode. 754 755 -- The following procedures are used in handling validity checking 756 757 procedure Apply_Subscript_Validity_Checks (Expr : Node_Id); 758 -- Expr is the node for an indexed component. If validity checking and 759 -- range checking are enabled, all subscripts for this indexed component 760 -- are checked for validity. 761 762 procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id); 763 -- Expr is a lvalue, i.e. an expression representing the target of an 764 -- assignment. This procedure checks for this expression involving an 765 -- assignment to an array value. We have to be sure that all the subscripts 766 -- in such a case are valid, since according to the rules in (RM 767 -- 13.9.1(9-11)) such assignments are not permitted to result in erroneous 768 -- behavior in the case of invalid subscript values. 769 770 procedure Ensure_Valid (Expr : Node_Id; Holes_OK : Boolean := False); 771 -- Ensure that Expr represents a valid value of its type. If this type 772 -- is not a scalar type, then the call has no effect, since validity 773 -- is only an issue for scalar types. The effect of this call is to 774 -- check if the value is known valid, if so, nothing needs to be done. 775 -- If this is not known, then either Expr is set to be range checked, 776 -- or specific checking code is inserted so that an exception is raised 777 -- if the value is not valid. 778 -- 779 -- The optional argument Holes_OK indicates whether it is necessary to 780 -- worry about enumeration types with non-standard representations leading 781 -- to "holes" in the range of possible representations. If Holes_OK is 782 -- True, then such values are assumed valid (this is used when the caller 783 -- will make a separate check for this case anyway). If Holes_OK is False, 784 -- then this case is checked, and code is inserted to ensure that Expr is 785 -- valid, raising Constraint_Error if the value is not valid. 786 787 function Expr_Known_Valid (Expr : Node_Id) return Boolean; 788 -- This function tests it the value of Expr is known to be valid in the 789 -- sense of RM 13.9.1(9-11). In the case of GNAT, it is only discrete types 790 -- which are a concern, since for non-discrete types we simply continue 791 -- computation with invalid values, which does not lead to erroneous 792 -- behavior. Thus Expr_Known_Valid always returns True if the type of Expr 793 -- is non-discrete. For discrete types the value returned is True only if 794 -- it can be determined that the value is Valid. Otherwise False is 795 -- returned. 796 797 procedure Insert_Valid_Check (Expr : Node_Id); 798 -- Inserts code that will check for the value of Expr being valid, in 799 -- the sense of the 'Valid attribute returning True. Constraint_Error 800 -- will be raised if the value is not valid. 801 802 procedure Null_Exclusion_Static_Checks (N : Node_Id); 803 -- Ada 2005 (AI-231): Check bad usages of the null-exclusion issue 804 805 procedure Remove_Checks (Expr : Node_Id); 806 -- Remove all checks from Expr except those that are only executed 807 -- conditionally (on the right side of And Then/Or Else. This call 808 -- removes only embedded checks (Do_Range_Check, Do_Overflow_Check). 809 810 procedure Validity_Check_Range (N : Node_Id); 811 -- If N is an N_Range node, then Ensure_Valid is called on its bounds, 812 -- if validity checking of operands is enabled. 813 814 ----------------------------- 815 -- Handling of Check Names -- 816 ----------------------------- 817 818 -- The following table contains Name_Id's for recognized checks. The first 819 -- entries (corresponding to the values of the subtype Predefined_Check_Id) 820 -- contain the Name_Id values for the checks that are predefined, including 821 -- All_Checks (see Types). Remaining entries are those that are introduced 822 -- by pragma Check_Names. 823 824 package Check_Names is new Table.Table ( 825 Table_Component_Type => Name_Id, 826 Table_Index_Type => Check_Id, 827 Table_Low_Bound => 1, 828 Table_Initial => 30, 829 Table_Increment => 200, 830 Table_Name => "Name_Check_Names"); 831 832 function Get_Check_Id (N : Name_Id) return Check_Id; 833 -- Function to search above table for matching name. If found returns the 834 -- corresponding Check_Id value in the range 1 .. Check_Name.Last. If not 835 -- found returns No_Check_Id. 836 837private 838 839 type Check_Result is array (Positive range 1 .. 2) of Node_Id; 840 -- There are two cases for the result returned by Range_Check: 841 -- 842 -- For the static case the result is one or two nodes that should cause 843 -- a Constraint_Error. Typically these will include Expr itself or the 844 -- direct descendents of Expr, such as Low/High_Bound (Expr)). It is the 845 -- responsibility of the caller to rewrite and substitute the nodes with 846 -- N_Raise_Constraint_Error nodes. 847 -- 848 -- For the non-static case a single N_Raise_Constraint_Error node with a 849 -- non-empty Condition field is returned. 850 -- 851 -- Unused entries in Check_Result, if any, are simply set to Empty For 852 -- external clients, the required processing on this result is achieved 853 -- using the Insert_Range_Checks routine. 854 855 pragma Inline (Apply_Length_Check); 856 pragma Inline (Apply_Range_Check); 857 pragma Inline (Apply_Static_Length_Check); 858end Checks; 859