1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- C H E C K S -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2019, 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 Errout; use Errout; 39with Namet; use Namet; 40with Table; 41with Types; use Types; 42with Uintp; use Uintp; 43with Urealp; use Urealp; 44 45package Checks is 46 47 procedure Initialize; 48 -- Called for each new main source program, to initialize internal 49 -- variables used in the package body of the Checks unit. 50 51 function Access_Checks_Suppressed (E : Entity_Id) return Boolean; 52 function Accessibility_Checks_Suppressed (E : Entity_Id) return Boolean; 53 function Alignment_Checks_Suppressed (E : Entity_Id) return Boolean; 54 function Allocation_Checks_Suppressed (E : Entity_Id) return Boolean; 55 function Atomic_Synchronization_Disabled (E : Entity_Id) return Boolean; 56 function Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean; 57 function Division_Checks_Suppressed (E : Entity_Id) return Boolean; 58 function Duplicated_Tag_Checks_Suppressed (E : Entity_Id) return Boolean; 59 function Elaboration_Checks_Suppressed (E : Entity_Id) return Boolean; 60 function Index_Checks_Suppressed (E : Entity_Id) return Boolean; 61 function Length_Checks_Suppressed (E : Entity_Id) return Boolean; 62 function Overflow_Checks_Suppressed (E : Entity_Id) return Boolean; 63 function Predicate_Checks_Suppressed (E : Entity_Id) return Boolean; 64 function Range_Checks_Suppressed (E : Entity_Id) return Boolean; 65 function Storage_Checks_Suppressed (E : Entity_Id) return Boolean; 66 function Tag_Checks_Suppressed (E : Entity_Id) return Boolean; 67 function Validity_Checks_Suppressed (E : Entity_Id) return Boolean; 68 -- These functions check to see if the named check is suppressed, either 69 -- by an active scope suppress setting, or because the check has been 70 -- specifically suppressed for the given entity. If no entity is relevant 71 -- for the current check, then Empty is used as an argument. Note: the 72 -- reason we insist on specifying Empty is to force the caller to think 73 -- about whether there is any relevant entity that should be checked. 74 75 function Is_Check_Suppressed (E : Entity_Id; C : Check_Id) return Boolean; 76 -- This function is called if Checks_May_Be_Suppressed (E) is True to 77 -- determine whether check C is suppressed either on the entity E or 78 -- as the result of a scope suppress pragma. If Checks_May_Be_Suppressed 79 -- is False, then the status of the check can be determined simply by 80 -- examining Scope_Suppress, so this routine is not called in that case. 81 82 function Overflow_Check_Mode return Overflow_Mode_Type; 83 -- Returns current overflow checking mode, taking into account whether 84 -- we are inside an assertion expression and the assertion policy. 85 86 ----------------------------------------- 87 -- Control of Alignment Check Warnings -- 88 ----------------------------------------- 89 90 -- When we have address clauses, there is an issue of whether the address 91 -- specified is appropriate to the alignment. In the general case where the 92 -- address is dynamic, we generate a check and a possible warning (this 93 -- warning occurs for example if we have a restricted runtime with the 94 -- restriction No_Exception_Propagation). We also issue this warning in 95 -- the case where the address is static, but we don't know the alignment 96 -- at the time we process the address clause. In such a case, we issue the 97 -- warning, but we may be able to find out later (after the back end has 98 -- annotated the actual alignment chosen) that the warning was not needed. 99 100 -- To deal with deleting these potentially annoying warnings, we save the 101 -- warning information in a table, and then delete the warnings in the 102 -- post compilation validation stage if we can tell that the check would 103 -- never fail (in general the back end will also optimize away the check 104 -- in such cases). 105 106 -- Table used to record information 107 108 type Alignment_Warnings_Record is record 109 E : Entity_Id; 110 -- Entity whose alignment possibly warrants a warning 111 112 A : Uint; 113 -- Compile time known value of address clause for which the alignment 114 -- is to be checked once we know the alignment. 115 116 P : Node_Id; 117 -- Prefix of address clause when it is of the form X'Address 118 119 W : Error_Msg_Id; 120 -- Id of warning message we might delete 121 end record; 122 123 package Alignment_Warnings is new Table.Table ( 124 Table_Component_Type => Alignment_Warnings_Record, 125 Table_Index_Type => Int, 126 Table_Low_Bound => 0, 127 Table_Initial => 10, 128 Table_Increment => 200, 129 Table_Name => "Alignment_Warnings"); 130 131 procedure Validate_Alignment_Check_Warnings; 132 -- This routine is called after back annotation of type data to delete any 133 -- alignment warnings that turn out to be false alarms, based on knowing 134 -- the actual alignment, and a compile-time known alignment value. 135 136 ------------------------------------------- 137 -- Procedures to Activate Checking Flags -- 138 ------------------------------------------- 139 140 procedure Activate_Division_Check (N : Node_Id); 141 pragma Inline (Activate_Division_Check); 142 -- Sets Do_Division_Check flag in node N, and handles possible local raise. 143 -- Always call this routine rather than calling Set_Do_Division_Check to 144 -- set an explicit value of True, to ensure handling the local raise case. 145 146 procedure Activate_Overflow_Check (N : Node_Id); 147 pragma Inline (Activate_Overflow_Check); 148 -- Sets Do_Overflow_Check flag in node N, and handles possible local raise. 149 -- Always call this routine rather than calling Set_Do_Overflow_Check to 150 -- set an explicit value of True, to ensure handling the local raise case. 151 -- Note that for discrete types, this call has no effect for MOD, REM, and 152 -- unary "+" for which overflow is never possible in any case. 153 -- 154 -- Note: for the discrete-type case, it is legitimate to call this routine 155 -- on an unanalyzed node where the Etype field is not set. However, for the 156 -- floating-point case, Etype must be set (to a floating-point type). 157 -- 158 -- For floating-point, we set the flag if we have automatic overflow checks 159 -- on the target, or if Check_Float_Overflow mode is set. For the floating- 160 -- point case, we ignore all the unary operators ("+", "-", and abs) since 161 -- none of these can result in overflow. If there are no overflow checks on 162 -- the target, and Check_Float_Overflow mode is not set, then the call has 163 -- no effect, since in such cases we want to generate NaN's and infinities. 164 165 procedure Activate_Range_Check (N : Node_Id); 166 pragma Inline (Activate_Range_Check); 167 -- Sets Do_Range_Check flag in node N, and handles possible local raise. 168 -- Always call this routine rather than calling Set_Do_Range_Check to 169 -- set an explicit value of True, to ensure handling the local raise case. 170 171 -------------------------------- 172 -- Procedures to Apply Checks -- 173 -------------------------------- 174 175 -- General note on following checks. These checks are always active if 176 -- Expander_Active and not Inside_A_Generic. They are inactive and have 177 -- no effect Inside_A_Generic. In the case where not Expander_Active 178 -- and not Inside_A_Generic, most of them are inactive, but some of them 179 -- operate anyway since they may generate useful compile time warnings. 180 181 procedure Apply_Access_Check (N : Node_Id); 182 -- Determines whether an expression node requires a runtime access 183 -- check and if so inserts the appropriate run-time check. 184 185 procedure Apply_Accessibility_Check 186 (N : Node_Id; 187 Typ : Entity_Id; 188 Insert_Node : Node_Id); 189 -- Given a name N denoting an access parameter, emits a run-time 190 -- accessibility check (if necessary), checking that the level of 191 -- the object denoted by the access parameter is not deeper than the 192 -- level of the type Typ. Program_Error is raised if the check fails. 193 -- Insert_Node indicates the node where the check should be inserted. 194 195 procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id); 196 -- E is the entity for an object which has an address clause. If checks 197 -- are enabled, then this procedure generates a check that the specified 198 -- address has an alignment consistent with the alignment of the object, 199 -- raising PE if this is not the case. The resulting check (if one is 200 -- generated) is prepended to the Actions list of N_Freeze_Entity node N. 201 -- Note that the check references E'Alignment, so it cannot be emitted 202 -- before N (its freeze node), otherwise this would cause an illegal 203 -- access before elaboration error in GIGI. For the case of a clear overlay 204 -- situation, we also check that the size of the overlaying object is not 205 -- larger than the overlaid object. 206 207 procedure Apply_Arithmetic_Overflow_Check (N : Node_Id); 208 -- Handle overflow checking for an arithmetic operator. Also handles the 209 -- cases of ELIMINATED and MINIMIZED overflow checking mode. If the mode 210 -- is one of the latter two, then this routine can also be called with 211 -- an if or case expression node to make sure that we properly handle 212 -- overflow checking for dependent expressions. This routine handles 213 -- front end vs back end overflow checks (in the front end case it expands 214 -- the necessary check). Note that divide is handled separately using 215 -- Apply_Divide_Checks. Node N may or may not have Do_Overflow_Check. 216 -- In STRICT mode, there is nothing to do if this flag is off, but in 217 -- MINIMIZED/ELIMINATED mode we still have to deal with possible use 218 -- of doing operations in Long_Long_Integer or Bignum mode. 219 220 procedure Apply_Constraint_Check 221 (N : Node_Id; 222 Typ : Entity_Id; 223 No_Sliding : Boolean := False); 224 -- Top-level procedure, calls all the others depending on the class of 225 -- Typ. Checks that expression N satisfies the constraint of type Typ. 226 -- No_Sliding is only relevant for constrained array types, if set to 227 -- True, it checks that indexes are in range. 228 229 procedure Apply_Discriminant_Check 230 (N : Node_Id; 231 Typ : Entity_Id; 232 Lhs : Node_Id := Empty); 233 -- Given an expression N of a discriminated type, or of an access type 234 -- whose designated type is a discriminanted type, generates a check to 235 -- ensure that the expression can be converted to the subtype given as 236 -- the second parameter. Lhs is empty except in the case of assignments, 237 -- where the target object may be needed to determine the subtype to 238 -- check against (such as the cases of unconstrained formal parameters 239 -- and unconstrained aliased objects). For the case of unconstrained 240 -- formals, the check is performed only if the corresponding actual is 241 -- constrained, i.e., whether Lhs'Constrained is True. 242 243 procedure Apply_Divide_Checks (N : Node_Id); 244 -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem if either of the 245 -- flags Do_Division_Check or Do_Overflow_Check is set, then this routine 246 -- ensures that the appropriate checks are made. Note that overflow can 247 -- occur in the signed case for the case of the largest negative number 248 -- divided by minus one. This procedure only applies to Integer types. 249 250 procedure Apply_Parameter_Aliasing_Checks 251 (Call : Node_Id; 252 Subp : Entity_Id); 253 -- Given a subprogram call Call, add a check to verify that none of the 254 -- actuals overlap. Subp denotes the subprogram being called. 255 256 procedure Apply_Parameter_Validity_Checks (Subp : Entity_Id); 257 -- Given a subprogram Subp, add both a pre and post condition pragmas that 258 -- verify the proper initialization of scalars in parameters and function 259 -- results. 260 261 procedure Apply_Predicate_Check 262 (N : Node_Id; 263 Typ : Entity_Id; 264 Fun : Entity_Id := Empty); 265 -- N is an expression to which a predicate check may need to be applied for 266 -- Typ, if Typ has a predicate function. When N is an actual in a call, Fun 267 -- is the function being called, which is used to generate a better warning 268 -- if the call leads to an infinite recursion. 269 270 procedure Apply_Type_Conversion_Checks (N : Node_Id); 271 -- N is an N_Type_Conversion node. A type conversion actually involves 272 -- two sorts of checks. The first check is the checks that ensures that 273 -- the operand in the type conversion fits onto the base type of the 274 -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second 275 -- check is there to ensure that once the operand has been converted to 276 -- a value of the target type, this converted value meets the 277 -- constraints imposed by the target subtype (see RM 4.6 (51)). 278 279 procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id); 280 -- The argument N is an attribute reference node intended for processing 281 -- by gigi. The attribute is one that returns a universal integer, but 282 -- the attribute reference node is currently typed with the expected 283 -- result type. This routine deals with range and overflow checks needed 284 -- to make sure that the universal result is in range. 285 286 function Build_Discriminant_Checks 287 (N : Node_Id; 288 T_Typ : Entity_Id) 289 return Node_Id; 290 -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression 291 -- that compares discriminants of the expression with discriminants of the 292 -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In). 293 294 function Convert_From_Bignum (N : Node_Id) return Node_Id; 295 -- Returns result of converting node N from Bignum. The returned value is 296 -- not analyzed, the caller takes responsibility for this. Node N must be 297 -- a subexpression node of type Bignum. The result is Long_Long_Integer. 298 299 function Convert_To_Bignum (N : Node_Id) return Node_Id; 300 -- Returns result of converting node N to Bignum. The returned value is not 301 -- analyzed, the caller takes responsibility for this. Node N must be a 302 -- subexpression node of a signed integer type or Bignum type (if it is 303 -- already a Bignum, the returned value is Relocate_Node (N)). 304 305 procedure Determine_Range 306 (N : Node_Id; 307 OK : out Boolean; 308 Lo : out Uint; 309 Hi : out Uint; 310 Assume_Valid : Boolean := False); 311 -- N is a node for a subexpression. If N is of a discrete type with no 312 -- error indications, and no other peculiarities (e.g. missing Etype), 313 -- then OK is True on return, and Lo and Hi are set to a conservative 314 -- estimate of the possible range of values of N. Thus if OK is True on 315 -- return, the value of the subexpression N is known to lie in the range 316 -- Lo .. Hi (inclusive). For enumeration and character literals the values 317 -- returned are the Pos value in the relevant enumeration type. If the 318 -- expression is not of a discrete type, or some kind of error condition 319 -- is detected, then OK is False on exit, and Lo/Hi are set to No_Uint. 320 -- Thus the significance of OK being False on return is that no useful 321 -- information is available on the range of the expression. Assume_Valid 322 -- determines whether the processing is allowed to assume that values are 323 -- in range of their subtypes. If it is set to True, then this assumption 324 -- is valid, if False, then processing is done using base types to allow 325 -- invalid values. 326 327 procedure Determine_Range_R 328 (N : Node_Id; 329 OK : out Boolean; 330 Lo : out Ureal; 331 Hi : out Ureal; 332 Assume_Valid : Boolean := False); 333 -- Similar to Determine_Range, but for a node N of floating-point type. OK 334 -- is True on return only for IEEE floating-point types and only if we do 335 -- not have to worry about extended precision (i.e. on the x86, we must be 336 -- using -msse2 -mfpmath=sse). At the current time, this is used only in 337 -- GNATprove, though we could consider using it more generally in future. 338 -- For that to happen, the possibility of arguments of infinite or NaN 339 -- value should be taken into account, which is not the case currently. 340 341 procedure Install_Null_Excluding_Check (N : Node_Id); 342 -- Determines whether an access node requires a runtime access check and 343 -- if so inserts the appropriate run-time check. 344 345 procedure Install_Primitive_Elaboration_Check (Subp_Body : Node_Id); 346 -- Insert a check which ensures that subprogram body Subp_Body has been 347 -- properly elaborated. The check is installed only when Subp_Body is the 348 -- body of a nonabstract library-level primitive of a tagged type. Further 349 -- restrictions may apply, see the body for details. 350 351 function Make_Bignum_Block (Loc : Source_Ptr) return Node_Id; 352 -- This function is used by top level overflow checking routines to do a 353 -- mark/release operation on the secondary stack around bignum operations. 354 -- The block created looks like: 355 -- 356 -- declare 357 -- M : Mark_Id := SS_Mark; 358 -- begin 359 -- SS_Release (M); 360 -- end; 361 -- 362 -- The idea is that the caller will insert any needed extra declarations 363 -- after the declaration of M, and any needed statements (in particular 364 -- the bignum operations) before the call to SS_Release, and then do an 365 -- Insert_Action of the whole block (it is returned unanalyzed). The Loc 366 -- parameter is used to supply Sloc values for the constructed tree. 367 368 procedure Minimize_Eliminate_Overflows 369 (N : Node_Id; 370 Lo : out Uint; 371 Hi : out Uint; 372 Top_Level : Boolean); 373 -- This is the main routine for handling MINIMIZED and ELIMINATED overflow 374 -- processing. On entry N is a node whose result is a signed integer 375 -- subtype. The Do_Overflow_Check flag may or may not be set on N. If the 376 -- node is an arithmetic operation, then a range analysis is carried out, 377 -- and there are three possibilities: 378 -- 379 -- The node is left unchanged (apart from expansion of an exponentiation 380 -- operation). This happens if the routine can determine that the result 381 -- is definitely in range. The Do_Overflow_Check flag is turned off in 382 -- this case. 383 -- 384 -- The node is transformed into an arithmetic operation with a result 385 -- type of Long_Long_Integer. 386 -- 387 -- The node is transformed into a function call that calls an appropriate 388 -- function in the System.Bignums package to compute a Bignum result. 389 -- 390 -- In the first two cases, Lo and Hi are set to the bounds of the possible 391 -- range of results, computed as accurately as possible. In the third case 392 -- Lo and Hi are set to No_Uint (there are some cases where we could get an 393 -- advantage from keeping result ranges for Bignum values, but it could use 394 -- a lot of space and is very unlikely to be valuable). 395 -- 396 -- If the node is not an arithmetic operation, then it is unchanged but 397 -- Lo and Hi are still set (to the bounds of the result subtype if nothing 398 -- better can be determined). 399 -- 400 -- Note: this function is recursive, if called with an arithmetic operator, 401 -- recursive calls are made to process the operands using this procedure. 402 -- So we end up doing things top down. Nothing happens to an arithmetic 403 -- expression until this procedure is called on the top level node and 404 -- then the recursive calls process all the children. We have to do it 405 -- this way. If we try to do it bottom up in natural expansion order, then 406 -- there are two problems. First, where do we stash the bounds, and more 407 -- importantly, semantic processing will be messed up. Consider A+B+C where 408 -- A,B,C are all of type integer, if we processed A+B before doing semantic 409 -- analysis of the addition of this result to C, that addition could end up 410 -- with a Long_Long_Integer left operand and an Integer right operand, and 411 -- we would get a semantic error. 412 -- 413 -- The routine is called in three situations if we are operating in either 414 -- MINIMIZED or ELIMINATED modes. 415 -- 416 -- Overflow processing applied to the top node of an expression tree when 417 -- that node is an arithmetic operator. In this case the result is 418 -- converted to the appropriate result type (there is special processing 419 -- when the parent is a conversion, see body for details). 420 -- 421 -- Overflow processing applied to the operands of a comparison operation. 422 -- In this case, the comparison is done on the result Long_Long_Integer 423 -- or Bignum values, without raising any exceptions. 424 -- 425 -- Overflow processing applied to the left operand of a membership test. 426 -- In this case no exception is raised if a Long_Long_Integer or Bignum 427 -- result is outside the range of the type of that left operand (it is 428 -- just that the result of IN is false in that case). 429 -- 430 -- Note that if Bignum values appear, the caller must take care of doing 431 -- the appropriate mark/release operations on the secondary stack. 432 -- 433 -- Top_Level is used to avoid inefficient unnecessary transitions into the 434 -- Bignum domain. If Top_Level is True, it means that the caller will have 435 -- to convert any Bignum value back to Long_Long_Integer, possibly checking 436 -- that the value is in range. This is the normal case for a top level 437 -- operator in a subexpression. There is no point in going into Bignum mode 438 -- to avoid an overflow just so we can check for overflow the next moment. 439 -- For calls from comparisons and membership tests, and for all recursive 440 -- calls, we do want to transition into the Bignum domain if necessary. 441 -- Note that this setting is only relevant in ELIMINATED mode. 442 443 ------------------------------------------------------- 444 -- Control and Optimization of Range/Overflow Checks -- 445 ------------------------------------------------------- 446 447 -- Range checks are controlled by the Do_Range_Check flag. The front end 448 -- is responsible for setting this flag in relevant nodes. Originally 449 -- the back end generated all corresponding range checks. But later on 450 -- we decided to generate many range checks in the front end. We are now 451 -- in the transitional phase where some of these checks are still done 452 -- by the back end, but many are done by the front end. It is possible 453 -- that in the future we might move all the checks to the front end. The 454 -- main remaining back end checks are for subscript checking. 455 456 -- Overflow checks are similarly controlled by the Do_Overflow_Check flag. 457 -- The difference here is that if back end overflow checks are inactive 458 -- (Backend_Overflow_Checks_On_Target set False), then the actual overflow 459 -- checks are generated by the front end, but if back end overflow checks 460 -- are active (Backend_Overflow_Checks_On_Target set True), then the back 461 -- end does generate the checks. 462 463 -- The following two routines are used to set these flags, they allow 464 -- for the possibility of eliminating checks. Checks can be eliminated 465 -- if an identical check has already been performed. 466 467 procedure Enable_Overflow_Check (N : Node_Id); 468 -- First this routine determines if an overflow check is needed by doing 469 -- an appropriate range check. If a check is not needed, then the call 470 -- has no effect. If a check is needed then this routine sets the flag 471 -- Do_Overflow_Check in node N to True, unless it can be determined that 472 -- the check is not needed. The only condition under which this is the 473 -- case is if there was an identical check earlier on. 474 475 procedure Enable_Range_Check (N : Node_Id); 476 -- Set Do_Range_Check flag in node N True, unless it can be determined 477 -- that the check is not needed. The only condition under which this is 478 -- the case is if there was an identical check earlier on. This routine 479 -- is not responsible for doing range analysis to determine whether or 480 -- not such a check is needed -- the caller is expected to do this. The 481 -- one other case in which the request to set the flag is ignored is 482 -- when Kill_Range_Check is set in an N_Unchecked_Conversion node. 483 484 -- The following routines are used to keep track of processing sequences 485 -- of statements (e.g. the THEN statements of an IF statement). A check 486 -- that appears within such a sequence can eliminate an identical check 487 -- within this sequence of statements. However, after the end of the 488 -- sequence of statements, such a check is no longer of interest, since 489 -- it may not have been executed. 490 491 procedure Conditional_Statements_Begin; 492 -- This call marks the start of processing of a sequence of statements. 493 -- Every call to this procedure must be followed by a matching call to 494 -- Conditional_Statements_End. 495 496 procedure Conditional_Statements_End; 497 -- This call removes from consideration all saved checks since the 498 -- corresponding call to Conditional_Statements_Begin. These two 499 -- procedures operate in a stack like manner. 500 501 -- The mechanism for optimizing checks works by remembering checks 502 -- that have already been made, but certain conditions, for example 503 -- an assignment to a variable involved in a check, may mean that the 504 -- remembered check is no longer valid, in the sense that if the same 505 -- expression appears again, another check is required because the 506 -- value may have changed. 507 508 -- The following routines are used to note conditions which may render 509 -- some or all of the stored and remembered checks to be invalidated. 510 511 procedure Kill_Checks (V : Entity_Id); 512 -- This procedure records an assignment or other condition that causes 513 -- the value of the variable to be changed, invalidating any stored 514 -- checks that reference the value. Note that all such checks must 515 -- be discarded, even if they are not in the current statement range. 516 517 procedure Kill_All_Checks; 518 -- This procedure kills all remembered checks 519 520 ----------------------------- 521 -- Length and Range Checks -- 522 ----------------------------- 523 524 -- In the following procedures, there are three arguments which have 525 -- a common meaning as follows: 526 527 -- Expr The expression to be checked. If a check is required, 528 -- the appropriate flag will be placed on this node. Whether 529 -- this node is further examined depends on the setting of 530 -- the parameter Source_Typ, as described below. 531 532 -- ??? Apply_Length_Check and Apply_Range_Check do not have an Expr 533 -- formal 534 535 -- ??? Apply_Length_Check and Apply_Range_Check have a Ck_Node formal 536 -- which is undocumented, is it the same as Expr? 537 538 -- Target_Typ The target type on which the check is to be based. For 539 -- example, if we have a scalar range check, then the check 540 -- is that we are in range of this type. 541 542 -- Source_Typ Normally Empty, but can be set to a type, in which case 543 -- this type is used for the check, see below. 544 545 -- The checks operate in one of two modes: 546 547 -- If Source_Typ is Empty, then the node Expr is examined, at the very 548 -- least to get the source subtype. In addition for some of the checks, 549 -- the actual form of the node may be examined. For example, a node of 550 -- type Integer whose actual form is an Integer conversion from a type 551 -- with range 0 .. 3 can be determined to have a value in range 0 .. 3. 552 553 -- If Source_Typ is given, then nothing can be assumed about the Expr, 554 -- and indeed its contents are not examined. In this case the check is 555 -- based on the assumption that Expr can be an arbitrary value of the 556 -- given Source_Typ. 557 558 -- Currently, the only case in which a Source_Typ is explicitly supplied 559 -- is for the case of Out and In_Out parameters, where, for the conversion 560 -- on return (the Out direction), the types must be reversed. This is 561 -- handled by the caller. 562 563 procedure Apply_Length_Check 564 (Ck_Node : Node_Id; 565 Target_Typ : Entity_Id; 566 Source_Typ : Entity_Id := Empty); 567 -- This procedure builds a sequence of declarations to do a length check 568 -- that checks if the lengths of the two arrays Target_Typ and source type 569 -- are the same. The resulting actions are inserted at Node using a call 570 -- to Insert_Actions. 571 -- 572 -- For access types, the Directly_Designated_Type is retrieved and 573 -- processing continues as enumerated above, with a guard against null 574 -- values. 575 -- 576 -- Note: calls to Apply_Length_Check currently never supply an explicit 577 -- Source_Typ parameter, but Apply_Length_Check takes this parameter and 578 -- processes it as described above for consistency with the other routines 579 -- in this section. 580 581 procedure Apply_Range_Check 582 (Ck_Node : Node_Id; 583 Target_Typ : Entity_Id; 584 Source_Typ : Entity_Id := Empty); 585 -- For a Node of kind N_Range, constructs a range check action that tests 586 -- first that the range is not null and then that the range is contained in 587 -- the Target_Typ range. 588 -- 589 -- For scalar types, constructs a range check action that first tests that 590 -- the expression is contained in the Target_Typ range. The difference 591 -- between this and Apply_Scalar_Range_Check is that the latter generates 592 -- the actual checking code against the Etype of the expression. 593 -- 594 -- For constrained array types, construct series of range check actions 595 -- to check that each Expr range is properly contained in the range of 596 -- Target_Typ. 597 -- 598 -- For a type conversion to an unconstrained array type, constructs a range 599 -- check action to check that the bounds of the source type are within the 600 -- constraints imposed by the Target_Typ. 601 -- 602 -- For access types, the Directly_Designated_Type is retrieved and 603 -- processing continues as enumerated above, with a guard against null 604 -- values. 605 -- 606 -- The source type is used by type conversions to unconstrained array 607 -- types to retrieve the corresponding bounds. 608 609 procedure Apply_Static_Length_Check 610 (Expr : Node_Id; 611 Target_Typ : Entity_Id; 612 Source_Typ : Entity_Id := Empty); 613 -- Tries to determine statically whether the two array types source type 614 -- and Target_Typ have the same length. If it can be determined at compile 615 -- time that they do not, then an N_Raise_Constraint_Error node replaces 616 -- Expr, and a warning message is issued. 617 618 procedure Apply_Scalar_Range_Check 619 (Expr : Node_Id; 620 Target_Typ : Entity_Id; 621 Source_Typ : Entity_Id := Empty; 622 Fixed_Int : Boolean := False); 623 -- For scalar types, determines whether an expression node should be 624 -- flagged as needing a runtime range check. If the node requires such a 625 -- check, the Do_Range_Check flag is turned on. The Fixed_Int flag if set 626 -- causes any fixed-point values to be treated as though they were discrete 627 -- values (i.e. the underlying integer value is used). 628 629 type Check_Result is private; 630 -- Type used to return result of Get_Range_Checks call, for later use in 631 -- call to Insert_Range_Checks procedure. 632 633 function Get_Range_Checks 634 (Ck_Node : Node_Id; 635 Target_Typ : Entity_Id; 636 Source_Typ : Entity_Id := Empty; 637 Warn_Node : Node_Id := Empty) return Check_Result; 638 -- Like Apply_Range_Check, except it does not modify anything. Instead 639 -- it returns an encapsulated result of the check operations for later 640 -- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its 641 -- Sloc is used, in the static case, for the generated warning or error. 642 -- Additionally, it is used rather than Expr (or Low/High_Bound of Expr) 643 -- in constructing the check. 644 645 procedure Append_Range_Checks 646 (Checks : Check_Result; 647 Stmts : List_Id; 648 Suppress_Typ : Entity_Id; 649 Static_Sloc : Source_Ptr; 650 Flag_Node : Node_Id); 651 -- Called to append range checks as returned by a call to Get_Range_Checks. 652 -- Stmts is a list to which either the dynamic check is appended or the 653 -- raise Constraint_Error statement is appended (for static checks). 654 -- Static_Sloc is the Sloc at which the raise CE node points, Flag_Node is 655 -- used as the node at which to set the Has_Dynamic_Check flag. Checks_On 656 -- is a boolean value that says if range and index checking is on or not. 657 658 procedure Insert_Range_Checks 659 (Checks : Check_Result; 660 Node : Node_Id; 661 Suppress_Typ : Entity_Id; 662 Static_Sloc : Source_Ptr := No_Location; 663 Flag_Node : Node_Id := Empty; 664 Do_Before : Boolean := False); 665 -- Called to insert range checks as returned by a call to Get_Range_Checks. 666 -- Node is the node after which either the dynamic check is inserted or 667 -- the raise Constraint_Error statement is inserted (for static checks). 668 -- Suppress_Typ is the type to check to determine if checks are suppressed. 669 -- Static_Sloc, if passed, is the Sloc at which the raise CE node points, 670 -- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally 671 -- set at Node. If Flag_Node is present, then this is used instead as the 672 -- node at which to set the Has_Dynamic_Check flag. Normally the check is 673 -- inserted after, if Do_Before is True, the check is inserted before 674 -- Node. 675 676 ----------------------- 677 -- Expander Routines -- 678 ----------------------- 679 680 -- Some of the earlier processing for checks results in temporarily setting 681 -- the Do_Range_Check flag rather than actually generating checks. Now we 682 -- are moving the generation of such checks into the front end for reasons 683 -- of efficiency and simplicity (there were difficulties in handling this 684 -- in the back end when side effects were present in the expressions being 685 -- checked). 686 687 -- Probably we could eliminate the Do_Range_Check flag entirely and 688 -- generate the checks earlier, but this is a delicate area and it 689 -- seemed safer to implement the following routines, which are called 690 -- late on in the expansion process. They check the Do_Range_Check flag 691 -- and if it is set, generate the actual checks and reset the flag. 692 693 procedure Generate_Range_Check 694 (N : Node_Id; 695 Target_Type : Entity_Id; 696 Reason : RT_Exception_Code); 697 -- This procedure is called to actually generate and insert a range check. 698 -- A check is generated to ensure that the value of N lies within the range 699 -- of the target type. Note that the base type of N may be different from 700 -- the base type of the target type. This happens in the conversion case. 701 -- The Reason parameter is the exception code to be used for the exception 702 -- if raised. 703 -- 704 -- Note: if the expander is not active, or if we are in GNATprove mode, 705 -- then we do not generate explicit range code. Instead we just turn the 706 -- Do_Range_Check flag on, since in these cases that's what we want to see 707 -- in the tree (GNATprove in particular depends on this flag being set). If 708 -- we generate the actual range check, then we make sure the flag is off, 709 -- since the code we generate takes complete care of the check. 710 -- 711 -- Historical note: We used to just pass on the Do_Range_Check flag to the 712 -- back end to generate the check, but now in code-generation mode we never 713 -- have this flag set, since the front end takes care of the check. The 714 -- normal processing flow now is that the analyzer typically turns on the 715 -- Do_Range_Check flag, and if it is set, this routine is called, which 716 -- turns the flag off in code-generation mode. 717 718 procedure Generate_Index_Checks (N : Node_Id); 719 -- This procedure is called to generate index checks on the subscripts for 720 -- the indexed component node N. Each subscript expression is examined, and 721 -- if the Do_Range_Check flag is set, an appropriate index check is 722 -- generated and the flag is reset. 723 724 -- Similarly, we set the flag Do_Discriminant_Check in the semantic 725 -- analysis to indicate that a discriminant check is required for selected 726 -- component of a discriminated type. The following routine is called from 727 -- the expander to actually generate the call. 728 729 procedure Generate_Discriminant_Check (N : Node_Id); 730 -- N is a selected component for which a discriminant check is required to 731 -- make sure that the discriminants have appropriate values for the 732 -- selection. This is done by calling the appropriate discriminant checking 733 -- routine for the selector. 734 735 ----------------------- 736 -- Validity Checking -- 737 ----------------------- 738 739 -- In (RM 13.9.1(9-11)) we have the following rules on invalid values 740 741 -- If the representation of a scalar object does not represent value of 742 -- the object's subtype (perhaps because the object was not initialized), 743 -- the object is said to have an invalid representation. It is a bounded 744 -- error to evaluate the value of such an object. If the error is 745 -- detected, either Constraint_Error or Program_Error is raised. 746 -- Otherwise, execution continues using the invalid representation. The 747 -- rules of the language outside this subclause assume that all objects 748 -- have valid representations. The semantics of operations on invalid 749 -- representations are as follows: 750 -- 751 -- 10 If the representation of the object represents a value of the 752 -- object's type, the value of the type is used. 753 -- 754 -- 11 If the representation of the object does not represent a value 755 -- of the object's type, the semantics of operations on such 756 -- representations is implementation-defined, but does not by 757 -- itself lead to erroneous or unpredictable execution, or to 758 -- other objects becoming abnormal. 759 760 -- We quote the rules in full here since they are quite delicate. Most 761 -- of the time, we can just compute away with wrong values, and get a 762 -- possibly wrong result, which is well within the range of allowed 763 -- implementation defined behavior. The two tricky cases are subscripted 764 -- array assignments, where we don't want to do wild stores, and case 765 -- statements where we don't want to do wild jumps. 766 767 -- In GNAT, we control validity checking with a switch -gnatV that can take 768 -- three parameters, n/d/f for None/Default/Full. These modes have the 769 -- following meanings: 770 771 -- None (no validity checking) 772 773 -- In this mode, there is no specific checking for invalid values 774 -- and the code generator assumes that all stored values are always 775 -- within the bounds of the object subtype. The consequences are as 776 -- follows: 777 778 -- For case statements, an out of range invalid value will cause 779 -- Constraint_Error to be raised, or an arbitrary one of the case 780 -- alternatives will be executed. Wild jumps cannot result even 781 -- in this mode, since we always do a range check 782 783 -- For subscripted array assignments, wild stores will result in 784 -- the expected manner when addresses are calculated using values 785 -- of subscripts that are out of range. 786 787 -- It could perhaps be argued that this mode is still conformant with 788 -- the letter of the RM, since implementation defined is a rather 789 -- broad category, but certainly it is not in the spirit of the 790 -- RM requirement, since wild stores certainly seem to be a case of 791 -- erroneous behavior. 792 793 -- Default (default standard RM-compatible validity checking) 794 795 -- In this mode, which is the default, minimal validity checking is 796 -- performed to ensure no erroneous behavior as follows: 797 798 -- For case statements, an out of range invalid value will cause 799 -- Constraint_Error to be raised. 800 801 -- For subscripted array assignments, invalid out of range 802 -- subscript values will cause Constraint_Error to be raised. 803 804 -- Full (Full validity checking) 805 806 -- In this mode, the protections guaranteed by the standard mode are 807 -- in place, and the following additional checks are made: 808 809 -- For every assignment, the right side is checked for validity 810 811 -- For every call, IN and IN OUT parameters are checked for validity 812 813 -- For every subscripted array reference, both for stores and loads, 814 -- all subscripts are checked for validity. 815 816 -- These checks are not required by the RM, but will in practice 817 -- improve the detection of uninitialized variables, particularly 818 -- if used in conjunction with pragma Normalize_Scalars. 819 820 -- In the above description, we talk about performing validity checks, 821 -- but we don't actually generate a check in a case where the compiler 822 -- can be sure that the value is valid. Note that this assurance must 823 -- be achieved without assuming that any uninitialized value lies within 824 -- the range of its type. The following are cases in which values are 825 -- known to be valid. The flag Is_Known_Valid is used to keep track of 826 -- some of these cases. 827 828 -- If all possible stored values are valid, then any uninitialized 829 -- value must be valid. 830 831 -- Literals, including enumeration literals, are clearly always valid 832 833 -- Constants are always assumed valid, with a validity check being 834 -- performed on the initializing value where necessary to ensure that 835 -- this is the case. 836 837 -- For variables, the status is set to known valid if there is an 838 -- initializing expression. Again a check is made on the initializing 839 -- value if necessary to ensure that this assumption is valid. The 840 -- status can change as a result of local assignments to a variable. 841 -- If a known valid value is unconditionally assigned, then we mark 842 -- the left side as known valid. If a value is assigned that is not 843 -- known to be valid, then we mark the left side as invalid. This 844 -- kind of processing does NOT apply to non-local variables since we 845 -- are not following the flow graph (more properly the flow of actual 846 -- processing only corresponds to the flow graph for local assignments). 847 -- For non-local variables, we preserve the current setting, i.e. a 848 -- validity check is performed when assigning to a knonwn valid global. 849 850 -- Note: no validity checking is required if range checks are suppressed 851 -- regardless of the setting of the validity checking mode. 852 853 -- The following procedures are used in handling validity checking 854 855 procedure Apply_Subscript_Validity_Checks (Expr : Node_Id); 856 -- Expr is the node for an indexed component. If validity checking and 857 -- range checking are enabled, all subscripts for this indexed component 858 -- are checked for validity. 859 860 procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id); 861 -- Expr is a lvalue, i.e. an expression representing the target of an 862 -- assignment. This procedure checks for this expression involving an 863 -- assignment to an array value. We have to be sure that all the subscripts 864 -- in such a case are valid, since according to the rules in (RM 865 -- 13.9.1(9-11)) such assignments are not permitted to result in erroneous 866 -- behavior in the case of invalid subscript values. 867 868 procedure Ensure_Valid 869 (Expr : Node_Id; 870 Holes_OK : Boolean := False; 871 Related_Id : Entity_Id := Empty; 872 Is_Low_Bound : Boolean := False; 873 Is_High_Bound : Boolean := False); 874 -- Ensure that Expr represents a valid value of its type. If this type 875 -- is not a scalar type, then the call has no effect, since validity 876 -- is only an issue for scalar types. The effect of this call is to 877 -- check if the value is known valid, if so, nothing needs to be done. 878 -- If this is not known, then either Expr is set to be range checked, 879 -- or specific checking code is inserted so that an exception is raised 880 -- if the value is not valid. 881 -- 882 -- The optional argument Holes_OK indicates whether it is necessary to 883 -- worry about enumeration types with non-standard representations leading 884 -- to "holes" in the range of possible representations. If Holes_OK is 885 -- True, then such values are assumed valid (this is used when the caller 886 -- will make a separate check for this case anyway). If Holes_OK is False, 887 -- then this case is checked, and code is inserted to ensure that Expr is 888 -- valid, raising Constraint_Error if the value is not valid. 889 -- 890 -- Related_Id denotes the entity of the context where Expr appears. Flags 891 -- Is_Low_Bound and Is_High_Bound specify whether the expression to check 892 -- is the low or the high bound of a range. These three optional arguments 893 -- signal Remove_Side_Effects to create an external symbol of the form 894 -- Chars (Related_Id)_FIRST/_LAST. For suggested use of these parameters 895 -- see the warning in the body of Sem_Ch3.Process_Range_Expr_In_Decl. 896 897 function Expr_Known_Valid (Expr : Node_Id) return Boolean; 898 -- This function tests it the value of Expr is known to be valid in the 899 -- sense of RM 13.9.1(9-11). In the case of GNAT, it is only discrete types 900 -- which are a concern, since for non-discrete types we simply continue 901 -- computation with invalid values, which does not lead to erroneous 902 -- behavior. Thus Expr_Known_Valid always returns True if the type of Expr 903 -- is non-discrete. For discrete types the value returned is True only if 904 -- it can be determined that the value is Valid. Otherwise False is 905 -- returned. 906 907 procedure Insert_Valid_Check 908 (Expr : Node_Id; 909 Related_Id : Entity_Id := Empty; 910 Is_Low_Bound : Boolean := False; 911 Is_High_Bound : Boolean := False); 912 -- Inserts code that will check for the value of Expr being valid, in the 913 -- sense of the 'Valid attribute returning True. Constraint_Error will be 914 -- raised if the value is not valid. 915 -- 916 -- Related_Id denotes the entity of the context where Expr appears. Flags 917 -- Is_Low_Bound and Is_High_Bound specify whether the expression to check 918 -- is the low or the high bound of a range. These three optional arguments 919 -- signal Remove_Side_Effects to create an external symbol of the form 920 -- Chars (Related_Id)_FIRST/_LAST. For suggested use of these parameters 921 -- see the warning in the body of Sem_Ch3.Process_Range_Expr_In_Decl. 922 923 procedure Null_Exclusion_Static_Checks 924 (N : Node_Id; 925 Comp : Node_Id := Empty; 926 Array_Comp : Boolean := False); 927 -- Ada 2005 (AI-231): Test for and warn on null-excluding objects or 928 -- components that will raise an exception due to initialization by null. 929 -- 930 -- When a value for Comp is supplied (as in the case of an uninitialized 931 -- null-excluding component within a composite object), a reported warning 932 -- will indicate the offending component instead of the object itself. 933 -- Array_Comp being True indicates an array object with null-excluding 934 -- components, and any reported warning will indicate that. 935 936 procedure Remove_Checks (Expr : Node_Id); 937 -- Remove all checks from Expr except those that are only executed 938 -- conditionally (on the right side of And Then/Or Else. This call 939 -- removes only embedded checks (Do_Range_Check, Do_Overflow_Check). 940 941 procedure Validity_Check_Range 942 (N : Node_Id; 943 Related_Id : Entity_Id := Empty); 944 -- If N is an N_Range node, then Ensure_Valid is called on its bounds, if 945 -- validity checking of operands is enabled. Related_Id denotes the entity 946 -- of the context where N appears. 947 948 ----------------------------- 949 -- Handling of Check Names -- 950 ----------------------------- 951 952 -- The following table contains Name_Id's for recognized checks. The first 953 -- entries (corresponding to the values of the subtype Predefined_Check_Id) 954 -- contain the Name_Id values for the checks that are predefined, including 955 -- All_Checks (see Types). Remaining entries are those that are introduced 956 -- by pragma Check_Names. 957 958 package Check_Names is new Table.Table ( 959 Table_Component_Type => Name_Id, 960 Table_Index_Type => Check_Id, 961 Table_Low_Bound => 1, 962 Table_Initial => 30, 963 Table_Increment => 200, 964 Table_Name => "Name_Check_Names"); 965 966 function Get_Check_Id (N : Name_Id) return Check_Id; 967 -- Function to search above table for matching name. If found returns the 968 -- corresponding Check_Id value in the range 1 .. Check_Name.Last. If not 969 -- found returns No_Check_Id. 970 971private 972 973 type Check_Result is array (Positive range 1 .. 2) of Node_Id; 974 -- There are two cases for the result returned by Range_Check: 975 -- 976 -- For the static case the result is one or two nodes that should cause 977 -- a Constraint_Error. Typically these will include Expr itself or the 978 -- direct descendants of Expr, such as Low/High_Bound (Expr)). It is the 979 -- responsibility of the caller to rewrite and substitute the nodes with 980 -- N_Raise_Constraint_Error nodes. 981 -- 982 -- For the non-static case a single N_Raise_Constraint_Error node with a 983 -- non-empty Condition field is returned. 984 -- 985 -- Unused entries in Check_Result, if any, are simply set to Empty For 986 -- external clients, the required processing on this result is achieved 987 -- using the Insert_Range_Checks routine. 988 989 pragma Inline (Apply_Length_Check); 990 pragma Inline (Apply_Range_Check); 991 pragma Inline (Apply_Static_Length_Check); 992end Checks; 993