1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- C H E C K S -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2015, 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 run time 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 waranings 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 W : Error_Msg_Id; 117 -- Id of warning message we might delete 118 end record; 119 120 package Alignment_Warnings is new Table.Table ( 121 Table_Component_Type => Alignment_Warnings_Record, 122 Table_Index_Type => Int, 123 Table_Low_Bound => 0, 124 Table_Initial => 10, 125 Table_Increment => 200, 126 Table_Name => "Alignment_Warnings"); 127 128 procedure Validate_Alignment_Check_Warnings; 129 -- This routine is called after back annotation of type data to delete any 130 -- alignment warnings that turn out to be false alarms, based on knowing 131 -- the actual alignment, and a compile-time known alignment value. 132 133 ------------------------------------------- 134 -- Procedures to Activate Checking Flags -- 135 ------------------------------------------- 136 137 procedure Activate_Division_Check (N : Node_Id); 138 pragma Inline (Activate_Division_Check); 139 -- Sets Do_Division_Check flag in node N, and handles possible local raise. 140 -- Always call this routine rather than calling Set_Do_Division_Check to 141 -- set an explicit value of True, to ensure handling the local raise case. 142 143 procedure Activate_Overflow_Check (N : Node_Id); 144 pragma Inline (Activate_Overflow_Check); 145 -- Sets Do_Overflow_Check flag in node N, and handles possible local raise. 146 -- Always call this routine rather than calling Set_Do_Overflow_Check to 147 -- set an explicit value of True, to ensure handling the local raise case. 148 -- Note that for discrete types, this call has no effect for MOD, REM, and 149 -- unary "+" for which overflow is never possible in any case. 150 -- 151 -- Note: for the discrete-type case, it is legitimate to call this routine 152 -- on an unanalyzed node where the Etype field is not set. However, for the 153 -- floating-point case, Etype must be set (to a floating-point type). 154 -- 155 -- For floating-point, we set the flag if we have automatic overflow checks 156 -- on the target, or if Check_Float_Overflow mode is set. For the floating- 157 -- point case, we ignore all the unary operators ("+", "-", and abs) since 158 -- none of these can result in overflow. If there are no overflow checks on 159 -- the target, and Check_Float_Overflow mode is not set, then the call has 160 -- no effect, since in such cases we want to generate NaN's and infinities. 161 162 procedure Activate_Range_Check (N : Node_Id); 163 pragma Inline (Activate_Range_Check); 164 -- Sets Do_Range_Check flag in node N, and handles possible local raise 165 -- Always call this routine rather than calling Set_Do_Range_Check to 166 -- set an explicit value of True, to ensure handling the local raise case. 167 168 -------------------------------- 169 -- Procedures to Apply Checks -- 170 -------------------------------- 171 172 -- General note on following checks. These checks are always active if 173 -- Expander_Active and not Inside_A_Generic. They are inactive and have 174 -- no effect Inside_A_Generic. In the case where not Expander_Active 175 -- and not Inside_A_Generic, most of them are inactive, but some of them 176 -- operate anyway since they may generate useful compile time warnings. 177 178 procedure Apply_Access_Check (N : Node_Id); 179 -- Determines whether an expression node requires a runtime access 180 -- check and if so inserts the appropriate run-time check. 181 182 procedure Apply_Accessibility_Check 183 (N : Node_Id; 184 Typ : Entity_Id; 185 Insert_Node : Node_Id); 186 -- Given a name N denoting an access parameter, emits a run-time 187 -- accessibility check (if necessary), checking that the level of 188 -- the object denoted by the access parameter is not deeper than the 189 -- level of the type Typ. Program_Error is raised if the check fails. 190 -- Insert_Node indicates the node where the check should be inserted. 191 192 procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id); 193 -- E is the entity for an object which has an address clause. If checks 194 -- are enabled, then this procedure generates a check that the specified 195 -- address has an alignment consistent with the alignment of the object, 196 -- raising PE if this is not the case. The resulting check (if one is 197 -- generated) is prepended to the Actions list of N_Freeze_Entity node N. 198 -- Note that the check references E'Alignment, so it cannot be emitted 199 -- before N (its freeze node), otherwise this would cause an illegal 200 -- access before elaboration error in GIGI. For the case of a clear overlay 201 -- situation, we also check that the size of the overlaying object is not 202 -- larger than the overlaid object. 203 204 procedure Apply_Arithmetic_Overflow_Check (N : Node_Id); 205 -- Handle overflow checking for an arithmetic operator. Also handles the 206 -- cases of ELIMINATED and MINIMIZED overflow checking mode. If the mode 207 -- is one of the latter two, then this routine can also be called with 208 -- an if or case expression node to make sure that we properly handle 209 -- overflow checking for dependent expressions. This routine handles 210 -- front end vs back end overflow checks (in the front end case it expands 211 -- the necessary check). Note that divide is handled separately using 212 -- Apply_Divide_Checks. Node N may or may not have Do_Overflow_Check. 213 -- In STRICT mode, there is nothing to do if this flag is off, but in 214 -- MINIMIZED/ELIMINATED mode we still have to deal with possible use 215 -- of doing operations in Long_Long_Integer or Bignum mode. 216 217 procedure Apply_Constraint_Check 218 (N : Node_Id; 219 Typ : Entity_Id; 220 No_Sliding : Boolean := False); 221 -- Top-level procedure, calls all the others depending on the class of 222 -- Typ. Checks that expression N satisfies the constraint of type Typ. 223 -- No_Sliding is only relevant for constrained array types, if set to 224 -- True, it checks that indexes are in range. 225 226 procedure Apply_Discriminant_Check 227 (N : Node_Id; 228 Typ : Entity_Id; 229 Lhs : Node_Id := Empty); 230 -- Given an expression N of a discriminated type, or of an access type 231 -- whose designated type is a discriminanted type, generates a check to 232 -- ensure that the expression can be converted to the subtype given as 233 -- the second parameter. Lhs is empty except in the case of assignments, 234 -- where the target object may be needed to determine the subtype to 235 -- check against (such as the cases of unconstrained formal parameters 236 -- and unconstrained aliased objects). For the case of unconstrained 237 -- formals, the check is performed only if the corresponding actual is 238 -- constrained, i.e., whether Lhs'Constrained is True. 239 240 procedure Apply_Divide_Checks (N : Node_Id); 241 -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem if either of the 242 -- flags Do_Division_Check or Do_Overflow_Check is set, then this routine 243 -- ensures that the appropriate checks are made. Note that overflow can 244 -- occur in the signed case for the case of the largest negative number 245 -- divided by minus one. This procedure only applies to Integer types. 246 247 procedure Apply_Parameter_Aliasing_Checks 248 (Call : Node_Id; 249 Subp : Entity_Id); 250 -- Given a subprogram call Call, add a check to verify that none of the 251 -- actuals overlap. Subp denotes the subprogram being called. 252 253 procedure Apply_Parameter_Validity_Checks (Subp : Entity_Id); 254 -- Given a subprogram Subp, add both a pre and post condition pragmas that 255 -- verify the proper initialization of scalars in parameters and function 256 -- results. 257 258 procedure Apply_Predicate_Check (N : Node_Id; Typ : Entity_Id); 259 -- N is an expression to which a predicate check may need to be applied 260 -- for Typ, if Typ has a predicate function. 261 262 procedure Apply_Type_Conversion_Checks (N : Node_Id); 263 -- N is an N_Type_Conversion node. A type conversion actually involves 264 -- two sorts of checks. The first check is the checks that ensures that 265 -- the operand in the type conversion fits onto the base type of the 266 -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second 267 -- check is there to ensure that once the operand has been converted to 268 -- a value of the target type, this converted value meets the 269 -- constraints imposed by the target subtype (see RM 4.6 (51)). 270 271 procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id); 272 -- The argument N is an attribute reference node intended for processing 273 -- by gigi. The attribute is one that returns a universal integer, but 274 -- the attribute reference node is currently typed with the expected 275 -- result type. This routine deals with range and overflow checks needed 276 -- to make sure that the universal result is in range. 277 278 function Build_Discriminant_Checks 279 (N : Node_Id; 280 T_Typ : Entity_Id) 281 return Node_Id; 282 -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression 283 -- that compares discriminants of the expression with discriminants of the 284 -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In). 285 286 function Convert_From_Bignum (N : Node_Id) return Node_Id; 287 -- Returns result of converting node N from Bignum. The returned value is 288 -- not analyzed, the caller takes responsibility for this. Node N must be 289 -- a subexpression node of type Bignum. The result is Long_Long_Integer. 290 291 function Convert_To_Bignum (N : Node_Id) return Node_Id; 292 -- Returns result of converting node N to Bignum. The returned value is not 293 -- analyzed, the caller takes responsibility for this. Node N must be a 294 -- subexpression node of a signed integer type or Bignum type (if it is 295 -- already a Bignum, the returned value is Relocate_Node (N)). 296 297 procedure Determine_Range 298 (N : Node_Id; 299 OK : out Boolean; 300 Lo : out Uint; 301 Hi : out Uint; 302 Assume_Valid : Boolean := False); 303 -- N is a node for a subexpression. If N is of a discrete type with no 304 -- error indications, and no other peculiarities (e.g. missing Etype), 305 -- then OK is True on return, and Lo and Hi are set to a conservative 306 -- estimate of the possible range of values of N. Thus if OK is True on 307 -- return, the value of the subexpression N is known to lie in the range 308 -- Lo .. Hi (inclusive). If the expression is not of a discrete type, or 309 -- some kind of error condition is detected, then OK is False on exit, and 310 -- Lo/Hi are set to No_Uint. Thus the significance of OK being False on 311 -- return is that no useful information is available on the range of the 312 -- expression. Assume_Valid determines whether the processing is allowed to 313 -- assume that values are in range of their subtypes. If it is set to True, 314 -- then this assumption is valid, if False, then processing is done using 315 -- base types to allow invalid values. 316 317 procedure Determine_Range_R 318 (N : Node_Id; 319 OK : out Boolean; 320 Lo : out Ureal; 321 Hi : out Ureal; 322 Assume_Valid : Boolean := False); 323 -- Similar to Determine_Range, but for a node N of floating-point type. OK 324 -- is True on return only for IEEE floating-point types and only if we do 325 -- not have to worry about extended precision (i.e. on the x86, we must be 326 -- using -msse2 -mfpmath=sse). At the current time, this is used only in 327 -- GNATprove, though we could consider using it more generally in future. 328 -- For that to happen, the possibility of arguments of infinite or NaN 329 -- value should be taken into account, which is not the case currently. 330 331 procedure Install_Null_Excluding_Check (N : Node_Id); 332 -- Determines whether an access node requires a runtime access check and 333 -- if so inserts the appropriate run-time check. 334 335 function Make_Bignum_Block (Loc : Source_Ptr) return Node_Id; 336 -- This function is used by top level overflow checking routines to do a 337 -- mark/release operation on the secondary stack around bignum operations. 338 -- The block created looks like: 339 -- 340 -- declare 341 -- M : Mark_Id := SS_Mark; 342 -- begin 343 -- SS_Release (M); 344 -- end; 345 -- 346 -- The idea is that the caller will insert any needed extra declarations 347 -- after the declaration of M, and any needed statements (in particular 348 -- the bignum operations) before the call to SS_Release, and then do an 349 -- Insert_Action of the whole block (it is returned unanalyzed). The Loc 350 -- parameter is used to supply Sloc values for the constructed tree. 351 352 procedure Minimize_Eliminate_Overflows 353 (N : Node_Id; 354 Lo : out Uint; 355 Hi : out Uint; 356 Top_Level : Boolean); 357 -- This is the main routine for handling MINIMIZED and ELIMINATED overflow 358 -- processing. On entry N is a node whose result is a signed integer 359 -- subtype. The Do_Overflow_Check flag may or may not be set on N. If the 360 -- node is an arithmetic operation, then a range analysis is carried out, 361 -- and there are three possibilities: 362 -- 363 -- The node is left unchanged (apart from expansion of an exponentiation 364 -- operation). This happens if the routine can determine that the result 365 -- is definitely in range. The Do_Overflow_Check flag is turned off in 366 -- this case. 367 -- 368 -- The node is transformed into an arithmetic operation with a result 369 -- type of Long_Long_Integer. 370 -- 371 -- The node is transformed into a function call that calls an appropriate 372 -- function in the System.Bignums package to compute a Bignum result. 373 -- 374 -- In the first two cases, Lo and Hi are set to the bounds of the possible 375 -- range of results, computed as accurately as possible. In the third case 376 -- Lo and Hi are set to No_Uint (there are some cases where we could get an 377 -- advantage from keeping result ranges for Bignum values, but it could use 378 -- a lot of space and is very unlikely to be valuable). 379 -- 380 -- If the node is not an arithmetic operation, then it is unchanged but 381 -- Lo and Hi are still set (to the bounds of the result subtype if nothing 382 -- better can be determined). 383 -- 384 -- Note: this function is recursive, if called with an arithmetic operator, 385 -- recursive calls are made to process the operands using this procedure. 386 -- So we end up doing things top down. Nothing happens to an arithmetic 387 -- expression until this procedure is called on the top level node and 388 -- then the recursive calls process all the children. We have to do it 389 -- this way. If we try to do it bottom up in natural expansion order, then 390 -- there are two problems. First, where do we stash the bounds, and more 391 -- importantly, semantic processing will be messed up. Consider A+B+C where 392 -- A,B,C are all of type integer, if we processed A+B before doing semantic 393 -- analysis of the addition of this result to C, that addition could end up 394 -- with a Long_Long_Integer left operand and an Integer right operand, and 395 -- we would get a semantic error. 396 -- 397 -- The routine is called in three situations if we are operating in either 398 -- MINIMIZED or ELIMINATED modes. 399 -- 400 -- Overflow processing applied to the top node of an expression tree when 401 -- that node is an arithmetic operator. In this case the result is 402 -- converted to the appropriate result type (there is special processing 403 -- when the parent is a conversion, see body for details). 404 -- 405 -- Overflow processing applied to the operands of a comparison operation. 406 -- In this case, the comparison is done on the result Long_Long_Integer 407 -- or Bignum values, without raising any exceptions. 408 -- 409 -- Overflow processing applied to the left operand of a membership test. 410 -- In this case no exception is raised if a Long_Long_Integer or Bignum 411 -- result is outside the range of the type of that left operand (it is 412 -- just that the result of IN is false in that case). 413 -- 414 -- Note that if Bignum values appear, the caller must take care of doing 415 -- the appropriate mark/release operations on the secondary stack. 416 -- 417 -- Top_Level is used to avoid inefficient unnecessary transitions into the 418 -- Bignum domain. If Top_Level is True, it means that the caller will have 419 -- to convert any Bignum value back to Long_Long_Integer, possibly checking 420 -- that the value is in range. This is the normal case for a top level 421 -- operator in a subexpression. There is no point in going into Bignum mode 422 -- to avoid an overflow just so we can check for overflow the next moment. 423 -- For calls from comparisons and membership tests, and for all recursive 424 -- calls, we do want to transition into the Bignum domain if necessary. 425 -- Note that this setting is only relevant in ELIMINATED mode. 426 427 ------------------------------------------------------- 428 -- Control and Optimization of Range/Overflow Checks -- 429 ------------------------------------------------------- 430 431 -- Range checks are controlled by the Do_Range_Check flag. The front end 432 -- is responsible for setting this flag in relevant nodes. Originally 433 -- the back end generated all corresponding range checks. But later on 434 -- we decided to generate many range checks in the front end. We are now 435 -- in the transitional phase where some of these checks are still done 436 -- by the back end, but many are done by the front end. It is possible 437 -- that in the future we might move all the checks to the front end. The 438 -- main remaining back end checks are for subscript checking. 439 440 -- Overflow checks are similarly controlled by the Do_Overflow_Check flag. 441 -- The difference here is that if back end overflow checks are inactive 442 -- (Backend_Overflow_Checks_On_Target set False), then the actual overflow 443 -- checks are generated by the front end, but if back end overflow checks 444 -- are active (Backend_Overflow_Checks_On_Target set True), then the back 445 -- end does generate the checks. 446 447 -- The following two routines are used to set these flags, they allow 448 -- for the possibility of eliminating checks. Checks can be eliminated 449 -- if an identical check has already been performed. 450 451 procedure Enable_Overflow_Check (N : Node_Id); 452 -- First this routine determines if an overflow check is needed by doing 453 -- an appropriate range check. If a check is not needed, then the call 454 -- has no effect. If a check is needed then this routine sets the flag 455 -- Do_Overflow_Check in node N to True, unless it can be determined that 456 -- the check is not needed. The only condition under which this is the 457 -- case is if there was an identical check earlier on. 458 459 procedure Enable_Range_Check (N : Node_Id); 460 -- Set Do_Range_Check flag in node N True, unless it can be determined 461 -- that the check is not needed. The only condition under which this is 462 -- the case is if there was an identical check earlier on. This routine 463 -- is not responsible for doing range analysis to determine whether or 464 -- not such a check is needed -- the caller is expected to do this. The 465 -- one other case in which the request to set the flag is ignored is 466 -- when Kill_Range_Check is set in an N_Unchecked_Conversion node. 467 468 -- The following routines are used to keep track of processing sequences 469 -- of statements (e.g. the THEN statements of an IF statement). A check 470 -- that appears within such a sequence can eliminate an identical check 471 -- within this sequence of statements. However, after the end of the 472 -- sequence of statements, such a check is no longer of interest, since 473 -- it may not have been executed. 474 475 procedure Conditional_Statements_Begin; 476 -- This call marks the start of processing of a sequence of statements. 477 -- Every call to this procedure must be followed by a matching call to 478 -- Conditional_Statements_End. 479 480 procedure Conditional_Statements_End; 481 -- This call removes from consideration all saved checks since the 482 -- corresponding call to Conditional_Statements_Begin. These two 483 -- procedures operate in a stack like manner. 484 485 -- The mechanism for optimizing checks works by remembering checks 486 -- that have already been made, but certain conditions, for example 487 -- an assignment to a variable involved in a check, may mean that the 488 -- remembered check is no longer valid, in the sense that if the same 489 -- expression appears again, another check is required because the 490 -- value may have changed. 491 492 -- The following routines are used to note conditions which may render 493 -- some or all of the stored and remembered checks to be invalidated. 494 495 procedure Kill_Checks (V : Entity_Id); 496 -- This procedure records an assignment or other condition that causes 497 -- the value of the variable to be changed, invalidating any stored 498 -- checks that reference the value. Note that all such checks must 499 -- be discarded, even if they are not in the current statement range. 500 501 procedure Kill_All_Checks; 502 -- This procedure kills all remembered checks 503 504 ----------------------------- 505 -- Length and Range Checks -- 506 ----------------------------- 507 508 -- In the following procedures, there are three arguments which have 509 -- a common meaning as follows: 510 511 -- Expr The expression to be checked. If a check is required, 512 -- the appropriate flag will be placed on this node. Whether 513 -- this node is further examined depends on the setting of 514 -- the parameter Source_Typ, as described below. 515 516 -- ??? Apply_Length_Check and Apply_Range_Check do not have an Expr 517 -- formal 518 519 -- ??? Apply_Length_Check and Apply_Range_Check have a Ck_Node formal 520 -- which is undocumented, is it the same as Expr? 521 522 -- Target_Typ The target type on which the check is to be based. For 523 -- example, if we have a scalar range check, then the check 524 -- is that we are in range of this type. 525 526 -- Source_Typ Normally Empty, but can be set to a type, in which case 527 -- this type is used for the check, see below. 528 529 -- The checks operate in one of two modes: 530 531 -- If Source_Typ is Empty, then the node Expr is examined, at the very 532 -- least to get the source subtype. In addition for some of the checks, 533 -- the actual form of the node may be examined. For example, a node of 534 -- type Integer whose actual form is an Integer conversion from a type 535 -- with range 0 .. 3 can be determined to have a value in range 0 .. 3. 536 537 -- If Source_Typ is given, then nothing can be assumed about the Expr, 538 -- and indeed its contents are not examined. In this case the check is 539 -- based on the assumption that Expr can be an arbitrary value of the 540 -- given Source_Typ. 541 542 -- Currently, the only case in which a Source_Typ is explicitly supplied 543 -- is for the case of Out and In_Out parameters, where, for the conversion 544 -- on return (the Out direction), the types must be reversed. This is 545 -- handled by the caller. 546 547 procedure Apply_Length_Check 548 (Ck_Node : Node_Id; 549 Target_Typ : Entity_Id; 550 Source_Typ : Entity_Id := Empty); 551 -- This procedure builds a sequence of declarations to do a length check 552 -- that checks if the lengths of the two arrays Target_Typ and source type 553 -- are the same. The resulting actions are inserted at Node using a call 554 -- to Insert_Actions. 555 -- 556 -- For access types, the Directly_Designated_Type is retrieved and 557 -- processing continues as enumerated above, with a guard against null 558 -- values. 559 -- 560 -- Note: calls to Apply_Length_Check currently never supply an explicit 561 -- Source_Typ parameter, but Apply_Length_Check takes this parameter and 562 -- processes it as described above for consistency with the other routines 563 -- in this section. 564 565 procedure Apply_Range_Check 566 (Ck_Node : Node_Id; 567 Target_Typ : Entity_Id; 568 Source_Typ : Entity_Id := Empty); 569 -- For a Node of kind N_Range, constructs a range check action that tests 570 -- first that the range is not null and then that the range is contained in 571 -- the Target_Typ range. 572 -- 573 -- For scalar types, constructs a range check action that first tests that 574 -- the expression is contained in the Target_Typ range. The difference 575 -- between this and Apply_Scalar_Range_Check is that the latter generates 576 -- the actual checking code against the Etype of the expression. 577 -- 578 -- For constrained array types, construct series of range check actions 579 -- to check that each Expr range is properly contained in the range of 580 -- Target_Typ. 581 -- 582 -- For a type conversion to an unconstrained array type, constructs a range 583 -- check action to check that the bounds of the source type are within the 584 -- constraints imposed by the Target_Typ. 585 -- 586 -- For access types, the Directly_Designated_Type is retrieved and 587 -- processing continues as enumerated above, with a guard against null 588 -- values. 589 -- 590 -- The source type is used by type conversions to unconstrained array 591 -- types to retrieve the corresponding bounds. 592 593 procedure Apply_Static_Length_Check 594 (Expr : Node_Id; 595 Target_Typ : Entity_Id; 596 Source_Typ : Entity_Id := Empty); 597 -- Tries to determine statically whether the two array types source type 598 -- and Target_Typ have the same length. If it can be determined at compile 599 -- time that they do not, then an N_Raise_Constraint_Error node replaces 600 -- Expr, and a warning message is issued. 601 602 procedure Apply_Scalar_Range_Check 603 (Expr : Node_Id; 604 Target_Typ : Entity_Id; 605 Source_Typ : Entity_Id := Empty; 606 Fixed_Int : Boolean := False); 607 -- For scalar types, determines whether an expression node should be 608 -- flagged as needing a runtime range check. If the node requires such a 609 -- check, the Do_Range_Check flag is turned on. The Fixed_Int flag if set 610 -- causes any fixed-point values to be treated as though they were discrete 611 -- values (i.e. the underlying integer value is used). 612 613 type Check_Result is private; 614 -- Type used to return result of Get_Range_Checks call, for later use in 615 -- call to Insert_Range_Checks procedure. 616 617 function Get_Range_Checks 618 (Ck_Node : Node_Id; 619 Target_Typ : Entity_Id; 620 Source_Typ : Entity_Id := Empty; 621 Warn_Node : Node_Id := Empty) return Check_Result; 622 -- Like Apply_Range_Check, except it does not modify anything. Instead 623 -- it returns an encapsulated result of the check operations for later 624 -- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its 625 -- Sloc is used, in the static case, for the generated warning or error. 626 -- Additionally, it is used rather than Expr (or Low/High_Bound of Expr) 627 -- in constructing the check. 628 629 procedure Append_Range_Checks 630 (Checks : Check_Result; 631 Stmts : List_Id; 632 Suppress_Typ : Entity_Id; 633 Static_Sloc : Source_Ptr; 634 Flag_Node : Node_Id); 635 -- Called to append range checks as returned by a call to Get_Range_Checks. 636 -- Stmts is a list to which either the dynamic check is appended or the 637 -- raise Constraint_Error statement is appended (for static checks). 638 -- Static_Sloc is the Sloc at which the raise CE node points, Flag_Node is 639 -- used as the node at which to set the Has_Dynamic_Check flag. Checks_On 640 -- is a boolean value that says if range and index checking is on or not. 641 642 procedure Insert_Range_Checks 643 (Checks : Check_Result; 644 Node : Node_Id; 645 Suppress_Typ : Entity_Id; 646 Static_Sloc : Source_Ptr := No_Location; 647 Flag_Node : Node_Id := Empty; 648 Do_Before : Boolean := False); 649 -- Called to insert range checks as returned by a call to Get_Range_Checks. 650 -- Node is the node after which either the dynamic check is inserted or 651 -- the raise Constraint_Error statement is inserted (for static checks). 652 -- Suppress_Typ is the type to check to determine if checks are suppressed. 653 -- Static_Sloc, if passed, is the Sloc at which the raise CE node points, 654 -- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally 655 -- set at Node. If Flag_Node is present, then this is used instead as the 656 -- node at which to set the Has_Dynamic_Check flag. Normally the check is 657 -- inserted after, if Do_Before is True, the check is inserted before 658 -- Node. 659 660 ----------------------- 661 -- Expander Routines -- 662 ----------------------- 663 664 -- Some of the earlier processing for checks results in temporarily setting 665 -- the Do_Range_Check flag rather than actually generating checks. Now we 666 -- are moving the generation of such checks into the front end for reasons 667 -- of efficiency and simplicity (there were difficulties in handling this 668 -- in the back end when side effects were present in the expressions being 669 -- checked). 670 671 -- Probably we could eliminate the Do_Range_Check flag entirely and 672 -- generate the checks earlier, but this is a delicate area and it 673 -- seemed safer to implement the following routines, which are called 674 -- late on in the expansion process. They check the Do_Range_Check flag 675 -- and if it is set, generate the actual checks and reset the flag. 676 677 procedure Generate_Range_Check 678 (N : Node_Id; 679 Target_Type : Entity_Id; 680 Reason : RT_Exception_Code); 681 -- This procedure is called to actually generate and insert a range check. 682 -- A check is generated to ensure that the value of N lies within the range 683 -- of the target type. Note that the base type of N may be different from 684 -- the base type of the target type. This happens in the conversion case. 685 -- The Reason parameter is the exception code to be used for the exception 686 -- if raised. 687 -- 688 -- Note: if the expander is not active, or if we are in GNATprove mode, 689 -- then we do not generate explicit range code. Instead we just turn the 690 -- Do_Range_Check flag on, since in these cases that's what we want to see 691 -- in the tree (GNATprove in particular depends on this flag being set). If 692 -- we generate the actual range check, then we make sure the flag is off, 693 -- since the code we generate takes complete care of the check. 694 -- 695 -- Historical note: We used to just pass on the Do_Range_Check flag to the 696 -- back end to generate the check, but now in code-generation mode we never 697 -- have this flag set, since the front end takes care of the check. The 698 -- normal processing flow now is that the analyzer typically turns on the 699 -- Do_Range_Check flag, and if it is set, this routine is called, which 700 -- turns the flag off in code-generation mode. 701 702 procedure Generate_Index_Checks (N : Node_Id); 703 -- This procedure is called to generate index checks on the subscripts for 704 -- the indexed component node N. Each subscript expression is examined, and 705 -- if the Do_Range_Check flag is set, an appropriate index check is 706 -- generated and the flag is reset. 707 708 -- Similarly, we set the flag Do_Discriminant_Check in the semantic 709 -- analysis to indicate that a discriminant check is required for selected 710 -- component of a discriminated type. The following routine is called from 711 -- the expander to actually generate the call. 712 713 procedure Generate_Discriminant_Check (N : Node_Id); 714 -- N is a selected component for which a discriminant check is required to 715 -- make sure that the discriminants have appropriate values for the 716 -- selection. This is done by calling the appropriate discriminant checking 717 -- routine for the selector. 718 719 ----------------------- 720 -- Validity Checking -- 721 ----------------------- 722 723 -- In (RM 13.9.1(9-11)) we have the following rules on invalid values 724 725 -- If the representation of a scalar object does not represent value of 726 -- the object's subtype (perhaps because the object was not initialized), 727 -- the object is said to have an invalid representation. It is a bounded 728 -- error to evaluate the value of such an object. If the error is 729 -- detected, either Constraint_Error or Program_Error is raised. 730 -- Otherwise, execution continues using the invalid representation. The 731 -- rules of the language outside this subclause assume that all objects 732 -- have valid representations. The semantics of operations on invalid 733 -- representations are as follows: 734 -- 735 -- 10 If the representation of the object represents a value of the 736 -- object's type, the value of the type is used. 737 -- 738 -- 11 If the representation of the object does not represent a value 739 -- of the object's type, the semantics of operations on such 740 -- representations is implementation-defined, but does not by 741 -- itself lead to erroneous or unpredictable execution, or to 742 -- other objects becoming abnormal. 743 744 -- We quote the rules in full here since they are quite delicate. Most 745 -- of the time, we can just compute away with wrong values, and get a 746 -- possibly wrong result, which is well within the range of allowed 747 -- implementation defined behavior. The two tricky cases are subscripted 748 -- array assignments, where we don't want to do wild stores, and case 749 -- statements where we don't want to do wild jumps. 750 751 -- In GNAT, we control validity checking with a switch -gnatV that can take 752 -- three parameters, n/d/f for None/Default/Full. These modes have the 753 -- following meanings: 754 755 -- None (no validity checking) 756 757 -- In this mode, there is no specific checking for invalid values 758 -- and the code generator assumes that all stored values are always 759 -- within the bounds of the object subtype. The consequences are as 760 -- follows: 761 762 -- For case statements, an out of range invalid value will cause 763 -- Constraint_Error to be raised, or an arbitrary one of the case 764 -- alternatives will be executed. Wild jumps cannot result even 765 -- in this mode, since we always do a range check 766 767 -- For subscripted array assignments, wild stores will result in 768 -- the expected manner when addresses are calculated using values 769 -- of subscripts that are out of range. 770 771 -- It could perhaps be argued that this mode is still conformant with 772 -- the letter of the RM, since implementation defined is a rather 773 -- broad category, but certainly it is not in the spirit of the 774 -- RM requirement, since wild stores certainly seem to be a case of 775 -- erroneous behavior. 776 777 -- Default (default standard RM-compatible validity checking) 778 779 -- In this mode, which is the default, minimal validity checking is 780 -- performed to ensure no erroneous behavior as follows: 781 782 -- For case statements, an out of range invalid value will cause 783 -- Constraint_Error to be raised. 784 785 -- For subscripted array assignments, invalid out of range 786 -- subscript values will cause Constraint_Error to be raised. 787 788 -- Full (Full validity checking) 789 790 -- In this mode, the protections guaranteed by the standard mode are 791 -- in place, and the following additional checks are made: 792 793 -- For every assignment, the right side is checked for validity 794 795 -- For every call, IN and IN OUT parameters are checked for validity 796 797 -- For every subscripted array reference, both for stores and loads, 798 -- all subscripts are checked for validity. 799 800 -- These checks are not required by the RM, but will in practice 801 -- improve the detection of uninitialized variables, particularly 802 -- if used in conjunction with pragma Normalize_Scalars. 803 804 -- In the above description, we talk about performing validity checks, 805 -- but we don't actually generate a check in a case where the compiler 806 -- can be sure that the value is valid. Note that this assurance must 807 -- be achieved without assuming that any uninitialized value lies within 808 -- the range of its type. The following are cases in which values are 809 -- known to be valid. The flag Is_Known_Valid is used to keep track of 810 -- some of these cases. 811 812 -- If all possible stored values are valid, then any uninitialized 813 -- value must be valid. 814 815 -- Literals, including enumeration literals, are clearly always valid 816 817 -- Constants are always assumed valid, with a validity check being 818 -- performed on the initializing value where necessary to ensure that 819 -- this is the case. 820 821 -- For variables, the status is set to known valid if there is an 822 -- initializing expression. Again a check is made on the initializing 823 -- value if necessary to ensure that this assumption is valid. The 824 -- status can change as a result of local assignments to a variable. 825 -- If a known valid value is unconditionally assigned, then we mark 826 -- the left side as known valid. If a value is assigned that is not 827 -- known to be valid, then we mark the left side as invalid. This 828 -- kind of processing does NOT apply to non-local variables since we 829 -- are not following the flow graph (more properly the flow of actual 830 -- processing only corresponds to the flow graph for local assignments). 831 -- For non-local variables, we preserve the current setting, i.e. a 832 -- validity check is performed when assigning to a knonwn valid global. 833 834 -- Note: no validity checking is required if range checks are suppressed 835 -- regardless of the setting of the validity checking mode. 836 837 -- The following procedures are used in handling validity checking 838 839 procedure Apply_Subscript_Validity_Checks (Expr : Node_Id); 840 -- Expr is the node for an indexed component. If validity checking and 841 -- range checking are enabled, all subscripts for this indexed component 842 -- are checked for validity. 843 844 procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id); 845 -- Expr is a lvalue, i.e. an expression representing the target of an 846 -- assignment. This procedure checks for this expression involving an 847 -- assignment to an array value. We have to be sure that all the subscripts 848 -- in such a case are valid, since according to the rules in (RM 849 -- 13.9.1(9-11)) such assignments are not permitted to result in erroneous 850 -- behavior in the case of invalid subscript values. 851 852 procedure Ensure_Valid 853 (Expr : Node_Id; 854 Holes_OK : Boolean := False; 855 Related_Id : Entity_Id := Empty; 856 Is_Low_Bound : Boolean := False; 857 Is_High_Bound : Boolean := False); 858 -- Ensure that Expr represents a valid value of its type. If this type 859 -- is not a scalar type, then the call has no effect, since validity 860 -- is only an issue for scalar types. The effect of this call is to 861 -- check if the value is known valid, if so, nothing needs to be done. 862 -- If this is not known, then either Expr is set to be range checked, 863 -- or specific checking code is inserted so that an exception is raised 864 -- if the value is not valid. 865 -- 866 -- The optional argument Holes_OK indicates whether it is necessary to 867 -- worry about enumeration types with non-standard representations leading 868 -- to "holes" in the range of possible representations. If Holes_OK is 869 -- True, then such values are assumed valid (this is used when the caller 870 -- will make a separate check for this case anyway). If Holes_OK is False, 871 -- then this case is checked, and code is inserted to ensure that Expr is 872 -- valid, raising Constraint_Error if the value is not valid. 873 -- 874 -- Related_Id denotes the entity of the context where Expr appears. Flags 875 -- Is_Low_Bound and Is_High_Bound specify whether the expression to check 876 -- is the low or the high bound of a range. These three optional arguments 877 -- signal Remove_Side_Effects to create an external symbol of the form 878 -- Chars (Related_Id)_FIRST/_LAST. For suggested use of these parameters 879 -- see the warning in the body of Sem_Ch3.Process_Range_Expr_In_Decl. 880 881 function Expr_Known_Valid (Expr : Node_Id) return Boolean; 882 -- This function tests it the value of Expr is known to be valid in the 883 -- sense of RM 13.9.1(9-11). In the case of GNAT, it is only discrete types 884 -- which are a concern, since for non-discrete types we simply continue 885 -- computation with invalid values, which does not lead to erroneous 886 -- behavior. Thus Expr_Known_Valid always returns True if the type of Expr 887 -- is non-discrete. For discrete types the value returned is True only if 888 -- it can be determined that the value is Valid. Otherwise False is 889 -- returned. 890 891 procedure Insert_Valid_Check 892 (Expr : Node_Id; 893 Related_Id : Entity_Id := Empty; 894 Is_Low_Bound : Boolean := False; 895 Is_High_Bound : Boolean := False); 896 -- Inserts code that will check for the value of Expr being valid, in the 897 -- sense of the 'Valid attribute returning True. Constraint_Error will be 898 -- raised if the value is not valid. 899 -- 900 -- Related_Id denotes the entity of the context where Expr appears. Flags 901 -- Is_Low_Bound and Is_High_Bound specify whether the expression to check 902 -- is the low or the high bound of a range. These three optional arguments 903 -- signal Remove_Side_Effects to create an external symbol of the form 904 -- Chars (Related_Id)_FIRST/_LAST. For suggested use of these parameters 905 -- see the warning in the body of Sem_Ch3.Process_Range_Expr_In_Decl. 906 907 procedure Null_Exclusion_Static_Checks (N : Node_Id); 908 -- Ada 2005 (AI-231): Check bad usages of the null-exclusion issue 909 910 procedure Remove_Checks (Expr : Node_Id); 911 -- Remove all checks from Expr except those that are only executed 912 -- conditionally (on the right side of And Then/Or Else. This call 913 -- removes only embedded checks (Do_Range_Check, Do_Overflow_Check). 914 915 procedure Validity_Check_Range 916 (N : Node_Id; 917 Related_Id : Entity_Id := Empty); 918 -- If N is an N_Range node, then Ensure_Valid is called on its bounds, if 919 -- validity checking of operands is enabled. Related_Id denotes the entity 920 -- of the context where N appears. 921 922 ----------------------------- 923 -- Handling of Check Names -- 924 ----------------------------- 925 926 -- The following table contains Name_Id's for recognized checks. The first 927 -- entries (corresponding to the values of the subtype Predefined_Check_Id) 928 -- contain the Name_Id values for the checks that are predefined, including 929 -- All_Checks (see Types). Remaining entries are those that are introduced 930 -- by pragma Check_Names. 931 932 package Check_Names is new Table.Table ( 933 Table_Component_Type => Name_Id, 934 Table_Index_Type => Check_Id, 935 Table_Low_Bound => 1, 936 Table_Initial => 30, 937 Table_Increment => 200, 938 Table_Name => "Name_Check_Names"); 939 940 function Get_Check_Id (N : Name_Id) return Check_Id; 941 -- Function to search above table for matching name. If found returns the 942 -- corresponding Check_Id value in the range 1 .. Check_Name.Last. If not 943 -- found returns No_Check_Id. 944 945private 946 947 type Check_Result is array (Positive range 1 .. 2) of Node_Id; 948 -- There are two cases for the result returned by Range_Check: 949 -- 950 -- For the static case the result is one or two nodes that should cause 951 -- a Constraint_Error. Typically these will include Expr itself or the 952 -- direct descendents of Expr, such as Low/High_Bound (Expr)). It is the 953 -- responsibility of the caller to rewrite and substitute the nodes with 954 -- N_Raise_Constraint_Error nodes. 955 -- 956 -- For the non-static case a single N_Raise_Constraint_Error node with a 957 -- non-empty Condition field is returned. 958 -- 959 -- Unused entries in Check_Result, if any, are simply set to Empty For 960 -- external clients, the required processing on this result is achieved 961 -- using the Insert_Range_Checks routine. 962 963 pragma Inline (Apply_Length_Check); 964 pragma Inline (Apply_Range_Check); 965 pragma Inline (Apply_Static_Length_Check); 966end Checks; 967