1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- S E M _ E V A L -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2018, 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-- This package contains various subprograms involved in compile time 27-- evaluation of expressions and checks for staticness of expressions and 28-- types. It also contains the circuitry for checking for violations of pure 29-- and preelaborated conditions (this naturally goes here, since these rules 30-- involve consideration of staticness). 31 32-- Note: the static evaluation for attributes is found in Sem_Attr even though 33-- logically it belongs here. We have done this so that it is easier to add 34-- new attributes to GNAT. 35 36with Types; use Types; 37with Uintp; use Uintp; 38with Urealp; use Urealp; 39 40package Sem_Eval is 41 42 ------------------------------------ 43 -- Handling of Static Expressions -- 44 ------------------------------------ 45 46 -- This package contains a set of routines that process individual 47 -- subexpression nodes with the objective of folding (precomputing) the 48 -- value of static expressions that are known at compile time and properly 49 -- computing the setting of two flags that appear in every subexpression 50 -- node: 51 52 -- Is_Static_Expression 53 54 -- This flag is set on any expression that is static according to the 55 -- rules in (RM 4.9(3-32)). This flag should be tested during testing 56 -- of legality of parts of a larger static expression. For all other 57 -- contexts that require static expressions, use the separate predicate 58 -- Is_OK_Static_Expression, since an expression that meets the RM 4.9 59 -- requirements, but raises a constraint error when evaluated in a non- 60 -- static context does not meet the legality requirements. 61 62 -- Raises_Constraint_Error 63 64 -- This flag indicates that it is known at compile time that the 65 -- evaluation of an expression raises constraint error. If the 66 -- expression is static, and this flag is off, then it is also known at 67 -- compile time that the expression does not raise constraint error 68 -- (i.e. the flag is accurate for static expressions, and conservative 69 -- for non-static expressions. 70 71 -- If a static expression does not raise constraint error, then it will 72 -- have the flag Raises_Constraint_Error flag False, and the expression 73 -- must be computed at compile time, which means that it has the form of 74 -- either a literal, or a constant that is itself (recursively) either a 75 -- literal or a constant. 76 77 -- The above rules must be followed exactly in order for legality checks to 78 -- be accurate. For subexpressions that are not static according to the RM 79 -- definition, they are sometimes folded anyway, but of course in this case 80 -- Is_Static_Expression is not set. 81 82 -- When we are analyzing and evaluating static expressions, we propagate 83 -- both flags accurately. Usually if a subexpression raises a constraint 84 -- error, then so will its parent expression, and Raise_Constraint_Error 85 -- will be propagated to this parent. The exception is conditional cases 86 -- like (True or else 1/0 = 0) which results in an expresion that has the 87 -- Is_Static_Expression flag True, and Raises_Constraint_Error False. Even 88 -- though 1/0 would raise an exception, the right operand is never actually 89 -- executed, so the expression as a whole does not raise CE. 90 91 -- For constructs in the language where static expressions are part of the 92 -- required semantics, we need an expression that meets the 4.9 rules and 93 -- does not raise CE. So nearly everywhere, callers should call function 94 -- Is_OK_Static_Expression rather than Is_Static_Expression. 95 96 -- Finally, the case of static predicates. These are applied only to entire 97 -- expressions, not to subexpressions, so we do not have the case of having 98 -- to propagate this information. We handle this case simply by resetting 99 -- the Is_Static_Expression flag if a static predicate fails. Note that we 100 -- can't use this simpler approach for the constraint error case because of 101 -- the (True or else 1/0 = 0) example discussed above. 102 103 ------------------------------- 104 -- Compile-Time Known Values -- 105 ------------------------------- 106 107 -- For most legality checking purposes the flag Is_Static_Expression 108 -- defined in Sinfo should be used. This package also provides a routine 109 -- called Is_OK_Static_Expression which in addition of checking that an 110 -- expression is static in the RM 4.9 sense, it checks that the expression 111 -- does not raise constraint error. In fact for certain legality checks not 112 -- only do we need to ascertain that the expression is static, but we must 113 -- also ensure that it does not raise constraint error. 114 115 -- Neither of Is_Static_Expression and Is_OK_Static_Expression should be 116 -- used for compile time evaluation purposes. In fact certain expression 117 -- whose value may be known at compile time are not static in the RM 4.9 118 -- sense. A typical example is: 119 120 -- C : constant Integer := Record_Type'Size; 121 122 -- The expression 'C' is not static in the technical RM sense, but for many 123 -- simple record types, the size is in fact known at compile time. When we 124 -- are trying to perform compile time constant folding (for instance for 125 -- expressions like C + 1, Is_Static_Expression or Is_OK_Static_Expression 126 -- are not the right functions to test if folding is possible. Instead, we 127 -- use Compile_Time_Known_Value. All static expressions that do not raise 128 -- constraint error (i.e. those for which Is_OK_Static_Expression is true) 129 -- are known at compile time, but as shown by the above example, there may 130 -- be cases of non-static expressions which are known at compile time. 131 132 ----------------- 133 -- Subprograms -- 134 ----------------- 135 136 procedure Check_Expression_Against_Static_Predicate 137 (Expr : Node_Id; 138 Typ : Entity_Id); 139 -- Determine whether an arbitrary expression satisfies the static predicate 140 -- of a type. The routine does nothing if Expr is not known at compile time 141 -- or Typ lacks a static predicate, otherwise it may emit a warning if the 142 -- expression is prohibited by the predicate. If the expression is a static 143 -- expression and it fails a predicate that was not explicitly stated to be 144 -- a dynamic predicate, then an additional warning is given, and the flag 145 -- Is_Static_Expression is reset on Expr. 146 147 procedure Check_Non_Static_Context (N : Node_Id); 148 -- Deals with the special check required for a static expression that 149 -- appears in a non-static context, i.e. is not part of a larger static 150 -- expression (see RM 4.9(35)), i.e. the value of the expression must be 151 -- within the base range of the base type of its expected type. A check is 152 -- also made for expressions that are inside the base range, but outside 153 -- the range of the expected subtype (this is a warning message rather than 154 -- an illegality). 155 -- 156 -- Note: most cases of non-static context checks are handled within 157 -- Sem_Eval itself, including all cases of expressions at the outer level 158 -- (i.e. those that are not a subexpression). Currently the only outside 159 -- customer for this procedure is Sem_Attr (because Eval_Attribute is 160 -- there). There is also one special case arising from ranges (see body of 161 -- Resolve_Range). 162 -- 163 -- Note: this procedure is also called by GNATprove on real literals 164 -- that are not sub-expressions of static expressions, to convert them to 165 -- machine numbers, as GNATprove cannot perform this conversion contrary 166 -- to gigi. 167 168 procedure Check_String_Literal_Length (N : Node_Id; Ttype : Entity_Id); 169 -- N is either a string literal, or a constraint error node. In the latter 170 -- case, the situation is already dealt with, and the call has no effect. 171 -- In the former case, if the target type, Ttyp is constrained, then a 172 -- check is made to see if the string literal is of appropriate length. 173 174 type Compare_Result is (LT, LE, EQ, GT, GE, NE, Unknown); 175 subtype Compare_GE is Compare_Result range EQ .. GE; 176 subtype Compare_LE is Compare_Result range LT .. EQ; 177 -- Result subtypes for Compile_Time_Compare subprograms 178 179 function Compile_Time_Compare 180 (L, R : Node_Id; 181 Assume_Valid : Boolean) return Compare_Result; 182 pragma Inline (Compile_Time_Compare); 183 -- Given two expression nodes, finds out whether it can be determined at 184 -- compile time how the runtime values will compare. An Unknown result 185 -- means that the result of a comparison cannot be determined at compile 186 -- time, otherwise the returned result indicates the known result of the 187 -- comparison, given as tightly as possible (i.e. EQ or LT is preferred 188 -- returned value to LE). If Assume_Valid is true, the result reflects 189 -- the result of assuming that entities involved in the comparison have 190 -- valid representations. If Assume_Valid is false, then the base type of 191 -- any involved entity is used so that no assumption of validity is made. 192 193 function Compile_Time_Compare 194 (L, R : Node_Id; 195 Diff : access Uint; 196 Assume_Valid : Boolean; 197 Rec : Boolean := False) return Compare_Result; 198 -- This version of Compile_Time_Compare returns extra information if the 199 -- result is GT or LT. In these cases, if the magnitude of the difference 200 -- can be determined at compile time, this (positive) magnitude is returned 201 -- in Diff.all. If the magnitude of the difference cannot be determined 202 -- then Diff.all contains No_Uint on return. Rec is a parameter that is set 203 -- True for a recursive call from within Compile_Time_Compare to avoid some 204 -- infinite recursion cases. It should never be set by a client. 205 206 function Compile_Time_Known_Bounds (T : Entity_Id) return Boolean; 207 -- If T is an array whose index bounds are all known at compile time, then 208 -- True is returned. If T is not an array type, or one or more of its index 209 -- bounds is not known at compile time, then False is returned. 210 211 function Compile_Time_Known_Value (Op : Node_Id) return Boolean; 212 -- Returns true if Op is an expression not raising Constraint_Error whose 213 -- value is known at compile time and for which a call to Expr_Value can 214 -- be used to determine this value. This is always true if Op is a static 215 -- expression, but can also be true for expressions which are technically 216 -- non-static but which are in fact known at compile time. Some examples of 217 -- such expressions are the static lower bound of a non-static range or the 218 -- value of a constant object whose initial value is itself compile time 219 -- known in the sense of this routine. Note that this routine is defended 220 -- against unanalyzed expressions. Such expressions will not cause a 221 -- blowup, they may cause pessimistic (i.e. False) results to be returned. 222 -- In general we take a pessimistic view. False does not mean the value 223 -- could not be known at compile time, but True means that absolutely 224 -- definition it is known at compile time and it is safe to call 225 -- Expr_Value[_XX] on the expression Op. 226 -- 227 -- Note that we don't define precisely the set of expressions that return 228 -- True. Callers should not make any assumptions regarding the value that 229 -- is returned for non-static expressions. Functional behavior should never 230 -- be affected by whether a given non-static expression returns True or 231 -- False when this function is called. In other words this is purely for 232 -- efficiency optimization purposes. The code generated can often be more 233 -- efficient with compile time known values, e.g. range analysis for the 234 -- purpose of removing checks is more effective if we know precise bounds. 235 236 function Compile_Time_Known_Value_Or_Aggr (Op : Node_Id) return Boolean; 237 -- Similar to Compile_Time_Known_Value, but also returns True if the value 238 -- is a compile-time-known aggregate, i.e. an aggregate all of whose 239 -- constituent expressions are either compile-time-known values (based on 240 -- calling Compile_Time_Known_Value) or compile-time-known aggregates. 241 -- Note that the aggregate could still involve run-time checks that might 242 -- fail (such as for subtype checks in component associations), but the 243 -- evaluation of the expressions themselves will not raise an exception. 244 245 function CRT_Safe_Compile_Time_Known_Value (Op : Node_Id) return Boolean; 246 -- In the case of configurable run-times, there may be an issue calling 247 -- Compile_Time_Known_Value with non-static expressions where the legality 248 -- of the program is not well-defined. Consider this example: 249 -- 250 -- X := B ** C; 251 -- 252 -- Now if C is compile time known, and has the value 4, then inline code 253 -- can be generated at compile time, instead of calling a run-time routine. 254 -- That's fine in the normal case, but when we have a configurable run-time 255 -- the run-time routine may not be available. This means that the program 256 -- will be rejected if C is not known at compile time. We don't want the 257 -- legality of a program to depend on how clever the implementation of this 258 -- function is. If the run-time in use lacks the exponentiation routine, 259 -- then what we say is that exponentiation is permitted if the exponent is 260 -- officially static and has a value in the range 0 .. 4. 261 -- 262 -- In a case like this, we use CRT_Safe_Compile_Time_Known_Value to avoid 263 -- this effect. This routine will return False for a non-static expression 264 -- if we are in configurable run-time mode, even if the expression would 265 -- normally be considered compile-time known. 266 267 function Expr_Rep_Value (N : Node_Id) return Uint; 268 -- This is identical to Expr_Value, except in the case of enumeration 269 -- literals of types for which an enumeration representation clause has 270 -- been given, in which case it returns the representation value rather 271 -- than the pos value. This is the value that is needed for generating code 272 -- sequences, while the Expr_Value value is appropriate for compile time 273 -- constraint errors or getting the logical value. Note that this function 274 -- does NOT concern itself with biased values, if the caller needs a 275 -- properly biased value, the subtraction of the bias must be handled 276 -- explicitly. 277 278 function Expr_Value (N : Node_Id) return Uint; 279 -- Returns the folded value of the expression N. This function is called in 280 -- instances where it has already been determined that the expression is 281 -- static or its value is compile time known (Compile_Time_Known_Value (N) 282 -- returns True). This version is used for integer values, and enumeration 283 -- or character literals. In the latter two cases, the value returned is 284 -- the Pos value in the relevant enumeration type. It can also be used for 285 -- fixed-point values, in which case it returns the corresponding integer 286 -- value. It cannot be used for floating-point values. 287 288 function Expr_Value_E (N : Node_Id) return Entity_Id; 289 -- Returns the folded value of the expression. This function is called in 290 -- instances where it has already been determined that the expression is 291 -- static or its value known at compile time. This version is used for 292 -- enumeration types and returns the corresponding enumeration literal. 293 294 function Expr_Value_R (N : Node_Id) return Ureal; 295 -- Returns the folded value of the expression. This function is called in 296 -- instances where it has already been determined that the expression is 297 -- static or its value known at compile time. This version is used for real 298 -- values (including both the floating-point and fixed-point cases). In the 299 -- case of a fixed-point type, the real value is returned (cf above version 300 -- returning Uint). 301 302 function Expr_Value_S (N : Node_Id) return Node_Id; 303 -- Returns the folded value of the expression. This function is called 304 -- in instances where it has already been determined that the expression 305 -- is static or its value is known at compile time. This version is used 306 -- for string types and returns the corresponding N_String_Literal node. 307 308 procedure Eval_Actual (N : Node_Id); 309 procedure Eval_Allocator (N : Node_Id); 310 procedure Eval_Arithmetic_Op (N : Node_Id); 311 procedure Eval_Call (N : Node_Id); 312 procedure Eval_Case_Expression (N : Node_Id); 313 procedure Eval_Character_Literal (N : Node_Id); 314 procedure Eval_Concatenation (N : Node_Id); 315 procedure Eval_Entity_Name (N : Node_Id); 316 procedure Eval_If_Expression (N : Node_Id); 317 procedure Eval_Indexed_Component (N : Node_Id); 318 procedure Eval_Integer_Literal (N : Node_Id); 319 procedure Eval_Logical_Op (N : Node_Id); 320 procedure Eval_Membership_Op (N : Node_Id); 321 procedure Eval_Named_Integer (N : Node_Id); 322 procedure Eval_Named_Real (N : Node_Id); 323 procedure Eval_Op_Expon (N : Node_Id); 324 procedure Eval_Op_Not (N : Node_Id); 325 procedure Eval_Real_Literal (N : Node_Id); 326 procedure Eval_Relational_Op (N : Node_Id); 327 procedure Eval_Shift (N : Node_Id); 328 procedure Eval_Short_Circuit (N : Node_Id); 329 procedure Eval_Slice (N : Node_Id); 330 procedure Eval_String_Literal (N : Node_Id); 331 procedure Eval_Qualified_Expression (N : Node_Id); 332 procedure Eval_Type_Conversion (N : Node_Id); 333 procedure Eval_Unary_Op (N : Node_Id); 334 procedure Eval_Unchecked_Conversion (N : Node_Id); 335 336 procedure Flag_Non_Static_Expr (Msg : String; Expr : Node_Id); 337 -- This procedure is called after it has been determined that Expr is not 338 -- static when it is required to be. Msg is the text of a message that 339 -- explains the error. This procedure checks if an error is already posted 340 -- on Expr, if so, it does nothing unless All_Errors_Mode is set in which 341 -- case this flag is ignored. Otherwise the given message is posted using 342 -- Error_Msg_F, and then Why_Not_Static is called on Expr to generate 343 -- additional messages. The string given as Msg should end with ! to make 344 -- it an unconditional message, to ensure that if it is posted, the entire 345 -- set of messages is all posted. 346 347 procedure Fold_Str (N : Node_Id; Val : String_Id; Static : Boolean); 348 -- Rewrite N with a new N_String_Literal node as the result of the compile 349 -- time evaluation of the node N. Val is the resulting string value from 350 -- the folding operation. The Is_Static_Expression flag is set in the 351 -- result node. The result is fully analyzed and resolved. Static indicates 352 -- whether the result should be considered static or not (True = consider 353 -- static). The point here is that normally all string literals are static, 354 -- but if this was the result of some sequence of evaluation where values 355 -- were known at compile time but not static, then the result is not 356 -- static. The call has no effect if Raises_Constraint_Error (N) is True, 357 -- since there is no point in folding if we have an error. 358 359 procedure Fold_Uint (N : Node_Id; Val : Uint; Static : Boolean); 360 -- Rewrite N with a (N_Integer_Literal, N_Identifier, N_Character_Literal) 361 -- node as the result of the compile time evaluation of the node N. Val is 362 -- the result in the integer case and is the position of the literal in the 363 -- literals list for the enumeration case. Is_Static_Expression is set True 364 -- in the result node. The result is fully analyzed/resolved. Static 365 -- indicates whether the result should be considered static or not (True = 366 -- consider static). The point here is that normally all integer literals 367 -- are static, but if this was the result of some sequence of evaluation 368 -- where values were known at compile time but not static, then the result 369 -- is not static. The call has no effect if Raises_Constraint_Error (N) is 370 -- True, since there is no point in folding if we have an error. 371 372 procedure Fold_Ureal (N : Node_Id; Val : Ureal; Static : Boolean); 373 -- Rewrite N with a new N_Real_Literal node as the result of the compile 374 -- time evaluation of the node N. Val is the resulting real value from the 375 -- folding operation. The Is_Static_Expression flag is set in the result 376 -- node. The result is fully analyzed and result. Static indicates whether 377 -- the result should be considered static or not (True = consider static). 378 -- The point here is that normally all string literals are static, but if 379 -- this was the result of some sequence of evaluation where values were 380 -- known at compile time but not static, then the result is not static. 381 -- The call has no effect if Raises_Constraint_Error (N) is True, since 382 -- there is no point in folding if we have an error. 383 384 function Is_In_Range 385 (N : Node_Id; 386 Typ : Entity_Id; 387 Assume_Valid : Boolean := False; 388 Fixed_Int : Boolean := False; 389 Int_Real : Boolean := False) return Boolean; 390 -- Returns True if it can be guaranteed at compile time that expression 391 -- N is known to be in range of the subtype Typ. A result of False does 392 -- not mean that the expression is out of range, merely that it cannot be 393 -- determined at compile time that it is in range. If Typ is a floating 394 -- point type or Int_Real is set, any integer value is treated as though it 395 -- was a real value (i.e. the underlying real value is used). In this case 396 -- we use the corresponding real value, both for the bounds of Typ, and for 397 -- the value of the expression N. If Typ is a fixed type or a discrete type 398 -- and Int_Real is False but flag Fixed_Int is True then any fixed-point 399 -- value is treated as though it was discrete value (i.e. the underlying 400 -- integer value is used). In this case we use the corresponding integer 401 -- value, both for the bounds of Typ, and for the value of the expression 402 -- N. If Typ is a discrete type and Fixed_Int as well as Int_Real are 403 -- false, integer values are used throughout. 404 -- 405 -- If Assume_Valid is set True, then N is always assumed to contain a valid 406 -- value. If Assume_Valid is set False, then N may be invalid (unless there 407 -- is some independent way of knowing that it is valid, i.e. either it is 408 -- an entity with Is_Known_Valid set, or Assume_No_Invalid_Values is True. 409 410 function Is_Null_Range (Lo : Node_Id; Hi : Node_Id) return Boolean; 411 -- Returns True if it can guarantee that Lo .. Hi is a null range. If it 412 -- cannot (because the value of Lo or Hi is not known at compile time) then 413 -- it returns False. 414 415 function Is_OK_Static_Expression (N : Node_Id) return Boolean; 416 -- An OK static expression is one that is static in the RM definition sense 417 -- and which does not raise constraint error. For most legality checking 418 -- purposes you should use Is_Static_Expression. For those legality checks 419 -- where the expression N should not raise constraint error use this 420 -- routine. This routine is *not* to be used in contexts where the test is 421 -- for compile time evaluation purposes. Use Compile_Time_Known_Value 422 -- instead (see section on "Compile-Time Known Values" above). 423 424 function Is_OK_Static_Range (N : Node_Id) return Boolean; 425 -- Determines if range is static, as defined in RM 4.9(26), and also checks 426 -- that neither bound of the range raises constraint error, thus ensuring 427 -- that both bounds of the range are compile-time evaluable (i.e. do not 428 -- raise constraint error). A result of true means that the bounds are 429 -- compile time evaluable. A result of false means they are not (either 430 -- because the range is not static, or because one or the other bound 431 -- raises CE). 432 433 function Is_OK_Static_Subtype (Typ : Entity_Id) return Boolean; 434 -- Determines whether a subtype fits the definition of an Ada static 435 -- subtype as given in (RM 4.9(26)) with the additional check that neither 436 -- bound raises constraint error (meaning that Expr_Value[_R|S] can be used 437 -- on these bounds). 438 -- 439 -- This differs from Is_Static_Subtype in that it includes the constraint 440 -- error checks, which are missing from Is_Static_Subtype. 441 442 function Is_Out_Of_Range 443 (N : Node_Id; 444 Typ : Entity_Id; 445 Assume_Valid : Boolean := False; 446 Fixed_Int : Boolean := False; 447 Int_Real : Boolean := False) return Boolean; 448 -- Returns True if it can be guaranteed at compile time that expression is 449 -- known to be out of range of the subtype Typ. True is returned if Typ is 450 -- a scalar type, and the value of N can be determined to be outside the 451 -- range of Typ. A result of False does not mean that the expression is in 452 -- range, but rather merely that it cannot be determined at compile time 453 -- that it is out of range. The parameters Assume_Valid, Fixed_Int, and 454 -- Int_Real are as described for Is_In_Range above. 455 456 function Is_Static_Subtype (Typ : Entity_Id) return Boolean; 457 -- Determines whether a subtype fits the definition of an Ada static 458 -- subtype as given in (RM 4.9(26)). 459 -- 460 -- This differs from Is_OK_Static_Subtype (which is what must be used by 461 -- clients) in that it does not care whether the bounds raise a constraint 462 -- error exception or not. Used for checking whether expressions are static 463 -- in the 4.9 sense (without worrying about exceptions). 464 465 function Is_Statically_Unevaluated (Expr : Node_Id) return Boolean; 466 -- This function returns True if the given expression Expr is statically 467 -- unevaluated, as defined in (RM 4.9 (32.1-32.6)). 468 469 function In_Subrange_Of 470 (T1 : Entity_Id; 471 T2 : Entity_Id; 472 Fixed_Int : Boolean := False) return Boolean; 473 -- Returns True if it can be guaranteed at compile time that the range of 474 -- values for scalar type T1 are always in the range of scalar type T2. A 475 -- result of False does not mean that T1 is not in T2's subrange, only that 476 -- it cannot be determined at compile time. Flag Fixed_Int is used as in 477 -- routine Is_In_Range above. 478 479 function Not_Null_Range (Lo : Node_Id; Hi : Node_Id) return Boolean; 480 -- Returns True if it can guarantee that Lo .. Hi is not a null range. If 481 -- it cannot (because the value of Lo or Hi is not known at compile time) 482 -- then it returns False. 483 484 function Predicates_Match (T1, T2 : Entity_Id) return Boolean; 485 -- In Ada 2012, subtypes statically match if their static predicates 486 -- match as well. This function performs the required check that 487 -- predicates match. Separated out from Subtypes_Statically_Match so 488 -- that it can be used in specializing error messages. 489 490 function Subtypes_Statically_Compatible 491 (T1 : Entity_Id; 492 T2 : Entity_Id; 493 Formal_Derived_Matching : Boolean := False) return Boolean; 494 -- Returns true if the subtypes are unconstrained or the constraint on 495 -- on T1 is statically compatible with T2 (as defined by 4.9.1(4)). 496 -- Otherwise returns false. Formal_Derived_Matching indicates whether 497 -- the type T1 is a generic actual being checked against ancestor T2 498 -- in a formal derived type association. 499 500 function Subtypes_Statically_Match 501 (T1 : Entity_Id; 502 T2 : Entity_Id; 503 Formal_Derived_Matching : Boolean := False) return Boolean; 504 -- Determine whether two types T1, T2, which have the same base type, 505 -- are statically matching subtypes (RM 4.9.1(1-2)). Also includes the 506 -- extra GNAT rule that object sizes must match (this can be false for 507 -- types that match in the RM sense because of use of 'Object_Size), 508 -- except when testing a generic actual T1 against an ancestor T2 in a 509 -- formal derived type association (indicated by Formal_Derived_Matching). 510 511 procedure Test_Comparison 512 (Op : Node_Id; 513 Assume_Valid : Boolean; 514 True_Result : out Boolean; 515 False_Result : out Boolean); 516 -- Determine the outcome of evaluating comparison operator Op using routine 517 -- Compile_Time_Compare. Assume_Valid should be set when the operands are 518 -- to be assumed valid. Flags True_Result and False_Result are set when the 519 -- comparison evaluates to True or False respectively. 520 521 procedure Why_Not_Static (Expr : Node_Id); 522 -- This procedure may be called after generating an error message that 523 -- complains that something is non-static. If it finds good reasons, it 524 -- generates one or more error messages pointing the appropriate offending 525 -- component of the expression. If no good reasons can be figured out, then 526 -- no messages are generated. The expectation here is that the caller has 527 -- already issued a message complaining that the expression is non-static. 528 -- Note that this message should be placed using Error_Msg_F or 529 -- Error_Msg_FE, so that it will sort before any messages placed by this 530 -- call. Note that it is fine to call Why_Not_Static with something that 531 -- is not an expression, and usually this has no effect, but in some cases 532 -- (N_Parameter_Association or N_Range), it makes sense for the internal 533 -- recursive calls. 534 -- 535 -- Note that these messages are not continuation messages, instead they are 536 -- separate unconditional messages, marked with '!'. The reason for this is 537 -- that they can be posted at a different location from the main message as 538 -- documented above ("appropriate offending component"), and continuation 539 -- messages must always point to the same location as the parent message. 540 541 procedure Initialize; 542 -- Initializes the internal data structures. Must be called before each 543 -- separate main program unit (e.g. in a GNSA/ASIS context). 544 545private 546 -- The Eval routines are all marked inline, since they are called once 547 548 pragma Inline (Eval_Actual); 549 pragma Inline (Eval_Allocator); 550 pragma Inline (Eval_Character_Literal); 551 pragma Inline (Eval_If_Expression); 552 pragma Inline (Eval_Indexed_Component); 553 pragma Inline (Eval_Named_Integer); 554 pragma Inline (Eval_Named_Real); 555 pragma Inline (Eval_Real_Literal); 556 pragma Inline (Eval_Shift); 557 pragma Inline (Eval_Slice); 558 pragma Inline (Eval_String_Literal); 559 pragma Inline (Eval_Unchecked_Conversion); 560 561 pragma Inline (Is_OK_Static_Expression); 562 563end Sem_Eval; 564