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) 1992-2020, 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 -- True for static expressions, as defined in RM-4.9. 55 56 -- Raises_Constraint_Error 57 58 -- This flag indicates that it is known at compile time that the 59 -- evaluation of an expression raises constraint error. If the 60 -- expression is static, and this flag is off, then it is also known at 61 -- compile time that the expression does not raise constraint error 62 -- (i.e. the flag is accurate for static expressions, and conservative 63 -- for non-static expressions. 64 65 -- See also Is_OK_Static_Expression, which is True for static 66 -- expressions that do not raise Constraint_Error. This is used in most 67 -- legality checks, because static expressions that raise Constraint_Error 68 -- are usually illegal. 69 70 -- See also Compile_Time_Known_Value, which is True for an expression whose 71 -- value is known at compile time. In this case, the expression is folded 72 -- to a literal or to a constant that is itself (recursively) either a 73 -- literal or a constant 74 75 -- Is_[OK_]Static_Expression are used for legality checks, whereas 76 -- Compile_Time_Known_Value is used for optimization purposes. 77 78 -- When we are analyzing and evaluating static expressions, we propagate 79 -- both flags. Usually if a subexpression raises a Constraint_Error, then 80 -- so will its parent expression, and Raise_Constraint_Error will be 81 -- propagated to this parent. The exception is conditional cases like 82 -- (True or else 1/0 = 0), which results in an expression that has the 83 -- Is_Static_Expression flag True, and Raises_Constraint_Error False. Even 84 -- though 1/0 would raise an exception, the right operand is never actually 85 -- executed, so the expression as a whole does not raise CE. 86 87 -- Finally, the case of static predicates. These are applied only to entire 88 -- expressions, not to subexpressions, so we do not have the case of having 89 -- to propagate this information. We handle this case simply by resetting 90 -- the Is_Static_Expression flag if a static predicate fails. Note that we 91 -- can't use this simpler approach for the constraint error case because of 92 -- the (True or else 1/0 = 0) example discussed above. 93 94 ------------------------------- 95 -- Compile-Time Known Values -- 96 ------------------------------- 97 98 -- For most legality checking purposes the flag Is_Static_Expression 99 -- defined in Sinfo should be used. This package also provides a routine 100 -- called Is_OK_Static_Expression which in addition of checking that an 101 -- expression is static in the RM 4.9 sense, it checks that the expression 102 -- does not raise constraint error. In fact for certain legality checks not 103 -- only do we need to ascertain that the expression is static, but we must 104 -- also ensure that it does not raise constraint error. 105 106 -- Neither of Is_Static_Expression and Is_OK_Static_Expression should be 107 -- used for compile time evaluation purposes. In fact certain expression 108 -- whose value may be known at compile time are not static in the RM 4.9 109 -- sense. A typical example is: 110 111 -- C : constant Integer := Record_Type'Size; 112 113 -- The expression 'C' is not static in the technical RM sense, but for many 114 -- simple record types, the size is in fact known at compile time. When we 115 -- are trying to perform compile time constant folding (for instance for 116 -- expressions like C + 1, Is_Static_Expression or Is_OK_Static_Expression 117 -- are not the right functions to test if folding is possible. Instead, we 118 -- use Compile_Time_Known_Value. All static expressions that do not raise 119 -- constraint error (i.e. those for which Is_OK_Static_Expression is true) 120 -- are known at compile time, but as shown by the above example, there may 121 -- be cases of non-static expressions which are known at compile time. 122 123 ----------------- 124 -- Subprograms -- 125 ----------------- 126 127 procedure Check_Expression_Against_Static_Predicate 128 (Expr : Node_Id; 129 Typ : Entity_Id; 130 Static_Failure_Is_Error : Boolean := False); 131 -- Determine whether an arbitrary expression satisfies the static predicate 132 -- of a type. The routine does nothing if Expr is not known at compile time 133 -- or Typ lacks a static predicate; otherwise it may emit a warning if the 134 -- expression is prohibited by the predicate, or if Static_Failure_Is_Error 135 -- is True then an error will be flagged. If the expression is a static 136 -- expression, it fails a predicate that was not explicitly stated to be 137 -- a dynamic predicate, and Static_Failure_Is_Error is False, then an 138 -- additional warning is given, and the flag Is_Static_Expression is reset 139 -- on Expr. 140 141 procedure Check_Non_Static_Context (N : Node_Id); 142 -- Deals with the special check required for a static expression that 143 -- appears in a non-static context, i.e. is not part of a larger static 144 -- expression (see RM 4.9(35)), i.e. the value of the expression must be 145 -- within the base range of the base type of its expected type. A check is 146 -- also made for expressions that are inside the base range, but outside 147 -- the range of the expected subtype (this is a warning message rather than 148 -- an illegality). 149 -- 150 -- Note: most cases of non-static context checks are handled within 151 -- Sem_Eval itself, including all cases of expressions at the outer level 152 -- (i.e. those that are not a subexpression). Currently the only outside 153 -- customer for this procedure is Sem_Attr (because Eval_Attribute is 154 -- there). There is also one special case arising from ranges (see body of 155 -- Resolve_Range). 156 -- 157 -- Note: this procedure is also called by GNATprove on real literals 158 -- that are not sub-expressions of static expressions, to convert them to 159 -- machine numbers, as GNATprove cannot perform this conversion contrary 160 -- to gigi. 161 162 procedure Check_String_Literal_Length (N : Node_Id; Ttype : Entity_Id); 163 -- N is either a string literal, or a constraint error node. In the latter 164 -- case, the situation is already dealt with, and the call has no effect. 165 -- In the former case, if the target type, Ttyp is constrained, then a 166 -- check is made to see if the string literal is of appropriate length. 167 168 function Checking_Potentially_Static_Expression return Boolean; 169 -- Returns True if the checking for potentially static expressions is 170 -- enabled; otherwise returns False. 171 172 procedure Set_Checking_Potentially_Static_Expression (Value : Boolean); 173 -- Enables checking for potentially static expressions if Value is True, 174 -- and disables such checking if Value is False. 175 176 type Compare_Result is (LT, LE, EQ, GT, GE, NE, Unknown); 177 subtype Compare_GE is Compare_Result range EQ .. GE; 178 subtype Compare_LE is Compare_Result range LT .. EQ; 179 -- Result subtypes for Compile_Time_Compare subprograms 180 181 function Compile_Time_Compare 182 (L, R : Node_Id; 183 Assume_Valid : Boolean) return Compare_Result; 184 pragma Inline (Compile_Time_Compare); 185 -- Given two expression nodes, finds out whether it can be determined at 186 -- compile time how the runtime values will compare. An Unknown result 187 -- means that the result of a comparison cannot be determined at compile 188 -- time, otherwise the returned result indicates the known result of the 189 -- comparison, given as tightly as possible (i.e. EQ or LT is preferred 190 -- returned value to LE). If Assume_Valid is true, the result reflects 191 -- the result of assuming that entities involved in the comparison have 192 -- valid representations. If Assume_Valid is false, then the base type of 193 -- any involved entity is used so that no assumption of validity is made. 194 195 function Compile_Time_Compare 196 (L, R : Node_Id; 197 Diff : access Uint; 198 Assume_Valid : Boolean; 199 Rec : Boolean := False) return Compare_Result; 200 -- This version of Compile_Time_Compare returns extra information if the 201 -- result is GT or LT. In these cases, if the magnitude of the difference 202 -- can be determined at compile time, this (positive) magnitude is returned 203 -- in Diff.all. If the magnitude of the difference cannot be determined 204 -- then Diff.all contains No_Uint on return. Rec is a parameter that is set 205 -- True for a recursive call from within Compile_Time_Compare to avoid some 206 -- infinite recursion cases. It should never be set by a client. 207 208 function Compile_Time_Known_Bounds (T : Entity_Id) return Boolean; 209 -- If T is an array whose index bounds are all known at compile time, then 210 -- True is returned. If T is not an array type, or one or more of its index 211 -- bounds is not known at compile time, then False is returned. 212 213 function Compile_Time_Known_Value (Op : Node_Id) return Boolean; 214 -- Returns true if Op is an expression not raising Constraint_Error whose 215 -- value is known at compile time and for which a call to Expr_Value can 216 -- be used to determine this value. This is always true if Op is a static 217 -- expression, but can also be true for expressions which are technically 218 -- non-static but which are in fact known at compile time. Some examples of 219 -- such expressions are the static lower bound of a non-static range or the 220 -- value of a constant object whose initial value is itself compile time 221 -- known in the sense of this routine. Note that this routine is defended 222 -- against unanalyzed expressions. Such expressions will not cause a 223 -- blowup, they may cause pessimistic (i.e. False) results to be returned. 224 -- In general we take a pessimistic view. False does not mean the value 225 -- could not be known at compile time, but True means that absolutely 226 -- definition it is known at compile time and it is safe to call 227 -- Expr_Value[_XX] on the expression Op. 228 -- 229 -- Note that we don't define precisely the set of expressions that return 230 -- True. Callers should not make any assumptions regarding the value that 231 -- is returned for non-static expressions. Functional behavior should never 232 -- be affected by whether a given non-static expression returns True or 233 -- False when this function is called. In other words this is purely for 234 -- efficiency optimization purposes. The code generated can often be more 235 -- efficient with compile time known values, e.g. range analysis for the 236 -- purpose of removing checks is more effective if we know precise bounds. 237 238 -- WARNING: There is a matching C declaration of this subprogram in fe.h 239 240 function Compile_Time_Known_Value_Or_Aggr (Op : Node_Id) return Boolean; 241 -- Similar to Compile_Time_Known_Value, but also returns True if the value 242 -- is a compile-time-known aggregate, i.e. an aggregate all of whose 243 -- constituent expressions are either compile-time-known values (based on 244 -- calling Compile_Time_Known_Value) or compile-time-known aggregates. 245 -- Note that the aggregate could still involve run-time checks that might 246 -- fail (such as for subtype checks in component associations), but the 247 -- evaluation of the expressions themselves will not raise an exception. 248 249 function CRT_Safe_Compile_Time_Known_Value (Op : Node_Id) return Boolean; 250 -- In the case of configurable run-times, there may be an issue calling 251 -- Compile_Time_Known_Value with non-static expressions where the legality 252 -- of the program is not well-defined. Consider this example: 253 -- 254 -- X := B ** C; 255 -- 256 -- Now if C is compile time known, and has the value 4, then inline code 257 -- can be generated at compile time, instead of calling a run-time routine. 258 -- That's fine in the normal case, but when we have a configurable run-time 259 -- the run-time routine may not be available. This means that the program 260 -- will be rejected if C is not known at compile time. We don't want the 261 -- legality of a program to depend on how clever the implementation of this 262 -- function is. If the run-time in use lacks the exponentiation routine, 263 -- then what we say is that exponentiation is permitted if the exponent is 264 -- officially static and has a value in the range 0 .. 4. 265 -- 266 -- In a case like this, we use CRT_Safe_Compile_Time_Known_Value to avoid 267 -- this effect. This routine will return False for a non-static expression 268 -- if we are in configurable run-time mode, even if the expression would 269 -- normally be considered compile-time known. 270 271 function Expr_Rep_Value (N : Node_Id) return Uint; 272 -- This is identical to Expr_Value, except in the case of enumeration 273 -- literals of types for which an enumeration representation clause has 274 -- been given, in which case it returns the representation value rather 275 -- than the pos value. This is the value that is needed for generating code 276 -- sequences, while the Expr_Value value is appropriate for compile time 277 -- constraint errors or getting the logical value. Note that this function 278 -- does NOT concern itself with biased values, if the caller needs a 279 -- properly biased value, the subtraction of the bias must be handled 280 -- explicitly. 281 282 function Expr_Value (N : Node_Id) return Uint; 283 -- Returns the folded value of the expression N. This function is called in 284 -- instances where it has already been determined that the expression is 285 -- static or its value is compile time known (Compile_Time_Known_Value (N) 286 -- returns True). This version is used for integer values, and enumeration 287 -- or character literals. In the latter two cases, the value returned is 288 -- the Pos value in the relevant enumeration type. It can also be used for 289 -- fixed-point values, in which case it returns the corresponding integer 290 -- value, but it cannot be used for floating-point values. Finally, it can 291 -- also be used for the Null access value, as well as for the result of an 292 -- unchecked conversion of the aforementioned handled values. 293 294 function Expr_Value_E (N : Node_Id) return Entity_Id; 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 298 -- enumeration types and returns the corresponding enumeration literal. 299 300 function Expr_Value_R (N : Node_Id) return Ureal; 301 -- Returns the folded value of the expression. This function is called in 302 -- instances where it has already been determined that the expression is 303 -- static or its value known at compile time. This version is used for real 304 -- values (including both the floating-point and fixed-point cases). In the 305 -- case of a fixed-point type, the real value is returned (cf above version 306 -- returning Uint). 307 308 function Expr_Value_S (N : Node_Id) return Node_Id; 309 -- Returns the folded value of the expression. This function is called 310 -- in instances where it has already been determined that the expression 311 -- is static or its value is known at compile time. This version is used 312 -- for string types and returns the corresponding N_String_Literal node. 313 314 procedure Eval_Actual (N : Node_Id); 315 procedure Eval_Allocator (N : Node_Id); 316 procedure Eval_Arithmetic_Op (N : Node_Id); 317 procedure Eval_Call (N : Node_Id); 318 procedure Eval_Case_Expression (N : Node_Id); 319 procedure Eval_Character_Literal (N : Node_Id); 320 procedure Eval_Concatenation (N : Node_Id); 321 procedure Eval_Entity_Name (N : Node_Id); 322 procedure Eval_If_Expression (N : Node_Id); 323 procedure Eval_Indexed_Component (N : Node_Id); 324 procedure Eval_Integer_Literal (N : Node_Id); 325 procedure Eval_Logical_Op (N : Node_Id); 326 procedure Eval_Membership_Op (N : Node_Id); 327 procedure Eval_Named_Integer (N : Node_Id); 328 procedure Eval_Named_Real (N : Node_Id); 329 procedure Eval_Op_Expon (N : Node_Id); 330 procedure Eval_Op_Not (N : Node_Id); 331 procedure Eval_Real_Literal (N : Node_Id); 332 procedure Eval_Relational_Op (N : Node_Id); 333 procedure Eval_Selected_Component (N : Node_Id); 334 procedure Eval_Shift (N : Node_Id); 335 procedure Eval_Short_Circuit (N : Node_Id); 336 procedure Eval_Slice (N : Node_Id); 337 procedure Eval_String_Literal (N : Node_Id); 338 procedure Eval_Qualified_Expression (N : Node_Id); 339 procedure Eval_Type_Conversion (N : Node_Id); 340 procedure Eval_Unary_Op (N : Node_Id); 341 procedure Eval_Unchecked_Conversion (N : Node_Id); 342 343 procedure Flag_Non_Static_Expr (Msg : String; Expr : Node_Id); 344 -- This procedure is called after it has been determined that Expr is not 345 -- static when it is required to be. Msg is the text of a message that 346 -- explains the error. This procedure checks if an error is already posted 347 -- on Expr, if so, it does nothing unless All_Errors_Mode is set in which 348 -- case this flag is ignored. Otherwise the given message is posted using 349 -- Error_Msg_F, and then Why_Not_Static is called on Expr to generate 350 -- additional messages. The string given as Msg should end with ! to make 351 -- it an unconditional message, to ensure that if it is posted, the entire 352 -- set of messages is all posted. 353 354 procedure Fold_Str (N : Node_Id; Val : String_Id; Static : Boolean); 355 -- Rewrite N with a new N_String_Literal node as the result of the compile 356 -- time evaluation of the node N. Val is the resulting string value from 357 -- the folding operation. The Is_Static_Expression flag is set in the 358 -- result node. The result is fully analyzed and resolved. Static indicates 359 -- whether the result should be considered static or not (True = consider 360 -- static). The point here is that normally all string literals are static, 361 -- but if this was the result of some sequence of evaluation where values 362 -- were known at compile time but not static, then the result is not 363 -- static. The call has no effect if Raises_Constraint_Error (N) is True, 364 -- since there is no point in folding if we have an error. 365 366 procedure Fold_Uint (N : Node_Id; Val : Uint; Static : Boolean); 367 -- Rewrite N with a (N_Integer_Literal, N_Identifier, N_Character_Literal) 368 -- node as the result of the compile time evaluation of the node N. Val is 369 -- the result in the integer case and is the position of the literal in the 370 -- literals list for the enumeration case. Is_Static_Expression is set True 371 -- in the result node. The result is fully analyzed/resolved. Static 372 -- indicates whether the result should be considered static or not (True = 373 -- consider static). The point here is that normally all integer literals 374 -- are static, but if this was the result of some sequence of evaluation 375 -- where values were known at compile time but not static, then the result 376 -- is not static. The call has no effect if Raises_Constraint_Error (N) is 377 -- True, since there is no point in folding if we have an error. 378 379 procedure Fold_Ureal (N : Node_Id; Val : Ureal; Static : Boolean); 380 -- Rewrite N with a new N_Real_Literal node as the result of the compile 381 -- time evaluation of the node N. Val is the resulting real value from the 382 -- folding operation. The Is_Static_Expression flag is set in the result 383 -- node. The result is fully analyzed and result. Static indicates whether 384 -- the result should be considered static or not (True = consider static). 385 -- The point here is that normally all string literals are static, but if 386 -- this was the result of some sequence of evaluation where values were 387 -- known at compile time but not static, then the result is not static. 388 -- The call has no effect if Raises_Constraint_Error (N) is True, since 389 -- there is no point in folding if we have an error. 390 391 procedure Fold (N : Node_Id); 392 -- Rewrite N with the relevant value if Compile_Time_Known_Value (N) is 393 -- True, otherwise a no-op. 394 395 function Is_In_Range 396 (N : Node_Id; 397 Typ : Entity_Id; 398 Assume_Valid : Boolean := False; 399 Fixed_Int : Boolean := False; 400 Int_Real : Boolean := False) return Boolean; 401 -- Returns True if it can be guaranteed at compile time that expression 402 -- N is known to be in range of the subtype Typ. A result of False does 403 -- not mean that the expression is out of range, merely that it cannot be 404 -- determined at compile time that it is in range. If Typ is a floating 405 -- point type or Int_Real is set, any integer value is treated as though it 406 -- was a real value (i.e. the underlying real value is used). In this case 407 -- we use the corresponding real value, both for the bounds of Typ, and for 408 -- the value of the expression N. If Typ is a fixed type or a discrete type 409 -- and Int_Real is False but flag Fixed_Int is True then any fixed-point 410 -- value is treated as though it was discrete value (i.e. the underlying 411 -- integer value is used). In this case we use the corresponding integer 412 -- value, both for the bounds of Typ, and for the value of the expression 413 -- N. If Typ is a discrete type and Fixed_Int as well as Int_Real are 414 -- false, integer values are used throughout. 415 -- 416 -- If Assume_Valid is set True, then N is always assumed to contain a valid 417 -- value. If Assume_Valid is set False, then N may be invalid (unless there 418 -- is some independent way of knowing that it is valid, i.e. either it is 419 -- an entity with Is_Known_Valid set, or Assume_No_Invalid_Values is True. 420 421 function Is_Null_Range (Lo : Node_Id; Hi : Node_Id) return Boolean; 422 -- Returns True if it can guarantee that Lo .. Hi is a null range. If it 423 -- cannot (because the value of Lo or Hi is not known at compile time) then 424 -- it returns False. 425 426 function Is_OK_Static_Expression (N : Node_Id) return Boolean; 427 -- An OK static expression is one that is static in the RM definition sense 428 -- and which does not raise constraint error. For most legality checking 429 -- purposes you should use Is_Static_Expression. For those legality checks 430 -- where the expression N should not raise constraint error use this 431 -- routine. This routine is *not* to be used in contexts where the test is 432 -- for compile time evaluation purposes. Use Compile_Time_Known_Value 433 -- instead (see section on "Compile-Time Known Values" above). 434 435 function Is_OK_Static_Range (N : Node_Id) return Boolean; 436 -- Determines if range is static, as defined in RM 4.9(26), and also checks 437 -- that neither bound of the range raises constraint error, thus ensuring 438 -- that both bounds of the range are compile-time evaluable (i.e. do not 439 -- raise constraint error). A result of true means that the bounds are 440 -- compile time evaluable. A result of false means they are not (either 441 -- because the range is not static, or because one or the other bound 442 -- raises CE). 443 444 function Is_OK_Static_Subtype (Typ : Entity_Id) return Boolean; 445 -- Determines whether a subtype fits the definition of an Ada static 446 -- subtype as given in (RM 4.9(26)) with the additional check that neither 447 -- bound raises constraint error (meaning that Expr_Value[_R|S] can be used 448 -- on these bounds). 449 -- 450 -- This differs from Is_Static_Subtype in that it includes the constraint 451 -- error checks, which are missing from Is_Static_Subtype. 452 453 function Is_Out_Of_Range 454 (N : Node_Id; 455 Typ : Entity_Id; 456 Assume_Valid : Boolean := False; 457 Fixed_Int : Boolean := False; 458 Int_Real : Boolean := False) return Boolean; 459 -- Returns True if it can be guaranteed at compile time that expression is 460 -- known to be out of range of the subtype Typ. True is returned if Typ is 461 -- a scalar type, and the value of N can be determined to be outside the 462 -- range of Typ. A result of False does not mean that the expression is in 463 -- range, but rather merely that it cannot be determined at compile time 464 -- that it is out of range. The parameters Assume_Valid, Fixed_Int, and 465 -- Int_Real are as described for Is_In_Range above. 466 467 function Is_Static_Subtype (Typ : Entity_Id) return Boolean; 468 -- Determines whether a subtype fits the definition of an Ada static 469 -- subtype as given in (RM 4.9(26)). 470 -- 471 -- This differs from Is_OK_Static_Subtype (which is what must be used by 472 -- clients) in that it does not care whether the bounds raise a constraint 473 -- error exception or not. Used for checking whether expressions are static 474 -- in the 4.9 sense (without worrying about exceptions). 475 476 function Is_Statically_Unevaluated (Expr : Node_Id) return Boolean; 477 -- This function returns True if the given expression Expr is statically 478 -- unevaluated, as defined in (RM 4.9 (32.1-32.6)). 479 480 function In_Subrange_Of 481 (T1 : Entity_Id; 482 T2 : Entity_Id; 483 Fixed_Int : Boolean := False) return Boolean; 484 -- Returns True if it can be guaranteed at compile time that the range of 485 -- values for scalar type T1 are always in the range of scalar type T2. A 486 -- result of False does not mean that T1 is not in T2's subrange, only that 487 -- it cannot be determined at compile time. Flag Fixed_Int is used as in 488 -- routine Is_In_Range above. 489 490 function Not_Null_Range (Lo : Node_Id; Hi : Node_Id) return Boolean; 491 -- Returns True if it can guarantee that Lo .. Hi is not a null range. If 492 -- it cannot (because the value of Lo or Hi is not known at compile time) 493 -- then it returns False. 494 495 function Predicates_Compatible (T1, T2 : Entity_Id) return Boolean; 496 -- In Ada 2012, subtypes are statically compatible if the predicates are 497 -- compatible as well. This function performs the required check that 498 -- predicates are compatible. Split from Subtypes_Statically_Compatible 499 -- so that it can be used in specializing error messages. 500 501 function Predicates_Match (T1, T2 : Entity_Id) return Boolean; 502 -- In Ada 2012, subtypes statically match if their predicates match as 503 -- as well. This function performs the required check that predicates 504 -- match. Separated out from Subtypes_Statically_Match so that it can 505 -- be used in specializing error messages. 506 507 function Subtypes_Statically_Compatible 508 (T1 : Entity_Id; 509 T2 : Entity_Id; 510 Formal_Derived_Matching : Boolean := False) return Boolean; 511 -- Returns true if the subtypes are unconstrained or the constraint on 512 -- on T1 is statically compatible with T2 (as defined by 4.9.1(4)). 513 -- Otherwise returns false. Formal_Derived_Matching indicates whether 514 -- the type T1 is a generic actual being checked against ancestor T2 515 -- in a formal derived type association. 516 517 function Subtypes_Statically_Match 518 (T1 : Entity_Id; 519 T2 : Entity_Id; 520 Formal_Derived_Matching : Boolean := False) return Boolean; 521 -- Determine whether two types T1, T2, which have the same base type, 522 -- are statically matching subtypes (RM 4.9.1(1-2)). Also includes the 523 -- extra GNAT rule that object sizes must match (this can be false for 524 -- types that match in the RM sense because of use of 'Object_Size), 525 -- except when testing a generic actual T1 against an ancestor T2 in a 526 -- formal derived type association (indicated by Formal_Derived_Matching). 527 528 procedure Test_Comparison 529 (Op : Node_Id; 530 Assume_Valid : Boolean; 531 True_Result : out Boolean; 532 False_Result : out Boolean); 533 -- Determine the outcome of evaluating comparison operator Op using routine 534 -- Compile_Time_Compare. Assume_Valid should be set when the operands are 535 -- to be assumed valid. Flags True_Result and False_Result are set when the 536 -- comparison evaluates to True or False respectively. 537 538 procedure Why_Not_Static (Expr : Node_Id); 539 -- This procedure may be called after generating an error message that 540 -- complains that something is non-static. If it finds good reasons, it 541 -- generates one or more error messages pointing the appropriate offending 542 -- component of the expression. If no good reasons can be figured out, then 543 -- no messages are generated. The expectation here is that the caller has 544 -- already issued a message complaining that the expression is non-static. 545 -- Note that this message should be placed using Error_Msg_F or 546 -- Error_Msg_FE, so that it will sort before any messages placed by this 547 -- call. Note that it is fine to call Why_Not_Static with something that 548 -- is not an expression, and usually this has no effect, but in some cases 549 -- (N_Parameter_Association or N_Range), it makes sense for the internal 550 -- recursive calls. 551 -- 552 -- Note that these messages are not continuation messages, instead they are 553 -- separate unconditional messages, marked with '!'. The reason for this is 554 -- that they can be posted at a different location from the main message as 555 -- documented above ("appropriate offending component"), and continuation 556 -- messages must always point to the same location as the parent message. 557 558 procedure Initialize; 559 -- Initializes the internal data structures. Must be called before each 560 -- separate main program unit (e.g. in a GNSA/ASIS context). 561 562private 563 -- The Eval routines are all marked inline, since they are called once 564 565 pragma Inline (Eval_Actual); 566 pragma Inline (Eval_Allocator); 567 pragma Inline (Eval_Character_Literal); 568 pragma Inline (Eval_If_Expression); 569 pragma Inline (Eval_Indexed_Component); 570 pragma Inline (Eval_Named_Integer); 571 pragma Inline (Eval_Named_Real); 572 pragma Inline (Eval_Real_Literal); 573 pragma Inline (Eval_Shift); 574 pragma Inline (Eval_Slice); 575 pragma Inline (Eval_String_Literal); 576 pragma Inline (Eval_Unchecked_Conversion); 577 578 pragma Inline (Is_OK_Static_Expression); 579 580end Sem_Eval; 581