File : sem_eval.ads
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) 1992-2015, 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 -- 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
36 with Types; use Types;
37 with Uintp; use Uintp;
38 with Urealp; use Urealp;
39
40 package 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 Why_Not_Static (Expr : Node_Id);
512 -- This procedure may be called after generating an error message that
513 -- complains that something is non-static. If it finds good reasons, it
514 -- generates one or more error messages pointing the appropriate offending
515 -- component of the expression. If no good reasons can be figured out, then
516 -- no messages are generated. The expectation here is that the caller has
517 -- already issued a message complaining that the expression is non-static.
518 -- Note that this message should be placed using Error_Msg_F or
519 -- Error_Msg_FE, so that it will sort before any messages placed by this
520 -- call. Note that it is fine to call Why_Not_Static with something that
521 -- is not an expression, and usually this has no effect, but in some cases
522 -- (N_Parameter_Association or N_Range), it makes sense for the internal
523 -- recursive calls.
524 --
525 -- Note that these messages are not continuation messages, instead they are
526 -- separate unconditional messages, marked with '!'. The reason for this is
527 -- that they can be posted at a different location from the main message as
528 -- documented above ("appropriate offending component"), and continuation
529 -- messages must always point to the same location as the parent message.
530
531 procedure Initialize;
532 -- Initializes the internal data structures. Must be called before each
533 -- separate main program unit (e.g. in a GNSA/ASIS context).
534
535 private
536 -- The Eval routines are all marked inline, since they are called once
537
538 pragma Inline (Eval_Actual);
539 pragma Inline (Eval_Allocator);
540 pragma Inline (Eval_Character_Literal);
541 pragma Inline (Eval_If_Expression);
542 pragma Inline (Eval_Indexed_Component);
543 pragma Inline (Eval_Named_Integer);
544 pragma Inline (Eval_Named_Real);
545 pragma Inline (Eval_Real_Literal);
546 pragma Inline (Eval_Shift);
547 pragma Inline (Eval_Slice);
548 pragma Inline (Eval_String_Literal);
549 pragma Inline (Eval_Unchecked_Conversion);
550
551 pragma Inline (Is_OK_Static_Expression);
552
553 end Sem_Eval;