| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT COMPILER COMPONENTS -- |
| -- -- |
| -- S E M _ E V A L -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- Copyright (C) 1992-2012, Free Software Foundation, Inc. -- |
| -- -- |
| -- GNAT is free software; you can redistribute it and/or modify it under -- |
| -- terms of the GNU General Public License as published by the Free Soft- -- |
| -- ware Foundation; either version 3, or (at your option) any later ver- -- |
| -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- |
| -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- |
| -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License -- |
| -- for more details. You should have received a copy of the GNU General -- |
| -- Public License distributed with GNAT; see file COPYING3. If not, go to -- |
| -- http://www.gnu.org/licenses for a complete copy of the license. -- |
| -- -- |
| -- GNAT was originally developed by the GNAT team at New York University. -- |
| -- Extensive contributions were provided by Ada Core Technologies Inc. -- |
| -- -- |
| ------------------------------------------------------------------------------ |
| |
| -- This package contains various subprograms involved in compile time |
| -- evaluation of expressions and checks for staticness of expressions and |
| -- types. It also contains the circuitry for checking for violations of pure |
| -- and preelaborated conditions (this naturally goes here, since these rules |
| -- involve consideration of staticness). |
| |
| -- Note: the static evaluation for attributes is found in Sem_Attr even though |
| -- logically it belongs here. We have done this so that it is easier to add |
| -- new attributes to GNAT. |
| |
| with Types; use Types; |
| with Uintp; use Uintp; |
| with Urealp; use Urealp; |
| |
| package Sem_Eval is |
| |
| ------------------------------------ |
| -- Handling of Static Expressions -- |
| ------------------------------------ |
| |
| -- This package contains a set of routines that process individual |
| -- subexpression nodes with the objective of folding (precomputing) the |
| -- value of static expressions that are known at compile time and properly |
| -- computing the setting of two flags that appear in every subexpression |
| -- node: |
| |
| -- Is_Static_Expression |
| |
| -- This flag is set on any expression that is static according to the |
| -- rules in (RM 4.9(3-32)). |
| |
| -- Raises_Constraint_Error |
| |
| -- This flag indicates that it is known at compile time that the |
| -- evaluation of an expression raises constraint error. If the |
| -- expression is static, and this flag is off, then it is also known at |
| -- compile time that the expression does not raise constraint error |
| -- (i.e. the flag is accurate for static expressions, and conservative |
| -- for non-static expressions. |
| |
| -- If a static expression does not raise constraint error, then the |
| -- Raises_Constraint_Error flag is off, and the expression must be computed |
| -- at compile time, which means that it has the form of either a literal, |
| -- or a constant that is itself (recursively) either a literal or a |
| -- constant. |
| |
| -- The above rules must be followed exactly in order for legality checks to |
| -- be accurate. For subexpressions that are not static according to the RM |
| -- definition, they are sometimes folded anyway, but of course in this case |
| -- Is_Static_Expression is not set. |
| |
| ------------------------------- |
| -- Compile-Time Known Values -- |
| ------------------------------- |
| |
| -- For most legality checking purposes the flag Is_Static_Expression |
| -- defined in Sinfo should be used. This package also provides a routine |
| -- called Is_OK_Static_Expression which in addition of checking that an |
| -- expression is static in the RM 4.9 sense, it checks that the expression |
| -- does not raise constraint error. In fact for certain legality checks not |
| -- only do we need to ascertain that the expression is static, but we must |
| -- also ensure that it does not raise constraint error. |
| -- |
| -- Neither of Is_Static_Expression and Is_OK_Static_Expression should be |
| -- used for compile time evaluation purposes. In fact certain expression |
| -- whose value is known at compile time are not static in the RM 4.9 sense. |
| -- A typical example is: |
| -- |
| -- C : constant Integer := Record_Type'Size; |
| -- |
| -- The expression 'C' is not static in the technical RM sense, but for many |
| -- simple record types, the size is in fact known at compile time. When we |
| -- are trying to perform compile time constant folding (for instance for |
| -- expressions like C + 1, Is_Static_Expression or Is_OK_Static_Expression |
| -- are not the right functions to test if folding is possible. Instead, we |
| -- use Compile_Time_Known_Value. All static expressions that do not raise |
| -- constraint error (i.e. those for which Is_OK_Static_Expression is true) |
| -- are known at compile time, but as shown by the above example, there are |
| -- cases of non-static expressions which are known at compile time. |
| |
| ----------------- |
| -- Subprograms -- |
| ----------------- |
| |
| procedure Check_Non_Static_Context (N : Node_Id); |
| -- Deals with the special check required for a static expression that |
| -- appears in a non-static context, i.e. is not part of a larger static |
| -- expression (see RM 4.9(35)), i.e. the value of the expression must be |
| -- within the base range of the base type of its expected type. A check is |
| -- also made for expressions that are inside the base range, but outside |
| -- the range of the expected subtype (this is a warning message rather than |
| -- an illegality). |
| -- |
| -- Note: most cases of non-static context checks are handled within |
| -- Sem_Eval itself, including all cases of expressions at the outer level |
| -- (i.e. those that are not a subexpression). Currently the only outside |
| -- customer for this procedure is Sem_Attr (because Eval_Attribute is |
| -- there). There is also one special case arising from ranges (see body of |
| -- Resolve_Range). |
| |
| procedure Check_String_Literal_Length (N : Node_Id; Ttype : Entity_Id); |
| -- N is either a string literal, or a constraint error node. In the latter |
| -- case, the situation is already dealt with, and the call has no effect. |
| -- In the former case, if the target type, Ttyp is constrained, then a |
| -- check is made to see if the string literal is of appropriate length. |
| |
| type Compare_Result is (LT, LE, EQ, GT, GE, NE, Unknown); |
| subtype Compare_GE is Compare_Result range EQ .. GE; |
| subtype Compare_LE is Compare_Result range LT .. EQ; |
| -- Result subtypes for Compile_Time_Compare subprograms |
| |
| function Compile_Time_Compare |
| (L, R : Node_Id; |
| Assume_Valid : Boolean) return Compare_Result; |
| pragma Inline (Compile_Time_Compare); |
| -- Given two expression nodes, finds out whether it can be determined at |
| -- compile time how the runtime values will compare. An Unknown result |
| -- means that the result of a comparison cannot be determined at compile |
| -- time, otherwise the returned result indicates the known result of the |
| -- comparison, given as tightly as possible (i.e. EQ or LT is preferred |
| -- returned value to LE). If Assume_Valid is true, the result reflects |
| -- the result of assuming that entities involved in the comparison have |
| -- valid representations. If Assume_Valid is false, then the base type of |
| -- any involved entity is used so that no assumption of validity is made. |
| |
| function Compile_Time_Compare |
| (L, R : Node_Id; |
| Diff : access Uint; |
| Assume_Valid : Boolean; |
| Rec : Boolean := False) return Compare_Result; |
| -- This version of Compile_Time_Compare returns extra information if the |
| -- result is GT or LT. In these cases, if the magnitude of the difference |
| -- can be determined at compile time, this (positive) magnitude is returned |
| -- in Diff.all. If the magnitude of the difference cannot be determined |
| -- then Diff.all contains No_Uint on return. Rec is a parameter that is set |
| -- True for a recursive call from within Compile_Time_Compare to avoid some |
| -- infinite recursion cases. It should never be set by a client. |
| |
| procedure Flag_Non_Static_Expr (Msg : String; Expr : Node_Id); |
| -- This procedure is called after it has been determined that Expr is not |
| -- static when it is required to be. Msg is the text of a message that |
| -- explains the error. This procedure checks if an error is already posted |
| -- on Expr, if so, it does nothing unless All_Errors_Mode is set in which |
| -- case this flag is ignored. Otherwise the given message is posted using |
| -- Error_Msg_F, and then Why_Not_Static is called on Expr to generate |
| -- additional messages. The string given as Msg should end with ! to make |
| -- it an unconditional message, to ensure that if it is posted, the entire |
| -- set of messages is all posted. |
| |
| function Is_OK_Static_Expression (N : Node_Id) return Boolean; |
| -- An OK static expression is one that is static in the RM definition sense |
| -- and which does not raise constraint error. For most legality checking |
| -- purposes you should use Is_Static_Expression. For those legality checks |
| -- where the expression N should not raise constraint error use this |
| -- routine. This routine is *not* to be used in contexts where the test is |
| -- for compile time evaluation purposes. Use Compile_Time_Known_Value |
| -- instead (see section on "Compile-Time Known Values" above). |
| |
| function Is_Static_Range (N : Node_Id) return Boolean; |
| -- Determine if range is static, as defined in RM 4.9(26). The only allowed |
| -- argument is an N_Range node (but note that the semantic analysis of |
| -- equivalent range attribute references already turned them into the |
| -- equivalent range). |
| |
| function Is_OK_Static_Range (N : Node_Id) return Boolean; |
| -- Like Is_Static_Range, but also makes sure that the bounds of the range |
| -- are compile-time evaluable (i.e. do not raise constraint error). A |
| -- result of true means that the bounds are compile time evaluable. A |
| -- result of false means they are not (either because the range is not |
| -- static, or because one or the other bound raises CE). |
| |
| function Is_Static_Subtype (Typ : Entity_Id) return Boolean; |
| -- Determines whether a subtype fits the definition of an Ada static |
| -- subtype as given in (RM 4.9(26)). Important note: This check does not |
| -- include the Ada 2012 case of a non-static predicate which results in an |
| -- otherwise static subtype being non-static. Such a subtype will return |
| -- True for this test, so if the distinction is important, the caller must |
| -- deal with this. |
| -- |
| -- Implementation note: an attempt to include this Ada 2012 case failed, |
| -- since it appears that this routine is called in some cases before the |
| -- Static_Predicate field is set ??? |
| |
| function Is_OK_Static_Subtype (Typ : Entity_Id) return Boolean; |
| -- Like Is_Static_Subtype but also makes sure that the bounds of the |
| -- subtype are compile-time evaluable (i.e. do not raise constraint error). |
| -- A result of true means that the bounds are compile time evaluable. A |
| -- result of false means they are not (either because the range is not |
| -- static, or because one or the other bound raises CE). |
| |
| function Subtypes_Statically_Compatible |
| (T1 : Entity_Id; |
| T2 : Entity_Id) return Boolean; |
| -- Returns true if the subtypes are unconstrained or the constraint on |
| -- on T1 is statically compatible with T2 (as defined by 4.9.1(4)). |
| -- Otherwise returns false. |
| |
| function Subtypes_Statically_Match (T1, T2 : Entity_Id) return Boolean; |
| -- Determine whether two types T1, T2, which have the same base type, |
| -- are statically matching subtypes (RM 4.9.1(1-2)). |
| |
| function Compile_Time_Known_Value (Op : Node_Id) return Boolean; |
| -- Returns true if Op is an expression not raising Constraint_Error whose |
| -- value is known at compile time. This is true if Op is a static |
| -- expression, but can also be true for expressions which are technically |
| -- non-static but which are in fact known at compile time, such as the |
| -- static lower bound of a non-static range or the value of a constant |
| -- object whose initial value is static. Note that this routine is defended |
| -- against unanalyzed expressions. Such expressions will not cause a |
| -- blowup, they may cause pessimistic (i.e. False) results to be returned. |
| |
| function Compile_Time_Known_Value_Or_Aggr (Op : Node_Id) return Boolean; |
| -- Similar to Compile_Time_Known_Value, but also returns True if the value |
| -- is a compile-time-known aggregate, i.e. an aggregate all of whose |
| -- constituent expressions are either compile-time-known values (based on |
| -- calling Compile_Time_Known_Value) or compile-time-known aggregates. |
| -- Note that the aggregate could still involve run-time checks that might |
| -- fail (such as for subtype checks in component associations), but the |
| -- evaluation of the expressions themselves will not raise an exception. |
| |
| function Compile_Time_Known_Bounds (T : Entity_Id) return Boolean; |
| -- If T is an array whose index bounds are all known at compile time, then |
| -- True is returned, if T is not an array, or one or more of its index |
| -- bounds is not known at compile time, then False is returned. |
| |
| function Expr_Value (N : Node_Id) return Uint; |
| -- Returns the folded value of the expression N. This function is called in |
| -- instances where it has already been determined that the expression is |
| -- static or its value is compile time known (Compile_Time_Known_Value (N) |
| -- returns True). This version is used for integer values, and enumeration |
| -- or character literals. In the latter two cases, the value returned is |
| -- the Pos value in the relevant enumeration type. It can also be used for |
| -- fixed-point values, in which case it returns the corresponding integer |
| -- value. It cannot be used for floating-point values. |
| |
| function Expr_Value_E (N : Node_Id) return Entity_Id; |
| -- Returns the folded value of the expression. This function is called in |
| -- instances where it has already been determined that the expression is |
| -- static or its value known at compile time. This version is used for |
| -- enumeration types and returns the corresponding enumeration literal. |
| |
| function Expr_Value_R (N : Node_Id) return Ureal; |
| -- Returns the folded value of the expression. This function is called in |
| -- instances where it has already been determined that the expression is |
| -- static or its value known at compile time. This version is used for real |
| -- values (including both the floating-point and fixed-point cases). In the |
| -- case of a fixed-point type, the real value is returned (cf above version |
| -- returning Uint). |
| |
| function Expr_Value_S (N : Node_Id) return Node_Id; |
| -- Returns the folded value of the expression. This function is called |
| -- in instances where it has already been determined that the expression |
| -- is static or its value is known at compile time. This version is used |
| -- for string types and returns the corresponding N_String_Literal node. |
| |
| function Expr_Rep_Value (N : Node_Id) return Uint; |
| -- This is identical to Expr_Value, except in the case of enumeration |
| -- literals of types for which an enumeration representation clause has |
| -- been given, in which case it returns the representation value rather |
| -- than the pos value. This is the value that is needed for generating code |
| -- sequences, while the Expr_Value value is appropriate for compile time |
| -- constraint errors or getting the logical value. Note that this function |
| -- does NOT concern itself with biased values, if the caller needs a |
| -- properly biased value, the subtraction of the bias must be handled |
| -- explicitly. |
| |
| procedure Eval_Actual (N : Node_Id); |
| procedure Eval_Allocator (N : Node_Id); |
| procedure Eval_Arithmetic_Op (N : Node_Id); |
| procedure Eval_Call (N : Node_Id); |
| procedure Eval_Case_Expression (N : Node_Id); |
| procedure Eval_Character_Literal (N : Node_Id); |
| procedure Eval_Concatenation (N : Node_Id); |
| procedure Eval_Entity_Name (N : Node_Id); |
| procedure Eval_If_Expression (N : Node_Id); |
| procedure Eval_Indexed_Component (N : Node_Id); |
| procedure Eval_Integer_Literal (N : Node_Id); |
| procedure Eval_Logical_Op (N : Node_Id); |
| procedure Eval_Membership_Op (N : Node_Id); |
| procedure Eval_Named_Integer (N : Node_Id); |
| procedure Eval_Named_Real (N : Node_Id); |
| procedure Eval_Op_Expon (N : Node_Id); |
| procedure Eval_Op_Not (N : Node_Id); |
| procedure Eval_Real_Literal (N : Node_Id); |
| procedure Eval_Relational_Op (N : Node_Id); |
| procedure Eval_Shift (N : Node_Id); |
| procedure Eval_Short_Circuit (N : Node_Id); |
| procedure Eval_Slice (N : Node_Id); |
| procedure Eval_String_Literal (N : Node_Id); |
| procedure Eval_Qualified_Expression (N : Node_Id); |
| procedure Eval_Type_Conversion (N : Node_Id); |
| procedure Eval_Unary_Op (N : Node_Id); |
| procedure Eval_Unchecked_Conversion (N : Node_Id); |
| |
| function Eval_Static_Predicate_Check |
| (N : Node_Id; |
| Typ : Entity_Id) return Boolean; |
| -- Evaluate a static predicate check applied to a scalar literal |
| |
| procedure Fold_Str (N : Node_Id; Val : String_Id; Static : Boolean); |
| -- Rewrite N with a new N_String_Literal node as the result of the compile |
| -- time evaluation of the node N. Val is the resulting string value from |
| -- the folding operation. The Is_Static_Expression flag is set in the |
| -- result node. The result is fully analyzed and resolved. Static indicates |
| -- whether the result should be considered static or not (True = consider |
| -- static). The point here is that normally all string literals are static, |
| -- but if this was the result of some sequence of evaluation where values |
| -- were known at compile time but not static, then the result is not |
| -- static. |
| |
| procedure Fold_Uint (N : Node_Id; Val : Uint; Static : Boolean); |
| -- Rewrite N with a (N_Integer_Literal, N_Identifier, N_Character_Literal) |
| -- node as the result of the compile time evaluation of the node N. Val is |
| -- the result in the integer case and is the position of the literal in the |
| -- literals list for the enumeration case. Is_Static_Expression is set True |
| -- in the result node. The result is fully analyzed/resolved. Static |
| -- indicates whether the result should be considered static or not (True = |
| -- consider static). The point here is that normally all integer literals |
| -- are static, but if this was the result of some sequence of evaluation |
| -- where values were known at compile time but not static, then the result |
| -- is not static. |
| |
| procedure Fold_Ureal (N : Node_Id; Val : Ureal; Static : Boolean); |
| -- Rewrite N with a new N_Real_Literal node as the result of the compile |
| -- time evaluation of the node N. Val is the resulting real value from the |
| -- folding operation. The Is_Static_Expression flag is set in the result |
| -- node. The result is fully analyzed and result. Static indicates whether |
| -- the result should be considered static or not (True = consider static). |
| -- The point here is that normally all string literals are static, but if |
| -- this was the result of some sequence of evaluation where values were |
| -- known at compile time but not static, then the result is not static. |
| |
| function Is_In_Range |
| (N : Node_Id; |
| Typ : Entity_Id; |
| Assume_Valid : Boolean := False; |
| Fixed_Int : Boolean := False; |
| Int_Real : Boolean := False) return Boolean; |
| -- Returns True if it can be guaranteed at compile time that expression is |
| -- known to be in range of the subtype Typ. A result of False does not mean |
| -- that the expression is out of range, merely that it cannot be determined |
| -- at compile time that it is in range. If Typ is a floating point type or |
| -- Int_Real is set, any integer value is treated as though it was a real |
| -- value (i.e. the underlying real value is used). In this case we use the |
| -- corresponding real value, both for the bounds of Typ, and for the value |
| -- of the expression N. If Typ is a fixed type or a discrete type and |
| -- Int_Real is False but flag Fixed_Int is True then any fixed-point value |
| -- is treated as though it was discrete value (i.e. the underlying integer |
| -- value is used). In this case we use the corresponding integer value, |
| -- both for the bounds of Typ, and for the value of the expression N. If |
| -- Typ is a discrete type and Fixed_Int as well as Int_Real are false, |
| -- integer values are used throughout. |
| -- |
| -- If Assume_Valid is set True, then N is always assumed to contain a valid |
| -- value. If Assume_Valid is set False, then N may be invalid (unless there |
| -- is some independent way of knowing that it is valid, i.e. either it is |
| -- an entity with Is_Known_Valid set, or Assume_No_Invalid_Values is True. |
| |
| function Is_Out_Of_Range |
| (N : Node_Id; |
| Typ : Entity_Id; |
| Assume_Valid : Boolean := False; |
| Fixed_Int : Boolean := False; |
| Int_Real : Boolean := False) return Boolean; |
| -- Returns True if it can be guaranteed at compile time that expression is |
| -- known to be out of range of the subtype Typ. True is returned if Typ is |
| -- a scalar type, and the value of N can be determined to be outside the |
| -- range of Typ. A result of False does not mean that the expression is in |
| -- range, but rather merely that it cannot be determined at compile time |
| -- that it is out of range. The parameters Assume_Valid, Fixed_Int, and |
| -- Int_Real are as described for Is_In_Range above. |
| |
| function In_Subrange_Of |
| (T1 : Entity_Id; |
| T2 : Entity_Id; |
| Fixed_Int : Boolean := False) return Boolean; |
| -- Returns True if it can be guaranteed at compile time that the range of |
| -- values for scalar type T1 are always in the range of scalar type T2. A |
| -- result of False does not mean that T1 is not in T2's subrange, only that |
| -- it cannot be determined at compile time. Flag Fixed_Int is used as in |
| -- routine Is_In_Range above. |
| |
| function Is_Null_Range (Lo : Node_Id; Hi : Node_Id) return Boolean; |
| -- Returns True if it can guarantee that Lo .. Hi is a null range. If it |
| -- cannot (because the value of Lo or Hi is not known at compile time) then |
| -- it returns False. |
| |
| function Not_Null_Range (Lo : Node_Id; Hi : Node_Id) return Boolean; |
| -- Returns True if it can guarantee that Lo .. Hi is not a null range. If |
| -- it cannot (because the value of Lo or Hi is not known at compile time) |
| -- then it returns False. |
| |
| procedure Why_Not_Static (Expr : Node_Id); |
| -- This procedure may be called after generating an error message that |
| -- complains that something is non-static. If it finds good reasons, it |
| -- generates one or more error messages pointing the appropriate offending |
| -- component of the expression. If no good reasons can be figured out, then |
| -- no messages are generated. The expectation here is that the caller has |
| -- already issued a message complaining that the expression is non-static. |
| -- Note that this message should be placed using Error_Msg_F or |
| -- Error_Msg_FE, so that it will sort before any messages placed by this |
| -- call. Note that it is fine to call Why_Not_Static with something that is |
| -- not an expression, and usually this has no effect, but in some cases |
| -- (N_Parameter_Association or N_Range), it makes sense for the internal |
| -- recursive calls. |
| |
| procedure Initialize; |
| -- Initializes the internal data structures. Must be called before each |
| -- separate main program unit (e.g. in a GNSA/ASIS context). |
| |
| private |
| -- The Eval routines are all marked inline, since they are called once |
| |
| pragma Inline (Eval_Actual); |
| pragma Inline (Eval_Allocator); |
| pragma Inline (Eval_Character_Literal); |
| pragma Inline (Eval_If_Expression); |
| pragma Inline (Eval_Indexed_Component); |
| pragma Inline (Eval_Named_Integer); |
| pragma Inline (Eval_Named_Real); |
| pragma Inline (Eval_Real_Literal); |
| pragma Inline (Eval_Shift); |
| pragma Inline (Eval_Slice); |
| pragma Inline (Eval_String_Literal); |
| pragma Inline (Eval_Unchecked_Conversion); |
| |
| pragma Inline (Is_OK_Static_Expression); |
| |
| end Sem_Eval; |
