------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S E M _ E V A L -- -- -- -- S p e c -- -- -- -- Copyright (C) 1992-2005 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 2, 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 COPYING. If not, write -- -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, -- -- MA 02111-1307, USA. -- -- -- -- 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 routine 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 indicatest 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 such as 'C + 1', Is_Static_Expression or -- Is_OK_Static_Expression are not the right functions to test to see -- 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; function Compile_Time_Compare (L, R : Node_Id; Rec : Boolean := False) return Compare_Result; -- 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 a -- preferred returned value to LE). 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 constaint -- error use this routine. This routine is *not* to be used in contexts -- where the test is for compile time evaluation purposes. Use routine -- 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)). 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 -- or compile time known aggregates. 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 known at compile time (ie the call to -- 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_Character_Literal (N : Node_Id); procedure Eval_Concatenation (N : Node_Id); procedure Eval_Conditional_Expression (N : Node_Id); procedure Eval_Entity_Name (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); 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 -- 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_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; Fixed_Int : Boolean := False; Int_Real : Boolean := False) return Boolean; -- Returns True if it can be guaranteed at compile time that expression -- N is known to be in range of the subtype Typ. If the values of N or -- of either bouds of Type are unknown at compile time, False will -- always be returned. 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 a 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 discret type and Fixed_Int as -- well as Int_Real are false, intere values are used throughout. function Is_Out_Of_Range (N : Node_Id; Typ : Entity_Id; Fixed_Int : Boolean := False; Int_Real : Boolean := False) return Boolean; -- Returns True if it can be guaranteed at compile time that expression -- N is known to be out of range of the subtype Typ. True is returned -- if Typ is a scalar type, at least one of whose bounds is known at -- compile time, and N is a compile time known expression which can be -- determined to be outside a compile_time known bound of Typ. A result -- of False does not mean that the expression is in range, merely that -- it cannot be determined at compile time that it is out of range. Flags -- Int_Real and Fixed_Int are used as in routine 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_Conditional_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;