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------------------------------------------------------------------------------
-- --
-- GNAT COMPILER COMPONENTS --
-- --
-- S E M _ E V A L --
-- --
-- S p e c --
-- --
-- Copyright (C) 1992-2003 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_Know_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_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_Integer_Literal);
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;