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-- --
-- --
-- C H E C K S --
-- --
-- S p e c --
-- --
-- Copyright (C) 1992-2018, 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 --
-- 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. --
-- --
-- Package containing routines used to deal with runtime checks. These
-- routines are used both by the semantics and by the expander. In some
-- cases, checks are enabled simply by setting flags for gigi, and in
-- other cases the code for the check is expanded.
-- The approach used for range and length checks, in regards to suppressed
-- checks, is to attempt to detect at compilation time that a constraint
-- error will occur. If this is detected a warning or error is issued and the
-- offending expression or statement replaced with a constraint error node.
-- This always occurs whether checks are suppressed or not. Dynamic range
-- checks are, of course, not inserted if checks are suppressed.
with Errout; use Errout;
with Namet; use Namet;
with Table;
with Types; use Types;
with Uintp; use Uintp;
with Urealp; use Urealp;
package Checks is
procedure Initialize;
-- Called for each new main source program, to initialize internal
-- variables used in the package body of the Checks unit.
function Access_Checks_Suppressed (E : Entity_Id) return Boolean;
function Accessibility_Checks_Suppressed (E : Entity_Id) return Boolean;
function Alignment_Checks_Suppressed (E : Entity_Id) return Boolean;
function Allocation_Checks_Suppressed (E : Entity_Id) return Boolean;
function Atomic_Synchronization_Disabled (E : Entity_Id) return Boolean;
function Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean;
function Division_Checks_Suppressed (E : Entity_Id) return Boolean;
function Duplicated_Tag_Checks_Suppressed (E : Entity_Id) return Boolean;
function Elaboration_Checks_Suppressed (E : Entity_Id) return Boolean;
function Index_Checks_Suppressed (E : Entity_Id) return Boolean;
function Length_Checks_Suppressed (E : Entity_Id) return Boolean;
function Overflow_Checks_Suppressed (E : Entity_Id) return Boolean;
function Predicate_Checks_Suppressed (E : Entity_Id) return Boolean;
function Range_Checks_Suppressed (E : Entity_Id) return Boolean;
function Storage_Checks_Suppressed (E : Entity_Id) return Boolean;
function Tag_Checks_Suppressed (E : Entity_Id) return Boolean;
function Validity_Checks_Suppressed (E : Entity_Id) return Boolean;
-- These functions check to see if the named check is suppressed, either
-- by an active scope suppress setting, or because the check has been
-- specifically suppressed for the given entity. If no entity is relevant
-- for the current check, then Empty is used as an argument. Note: the
-- reason we insist on specifying Empty is to force the caller to think
-- about whether there is any relevant entity that should be checked.
function Is_Check_Suppressed (E : Entity_Id; C : Check_Id) return Boolean;
-- This function is called if Checks_May_Be_Suppressed (E) is True to
-- determine whether check C is suppressed either on the entity E or
-- as the result of a scope suppress pragma. If Checks_May_Be_Suppressed
-- is False, then the status of the check can be determined simply by
-- examining Scope_Suppress, so this routine is not called in that case.
function Overflow_Check_Mode return Overflow_Mode_Type;
-- Returns current overflow checking mode, taking into account whether
-- we are inside an assertion expression and the assertion policy.
-- Control of Alignment Check Warnings --
-- When we have address clauses, there is an issue of whether the address
-- specified is appropriate to the alignment. In the general case where the
-- address is dynamic, we generate a check and a possible warning (this
-- warning occurs for example if we have a restricted run time with the
-- restriction No_Exception_Propagation). We also issue this warning in
-- the case where the address is static, but we don't know the alignment
-- at the time we process the address clause. In such a case, we issue the
-- warning, but we may be able to find out later (after the back end has
-- annotated the actual alignment chosen) that the warning was not needed.
-- To deal with deleting these potentially annoying warnings, we save the
-- warning information in a table, and then delete the waranings in the
-- post compilation validation stage if we can tell that the check would
-- never fail (in general the back end will also optimize away the check
-- in such cases).
-- Table used to record information
type Alignment_Warnings_Record is record
E : Entity_Id;
-- Entity whose alignment possibly warrants a warning
A : Uint;
-- Compile time known value of address clause for which the alignment
-- is to be checked once we know the alignment.
W : Error_Msg_Id;
-- Id of warning message we might delete
end record;
package Alignment_Warnings is new Table.Table (
Table_Component_Type => Alignment_Warnings_Record,
Table_Index_Type => Int,
Table_Low_Bound => 0,
Table_Initial => 10,
Table_Increment => 200,
Table_Name => "Alignment_Warnings");
procedure Validate_Alignment_Check_Warnings;
-- This routine is called after back annotation of type data to delete any
-- alignment warnings that turn out to be false alarms, based on knowing
-- the actual alignment, and a compile-time known alignment value.
-- Procedures to Activate Checking Flags --
procedure Activate_Division_Check (N : Node_Id);
pragma Inline (Activate_Division_Check);
-- Sets Do_Division_Check flag in node N, and handles possible local raise.
-- Always call this routine rather than calling Set_Do_Division_Check to
-- set an explicit value of True, to ensure handling the local raise case.
procedure Activate_Overflow_Check (N : Node_Id);
pragma Inline (Activate_Overflow_Check);
-- Sets Do_Overflow_Check flag in node N, and handles possible local raise.
-- Always call this routine rather than calling Set_Do_Overflow_Check to
-- set an explicit value of True, to ensure handling the local raise case.
-- Note that for discrete types, this call has no effect for MOD, REM, and
-- unary "+" for which overflow is never possible in any case.
-- Note: for the discrete-type case, it is legitimate to call this routine
-- on an unanalyzed node where the Etype field is not set. However, for the
-- floating-point case, Etype must be set (to a floating-point type).
-- For floating-point, we set the flag if we have automatic overflow checks
-- on the target, or if Check_Float_Overflow mode is set. For the floating-
-- point case, we ignore all the unary operators ("+", "-", and abs) since
-- none of these can result in overflow. If there are no overflow checks on
-- the target, and Check_Float_Overflow mode is not set, then the call has
-- no effect, since in such cases we want to generate NaN's and infinities.
procedure Activate_Range_Check (N : Node_Id);
pragma Inline (Activate_Range_Check);
-- Sets Do_Range_Check flag in node N, and handles possible local raise
-- Always call this routine rather than calling Set_Do_Range_Check to
-- set an explicit value of True, to ensure handling the local raise case.
-- Procedures to Apply Checks --
-- General note on following checks. These checks are always active if
-- Expander_Active and not Inside_A_Generic. They are inactive and have
-- no effect Inside_A_Generic. In the case where not Expander_Active
-- and not Inside_A_Generic, most of them are inactive, but some of them
-- operate anyway since they may generate useful compile time warnings.
procedure Apply_Access_Check (N : Node_Id);
-- Determines whether an expression node requires a runtime access
-- check and if so inserts the appropriate run-time check.
procedure Apply_Accessibility_Check
(N : Node_Id;
Typ : Entity_Id;
Insert_Node : Node_Id);
-- Given a name N denoting an access parameter, emits a run-time
-- accessibility check (if necessary), checking that the level of
-- the object denoted by the access parameter is not deeper than the
-- level of the type Typ. Program_Error is raised if the check fails.
-- Insert_Node indicates the node where the check should be inserted.
procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id);
-- E is the entity for an object which has an address clause. If checks
-- are enabled, then this procedure generates a check that the specified
-- address has an alignment consistent with the alignment of the object,
-- raising PE if this is not the case. The resulting check (if one is
-- generated) is prepended to the Actions list of N_Freeze_Entity node N.
-- Note that the check references E'Alignment, so it cannot be emitted
-- before N (its freeze node), otherwise this would cause an illegal
-- access before elaboration error in GIGI. For the case of a clear overlay
-- situation, we also check that the size of the overlaying object is not
-- larger than the overlaid object.
procedure Apply_Arithmetic_Overflow_Check (N : Node_Id);
-- Handle overflow checking for an arithmetic operator. Also handles the
-- cases of ELIMINATED and MINIMIZED overflow checking mode. If the mode
-- is one of the latter two, then this routine can also be called with
-- an if or case expression node to make sure that we properly handle
-- overflow checking for dependent expressions. This routine handles
-- front end vs back end overflow checks (in the front end case it expands
-- the necessary check). Note that divide is handled separately using
-- Apply_Divide_Checks. Node N may or may not have Do_Overflow_Check.
-- In STRICT mode, there is nothing to do if this flag is off, but in
-- MINIMIZED/ELIMINATED mode we still have to deal with possible use
-- of doing operations in Long_Long_Integer or Bignum mode.
procedure Apply_Constraint_Check
(N : Node_Id;
Typ : Entity_Id;
No_Sliding : Boolean := False);
-- Top-level procedure, calls all the others depending on the class of
-- Typ. Checks that expression N satisfies the constraint of type Typ.
-- No_Sliding is only relevant for constrained array types, if set to
-- True, it checks that indexes are in range.
procedure Apply_Discriminant_Check
(N : Node_Id;
Typ : Entity_Id;
Lhs : Node_Id := Empty);
-- Given an expression N of a discriminated type, or of an access type
-- whose designated type is a discriminanted type, generates a check to
-- ensure that the expression can be converted to the subtype given as
-- the second parameter. Lhs is empty except in the case of assignments,
-- where the target object may be needed to determine the subtype to
-- check against (such as the cases of unconstrained formal parameters
-- and unconstrained aliased objects). For the case of unconstrained
-- formals, the check is performed only if the corresponding actual is
-- constrained, i.e., whether Lhs'Constrained is True.
procedure Apply_Divide_Checks (N : Node_Id);
-- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem if either of the
-- flags Do_Division_Check or Do_Overflow_Check is set, then this routine
-- ensures that the appropriate checks are made. Note that overflow can
-- occur in the signed case for the case of the largest negative number
-- divided by minus one. This procedure only applies to Integer types.
procedure Apply_Parameter_Aliasing_Checks
(Call : Node_Id;
Subp : Entity_Id);
-- Given a subprogram call Call, add a check to verify that none of the
-- actuals overlap. Subp denotes the subprogram being called.
procedure Apply_Parameter_Validity_Checks (Subp : Entity_Id);
-- Given a subprogram Subp, add both a pre and post condition pragmas that
-- verify the proper initialization of scalars in parameters and function
-- results.
procedure Apply_Predicate_Check
(N : Node_Id;
Typ : Entity_Id;
Fun : Entity_Id := Empty);
-- N is an expression to which a predicate check may need to be applied for
-- Typ, if Typ has a predicate function. When N is an actual in a call, Fun
-- is the function being called, which is used to generate a better warning
-- if the call leads to an infinite recursion.
procedure Apply_Type_Conversion_Checks (N : Node_Id);
-- N is an N_Type_Conversion node. A type conversion actually involves
-- two sorts of checks. The first check is the checks that ensures that
-- the operand in the type conversion fits onto the base type of the
-- subtype it is being converted to (see RM 4.6 (28)-(50)). The second
-- check is there to ensure that once the operand has been converted to
-- a value of the target type, this converted value meets the
-- constraints imposed by the target subtype (see RM 4.6 (51)).
procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id);
-- The argument N is an attribute reference node intended for processing
-- by gigi. The attribute is one that returns a universal integer, but
-- the attribute reference node is currently typed with the expected
-- result type. This routine deals with range and overflow checks needed
-- to make sure that the universal result is in range.
function Build_Discriminant_Checks
(N : Node_Id;
T_Typ : Entity_Id)
return Node_Id;
-- Subsidiary routine for Apply_Discriminant_Check. Builds the expression
-- that compares discriminants of the expression with discriminants of the
-- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In).
function Convert_From_Bignum (N : Node_Id) return Node_Id;
-- Returns result of converting node N from Bignum. The returned value is
-- not analyzed, the caller takes responsibility for this. Node N must be
-- a subexpression node of type Bignum. The result is Long_Long_Integer.
function Convert_To_Bignum (N : Node_Id) return Node_Id;
-- Returns result of converting node N to Bignum. The returned value is not
-- analyzed, the caller takes responsibility for this. Node N must be a
-- subexpression node of a signed integer type or Bignum type (if it is
-- already a Bignum, the returned value is Relocate_Node (N)).
procedure Determine_Range
(N : Node_Id;
OK : out Boolean;
Lo : out Uint;
Hi : out Uint;
Assume_Valid : Boolean := False);
-- N is a node for a subexpression. If N is of a discrete type with no
-- error indications, and no other peculiarities (e.g. missing Etype),
-- then OK is True on return, and Lo and Hi are set to a conservative
-- estimate of the possible range of values of N. Thus if OK is True on
-- return, the value of the subexpression N is known to lie in the range
-- Lo .. Hi (inclusive). If the expression is not of a discrete type, or
-- some kind of error condition is detected, then OK is False on exit, and
-- Lo/Hi are set to No_Uint. Thus the significance of OK being False on
-- return is that no useful information is available on the range of the
-- expression. Assume_Valid determines whether the processing is allowed to
-- assume that values are in range of their subtypes. If it is set to True,
-- then this assumption is valid, if False, then processing is done using
-- base types to allow invalid values.
procedure Determine_Range_R
(N : Node_Id;
OK : out Boolean;
Lo : out Ureal;
Hi : out Ureal;
Assume_Valid : Boolean := False);
-- Similar to Determine_Range, but for a node N of floating-point type. OK
-- is True on return only for IEEE floating-point types and only if we do
-- not have to worry about extended precision (i.e. on the x86, we must be
-- using -msse2 -mfpmath=sse). At the current time, this is used only in
-- GNATprove, though we could consider using it more generally in future.
-- For that to happen, the possibility of arguments of infinite or NaN
-- value should be taken into account, which is not the case currently.
procedure Install_Null_Excluding_Check (N : Node_Id);
-- Determines whether an access node requires a runtime access check and
-- if so inserts the appropriate run-time check.
procedure Install_Primitive_Elaboration_Check (Subp_Body : Node_Id);
-- Insert a check which ensures that subprogram body Subp_Body has been
-- properly elaborated. The check is installed only when Subp_Body is the
-- body of a nonabstract library-level primitive of a tagged type. Further
-- restrictions may apply, see the body for details.
function Make_Bignum_Block (Loc : Source_Ptr) return Node_Id;
-- This function is used by top level overflow checking routines to do a
-- mark/release operation on the secondary stack around bignum operations.
-- The block created looks like:
-- declare
-- M : Mark_Id := SS_Mark;
-- begin
-- SS_Release (M);
-- end;
-- The idea is that the caller will insert any needed extra declarations
-- after the declaration of M, and any needed statements (in particular
-- the bignum operations) before the call to SS_Release, and then do an
-- Insert_Action of the whole block (it is returned unanalyzed). The Loc
-- parameter is used to supply Sloc values for the constructed tree.
procedure Minimize_Eliminate_Overflows
(N : Node_Id;
Lo : out Uint;
Hi : out Uint;
Top_Level : Boolean);
-- This is the main routine for handling MINIMIZED and ELIMINATED overflow
-- processing. On entry N is a node whose result is a signed integer
-- subtype. The Do_Overflow_Check flag may or may not be set on N. If the
-- node is an arithmetic operation, then a range analysis is carried out,
-- and there are three possibilities:
-- The node is left unchanged (apart from expansion of an exponentiation
-- operation). This happens if the routine can determine that the result
-- is definitely in range. The Do_Overflow_Check flag is turned off in
-- this case.
-- The node is transformed into an arithmetic operation with a result
-- type of Long_Long_Integer.
-- The node is transformed into a function call that calls an appropriate
-- function in the System.Bignums package to compute a Bignum result.
-- In the first two cases, Lo and Hi are set to the bounds of the possible
-- range of results, computed as accurately as possible. In the third case
-- Lo and Hi are set to No_Uint (there are some cases where we could get an
-- advantage from keeping result ranges for Bignum values, but it could use
-- a lot of space and is very unlikely to be valuable).
-- If the node is not an arithmetic operation, then it is unchanged but
-- Lo and Hi are still set (to the bounds of the result subtype if nothing
-- better can be determined).
-- Note: this function is recursive, if called with an arithmetic operator,
-- recursive calls are made to process the operands using this procedure.
-- So we end up doing things top down. Nothing happens to an arithmetic
-- expression until this procedure is called on the top level node and
-- then the recursive calls process all the children. We have to do it
-- this way. If we try to do it bottom up in natural expansion order, then
-- there are two problems. First, where do we stash the bounds, and more
-- importantly, semantic processing will be messed up. Consider A+B+C where
-- A,B,C are all of type integer, if we processed A+B before doing semantic
-- analysis of the addition of this result to C, that addition could end up
-- with a Long_Long_Integer left operand and an Integer right operand, and
-- we would get a semantic error.
-- The routine is called in three situations if we are operating in either
-- Overflow processing applied to the top node of an expression tree when
-- that node is an arithmetic operator. In this case the result is
-- converted to the appropriate result type (there is special processing
-- when the parent is a conversion, see body for details).
-- Overflow processing applied to the operands of a comparison operation.
-- In this case, the comparison is done on the result Long_Long_Integer
-- or Bignum values, without raising any exceptions.
-- Overflow processing applied to the left operand of a membership test.
-- In this case no exception is raised if a Long_Long_Integer or Bignum
-- result is outside the range of the type of that left operand (it is
-- just that the result of IN is false in that case).
-- Note that if Bignum values appear, the caller must take care of doing
-- the appropriate mark/release operations on the secondary stack.
-- Top_Level is used to avoid inefficient unnecessary transitions into the
-- Bignum domain. If Top_Level is True, it means that the caller will have
-- to convert any Bignum value back to Long_Long_Integer, possibly checking
-- that the value is in range. This is the normal case for a top level
-- operator in a subexpression. There is no point in going into Bignum mode
-- to avoid an overflow just so we can check for overflow the next moment.
-- For calls from comparisons and membership tests, and for all recursive
-- calls, we do want to transition into the Bignum domain if necessary.
-- Note that this setting is only relevant in ELIMINATED mode.
-- Control and Optimization of Range/Overflow Checks --
-- Range checks are controlled by the Do_Range_Check flag. The front end
-- is responsible for setting this flag in relevant nodes. Originally
-- the back end generated all corresponding range checks. But later on
-- we decided to generate many range checks in the front end. We are now
-- in the transitional phase where some of these checks are still done
-- by the back end, but many are done by the front end. It is possible
-- that in the future we might move all the checks to the front end. The
-- main remaining back end checks are for subscript checking.
-- Overflow checks are similarly controlled by the Do_Overflow_Check flag.
-- The difference here is that if back end overflow checks are inactive
-- (Backend_Overflow_Checks_On_Target set False), then the actual overflow
-- checks are generated by the front end, but if back end overflow checks
-- are active (Backend_Overflow_Checks_On_Target set True), then the back
-- end does generate the checks.
-- The following two routines are used to set these flags, they allow
-- for the possibility of eliminating checks. Checks can be eliminated
-- if an identical check has already been performed.
procedure Enable_Overflow_Check (N : Node_Id);
-- First this routine determines if an overflow check is needed by doing
-- an appropriate range check. If a check is not needed, then the call
-- has no effect. If a check is needed then this routine sets the flag
-- Do_Overflow_Check in node N to True, unless it can be determined that
-- the check is not needed. The only condition under which this is the
-- case is if there was an identical check earlier on.
procedure Enable_Range_Check (N : Node_Id);
-- Set Do_Range_Check flag in node N True, unless it can be determined
-- that the check is not needed. The only condition under which this is
-- the case is if there was an identical check earlier on. This routine
-- is not responsible for doing range analysis to determine whether or
-- not such a check is needed -- the caller is expected to do this. The
-- one other case in which the request to set the flag is ignored is
-- when Kill_Range_Check is set in an N_Unchecked_Conversion node.
-- The following routines are used to keep track of processing sequences
-- of statements (e.g. the THEN statements of an IF statement). A check
-- that appears within such a sequence can eliminate an identical check
-- within this sequence of statements. However, after the end of the
-- sequence of statements, such a check is no longer of interest, since
-- it may not have been executed.
procedure Conditional_Statements_Begin;
-- This call marks the start of processing of a sequence of statements.
-- Every call to this procedure must be followed by a matching call to
-- Conditional_Statements_End.
procedure Conditional_Statements_End;
-- This call removes from consideration all saved checks since the
-- corresponding call to Conditional_Statements_Begin. These two
-- procedures operate in a stack like manner.
-- The mechanism for optimizing checks works by remembering checks
-- that have already been made, but certain conditions, for example
-- an assignment to a variable involved in a check, may mean that the
-- remembered check is no longer valid, in the sense that if the same
-- expression appears again, another check is required because the
-- value may have changed.
-- The following routines are used to note conditions which may render
-- some or all of the stored and remembered checks to be invalidated.
procedure Kill_Checks (V : Entity_Id);
-- This procedure records an assignment or other condition that causes
-- the value of the variable to be changed, invalidating any stored
-- checks that reference the value. Note that all such checks must
-- be discarded, even if they are not in the current statement range.
procedure Kill_All_Checks;
-- This procedure kills all remembered checks
-- Length and Range Checks --
-- In the following procedures, there are three arguments which have
-- a common meaning as follows:
-- Expr The expression to be checked. If a check is required,
-- the appropriate flag will be placed on this node. Whether
-- this node is further examined depends on the setting of
-- the parameter Source_Typ, as described below.
-- ??? Apply_Length_Check and Apply_Range_Check do not have an Expr
-- formal
-- ??? Apply_Length_Check and Apply_Range_Check have a Ck_Node formal
-- which is undocumented, is it the same as Expr?
-- Target_Typ The target type on which the check is to be based. For
-- example, if we have a scalar range check, then the check
-- is that we are in range of this type.
-- Source_Typ Normally Empty, but can be set to a type, in which case
-- this type is used for the check, see below.
-- The checks operate in one of two modes:
-- If Source_Typ is Empty, then the node Expr is examined, at the very
-- least to get the source subtype. In addition for some of the checks,
-- the actual form of the node may be examined. For example, a node of
-- type Integer whose actual form is an Integer conversion from a type
-- with range 0 .. 3 can be determined to have a value in range 0 .. 3.
-- If Source_Typ is given, then nothing can be assumed about the Expr,
-- and indeed its contents are not examined. In this case the check is
-- based on the assumption that Expr can be an arbitrary value of the
-- given Source_Typ.
-- Currently, the only case in which a Source_Typ is explicitly supplied
-- is for the case of Out and In_Out parameters, where, for the conversion
-- on return (the Out direction), the types must be reversed. This is
-- handled by the caller.
procedure Apply_Length_Check
(Ck_Node : Node_Id;
Target_Typ : Entity_Id;
Source_Typ : Entity_Id := Empty);
-- This procedure builds a sequence of declarations to do a length check
-- that checks if the lengths of the two arrays Target_Typ and source type
-- are the same. The resulting actions are inserted at Node using a call
-- to Insert_Actions.
-- For access types, the Directly_Designated_Type is retrieved and
-- processing continues as enumerated above, with a guard against null
-- values.
-- Note: calls to Apply_Length_Check currently never supply an explicit
-- Source_Typ parameter, but Apply_Length_Check takes this parameter and
-- processes it as described above for consistency with the other routines
-- in this section.
procedure Apply_Range_Check
(Ck_Node : Node_Id;
Target_Typ : Entity_Id;
Source_Typ : Entity_Id := Empty);
-- For a Node of kind N_Range, constructs a range check action that tests
-- first that the range is not null and then that the range is contained in
-- the Target_Typ range.
-- For scalar types, constructs a range check action that first tests that
-- the expression is contained in the Target_Typ range. The difference
-- between this and Apply_Scalar_Range_Check is that the latter generates
-- the actual checking code against the Etype of the expression.
-- For constrained array types, construct series of range check actions
-- to check that each Expr range is properly contained in the range of
-- Target_Typ.
-- For a type conversion to an unconstrained array type, constructs a range
-- check action to check that the bounds of the source type are within the
-- constraints imposed by the Target_Typ.
-- For access types, the Directly_Designated_Type is retrieved and
-- processing continues as enumerated above, with a guard against null
-- values.
-- The source type is used by type conversions to unconstrained array
-- types to retrieve the corresponding bounds.
procedure Apply_Static_Length_Check
(Expr : Node_Id;
Target_Typ : Entity_Id;
Source_Typ : Entity_Id := Empty);
-- Tries to determine statically whether the two array types source type
-- and Target_Typ have the same length. If it can be determined at compile
-- time that they do not, then an N_Raise_Constraint_Error node replaces
-- Expr, and a warning message is issued.
procedure Apply_Scalar_Range_Check
(Expr : Node_Id;
Target_Typ : Entity_Id;
Source_Typ : Entity_Id := Empty;
Fixed_Int : Boolean := False);
-- For scalar types, determines whether an expression node should be
-- flagged as needing a runtime range check. If the node requires such a
-- check, the Do_Range_Check flag is turned on. The Fixed_Int flag if set
-- causes any fixed-point values to be treated as though they were discrete
-- values (i.e. the underlying integer value is used).
type Check_Result is private;
-- Type used to return result of Get_Range_Checks call, for later use in
-- call to Insert_Range_Checks procedure.
function Get_Range_Checks
(Ck_Node : Node_Id;
Target_Typ : Entity_Id;
Source_Typ : Entity_Id := Empty;
Warn_Node : Node_Id := Empty) return Check_Result;
-- Like Apply_Range_Check, except it does not modify anything. Instead
-- it returns an encapsulated result of the check operations for later
-- use in a call to Insert_Range_Checks. If Warn_Node is non-empty, its
-- Sloc is used, in the static case, for the generated warning or error.
-- Additionally, it is used rather than Expr (or Low/High_Bound of Expr)
-- in constructing the check.
procedure Append_Range_Checks
(Checks : Check_Result;
Stmts : List_Id;
Suppress_Typ : Entity_Id;
Static_Sloc : Source_Ptr;
Flag_Node : Node_Id);
-- Called to append range checks as returned by a call to Get_Range_Checks.
-- Stmts is a list to which either the dynamic check is appended or the
-- raise Constraint_Error statement is appended (for static checks).
-- Static_Sloc is the Sloc at which the raise CE node points, Flag_Node is
-- used as the node at which to set the Has_Dynamic_Check flag. Checks_On
-- is a boolean value that says if range and index checking is on or not.
procedure Insert_Range_Checks
(Checks : Check_Result;
Node : Node_Id;
Suppress_Typ : Entity_Id;
Static_Sloc : Source_Ptr := No_Location;
Flag_Node : Node_Id := Empty;
Do_Before : Boolean := False);
-- Called to insert range checks as returned by a call to Get_Range_Checks.
-- Node is the node after which either the dynamic check is inserted or
-- the raise Constraint_Error statement is inserted (for static checks).
-- Suppress_Typ is the type to check to determine if checks are suppressed.
-- Static_Sloc, if passed, is the Sloc at which the raise CE node points,
-- otherwise Sloc (Node) is used. The Has_Dynamic_Check flag is normally
-- set at Node. If Flag_Node is present, then this is used instead as the
-- node at which to set the Has_Dynamic_Check flag. Normally the check is
-- inserted after, if Do_Before is True, the check is inserted before
-- Node.
-- Expander Routines --
-- Some of the earlier processing for checks results in temporarily setting
-- the Do_Range_Check flag rather than actually generating checks. Now we
-- are moving the generation of such checks into the front end for reasons
-- of efficiency and simplicity (there were difficulties in handling this
-- in the back end when side effects were present in the expressions being
-- checked).
-- Probably we could eliminate the Do_Range_Check flag entirely and
-- generate the checks earlier, but this is a delicate area and it
-- seemed safer to implement the following routines, which are called
-- late on in the expansion process. They check the Do_Range_Check flag
-- and if it is set, generate the actual checks and reset the flag.
procedure Generate_Range_Check
(N : Node_Id;
Target_Type : Entity_Id;
Reason : RT_Exception_Code);
-- This procedure is called to actually generate and insert a range check.
-- A check is generated to ensure that the value of N lies within the range
-- of the target type. Note that the base type of N may be different from
-- the base type of the target type. This happens in the conversion case.
-- The Reason parameter is the exception code to be used for the exception
-- if raised.
-- Note: if the expander is not active, or if we are in GNATprove mode,
-- then we do not generate explicit range code. Instead we just turn the
-- Do_Range_Check flag on, since in these cases that's what we want to see
-- in the tree (GNATprove in particular depends on this flag being set). If
-- we generate the actual range check, then we make sure the flag is off,
-- since the code we generate takes complete care of the check.
-- Historical note: We used to just pass on the Do_Range_Check flag to the
-- back end to generate the check, but now in code-generation mode we never
-- have this flag set, since the front end takes care of the check. The
-- normal processing flow now is that the analyzer typically turns on the
-- Do_Range_Check flag, and if it is set, this routine is called, which
-- turns the flag off in code-generation mode.
procedure Generate_Index_Checks (N : Node_Id);
-- This procedure is called to generate index checks on the subscripts for
-- the indexed component node N. Each subscript expression is examined, and
-- if the Do_Range_Check flag is set, an appropriate index check is
-- generated and the flag is reset.
-- Similarly, we set the flag Do_Discriminant_Check in the semantic
-- analysis to indicate that a discriminant check is required for selected
-- component of a discriminated type. The following routine is called from
-- the expander to actually generate the call.
procedure Generate_Discriminant_Check (N : Node_Id);
-- N is a selected component for which a discriminant check is required to
-- make sure that the discriminants have appropriate values for the
-- selection. This is done by calling the appropriate discriminant checking
-- routine for the selector.
-- Validity Checking --
-- In (RM 13.9.1(9-11)) we have the following rules on invalid values
-- If the representation of a scalar object does not represent value of
-- the object's subtype (perhaps because the object was not initialized),
-- the object is said to have an invalid representation. It is a bounded
-- error to evaluate the value of such an object. If the error is
-- detected, either Constraint_Error or Program_Error is raised.
-- Otherwise, execution continues using the invalid representation. The
-- rules of the language outside this subclause assume that all objects
-- have valid representations. The semantics of operations on invalid
-- representations are as follows:
-- 10 If the representation of the object represents a value of the
-- object's type, the value of the type is used.
-- 11 If the representation of the object does not represent a value
-- of the object's type, the semantics of operations on such
-- representations is implementation-defined, but does not by
-- itself lead to erroneous or unpredictable execution, or to
-- other objects becoming abnormal.
-- We quote the rules in full here since they are quite delicate. Most
-- of the time, we can just compute away with wrong values, and get a
-- possibly wrong result, which is well within the range of allowed
-- implementation defined behavior. The two tricky cases are subscripted
-- array assignments, where we don't want to do wild stores, and case
-- statements where we don't want to do wild jumps.
-- In GNAT, we control validity checking with a switch -gnatV that can take
-- three parameters, n/d/f for None/Default/Full. These modes have the
-- following meanings:
-- None (no validity checking)
-- In this mode, there is no specific checking for invalid values
-- and the code generator assumes that all stored values are always
-- within the bounds of the object subtype. The consequences are as
-- follows:
-- For case statements, an out of range invalid value will cause
-- Constraint_Error to be raised, or an arbitrary one of the case
-- alternatives will be executed. Wild jumps cannot result even
-- in this mode, since we always do a range check
-- For subscripted array assignments, wild stores will result in
-- the expected manner when addresses are calculated using values
-- of subscripts that are out of range.
-- It could perhaps be argued that this mode is still conformant with
-- the letter of the RM, since implementation defined is a rather
-- broad category, but certainly it is not in the spirit of the
-- RM requirement, since wild stores certainly seem to be a case of
-- erroneous behavior.
-- Default (default standard RM-compatible validity checking)
-- In this mode, which is the default, minimal validity checking is
-- performed to ensure no erroneous behavior as follows:
-- For case statements, an out of range invalid value will cause
-- Constraint_Error to be raised.
-- For subscripted array assignments, invalid out of range
-- subscript values will cause Constraint_Error to be raised.
-- Full (Full validity checking)
-- In this mode, the protections guaranteed by the standard mode are
-- in place, and the following additional checks are made:
-- For every assignment, the right side is checked for validity
-- For every call, IN and IN OUT parameters are checked for validity
-- For every subscripted array reference, both for stores and loads,
-- all subscripts are checked for validity.
-- These checks are not required by the RM, but will in practice
-- improve the detection of uninitialized variables, particularly
-- if used in conjunction with pragma Normalize_Scalars.
-- In the above description, we talk about performing validity checks,
-- but we don't actually generate a check in a case where the compiler
-- can be sure that the value is valid. Note that this assurance must
-- be achieved without assuming that any uninitialized value lies within
-- the range of its type. The following are cases in which values are
-- known to be valid. The flag Is_Known_Valid is used to keep track of
-- some of these cases.
-- If all possible stored values are valid, then any uninitialized
-- value must be valid.
-- Literals, including enumeration literals, are clearly always valid
-- Constants are always assumed valid, with a validity check being
-- performed on the initializing value where necessary to ensure that
-- this is the case.
-- For variables, the status is set to known valid if there is an
-- initializing expression. Again a check is made on the initializing
-- value if necessary to ensure that this assumption is valid. The
-- status can change as a result of local assignments to a variable.
-- If a known valid value is unconditionally assigned, then we mark
-- the left side as known valid. If a value is assigned that is not
-- known to be valid, then we mark the left side as invalid. This
-- kind of processing does NOT apply to non-local variables since we
-- are not following the flow graph (more properly the flow of actual
-- processing only corresponds to the flow graph for local assignments).
-- For non-local variables, we preserve the current setting, i.e. a
-- validity check is performed when assigning to a knonwn valid global.
-- Note: no validity checking is required if range checks are suppressed
-- regardless of the setting of the validity checking mode.
-- The following procedures are used in handling validity checking
procedure Apply_Subscript_Validity_Checks (Expr : Node_Id);
-- Expr is the node for an indexed component. If validity checking and
-- range checking are enabled, all subscripts for this indexed component
-- are checked for validity.
procedure Check_Valid_Lvalue_Subscripts (Expr : Node_Id);
-- Expr is a lvalue, i.e. an expression representing the target of an
-- assignment. This procedure checks for this expression involving an
-- assignment to an array value. We have to be sure that all the subscripts
-- in such a case are valid, since according to the rules in (RM
-- 13.9.1(9-11)) such assignments are not permitted to result in erroneous
-- behavior in the case of invalid subscript values.
procedure Ensure_Valid
(Expr : Node_Id;
Holes_OK : Boolean := False;
Related_Id : Entity_Id := Empty;
Is_Low_Bound : Boolean := False;
Is_High_Bound : Boolean := False);
-- Ensure that Expr represents a valid value of its type. If this type
-- is not a scalar type, then the call has no effect, since validity
-- is only an issue for scalar types. The effect of this call is to
-- check if the value is known valid, if so, nothing needs to be done.
-- If this is not known, then either Expr is set to be range checked,
-- or specific checking code is inserted so that an exception is raised
-- if the value is not valid.
-- The optional argument Holes_OK indicates whether it is necessary to
-- worry about enumeration types with non-standard representations leading
-- to "holes" in the range of possible representations. If Holes_OK is
-- True, then such values are assumed valid (this is used when the caller
-- will make a separate check for this case anyway). If Holes_OK is False,
-- then this case is checked, and code is inserted to ensure that Expr is
-- valid, raising Constraint_Error if the value is not valid.
-- Related_Id denotes the entity of the context where Expr appears. Flags
-- Is_Low_Bound and Is_High_Bound specify whether the expression to check
-- is the low or the high bound of a range. These three optional arguments
-- signal Remove_Side_Effects to create an external symbol of the form
-- Chars (Related_Id)_FIRST/_LAST. For suggested use of these parameters
-- see the warning in the body of Sem_Ch3.Process_Range_Expr_In_Decl.
function Expr_Known_Valid (Expr : Node_Id) return Boolean;
-- This function tests it the value of Expr is known to be valid in the
-- sense of RM 13.9.1(9-11). In the case of GNAT, it is only discrete types
-- which are a concern, since for non-discrete types we simply continue
-- computation with invalid values, which does not lead to erroneous
-- behavior. Thus Expr_Known_Valid always returns True if the type of Expr
-- is non-discrete. For discrete types the value returned is True only if
-- it can be determined that the value is Valid. Otherwise False is
-- returned.
procedure Insert_Valid_Check
(Expr : Node_Id;
Related_Id : Entity_Id := Empty;
Is_Low_Bound : Boolean := False;
Is_High_Bound : Boolean := False);
-- Inserts code that will check for the value of Expr being valid, in the
-- sense of the 'Valid attribute returning True. Constraint_Error will be
-- raised if the value is not valid.
-- Related_Id denotes the entity of the context where Expr appears. Flags
-- Is_Low_Bound and Is_High_Bound specify whether the expression to check
-- is the low or the high bound of a range. These three optional arguments
-- signal Remove_Side_Effects to create an external symbol of the form
-- Chars (Related_Id)_FIRST/_LAST. For suggested use of these parameters
-- see the warning in the body of Sem_Ch3.Process_Range_Expr_In_Decl.
procedure Null_Exclusion_Static_Checks
(N : Node_Id;
Comp : Node_Id := Empty;
Array_Comp : Boolean := False);
-- Ada 2005 (AI-231): Test for and warn on null-excluding objects or
-- components that will raise an exception due to initialization by null.
-- When a value for Comp is supplied (as in the case of an uninitialized
-- null-excluding component within a composite object), a reported warning
-- will indicate the offending component instead of the object itself.
-- Array_Comp being True indicates an array object with null-excluding
-- components, and any reported warning will indicate that.
procedure Remove_Checks (Expr : Node_Id);
-- Remove all checks from Expr except those that are only executed
-- conditionally (on the right side of And Then/Or Else. This call
-- removes only embedded checks (Do_Range_Check, Do_Overflow_Check).
procedure Validity_Check_Range
(N : Node_Id;
Related_Id : Entity_Id := Empty);
-- If N is an N_Range node, then Ensure_Valid is called on its bounds, if
-- validity checking of operands is enabled. Related_Id denotes the entity
-- of the context where N appears.
-- Handling of Check Names --
-- The following table contains Name_Id's for recognized checks. The first
-- entries (corresponding to the values of the subtype Predefined_Check_Id)
-- contain the Name_Id values for the checks that are predefined, including
-- All_Checks (see Types). Remaining entries are those that are introduced
-- by pragma Check_Names.
package Check_Names is new Table.Table (
Table_Component_Type => Name_Id,
Table_Index_Type => Check_Id,
Table_Low_Bound => 1,
Table_Initial => 30,
Table_Increment => 200,
Table_Name => "Name_Check_Names");
function Get_Check_Id (N : Name_Id) return Check_Id;
-- Function to search above table for matching name. If found returns the
-- corresponding Check_Id value in the range 1 .. Check_Name.Last. If not
-- found returns No_Check_Id.
type Check_Result is array (Positive range 1 .. 2) of Node_Id;
-- There are two cases for the result returned by Range_Check:
-- For the static case the result is one or two nodes that should cause
-- a Constraint_Error. Typically these will include Expr itself or the
-- direct descendants of Expr, such as Low/High_Bound (Expr)). It is the
-- responsibility of the caller to rewrite and substitute the nodes with
-- N_Raise_Constraint_Error nodes.
-- For the non-static case a single N_Raise_Constraint_Error node with a
-- non-empty Condition field is returned.
-- Unused entries in Check_Result, if any, are simply set to Empty For
-- external clients, the required processing on this result is achieved
-- using the Insert_Range_Checks routine.
pragma Inline (Apply_Length_Check);
pragma Inline (Apply_Range_Check);
pragma Inline (Apply_Static_Length_Check);
end Checks;