999 lines
52 KiB
Ada
999 lines
52 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT COMPILER COMPONENTS --
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-- --
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-- C H E C K S --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 1992-2020, Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING3. If not, go to --
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-- http://www.gnu.org/licenses for a complete copy of the license. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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-- Package containing routines used to deal with run-time checks. These
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-- routines are used both by the semantics and by the expander. In some
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-- cases, checks are enabled simply by setting a flag for the back end,
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-- and in other cases the code for the check is expanded.
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-- The approach used for range and length checks, in regards to suppressed
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-- checks, is to attempt to detect at compilation time that a constraint
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-- error will occur. If this is detected a warning or error is issued and the
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-- offending expression or statement replaced with a constraint error node.
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-- This always occurs whether checks are suppressed or not. Dynamic range
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-- checks are, of course, not inserted if checks are suppressed.
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with Errout; use Errout;
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with Namet; use Namet;
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with Table;
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with Types; use Types;
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with Uintp; use Uintp;
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with Urealp; use Urealp;
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package Checks is
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procedure Initialize;
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-- Called for each new main source program, to initialize internal
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-- variables used in the package body of the Checks unit.
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function Access_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Accessibility_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Alignment_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Allocation_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Atomic_Synchronization_Disabled (E : Entity_Id) return Boolean;
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function Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Division_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Duplicated_Tag_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Elaboration_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Index_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Length_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Overflow_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Predicate_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Range_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Storage_Checks_Suppressed (E : Entity_Id) return Boolean;
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function Tag_Checks_Suppressed (E : Entity_Id) return Boolean;
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-- These functions check to see if the named check is suppressed, either
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-- by an active scope suppress setting, or because the check has been
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-- specifically suppressed for the given entity. If no entity is relevant
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-- for the current check, then Empty is used as an argument. Note: the
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-- reason we insist on specifying Empty is to force the caller to think
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-- about whether there is any relevant entity that should be checked.
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function Is_Check_Suppressed (E : Entity_Id; C : Check_Id) return Boolean;
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-- This function is called if Checks_May_Be_Suppressed (E) is True to
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-- determine whether check C is suppressed either on the entity E or
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-- as the result of a scope suppress pragma. If Checks_May_Be_Suppressed
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-- is False, then the status of the check can be determined simply by
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-- examining Scope_Suppress, so this routine is not called in that case.
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function Overflow_Check_Mode return Overflow_Mode_Type;
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-- Returns current overflow checking mode, taking into account whether
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-- we are inside an assertion expression and the assertion policy.
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-----------------------------------------
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-- Control of Alignment Check Warnings --
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-----------------------------------------
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-- When we have address clauses, there is an issue of whether the address
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-- specified is appropriate to the alignment. In the general case where the
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-- address is dynamic, we generate a check and a possible warning (this
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-- warning occurs for example if we have a restricted runtime with the
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-- restriction No_Exception_Propagation). We also issue this warning in
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-- the case where the address is static, but we don't know the alignment
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-- at the time we process the address clause. In such a case, we issue the
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-- warning, but we may be able to find out later (after the back end has
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-- annotated the actual alignment chosen) that the warning was not needed.
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-- To deal with deleting these potentially annoying warnings, we save the
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-- warning information in a table, and then delete the warnings in the
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-- post compilation validation stage if we can tell that the check would
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-- never fail (in general the back end will also optimize away the check
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-- in such cases).
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-- Table used to record information
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type Alignment_Warnings_Record is record
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E : Entity_Id;
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-- Entity whose alignment possibly warrants a warning
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A : Uint;
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-- Compile time known value of address clause for which the alignment
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-- is to be checked once we know the alignment.
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P : Node_Id;
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-- Prefix of address clause when it is of the form X'Address
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W : Error_Msg_Id;
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-- Id of warning message we might delete
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end record;
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package Alignment_Warnings is new Table.Table (
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Table_Component_Type => Alignment_Warnings_Record,
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Table_Index_Type => Int,
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Table_Low_Bound => 0,
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Table_Initial => 10,
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Table_Increment => 200,
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Table_Name => "Alignment_Warnings");
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procedure Validate_Alignment_Check_Warnings;
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-- This routine is called after back annotation of type data to delete any
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-- alignment warnings that turn out to be false alarms, based on knowing
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-- the actual alignment, and a compile-time known alignment value.
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-------------------------------------------
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-- Procedures to Activate Checking Flags --
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-------------------------------------------
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procedure Activate_Division_Check (N : Node_Id);
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pragma Inline (Activate_Division_Check);
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-- Sets Do_Division_Check flag in node N, and handles possible local raise.
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-- Always call this routine rather than calling Set_Do_Division_Check to
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-- set an explicit value of True, to ensure handling the local raise case.
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procedure Activate_Overflow_Check (N : Node_Id);
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pragma Inline (Activate_Overflow_Check);
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-- Sets Do_Overflow_Check flag in node N, and handles possible local raise.
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-- Always call this routine rather than calling Set_Do_Overflow_Check to
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-- set an explicit value of True, to ensure handling the local raise case.
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-- Note that for discrete types, this call has no effect for MOD, REM, and
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-- unary "+" for which overflow is never possible in any case.
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--
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-- Note: for the discrete-type case, it is legitimate to call this routine
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-- on an unanalyzed node where the Etype field is not set. However, for the
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-- floating-point case, Etype must be set (to a floating-point type).
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--
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-- For floating-point, we set the flag if we have automatic overflow checks
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-- on the target, or if Check_Float_Overflow mode is set. For the floating-
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-- point case, we ignore all the unary operators ("+", "-", and abs) since
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-- none of these can result in overflow. If there are no overflow checks on
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-- the target, and Check_Float_Overflow mode is not set, then the call has
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-- no effect, since in such cases we want to generate NaN's and infinities.
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procedure Activate_Range_Check (N : Node_Id);
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pragma Inline (Activate_Range_Check);
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-- Sets Do_Range_Check flag in node N, and handles possible local raise.
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-- Always call this routine rather than calling Set_Do_Range_Check to
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-- set an explicit value of True, to ensure handling the local raise case.
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--------------------------------
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-- Procedures to Apply Checks --
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--------------------------------
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-- General note on following checks. These checks are always active if
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-- Expander_Active and not Inside_A_Generic. They are inactive and have
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-- no effect Inside_A_Generic. In the case where not Expander_Active
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-- and not Inside_A_Generic, most of them are inactive, but some of them
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-- operate anyway since they may generate useful compile time warnings.
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procedure Apply_Access_Check (N : Node_Id);
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-- Determines whether an expression node requires a run-time access
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-- check and if so inserts the appropriate run-time check.
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procedure Apply_Accessibility_Check
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(N : Node_Id;
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Typ : Entity_Id;
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Insert_Node : Node_Id);
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-- Given a name N denoting an access parameter, emits a run-time
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-- accessibility check (if necessary), checking that the level of
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-- the object denoted by the access parameter is not deeper than the
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-- level of the type Typ. Program_Error is raised if the check fails.
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-- Insert_Node indicates the node where the check should be inserted.
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procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id);
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-- E is the entity for an object which has an address clause. If checks
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-- are enabled, then this procedure generates a check that the specified
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-- address has an alignment consistent with the alignment of the object,
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-- raising PE if this is not the case. The resulting check (if one is
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-- generated) is prepended to the Actions list of N_Freeze_Entity node N.
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-- Note that the check references E'Alignment, so it cannot be emitted
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-- before N (its freeze node), otherwise this would cause an illegal
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-- access before elaboration error in gigi. For the case of a clear overlay
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-- situation, we also check that the size of the overlaying object is not
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-- larger than the overlaid object.
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procedure Apply_Arithmetic_Overflow_Check (N : Node_Id);
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-- Handle overflow checking for an arithmetic operator. Also handles the
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-- cases of ELIMINATED and MINIMIZED overflow checking mode. If the mode
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-- is one of the latter two, then this routine can also be called with
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-- an if or case expression node to make sure that we properly handle
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-- overflow checking for dependent expressions. This routine handles
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-- front end vs back end overflow checks (in the front end case it expands
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-- the necessary check). Note that divide is handled separately using
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-- Apply_Divide_Checks. Node N may or may not have Do_Overflow_Check.
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-- In STRICT mode, there is nothing to do if this flag is off, but in
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-- MINIMIZED/ELIMINATED mode we still have to deal with possible use
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-- of doing operations in Long_Long_Integer or Bignum mode.
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procedure Apply_Constraint_Check
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(N : Node_Id;
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Typ : Entity_Id;
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No_Sliding : Boolean := False);
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-- Top-level procedure, calls all the others depending on the class of
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-- Typ. Checks that expression N satisfies the constraint of type Typ.
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-- No_Sliding is only relevant for constrained array types, if set to
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-- True, it checks that indexes are in range.
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procedure Apply_Discriminant_Check
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(N : Node_Id;
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Typ : Entity_Id;
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Lhs : Node_Id := Empty);
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-- Given an expression N of a discriminated type, or of an access type
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-- whose designated type is a discriminanted type, generates a check to
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-- ensure that the expression can be converted to the subtype given as
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-- the second parameter. Lhs is empty except in the case of assignments,
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-- where the target object may be needed to determine the subtype to
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-- check against (such as the cases of unconstrained formal parameters
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-- and unconstrained aliased objects). For the case of unconstrained
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-- formals, the check is performed only if the corresponding actual is
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-- constrained, i.e., whether Lhs'Constrained is True.
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procedure Apply_Divide_Checks (N : Node_Id);
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-- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem if either of the
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-- flags Do_Division_Check or Do_Overflow_Check is set, then this routine
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-- ensures that the appropriate checks are made. Note that overflow can
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-- occur in the signed case for the case of the largest negative number
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-- divided by minus one. This procedure only applies to Integer types.
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procedure Apply_Parameter_Aliasing_Checks
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(Call : Node_Id;
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Subp : Entity_Id);
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-- Given a subprogram call Call, add a check to verify that none of the
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-- actuals overlap. Subp denotes the subprogram being called.
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procedure Apply_Parameter_Validity_Checks (Subp : Entity_Id);
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-- Given a subprogram Subp, add both a pre and post condition pragmas that
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-- verify the proper initialization of scalars in parameters and function
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-- results.
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procedure Apply_Predicate_Check
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(N : Node_Id;
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Typ : Entity_Id;
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Fun : Entity_Id := Empty);
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-- N is an expression to which a predicate check may need to be applied for
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-- Typ, if Typ has a predicate function. When N is an actual in a call, Fun
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-- is the function being called, which is used to generate a better warning
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-- if the call leads to an infinite recursion.
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procedure Apply_Type_Conversion_Checks (N : Node_Id);
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-- N is an N_Type_Conversion node. A type conversion actually involves
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-- two sorts of checks. The first check is the checks that ensures that
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-- the operand in the type conversion fits onto the base type of the
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-- subtype it is being converted to (see RM 4.6 (28)-(50)). The second
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-- check is there to ensure that once the operand has been converted to
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-- a value of the target type, this converted value meets the
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-- constraints imposed by the target subtype (see RM 4.6 (51)).
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procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id);
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-- The argument N is an attribute reference node intended for processing
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-- by gigi. The attribute is one that returns a universal integer, but
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-- the attribute reference node is currently typed with the expected
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-- result type. This routine deals with range and overflow checks needed
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-- to make sure that the universal result is in range.
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function Build_Discriminant_Checks
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(N : Node_Id;
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T_Typ : Entity_Id)
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return Node_Id;
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-- Subsidiary routine for Apply_Discriminant_Check. Builds the expression
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-- that compares discriminants of the expression with discriminants of the
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-- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In).
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function Convert_From_Bignum (N : Node_Id) return Node_Id;
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-- Returns result of converting node N from Bignum. The returned value is
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-- not analyzed, the caller takes responsibility for this. Node N must be
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-- a subexpression node of type Bignum. The result is Long_Long_Integer.
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function Convert_To_Bignum (N : Node_Id) return Node_Id;
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-- Returns result of converting node N to Bignum. The returned value is not
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-- analyzed, the caller takes responsibility for this. Node N must be a
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-- subexpression node of a signed integer type or Bignum type (if it is
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-- already a Bignum, the returned value is Relocate_Node (N)).
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procedure Determine_Range
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(N : Node_Id;
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OK : out Boolean;
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Lo : out Uint;
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Hi : out Uint;
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Assume_Valid : Boolean := False);
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-- N is a node for a subexpression. If N is of a discrete type with no
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-- error indications, and no other peculiarities (e.g. missing Etype),
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-- then OK is True on return, and Lo and Hi are set to a conservative
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-- estimate of the possible range of values of N. Thus if OK is True on
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-- return, the value of the subexpression N is known to lie in the range
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-- Lo .. Hi (inclusive). For enumeration and character literals the values
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-- returned are the Pos value in the relevant enumeration type. If the
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-- expression is not of a discrete type, or some kind of error condition
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-- is detected, then OK is False on exit, and Lo/Hi are set to No_Uint.
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-- Thus the significance of OK being False on return is that no useful
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-- information is available on the range of the expression. Assume_Valid
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-- determines whether the processing is allowed to assume that values are
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-- in range of their subtypes. If it is set to True, then this assumption
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-- is valid, if False, then processing is done using base types to allow
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-- invalid values.
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procedure Determine_Range_R
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(N : Node_Id;
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OK : out Boolean;
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Lo : out Ureal;
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Hi : out Ureal;
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Assume_Valid : Boolean := False);
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-- Similar to Determine_Range, but for a node N of floating-point type. OK
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-- is True on return only for IEEE floating-point types and only if we do
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-- not have to worry about extended precision (i.e. on the x86, we must be
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-- using -msse2 -mfpmath=sse). At the current time, this is used only in
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-- GNATprove, though we could consider using it more generally in future.
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-- For that to happen, the possibility of arguments of infinite or NaN
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-- value should be taken into account, which is not the case currently.
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procedure Determine_Range_To_Discrete
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(N : Node_Id;
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OK : out Boolean;
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Lo : out Uint;
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Hi : out Uint;
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Fixed_Int : Boolean := False;
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Assume_Valid : Boolean := False);
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-- Similar to Determine_Range, but attempts to return a discrete range even
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-- if N is not of a discrete type by doing a conversion. The Fixed_Int flag
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-- if set causes any fixed-point values to be treated as though they were
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-- discrete values (i.e. the underlying integer value is used), in which
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-- case no conversion is needed. At the current time, this is used only for
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-- discrete types, for fixed-point types if Fixed_Int is set, and also for
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-- floating-point types in GNATprove, see Determine_Range_R above.
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procedure Install_Null_Excluding_Check (N : Node_Id);
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-- Determines whether an access node requires a run-time access check and
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-- if so inserts the appropriate run-time check.
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procedure Install_Primitive_Elaboration_Check (Subp_Body : Node_Id);
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-- Insert a check which ensures that subprogram body Subp_Body has been
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-- properly elaborated. The check is installed only when Subp_Body is the
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-- body of a nonabstract library-level primitive of a tagged type. Further
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-- restrictions may apply, see the body for details.
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function Make_Bignum_Block (Loc : Source_Ptr) return Node_Id;
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-- This function is used by top level overflow checking routines to do a
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-- mark/release operation on the secondary stack around bignum operations.
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-- The block created looks like:
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--
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-- declare
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-- M : Mark_Id := SS_Mark;
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-- begin
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-- SS_Release (M);
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-- end;
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--
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-- The idea is that the caller will insert any needed extra declarations
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-- after the declaration of M, and any needed statements (in particular
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-- the bignum operations) before the call to SS_Release, and then do an
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-- Insert_Action of the whole block (it is returned unanalyzed). The Loc
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-- parameter is used to supply Sloc values for the constructed tree.
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procedure Minimize_Eliminate_Overflows
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(N : Node_Id;
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Lo : out Uint;
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Hi : out Uint;
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Top_Level : Boolean);
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-- This is the main routine for handling MINIMIZED and ELIMINATED overflow
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-- processing. On entry N is a node whose result is a signed integer
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-- subtype. The Do_Overflow_Check flag may or may not be set on N. If the
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-- node is an arithmetic operation, then a range analysis is carried out,
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-- and there are three possibilities:
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--
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-- The node is left unchanged (apart from expansion of an exponentiation
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-- operation). This happens if the routine can determine that the result
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-- is definitely in range. The Do_Overflow_Check flag is turned off in
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-- this case.
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--
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-- The node is transformed into an arithmetic operation with a result
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-- type of Long_Long_Integer.
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--
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-- The node is transformed into a function call that calls an appropriate
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-- function in the System.Bignums package to compute a Bignum result.
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--
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-- In the first two cases, Lo and Hi are set to the bounds of the possible
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-- range of results, computed as accurately as possible. In the third case
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-- Lo and Hi are set to No_Uint (there are some cases where we could get an
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-- advantage from keeping result ranges for Bignum values, but it could use
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-- a lot of space and is very unlikely to be valuable).
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--
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-- If the node is not an arithmetic operation, then it is unchanged but
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-- Lo and Hi are still set (to the bounds of the result subtype if nothing
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-- better can be determined).
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--
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-- Note: this function is recursive, if called with an arithmetic operator,
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-- recursive calls are made to process the operands using this procedure.
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-- So we end up doing things top down. Nothing happens to an arithmetic
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-- expression until this procedure is called on the top level node and
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-- then the recursive calls process all the children. We have to do it
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-- this way. If we try to do it bottom up in natural expansion order, then
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-- there are two problems. First, where do we stash the bounds, and more
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-- importantly, semantic processing will be messed up. Consider A+B+C where
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-- A,B,C are all of type integer, if we processed A+B before doing semantic
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-- analysis of the addition of this result to C, that addition could end up
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-- with a Long_Long_Integer left operand and an Integer right operand, and
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-- we would get a semantic error.
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|
--
|
|
-- The routine is called in three situations if we are operating in either
|
|
-- MINIMIZED or ELIMINATED modes.
|
|
--
|
|
-- 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 the corresponding range checks, but later on we
|
|
-- decided to generate all the range checks in the front end and this is
|
|
-- the current situation.
|
|
|
|
-- 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.
|
|
|
|
-- 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
|
|
(Expr : 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_Length_Check_On_Assignment
|
|
(Expr : Node_Id;
|
|
Target_Typ : Entity_Id;
|
|
Target : Node_Id;
|
|
Source_Typ : Entity_Id := Empty);
|
|
-- Similar to Apply_Length_Check, but takes the target of an assignment for
|
|
-- which the check is to be done. Used to filter out specific cases where
|
|
-- the check is superfluous.
|
|
|
|
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_Range_Check
|
|
(Expr : Node_Id;
|
|
Target_Typ : Entity_Id;
|
|
Source_Typ : Entity_Id := Empty;
|
|
Insert_Node : Node_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.
|
|
|
|
-- Insert_Node indicates the node where the check should be inserted.
|
|
-- If it is empty, then the check is inserted directly at Expr instead.
|
|
|
|
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 run-time 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
|
|
(Expr : 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);
|
|
-- 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).
|
|
-- Suppress_Typ is the type to check to determine if checks are suppressed.
|
|
-- Static_Sloc is the Sloc at which the raise CE node points.
|
|
|
|
procedure Insert_Range_Checks
|
|
(Checks : Check_Result;
|
|
Node : Node_Id;
|
|
Suppress_Typ : Entity_Id;
|
|
Static_Sloc : Source_Ptr;
|
|
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 is the Sloc at which the raise CE node points. Normally the
|
|
-- checks are inserted after Node; if Do_Before is True, they are before.
|
|
|
|
-----------------------
|
|
-- Expander Routines --
|
|
-----------------------
|
|
|
|
-- In most cases, the processing for range checks done by semantic analysis
|
|
-- only results in setting the Do_Range_Check flag, rather than actually
|
|
-- generating checks. The following routines must be called later on in the
|
|
-- expansion process upon seeing the Do_Range_Check flag; they generate the
|
|
-- actual checks and reset the flag. The remaining cases where range checks
|
|
-- are still directly generated during semantic analysis occur as part of
|
|
-- the processing of constraints in (sub)type and object declarations.
|
|
|
|
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 checks. 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 checks, then we make sure the flag is off
|
|
-- afterward, since the code we generate takes complete care of the checks.
|
|
--
|
|
-- 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.
|
|
|
|
private
|
|
|
|
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;
|