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-------------------------------------------------------------------------------
--- --
--- GNAT COMPILER COMPONENTS --
--- --
--- C H E C K S --
--- --
--- S p e c --
--- --
--- Copyright (C) 1992-2008, Free Software Foundation, Inc. --
--- --
--- GNAT is free software; you can redistribute it and/or modify it under --
--- terms of the GNU General Public License as published by the Free Soft- --
--- ware Foundation; either version 3, or (at your option) any later ver- --
--- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
--- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
--- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
--- for more details. You should have received a copy of the GNU General --
--- Public License distributed with GNAT; see file COPYING3. If not, go to --
--- http://www.gnu.org/licenses for a complete copy of the license. --
--- --
--- GNAT was originally developed by the GNAT team at New York University. --
--- Extensive contributions were provided by Ada Core Technologies Inc. --
--- --
-------------------------------------------------------------------------------
-
--- 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 Namet; use Namet;
-with Table;
-with Types; use Types;
-with Uintp; use Uintp;
-
-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 Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean;
- function Division_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 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.
-
- -------------------------------------------
- -- 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.
-
- 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 inserted before node N. check is also made for the case of
- -- a clear overlay situation that the size of the overlaying object is not
- -- larger than the overlaid object.
-
- procedure Apply_Arithmetic_Overflow_Check (N : Node_Id);
- -- Given a binary arithmetic operator (+ - *) expand a software integer
- -- overflow check using range checks on a larger checking type or a call
- -- to an appropriate runtime routine. This is used for all three operators
- -- for the signed integer case, and for +/- in the fixed-point case. The
- -- check is expanded only if Software_Overflow_Checking is enabled and
- -- Do_Overflow_Check is set on node N. Note that divide is handled
- -- separately using Apply_Arithmetic_Divide_Overflow_Check.
-
- 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 verifies 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 peformed only if the corresponding actual is
- -- constrained, i.e., whether Lhs'Constrained is True.
-
- 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).
-
- procedure Apply_Divide_Check (N : Node_Id);
- -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem. An appropriate
- -- check is generated to ensure that the right operand is non-zero. In
- -- the divide case, we also check that we do not have the annoying case
- -- of the largest negative number divided by minus one.
-
- 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.
-
- procedure Determine_Range
- (N : Node_Id;
- OK : out Boolean;
- Lo : out Uint;
- Hi : out Uint);
- -- 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 type
- -- fields), 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 like 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.
-
- 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.
-
- -------------------------------------------------------
- -- 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 all 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.
-
- -- 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
- -- Set 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 in gigi 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 difficutlies 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 on the relation of this routine to the Do_Range_Check flag. Mostly
- -- for historical reasons, we often set the Do_Range_Check flag and then
- -- later we call Generate_Range_Check if this flag is set. Most probably we
- -- could eliminate this intermediate setting of the flag (historically the
- -- back end dealt with range checks, using this flag to indicate if a check
- -- was required, then we moved checks into the front end).
-
- 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);
- -- 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.
-
- 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);
- -- 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.
-
- procedure Null_Exclusion_Static_Checks (N : Node_Id);
- -- Ada 2005 (AI-231): Check bad usages of the null-exclusion issue
-
- 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);
- -- If N is an N_Range node, then Ensure_Valid is called on its bounds,
- -- if validity checking of operands is enabled.
-
- -----------------------------
- -- 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 descendents 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;