| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT COMPILER COMPONENTS -- |
| -- -- |
| -- C H E C K S -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- Copyright (C) 1992-2022, 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 run-time checks. These |
| -- routines are used both by the semantics and by the expander. In some |
| -- cases, checks are enabled simply by setting a flag for the back end, |
| -- and in other cases the code for the check is expanded. |
| |
| -- The approach used for range and length checks, in regards to suppressed |
| -- checks, is to attempt to detect at compilation time that a constraint |
| -- error will occur. If this is detected a warning or error is issued and the |
| -- offending expression or statement replaced with a constraint error node. |
| -- This always occurs whether checks are suppressed or not. Dynamic range |
| -- checks are, of course, not inserted if checks are suppressed. |
| |
| with Errout; use Errout; |
| with Namet; use Namet; |
| with Table; |
| with Types; use Types; |
| with Uintp; use Uintp; |
| with Urealp; use Urealp; |
| |
| package Checks is |
| |
| type Bit_Vector is array (Pos range <>) of Boolean; |
| type Dimension_Set (Dimensions : Nat) is |
| record |
| Elements : Bit_Vector (1 .. Dimensions); |
| end record; |
| Empty_Dimension_Set : constant Dimension_Set |
| := (Dimensions => 0, Elements => (others => <>)); |
| |
| procedure Initialize; |
| -- Called for each new main source program, to initialize internal |
| -- variables used in the package body of the Checks unit. |
| |
| function Access_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Accessibility_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Alignment_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Allocation_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Atomic_Synchronization_Disabled (E : Entity_Id) return Boolean; |
| function Discriminant_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Division_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Duplicated_Tag_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Elaboration_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Index_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Length_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Overflow_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Predicate_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Range_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Storage_Checks_Suppressed (E : Entity_Id) return Boolean; |
| function Tag_Checks_Suppressed (E : Entity_Id) return Boolean; |
| -- These functions check to see if the named check is suppressed, either |
| -- by an active scope suppress setting, or because the check has been |
| -- specifically suppressed for the given entity. If no entity is relevant |
| -- for the current check, then Empty is used as an argument. Note: the |
| -- reason we insist on specifying Empty is to force the caller to think |
| -- about whether there is any relevant entity that should be checked. |
| |
| function Is_Check_Suppressed (E : Entity_Id; C : Check_Id) return Boolean; |
| -- This function is called if Checks_May_Be_Suppressed (E) is True to |
| -- determine whether check C is suppressed either on the entity E or |
| -- as the result of a scope suppress pragma. If Checks_May_Be_Suppressed |
| -- is False, then the status of the check can be determined simply by |
| -- examining Scope_Suppress, so this routine is not called in that case. |
| |
| function Overflow_Check_Mode return Overflow_Mode_Type; |
| -- Returns current overflow checking mode, taking into account whether |
| -- we are inside an assertion expression and the assertion policy. |
| |
| ----------------------------------------- |
| -- Control of Alignment Check Warnings -- |
| ----------------------------------------- |
| |
| -- When we have address clauses, there is an issue of whether the address |
| -- specified is appropriate to the alignment. In the general case where the |
| -- address is dynamic, we generate a check and a possible warning (this |
| -- warning occurs for example if we have a restricted runtime with the |
| -- restriction No_Exception_Propagation). We also issue this warning in |
| -- the case where the address is static, but we don't know the alignment |
| -- at the time we process the address clause. In such a case, we issue the |
| -- warning, but we may be able to find out later (after the back end has |
| -- annotated the actual alignment chosen) that the warning was not needed. |
| |
| -- To deal with deleting these potentially annoying warnings, we save the |
| -- warning information in a table, and then delete the warnings in the |
| -- post compilation validation stage if we can tell that the check would |
| -- never fail (in general the back end will also optimize away the check |
| -- in such cases). |
| |
| -- Table used to record information |
| |
| type Alignment_Warnings_Record is record |
| E : Entity_Id; |
| -- Entity whose alignment possibly warrants a warning |
| |
| A : Uint; |
| -- Compile time known value of address clause for which the alignment |
| -- is to be checked once we know the alignment. |
| |
| P : Node_Id; |
| -- Prefix of address clause when it is of the form X'Address |
| |
| W : Error_Msg_Id; |
| -- Id of warning message we might delete |
| end record; |
| |
| package Alignment_Warnings is new Table.Table ( |
| Table_Component_Type => Alignment_Warnings_Record, |
| Table_Index_Type => Int, |
| Table_Low_Bound => 0, |
| Table_Initial => 10, |
| Table_Increment => 200, |
| Table_Name => "Alignment_Warnings"); |
| |
| procedure Validate_Alignment_Check_Warnings; |
| -- This routine is called after back annotation of type data to delete any |
| -- alignment warnings that turn out to be false alarms, based on knowing |
| -- the actual alignment, and a compile-time known alignment value. |
| |
| ------------------------------------------- |
| -- Procedures to Activate Checking Flags -- |
| ------------------------------------------- |
| |
| procedure Activate_Division_Check (N : Node_Id); |
| pragma Inline (Activate_Division_Check); |
| -- Sets Do_Division_Check flag in node N, and handles possible local raise. |
| -- Always call this routine rather than calling Set_Do_Division_Check to |
| -- set an explicit value of True, to ensure handling the local raise case. |
| |
| procedure Activate_Overflow_Check (N : Node_Id); |
| pragma Inline (Activate_Overflow_Check); |
| -- Sets Do_Overflow_Check flag in node N, and handles possible local raise. |
| -- Always call this routine rather than calling Set_Do_Overflow_Check to |
| -- set an explicit value of True, to ensure handling the local raise case. |
| -- Note that for discrete types, this call has no effect for MOD, REM, and |
| -- unary "+" for which overflow is never possible in any case. |
| -- |
| -- Note: for the discrete-type case, it is legitimate to call this routine |
| -- on an unanalyzed node where the Etype field is not set. However, for the |
| -- floating-point case, Etype must be set (to a floating-point type). |
| -- |
| -- For floating-point, we set the flag if we have automatic overflow checks |
| -- on the target, or if Check_Float_Overflow mode is set. For the floating- |
| -- point case, we ignore all the unary operators ("+", "-", and abs) since |
| -- none of these can result in overflow. If there are no overflow checks on |
| -- the target, and Check_Float_Overflow mode is not set, then the call has |
| -- no effect, since in such cases we want to generate NaN's and infinities. |
| |
| procedure Activate_Range_Check (N : Node_Id); |
| pragma Inline (Activate_Range_Check); |
| -- Sets Do_Range_Check flag in node N, and handles possible local raise. |
| -- Always call this routine rather than calling Set_Do_Range_Check to |
| -- set an explicit value of True, to ensure handling the local raise case. |
| |
| -------------------------------- |
| -- Procedures to Apply Checks -- |
| -------------------------------- |
| |
| -- General note on following checks. These checks are always active if |
| -- Expander_Active and not Inside_A_Generic. They are inactive and have |
| -- no effect Inside_A_Generic. In the case where not Expander_Active |
| -- and not Inside_A_Generic, most of them are inactive, but some of them |
| -- operate anyway since they may generate useful compile time warnings. |
| |
| procedure Apply_Access_Check (N : Node_Id); |
| -- Determines whether an expression node requires a run-time access |
| -- check and if so inserts the appropriate run-time check. |
| |
| procedure Apply_Accessibility_Check |
| (N : Node_Id; |
| Typ : Entity_Id; |
| Insert_Node : Node_Id); |
| -- Given a name N denoting an access parameter, emits a run-time |
| -- accessibility check (if necessary), checking that the level of |
| -- the object denoted by the access parameter is not deeper than the |
| -- level of the type Typ. Program_Error is raised if the check fails. |
| -- Insert_Node indicates the node where the check should be inserted. |
| |
| procedure Apply_Address_Clause_Check (E : Entity_Id; N : Node_Id); |
| -- E is the entity for an object which has an address clause. If checks |
| -- are enabled, then this procedure generates a check that the specified |
| -- address has an alignment consistent with the alignment of the object, |
| -- raising PE if this is not the case. The resulting check (if one is |
| -- generated) is prepended to the Actions list of N_Freeze_Entity node N. |
| -- Note that the check references E'Alignment, so it cannot be emitted |
| -- before N (its freeze node), otherwise this would cause an illegal |
| -- access before elaboration error in gigi. For the case of a clear overlay |
| -- situation, we also check that the size of the overlaying object is not |
| -- larger than the overlaid object. |
| |
| procedure Apply_Arithmetic_Overflow_Check (N : Node_Id); |
| -- Handle overflow checking for an arithmetic operator. Also handles the |
| -- cases of ELIMINATED and MINIMIZED overflow checking mode. If the mode |
| -- is one of the latter two, then this routine can also be called with |
| -- an if or case expression node to make sure that we properly handle |
| -- overflow checking for dependent expressions. This routine handles |
| -- front end vs back end overflow checks (in the front end case it expands |
| -- the necessary check). Note that divide is handled separately using |
| -- Apply_Divide_Checks. Node N may or may not have Do_Overflow_Check. |
| -- In STRICT mode, there is nothing to do if this flag is off, but in |
| -- MINIMIZED/ELIMINATED mode we still have to deal with possible use |
| -- of doing operations in Long_Long_Integer or Bignum mode. |
| |
| procedure Apply_Constraint_Check |
| (N : Node_Id; |
| Typ : Entity_Id; |
| No_Sliding : Boolean := False); |
| -- Top-level procedure, calls all the others depending on the class of |
| -- Typ. Checks that expression N satisfies the constraint of type Typ. |
| -- No_Sliding is only relevant for constrained array types, if set to |
| -- True, it checks that indexes are in range. |
| |
| procedure Apply_Discriminant_Check |
| (N : Node_Id; |
| Typ : Entity_Id; |
| Lhs : Node_Id := Empty); |
| -- Given an expression N of a discriminated type, or of an access type |
| -- whose designated type is a discriminanted type, generates a check to |
| -- ensure that the expression can be converted to the subtype given as |
| -- the second parameter. Lhs is empty except in the case of assignments, |
| -- where the target object may be needed to determine the subtype to |
| -- check against (such as the cases of unconstrained formal parameters |
| -- and unconstrained aliased objects). For the case of unconstrained |
| -- formals, the check is performed only if the corresponding actual is |
| -- constrained, i.e., whether Lhs'Constrained is True. |
| |
| procedure Apply_Divide_Checks (N : Node_Id); |
| -- The node kind is N_Op_Divide, N_Op_Mod, or N_Op_Rem if either of the |
| -- flags Do_Division_Check or Do_Overflow_Check is set, then this routine |
| -- ensures that the appropriate checks are made. Note that overflow can |
| -- occur in the signed case for the case of the largest negative number |
| -- divided by minus one. This procedure only applies to Integer types. |
| |
| procedure Apply_Parameter_Aliasing_Checks |
| (Call : Node_Id; |
| Subp : Entity_Id); |
| -- Given a subprogram call Call, add a check to verify that none of the |
| -- actuals overlap. Subp denotes the subprogram being called. |
| |
| procedure Apply_Parameter_Validity_Checks (Subp : Entity_Id); |
| -- Given a subprogram Subp, add both a pre and post condition pragmas that |
| -- verify the proper initialization of scalars in parameters and function |
| -- results. |
| |
| procedure Apply_Predicate_Check |
| (N : Node_Id; |
| Typ : Entity_Id; |
| Fun : Entity_Id := Empty); |
| -- N is an expression to which a predicate check may need to be applied for |
| -- Typ, if Typ has a predicate function. When N is an actual in a call, Fun |
| -- is the function being called, which is used to generate a better warning |
| -- if the call leads to an infinite recursion. |
| |
| procedure Apply_Type_Conversion_Checks (N : Node_Id); |
| -- N is an N_Type_Conversion node. A type conversion actually involves |
| -- two sorts of checks. The first check is the checks that ensures that |
| -- the operand in the type conversion fits onto the base type of the |
| -- subtype it is being converted to (see RM 4.6 (28)-(50)). The second |
| -- check is there to ensure that once the operand has been converted to |
| -- a value of the target type, this converted value meets the |
| -- constraints imposed by the target subtype (see RM 4.6 (51)). |
| |
| procedure Apply_Universal_Integer_Attribute_Checks (N : Node_Id); |
| -- The argument N is an attribute reference node intended for processing |
| -- by gigi. The attribute is one that returns a universal integer, but |
| -- the attribute reference node is currently typed with the expected |
| -- result type. This routine deals with range and overflow checks needed |
| -- to make sure that the universal result is in range. |
| |
| function Build_Discriminant_Checks |
| (N : Node_Id; |
| T_Typ : Entity_Id) |
| return Node_Id; |
| -- Subsidiary routine for Apply_Discriminant_Check. Builds the expression |
| -- that compares discriminants of the expression with discriminants of the |
| -- type. Also used directly for membership tests (see Exp_Ch4.Expand_N_In). |
| |
| function Convert_From_Bignum (N : Node_Id) return Node_Id; |
| -- Returns result of converting node N from Bignum. The returned value is |
| -- not analyzed, the caller takes responsibility for this. Node N must be |
| -- a subexpression node of type Bignum. The result is Long_Long_Integer. |
| |
| function Convert_To_Bignum (N : Node_Id) return Node_Id; |
| -- Returns result of converting node N to Bignum. The returned value is not |
| -- analyzed, the caller takes responsibility for this. Node N must be a |
| -- subexpression node of a signed integer type or Bignum type (if it is |
| -- already a Bignum, the returned value is Relocate_Node (N)). |
| |
| procedure Determine_Range |
| (N : Node_Id; |
| OK : out Boolean; |
| Lo : out Uint; |
| Hi : out Uint; |
| Assume_Valid : Boolean := False); |
| -- N is a node for a subexpression. If N is of a discrete type with no |
| -- error indications, and no other peculiarities (e.g. missing Etype), |
| -- then OK is True on return, and Lo and Hi are set to a conservative |
| -- estimate of the possible range of values of N. Thus if OK is True on |
| -- return, the value of the subexpression N is known to lie in the range |
| -- Lo .. Hi (inclusive). For enumeration and character literals the values |
| -- returned are the Pos value in the relevant enumeration type. If the |
| -- expression is not of a discrete type, or some kind of error condition |
| -- is detected, then OK is False on exit, and Lo/Hi are set to No_Uint. |
| -- Thus the significance of OK being False on return is that no useful |
| -- information is available on the range of the expression. Assume_Valid |
| -- determines whether the processing is allowed to assume that values are |
| -- in range of their subtypes. If it is set to True, then this assumption |
| -- is valid, if False, then processing is done using base types to allow |
| -- invalid values. |
| |
| procedure Determine_Range_R |
| (N : Node_Id; |
| OK : out Boolean; |
| Lo : out Ureal; |
| Hi : out Ureal; |
| Assume_Valid : Boolean := False); |
| -- Similar to Determine_Range, but for a node N of floating-point type. OK |
| -- is True on return only for IEEE floating-point types and only if we do |
| -- not have to worry about extended precision (i.e. on the x86, we must be |
| -- using -msse2 -mfpmath=sse). At the current time, this is used only in |
| -- GNATprove, though we could consider using it more generally in future. |
| -- For that to happen, the possibility of arguments of infinite or NaN |
| -- value should be taken into account, which is not the case currently. |
| |
| procedure Determine_Range_To_Discrete |
| (N : Node_Id; |
| OK : out Boolean; |
| Lo : out Uint; |
| Hi : out Uint; |
| Fixed_Int : Boolean := False; |
| Assume_Valid : Boolean := False); |
| -- Similar to Determine_Range, but attempts to return a discrete range even |
| -- if N is not of a discrete type by doing a conversion. 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), in which |
| -- case no conversion is needed. At the current time, this is used only for |
| -- discrete types, for fixed-point types if Fixed_Int is set, and also for |
| -- floating-point types in GNATprove, see Determine_Range_R above. |
| |
| procedure Install_Null_Excluding_Check (N : Node_Id); |
| -- Determines whether an access node requires a run-time access check and |
| -- if so inserts the appropriate run-time check. |
| |
| procedure Install_Primitive_Elaboration_Check (Subp_Body : Node_Id); |
| -- Insert a check to ensure that subprogram body Subp_Body has been |
| -- properly elaborated. The check is installed only when Subp_Body is the |
| -- body of a nonabstract library-level primitive of a tagged type. Further |
| -- restrictions may apply, see the body for details. |
| |
| function Make_Bignum_Block (Loc : Source_Ptr) return Node_Id; |
| -- This function is used by top level overflow checking routines to do a |
| -- mark/release operation on the secondary stack around bignum operations. |
| -- The block created looks like: |
| -- |
| -- declare |
| -- M : Mark_Id := SS_Mark; |
| -- begin |
| -- SS_Release (M); |
| -- end; |
| -- |
| -- The idea is that the caller will insert any needed extra declarations |
| -- after the declaration of M, and any needed statements (in particular |
| -- the bignum operations) before the call to SS_Release, and then do an |
| -- Insert_Action of the whole block (it is returned unanalyzed). The Loc |
| -- parameter is used to supply Sloc values for the constructed tree. |
| |
| procedure Minimize_Eliminate_Overflows |
| (N : Node_Id; |
| Lo : out Uint; |
| Hi : out Uint; |
| Top_Level : Boolean); |
| -- This is the main routine for handling MINIMIZED and ELIMINATED overflow |
| -- processing. On entry N is a node whose result is a signed integer |
| -- subtype. The Do_Overflow_Check flag may or may not be set on N. If the |
| -- node is an arithmetic operation, then a range analysis is carried out, |
| -- and there are three possibilities: |
| -- |
| -- The node is left unchanged (apart from expansion of an exponentiation |
| -- operation). This happens if the routine can determine that the result |
| -- is definitely in range. The Do_Overflow_Check flag is turned off in |
| -- this case. |
| -- |
| -- The node is transformed into an arithmetic operation with a result |
| -- type of Long_Long_Integer. |
| -- |
| -- The node is transformed into a function call that calls an appropriate |
| -- function in the System.Bignums package to compute a Bignum result. |
| -- |
| -- In the first two cases, Lo and Hi are set to the bounds of the possible |
| -- range of results, computed as accurately as possible. In the third case |
| -- Lo and Hi are set to No_Uint (there are some cases where we could get an |
| -- advantage from keeping result ranges for Bignum values, but it could use |
| -- a lot of space and is very unlikely to be valuable). |
| -- |
| -- If the node is not an arithmetic operation, then it is unchanged but |
| -- Lo and Hi are still set (to the bounds of the result subtype if nothing |
| -- better can be determined). |
| -- |
| -- Note: this function is recursive, if called with an arithmetic operator, |
| -- recursive calls are made to process the operands using this procedure. |
| -- So we end up doing things top down. Nothing happens to an arithmetic |
| -- expression until this procedure is called on the top level node and |
| -- then the recursive calls process all the children. We have to do it |
| -- this way. If we try to do it bottom up in natural expansion order, then |
| -- there are two problems. First, where do we stash the bounds, and more |
| -- importantly, semantic processing will be messed up. Consider A+B+C where |
| -- A,B,C are all of type integer, if we processed A+B before doing semantic |
| -- analysis of the addition of this result to C, that addition could end up |
| -- with a Long_Long_Integer left operand and an Integer right operand, and |
| -- we would get a semantic error. |
| -- |
| -- The routine is called in three situations if we are operating in either |
| -- 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; |
| Checks_Generated : out Dimension_Set); |
| -- 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. |
| -- The out-mode parameter Checks_Generated indicates the dimensions for |
| -- which checks were generated. Checks_Generated.Dimensions must match |
| -- the number of dimensions of the array type. |
| |
| -- 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 known 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; |
| No_Check_Needed : Dimension_Set := Empty_Dimension_Set); |
| -- Expr is the node for an indexed component. If validity checking and |
| -- range checking are enabled, each subscript for this indexed component |
| -- whose dimension does not belong to the No_Check_Needed set is checked |
| -- for validity. No_Check_Needed.Dimensions must match the number of |
| -- dimensions of the array type or be zero. |
| |
| 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; |
