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From: Marc Poulhi?s <dkm@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-3734] ada: Deconstruct Safe_To_Capture_In_Parameter_Value Date: Mon, 7 Nov 2022 08:39:22 +0000 (GMT) [thread overview] Message-ID: <20221107083922.E2D4438582A2@sourceware.org> (raw) https://gcc.gnu.org/g:214b1cb8a829568c7ef675b7c3e6a2d8b9a96875 commit r13-3734-g214b1cb8a829568c7ef675b7c3e6a2d8b9a96875 Author: Piotr Trojanek <trojanek@adacore.com> Date: Tue May 19 21:07:07 2020 +0200 ada: Deconstruct Safe_To_Capture_In_Parameter_Value Recently routine Safe_To_Capture_Value was adapted, so that various data properties like validity/nullness/values are tracked also for in-parameters. Now a similar routine Safe_To_Capture_In_Parameter_Value, which was only used to track data nullness, is redundant, so this patch deconstructs it. Also the removed routine had at least few problems and limitations, for example: 1) it only worked for functions and procedures, but not for protected entries and task types (whose discriminants work very much like in-parameters) 2) it only worked for subprogram bodies with no spec, because of this dubious check (here simplified): if Nkind (Parent (Parent (Current_Scope))) /= N_Subprogram_Body then return False; 3) it only recognized references within short-circuit operators as certainly evaluated if they were directly their left hand expression, e.g.: X.all and then ... but not when they were certainly evaluated as part of a bigger expression on the left hand side, e.g.: (X.all > 0) and then ... 4) it categorizes parameters with 'Unrestricted_Access attribute as safe to capture, which is not necessarily wrong, but risky (because the object becomes aliased). Routine Safe_To_Capture_Value, which is kept by this patch, seems to behave better in all those situations, though it has its own problems as well and ideally should be further scrutinized. gcc/ada/ * checks.adb (Safe_To_Capture_In_Parameter_Value): Remove. * sem_util.adb (Safe_To_Capture_Value): Stop search at the current body. Diff: --- gcc/ada/checks.adb | 120 ++------------------------------------------------- gcc/ada/sem_util.adb | 5 ++- 2 files changed, 7 insertions(+), 118 deletions(-) diff --git a/gcc/ada/checks.adb b/gcc/ada/checks.adb index a91c1cd5568..96876672871 100644 --- a/gcc/ada/checks.adb +++ b/gcc/ada/checks.adb @@ -8408,115 +8408,10 @@ package body Checks is Loc : constant Source_Ptr := Sloc (Parent (N)); Typ : constant Entity_Id := Etype (N); - function Safe_To_Capture_In_Parameter_Value return Boolean; - -- Determines if it is safe to capture Known_Non_Null status for an - -- the entity referenced by node N. The caller ensures that N is indeed - -- an entity name. It is safe to capture the non-null status for an IN - -- parameter when the reference occurs within a declaration that is sure - -- to be executed as part of the declarative region. - procedure Mark_Non_Null; -- After installation of check, if the node in question is an entity -- name, then mark this entity as non-null if possible. - function Safe_To_Capture_In_Parameter_Value return Boolean is - E : constant Entity_Id := Entity (N); - S : constant Entity_Id := Current_Scope; - S_Par : Node_Id; - - begin - if Ekind (E) /= E_In_Parameter then - return False; - end if; - - -- Two initial context checks. We must be inside a subprogram body - -- with declarations and reference must not appear in nested scopes. - - if (Ekind (S) /= E_Function and then Ekind (S) /= E_Procedure) - or else Scope (E) /= S - then - return False; - end if; - - S_Par := Parent (Parent (S)); - - if Nkind (S_Par) /= N_Subprogram_Body - or else No (Declarations (S_Par)) - then - return False; - end if; - - declare - N_Decl : Node_Id; - P : Node_Id; - - begin - -- Retrieve the declaration node of N (if any). Note that N - -- may be a part of a complex initialization expression. - - P := Parent (N); - N_Decl := Empty; - while Present (P) loop - - -- If we have a short circuit form, and we are within the right - -- hand expression, we return false, since the right hand side - -- is not guaranteed to be elaborated. - - if Nkind (P) in N_Short_Circuit - and then N = Right_Opnd (P) - then - return False; - end if; - - -- Similarly, if we are in an if expression and not part of the - -- condition, then we return False, since neither the THEN or - -- ELSE dependent expressions will always be elaborated. - - if Nkind (P) = N_If_Expression - and then N /= First (Expressions (P)) - then - return False; - end if; - - -- If within a case expression, and not part of the expression, - -- then return False, since a particular dependent expression - -- may not always be elaborated - - if Nkind (P) = N_Case_Expression - and then N /= Expression (P) - then - return False; - end if; - - -- While traversing the parent chain, if node N belongs to a - -- statement, then it may never appear in a declarative region. - - if Nkind (P) in N_Statement_Other_Than_Procedure_Call - or else Nkind (P) = N_Procedure_Call_Statement - then - return False; - end if; - - -- If we are at a declaration, record it and exit - - if Nkind (P) in N_Declaration - and then Nkind (P) not in N_Subprogram_Specification - then - N_Decl := P; - exit; - end if; - - P := Parent (P); - end loop; - - if No (N_Decl) then - return False; - end if; - - return List_Containing (N_Decl) = Declarations (S_Par); - end; - end Safe_To_Capture_In_Parameter_Value; - ------------------- -- Mark_Non_Null -- ------------------- @@ -8532,19 +8427,10 @@ package body Checks is Set_Is_Known_Null (Entity (N), False); - -- We can mark the entity as known to be non-null if either it is - -- safe to capture the value, or in the case of an IN parameter, - -- which is a constant, if the check we just installed is in the - -- declarative region of the subprogram body. In this latter case, - -- a check is decisive for the rest of the body if the expression - -- is sure to be elaborated, since we know we have to elaborate - -- all declarations before executing the body. - - -- Couldn't this always be part of Safe_To_Capture_Value ??? + -- We can mark the entity as known to be non-null if it is safe to + -- capture the value. - if Safe_To_Capture_Value (N, Entity (N)) - or else Safe_To_Capture_In_Parameter_Value - then + if Safe_To_Capture_Value (N, Entity (N)) then Set_Is_Known_Non_Null (Entity (N)); end if; end if; diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb index 5965fa1fbb7..c00490cf55e 100644 --- a/gcc/ada/sem_util.adb +++ b/gcc/ada/sem_util.adb @@ -27912,7 +27912,10 @@ package body Sem_Util is P := Parent (N); while Present (P) loop - if Nkind (P) = N_If_Statement + if Is_Body (P) then + return True; + + elsif Nkind (P) = N_If_Statement or else Nkind (P) = N_Case_Statement or else (Nkind (P) in N_Short_Circuit and then Desc = Right_Opnd (P))
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