From: Bob Duff Date: Thu, 28 May 2015 12:52:55 +0000 (+0000) Subject: sem_util.adb (Requires_Transient_Scope): Avoid returning function results on the... X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=d3b1cbddab28e0b7188257f59acbbec5d47f1eb5;p=gcc.git sem_util.adb (Requires_Transient_Scope): Avoid returning function results on the secondary stack in so many cases. 2015-05-28 Bob Duff * sem_util.adb (Requires_Transient_Scope): Avoid returning function results on the secondary stack in so many cases. From-SVN: r223814 --- diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog index c618018346c..7975d323f5d 100644 --- a/gcc/ada/ChangeLog +++ b/gcc/ada/ChangeLog @@ -1,3 +1,8 @@ +2015-05-28 Bob Duff + + * sem_util.adb (Requires_Transient_Scope): Avoid returning + function results on the secondary stack in so many cases. + 2015-05-28 Ed Schonberg * sem_util.adb (Wrong_Type): In any instance, do not emit error diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb index 3fe6d67787b..ecead06b4f8 100644 --- a/gcc/ada/sem_util.adb +++ b/gcc/ada/sem_util.adb @@ -16951,13 +16951,49 @@ package body Sem_Util is ------------------------------ -- A transient scope is required when variable-sized temporaries are - -- allocated in the primary or secondary stack, or when finalization - -- actions must be generated before the next instruction. + -- allocated on the secondary stack, or when finalization actions must be + -- generated before the next instruction. + + function Old_Requires_Transient_Scope (Id : Entity_Id) return Boolean; + function New_Requires_Transient_Scope (Id : Entity_Id) return Boolean; + -- ???We retain the old and new algorithms for Requires_Transient_Scope for + -- the time being. New_Requires_Transient_Scope is used by default; the + -- debug switch -gnatdQ can be used to do Old_Requires_Transient_Scope + -- instead. The intent is to use this temporarily to measure before/after + -- efficiency. Note: when this temporary code is removed, the documentation + -- of dQ in debug.adb should be removed. function Requires_Transient_Scope (Id : Entity_Id) return Boolean is - Typ : constant Entity_Id := Underlying_Type (Id); + Old_Result : constant Boolean := Old_Requires_Transient_Scope (Id); + + begin + if Debug_Flag_QQ then + return Old_Result; + end if; + + declare + New_Result : constant Boolean := New_Requires_Transient_Scope (Id); + + begin + -- Assert that we're not putting things on the secondary stack if we + -- didn't before; we are trying to AVOID secondary stack when + -- possible. + + if not Old_Result then + pragma Assert (not New_Result); + null; + end if; + + return New_Result; + end; + end Requires_Transient_Scope; + + ---------------------------------- + -- Old_Requires_Transient_Scope -- + ---------------------------------- - -- Start of processing for Requires_Transient_Scope + function Old_Requires_Transient_Scope (Id : Entity_Id) return Boolean is + Typ : constant Entity_Id := Underlying_Type (Id); begin -- This is a private type which is not completed yet. This can only @@ -16989,9 +17025,7 @@ package body Sem_Util is -- returned value is allocated on the secondary stack. Controlled -- type temporaries need finalization. - elsif Is_Tagged_Type (Typ) - or else Has_Controlled_Component (Typ) - then + elsif Is_Tagged_Type (Typ) or else Has_Controlled_Component (Typ) then return not Is_Value_Type (Typ); -- Record type @@ -16999,18 +17033,20 @@ package body Sem_Util is elsif Is_Record_Type (Typ) then declare Comp : Entity_Id; + begin Comp := First_Entity (Typ); while Present (Comp) loop if Ekind (Comp) = E_Component then + -- ???It's not clear we need a full recursive call to - -- Requires_Transient_Scope here. Note that the following - -- can't happen. + -- Old_Requires_Transient_Scope here. Note that the + -- following can't happen. pragma Assert (Is_Definite_Subtype (Etype (Comp))); pragma Assert (not Has_Controlled_Component (Etype (Comp))); - if Requires_Transient_Scope (Etype (Comp)) then + if Old_Requires_Transient_Scope (Etype (Comp)) then return True; end if; end if; @@ -17033,7 +17069,7 @@ package body Sem_Util is -- If component type requires a transient scope, the array does too - if Requires_Transient_Scope (Component_Type (Typ)) then + if Old_Requires_Transient_Scope (Component_Type (Typ)) then return True; -- Otherwise, we only need a transient scope if the size depends on @@ -17049,7 +17085,132 @@ package body Sem_Util is pragma Assert (Is_Protected_Type (Typ) or else Is_Task_Type (Typ)); return False; end if; - end Requires_Transient_Scope; + end Old_Requires_Transient_Scope; + + ---------------------------------- + -- New_Requires_Transient_Scope -- + ---------------------------------- + + function New_Requires_Transient_Scope (Id : Entity_Id) return Boolean is + + function Caller_Known_Size_Record (Typ : Entity_Id) return Boolean; + -- This is called for untagged records and protected types, with + -- nondefaulted discriminants. Returns True if the size of function + -- results is known at the call site, False otherwise. Returns False + -- if there is a variant part that depends on the discriminants of + -- this type, or if there is an array constrained by the discriminants + -- of this type. ???Currently, this is overly conservative (the array + -- could be nested inside some other record that is constrained by + -- nondiscriminants). That is, the recursive calls are too conservative. + + function Caller_Known_Size_Record (Typ : Entity_Id) return Boolean is + pragma Assert (Typ = Underlying_Type (Typ)); + + begin + if Has_Variant_Part (Typ) and then not Is_Definite_Subtype (Typ) then + return False; + end if; + + declare + Comp : Entity_Id := First_Entity (Typ); + + begin + while Present (Comp) loop + + -- Only look at E_Component entities. No need to look at + -- E_Discriminant entities, and we must ignore internal + -- subtypes generated for constrained components. + + if Ekind (Comp) = E_Component then + declare + Comp_Type : constant Entity_Id := + Underlying_Type (Etype (Comp)); + + begin + if Is_Record_Type (Comp_Type) + or else + Is_Protected_Type (Comp_Type) + then + if not Caller_Known_Size_Record (Comp_Type) then + return False; + end if; + + elsif Is_Array_Type (Comp_Type) then + if Size_Depends_On_Discriminant (Comp_Type) then + return False; + end if; + end if; + end; + end if; + + Next_Entity (Comp); + end loop; + end; + + return True; + end Caller_Known_Size_Record; + + -- Local deeclarations + + Typ : constant Entity_Id := Underlying_Type (Id); + + -- Start of processing for New_Requires_Transient_Scope + + begin + -- This is a private type which is not completed yet. This can only + -- happen in a default expression (of a formal parameter or of a + -- record component). Do not expand transient scope in this case + + if No (Typ) then + return False; + + -- Do not expand transient scope for non-existent procedure return or + -- string literal types. + + elsif Typ = Standard_Void_Type + or else Ekind (Typ) = E_String_Literal_Subtype + then + return False; + + -- Functions returning tagged types may dispatch on result so their + -- returned value is allocated on the secondary stack, even in the + -- definite case. Is_Tagged_Type includes controlled types and + -- class-wide types. Controlled type temporaries need finalization. + -- ???It's not clear why we need to return noncontrolled types with + -- controlled components on the secondary stack. Also, it's not clear + -- why nonprimitive tagged type functions need the secondary stack, + -- since they can't be called via dispatching. + + elsif Is_Tagged_Type (Typ) or else Has_Controlled_Component (Typ) then + return not Is_Value_Type (Typ); + + -- Indefinite (discriminated) untagged record or protected type + + elsif Is_Record_Type (Typ) or else Is_Protected_Type (Typ) then + return not Caller_Known_Size_Record (Typ); + -- ???Should come after Is_Definite_Subtype below + + -- Untagged definite subtypes are known size. This includes all + -- elementary [sub]types. Tasks are known size even if they have + -- discriminants. + + elsif Is_Definite_Subtype (Typ) or else Is_Task_Type (Typ) then + if Is_Array_Type (Typ) -- ???Shouldn't be necessary + and then New_Requires_Transient_Scope + (Underlying_Type (Component_Type (Typ))) + then + return True; + end if; + + return False; + + -- Unconstrained array + + else + pragma Assert (Is_Array_Type (Typ) and not Is_Definite_Subtype (Typ)); + return True; + end if; + end New_Requires_Transient_Scope; -------------------------- -- Reset_Analyzed_Flags -- @@ -19028,14 +19189,12 @@ package body Sem_Util is then return; - -- Conversely, type of expression may be the private one. + -- Conversely, type of expression may be the private one elsif Is_Private_Type (Base_Type (Etype (Expr))) - and then Full_View (Base_Type (Etype (Expr))) = - Expected_Type + and then Full_View (Base_Type (Etype (Expr))) = Expected_Type then return; - end if; end if; @@ -19049,11 +19208,11 @@ package body Sem_Util is and then Has_One_Matching_Field then Error_Msg_N ("positional aggregate cannot have one component", Expr); + if Present (Matching_Field) then if Is_Array_Type (Expec_Type) then Error_Msg_NE ("\write instead `&''First ='> ...`", Expr, Matching_Field); - else Error_Msg_NE ("\write instead `& ='> ...`", Expr, Matching_Field);