This patch improves on the performance of an object initialization with a
build-in-place function call, when the return type is not a definite type
but has only access discriminants and no controlled components.
THe following must execute quietly:
gcc -c -gnatDG p.adb
grep secondary_stack p.adb.dg
---
with Discrim; use Discrim;
procedure P is
I : aliased Integer;
A_Obj : A_Type := Create (I'Access);
begin
null;
end;
---
package Discrim is
type A_Type (IA : access Integer) is limited private;
function Create (I : access Integer) return A_Type;
private
type A_Type (IA : access Integer) is limited record
Not_Dependent_On_IA : Boolean;
end record;
end;
---
package body Discrim is
function Create (I : access Integer) return A_Type is
begin
return A : A_Type (I) do
A.Not_Dependent_On_IA := False;
end return;
end;
end;
Tested on x86_64-pc-linux-gnu, committed on trunk
2016-04-27 Ed Schonberg <schonb...@adacore.com>
* exp_ch6.adb (Make_Build_In_Place_Call_In_Object_Declaration): If the
return type is an untagged limited record with only access
discriminants and no controlled components, the return value does not
need to use the secondary stack.
Index: exp_ch6.adb
===================================================================
--- exp_ch6.adb (revision 235482)
+++ exp_ch6.adb (working copy)
@@ -7783,7 +7783,12 @@
Result_Subt : Entity_Id;
Definite : Boolean;
- -- True for definite function result subtype
+ -- True if result subtype is definite, or has a size that does not
+ -- require secondary stack usage (i.e. no variant part or components
+ -- whose type depends on discriminants). In particular, untagged types
+ -- with only access discriminants do not require secondary stack use.
+ -- Note that if the return type is tagged we must always use the sec.
+ -- stack because the call may dispatch on result.
begin
-- Step past qualification or unchecked conversion (the latter can occur
@@ -7818,7 +7823,10 @@
end if;
Result_Subt := Etype (Function_Id);
- Definite := Is_Definite_Subtype (Underlying_Type (Result_Subt));
+ Definite :=
+ (Is_Definite_Subtype (Underlying_Type (Result_Subt))
+ and then not Is_Tagged_Type (Result_Subt))
+ or else not Requires_Transient_Scope (Underlying_Type (Result_Subt));
-- Create an access type designating the function's result subtype. We
-- use the type of the original call because it may be a call to an
