From: Eric Botcazou <ebotca...@adacore.com>
The recent removal of the unconditional call to Remove_Side_Effects on the
expression of an object declaration or an allocator with a class-wide type
has introduced a pessimization in the former case for function calls that
return a specific tagged type, because the object ultimately created on the
primary stack has changed from being of a specific tagged type to being of
the class-wide type, the latter type always formally requiring finalization.
With the current finalization machinery, this means that a dispatching call
to the Deep_Finalize routine is generated, which is unnecessary. Although
this is a generic finalization issue with class-wide objects, this restores
the previous behavior in this case to fix the pessimization for now.
gcc/ada/
* exp_ch3.adb (Expand_N_Object_Declaration): For a class-wide non-
interface stand-alone object initialized by a function call, call
Remove_Side_Effects on the expression to capture the result.
Tested on x86_64-pc-linux-gnu, committed on master.
---
gcc/ada/exp_ch3.adb | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/gcc/ada/exp_ch3.adb b/gcc/ada/exp_ch3.adb
index 6bc76aec5d1..6886bde7bd1 100644
--- a/gcc/ada/exp_ch3.adb
+++ b/gcc/ada/exp_ch3.adb
@@ -7797,6 +7797,25 @@ package body Exp_Ch3 is
-- Common case of explicit object initialization
else
+ -- Small optimization: if the expression is a function call and
+ -- the object is stand-alone, not declared at library level and of
+ -- a class-wide type, then we capture the result of the call into
+ -- a temporary, with the benefit that, if the result's type does
+ -- not need finalization, nothing will be finalized and, if it
+ -- does, the temporary only will be finalized by means of a direct
+ -- call to the Finalize primitive if the result's type is not a
+ -- class-wide type; whereas, in both cases, the stand-alone object
+ -- itself would be finalized by means of a dispatching call to the
+ -- Deep_Finalize routine.
+
+ if Nkind (Expr_Q) = N_Function_Call
+ and then not Special_Ret_Obj
+ and then not Is_Library_Level_Entity (Def_Id)
+ and then Is_Class_Wide_Type (Typ)
+ then
+ Remove_Side_Effects (Expr_Q);
+ end if;
+
-- In most cases, we must check that the initial value meets any
-- constraint imposed by the declared type. However, there is one
-- very important exception to this rule. If the entity has an
--
2.34.1
