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From: "iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/99576] [coroutines] destructor of a temporary called too
 early within co_await expression
Date: Wed, 30 Nov 2022 11:47:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99576

--- Comment #13 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Adrian Perl from comment #12)
> I have sent the patch and tests to gcc-patches@gcc.gnu.org

As noted there, the patch causes regressions in more complex library code (=
e.g.
some tests in folly) where CONSTRUCTOR trees might have nested await
expressions.

I mentioned that the real problem is to determine if a temporary should be
promoted - and, in the case of PR95736, the issue is that we promote a
temporary for a target expression that is subsequently elided; we can see t=
his
clearly if we print the object addresses in the test case:

START TASK
 Foo() 0x600001004071
IN LAMBDA
~Foo() 0x600001004070  << corresponds to the elided target expression.
~Foo() 0x600001004071


so this:
diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index ce7cf971e03..1bad509233c 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -2830,6 +2830,7 @@ find_interesting_subtree (tree *expr_p, int *dosub, v=
oid
*d)
        }
     }
   else if (tmp_target_expr_p (expr)
+          && !TARGET_EXPR_ELIDING_P (expr)
           && !p->temps_used->contains (expr))
     {
       p->entry =3D expr_p;


fixes that specific problem - but regresses other test cases (no detailed
analysis yet). Needs more thought ....=