From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 62EE738582A0; Tue, 27 Feb 2024 13:38:58 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 62EE738582A0
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1709041138;
	bh=gF73KmexDyoWgit/pmTN2ppUdBZ5IDm+7J5dkA3Dj40=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=oPIGoYmWv0sFCGotpbTkvbf1XZtAIwjlbc8roIFCfhoto/Q/VxiSlkNG9B0NKvobM
	 MVPb03AcKIWI2+VpOXXfHTLJnovJIuV/i1cDNo6Mt9UvrvdsCxK3fER6n+YUo6RBJ/
	 GCEywm7aiWj7zr2AJt8clASdjtwhL2aU9CpJFMEI=
From: "lukas.graetz@tu-darmstadt.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/38534] gcc 4.2.1 and above: No need to save
 called-saved registers in 'noreturn' function
Date: Tue, 27 Feb 2024 13:38:57 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 4.2.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: lukas.graetz@tu-darmstadt.de
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-38534-4-A8zxuLwUxY@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-38534-4@http.gcc.gnu.org/bugzilla/>
References: <bug-38534-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D38534

--- Comment #33 from Lukas Gr=C3=A4tz <lukas.graetz@tu-darmstadt.de> ---
(In reply to Jakub Jelinek from comment #32)
> (In reply to Lukas Gr=C3=A4tz from comment #31)
> > Even when I compile a simple program with gcc -O2 -g:
> >=20
> > #include <stdlib.h>
> > int main(int argc, char** argv) {
> >     abort();
> > }
> >=20
> >=20
> > I still get an "argc=3D<optimised out>":
>=20
> Sure, debugging info in optimized code is best effort.
>=20
> > Yes, for a better debugging, it would be nice if optimised code would j=
ust
> > not be optimised... But this goes against optimization.
>=20
> The significant difference between other optimizations and this one is
> that normal optimizations affect the debuggability of the optimized funct=
ion.
> This one affects the debuggability of all callers as well, even if they a=
re
> compiled in a way that should make them more debuggable.
> Normally, if debugging optimized code doesn't work out, one can simply
> rebuild that code with -O0 or -Og to make it more debuggable.
> Here one would also need to rebuild all the shared libraries it uses.

When the debugger is inside the debuggable -O0 or -Og compiled function, we
would see all parameters and current variable values. However, in the bt
example, we are in another function. So the parameters are only available at
best effort.

I just noticed that for my simple.c example above, I get "argc=3D<optimised=
 out>"
even with -Og. However, when breakpoint is somewhere else,

(gdb) break main
(gdb) run
(gdb) bt

I get the correct "argc=3D1". The same applies to your example with "break =
baz".
It is just not guaranteed that gdb is able to reconstruct function paramete=
rs
when we are in some other function.=