From: Segher Boessenkool <segher@kernel.crashing.org>
To: Martin Sebor <msebor@redhat.com>
Cc: Gcc Patch List <gcc-patches@gcc.gnu.org>, anton@samba.org
Subject: Re: [PATCH] pr 63354 - gcc -pg -mprofile-kernel creates unused stack frames on leaf functions on ppc64le
Date: Sat, 14 Mar 2015 14:34:00 -0000 [thread overview]
Message-ID: <20150314143434.GC3690@gate.crashing.org> (raw)
In-Reply-To: <55035CB1.4020801@redhat.com>
On Fri, Mar 13, 2015 at 03:54:57PM -0600, Martin Sebor wrote:
> Attached is a patch that eliminates the unused stack frame
> allocated by gcc 5 with -pg -mprofile-kernel on powepc64le
> and brings the code into parity with previous gcc versions.
>
> The patch doesn't do anything to change the emitted code
> when -mprofile-kernel is used without -pg. Since the former
> option isn't fully documented (as noted in pr 65372) it's
> unclear what effect it should be expected to have without
> -pg.
-mprofile-kernel does nothing without profiling enabled. Maybe it
should just have been called -pk or something horrid like that.
The effect it should have is to do what the only user of the option
(the 64-bit PowerPC Linux kernel) wants. The effect it does have
is to make the 64-bit ABI more like the 32-bit ABI for mcount.
> 2015-03-13 Anton Blanchard <anton@samba.org>
>
> PR target/63354
> * gcc/config/rs6000/linux64.h (ARGET_KEEP_LEAF_WHEN_PROFILED): Define.
^ typo
> * cc/config/rs6000/rs6000.c (rs6000_keep_leaf_when_profiled). New
^ typo ^ typo
It shouldn't have "gcc/" in the path names at all, actually.
> +/* -mprofile-kernel code calls mcount before the function prolog,
"prologue".
> + so a profiled leaf function should stay a leaf function. */
> +
> +static bool
> +rs6000_keep_leaf_when_profiled (void)
> +{
> + return TARGET_PROFILE_KERNEL;
> +}
Something like
switch (DEFAULT_ABI)
{
case ABI_AIX:
case ABI_ELFv2:
return TARGET_PROFILE_KERNEL;
default:
return true;
}
although I'm not sure about Darwin here. More conservative is to
return false for anything untested, of course.
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/pr63354.c
> @@ -0,0 +1,10 @@
> +/* { dg-do compile { target { powerpc*-*-* } } } */
> +/* { dg-options "-O2 -pg -mprofile-kernel" } */
> +
> +int foo (void)
> +{
> + return 1;
> +}
> +
> +/* { dg-final { scan-assembler "bl _mcount" } } */
> +/* { dg-final { scan-assembler-not "\(addi|stdu\) 1," } } */
Either you should run this only on AIX/ELFv2 ABIs, or you want to
test for "stwu" as well. Bare "1" does not work for all assemblers
(only Darwin again?)
Segher
next prev parent reply other threads:[~2015-03-14 14:34 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-13 21:55 Martin Sebor
2015-03-14 14:34 ` Segher Boessenkool [this message]
2015-03-15 23:40 ` Martin Sebor
2015-03-17 22:34 ` Segher Boessenkool
2015-03-21 19:48 ` Iain Sandoe
2015-03-24 2:50 ` Martin Sebor
2015-03-24 8:26 ` Iain Sandoe
2015-03-24 20:18 ` Martin Sebor
2015-03-24 11:51 ` Segher Boessenkool
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