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From: Andi Kleen <andi@firstfloor.org>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: Michael Matz <matz@suse.de>,  Richard Biener <richard.guenther@gmail.com>,  Richard Sandiford <richard.sandiford@linaro.org>,  GCC Patches <gcc-patches@gcc.gnu.org>,  Arjan van de Ven <arjan@linux.intel.com>,  Jakub Jelinek <jakub@redhat.com>,  Alexander Monakov <amonakov@ispras.ru>,  Uros Bizjak <ubizjak@gmail.com>
Subject: Re: [PATCH] i386: Don't use frame pointer without stack access
References: <20170806194037.GA25845@gmail.com>	<CAFULd4awp98Kw__PP0kL=U4zWgH3aZJ2ow6AuKNaKvGR0O9n7Q@mail.gmail.com>	<CAMe9rOqUP01UYJTcqNWktVCeQJYnjH7fYhwDj7hkYotG_p=HcA@mail.gmail.com>	<alpine.LSU.2.21.1708071531210.15613@wotan.suse.de>	<CAMe9rOqf8NYeeEEsmbc2g+d-X4SpyA2gTpubL-RiJXj13op3kA@mail.gmail.com>	<alpine.LSU.2.21.1708071543400.15613@wotan.suse.de>	<alpine.LNX.2.20.13.1708071653450.29517@monopod.intra.ispras.ru>	<CAMe9rOpRJFr4KvftoEWyU0OaC4CfWz9VBwx7=2S6z2C+=dguEg@mail.gmail.com>	<20170807154311.GN2123@tucnak>	<9c734d2b-7ba2-057b-7505-a7b300cde472@linux.intel.com>	<878tivdtz9.fsf@linaro.org>	<CAMe9rOphsdCFbXG63_Qsvdm5Rq3NDzoXLBzJ-vRWRZXMwSQzVQ@mail.gmail.com>	<B36DA6DB-FFCF-4485-B818-C96DBEE755A9@gmail.com>	<87wp6e7ykz.fsf@linaro.org> <87shh27yho.fsf@linaro.org>	<87d18589em.fsf@linaro.org>	<D780188F-2074-4B0B-AAAF-D882932ACC47@gmail.com>	<CAMe9rOrh8zdFZtCRw3GfEkApY1hqJ70OSugvSRnqUWxrk+8hsA@mail.gmail.com>	<alpine.LSU.2.21.1708091356230.15613@wotan.suse.de>	<CAMe9rOqYfswAq_3h=vADptn1v6NcpyvALLCxBLOMDJKdZR97=w@mail.gmail.com>
Date: Wed, 09 Aug 2017 15:04:00 -0000
In-Reply-To: <CAMe9rOqYfswAq_3h=vADptn1v6NcpyvALLCxBLOMDJKdZR97=w@mail.gmail.com>	(H. J. Lu's message of "Wed, 9 Aug 2017 05:26:58 -0700")
Message-ID: <874ltg4wb2.fsf@firstfloor.org>
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"H.J. Lu" <hjl.tools@gmail.com> writes:
>
> Like this?
>
> Note that @option{-fno-omit-frame-pointer} doesn't force a new stack
> frame for all functions if it isn't otherwise needed, and hence doesn't
> guarantee a new frame pointer for all functions.
>
> Here is the updated patch with a note for -fno-omit-frame-pointer.
>
> OK for trunk?

I suspect there will be still some unwinder or code patching
setups which rely on frame pointer everywhere become broken. But
doing the optimization for -fno-omit-frame-pointer by default
seems reasonable.

I would add a new option
-fforce-frame-pointer
that gives the old -fno-omit-frame-pointer back, so that
users relying on frame pointers everywhere have a workaround.

-Andi