linux-kernel - Re: [PATCH] ARC: build: Turn off -Wmaybe-uninitialized for ARC gcc 4.8

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Message-ID: <56EBFC41.7010803@synopsys.com>
Date:	Fri, 18 Mar 2016 18:31:53 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-snps-arc@...ts.infradead.org>,
	Claudiu Zissulescu <Claudiu.Zissulescu@...opsys.com>,
	Michal Marek <mmarek@...e.cz>,
	"Geert Uytterhoeven" <geert@...ux-m68k.org>,
	<linux-kbuild@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARC: build: Turn off -Wmaybe-uninitialized for ARC gcc
 4.8

On Friday 18 March 2016 05:43 PM, Arnd Bergmann wrote:
> I think it's dangerous to use -O3 in one architecture when nothing else
> uses it. If you don't have a strong reason to use -O3, maybe just drop that
> use the default -O2 -Wmaybe-uninitialized like everyone else does.

I know what u mean. In fact top level makefile change has bitten us atleast once.
However ARC gcc tends to generate better code (likely others do too) at -O3 and
increased inlining etc reflects in several benchmarks. Maybe its due to the
micro-architecture and smaller hardware call return stack - I'm not sure. So I'm
ready to pay that maintenance price. And it has been like this for 5+ years and I
fear that switching to -O2 might unravel something unwarranted for.

OTOH, I'd rather prefer -O3 for all arches but that ain't gonna happen for obvious
reasons :-)

> On a related note, I have submitted a patch that turns CONFIG_CC_OPTIMIZE_FOR_SIZE
> into a choice statement, so we actually get the -Wmaybe-uninitialized warnings
> in an allyesconfig or allmodconfig build. It would be trivial to extend that
> to give the choice between -Os, -O2 and -O3, and then pick -O3 in a defconfig,
> over the -O2 default.

Is it posted already. I couldn't find it with quick googling.

Thx,
-Vineet