linux-kernel - Re: [PATCH 46/74] x86, lto: Disable fancy hweight optimizations for LTO

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Date:	Mon, 20 Aug 2012 11:42:34 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org, mmarek@...e.cz, linux-kbuild@...r.kernel.org,
	JBeulich@...e.com, akpm@...ux-foundation.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 46/74] x86, lto: Disable fancy hweight optimizations for LTO

> >  config ARCH_HWEIGHT_CFLAGS
> >  	string
> > -	default "-fcall-saved-ecx -fcall-saved-edx" if X86_32
> > -	default "-fcall-saved-rdi -fcall-saved-rsi -fcall-saved-rdx -fcall-saved-rcx -fcall-saved-r8 -fcall-saved-r9 -fcall-saved-r10 -fcall-saved-r11" if X86_64
> > +	default "-fcall-saved-ecx -fcall-saved-edx" if X86_32 && !LTO
> > +	default "-fcall-saved-rdi -fcall-saved-rsi -fcall-saved-rdx -fcall-saved-rcx -fcall-saved-r8 -fcall-saved-r9 -fcall-saved-r10 -fcall-saved-r11" if X86_64 && !LTO
> > +	default "" if LTO
> >  
> 
> Seems heavy handed.  How about using __attribute__((optimize(...))) instead?

Doesn't work for this. In fact according to the gcc developers that
attribute is mostly broken.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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