linux-kernel - Re: [PATCH 0/4] amd64

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Date:	Mon, 1 Jun 2009 10:31:29 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <petkovbb@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <borislav.petkov@....com>, greg@...ah.com,
	mingo@...e.hu, norsk5@...oo.com, tglx@...utronix.de,
	mchehab@...hat.com, aris@...hat.com, edt@....ca,
	linux-kernel@...r.kernel.org, randy.dunlap@...cle.com,
	Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH 0/4] amd64_edac: misc fixes

On Mon, Jun 1, 2009 at 10:02 AM, H. Peter Anvin <hpa@...or.com> wrote:
> H. Peter Anvin wrote:
>>
>> Yes, we would have to do something like that.
>>
>> However, if you're doing that you shouldn't use typeof() there...
>> instead this should be turned into an inline function with explicit
>> 64-bit types.
>>
>> It would be good if we could get Kbuild to export some kind of macro
>> that we can use to test binutils version, so we can do something like:
>>
>> #if BINUTILS_VERSION >= KERNEL_VERSION(2,18,50)
>> /* Do the right thing */
>> #else
>> /* Do the wrong thing */
>> #endif
>>
>
> The other option, and perhaps a better option, is to key it on the
> version of gcc; then we can use the gcc intrinsics __builtin_popcount(),
> __builtin_popcountl() and __builtin_popcountll(), which should produce
> better code since gcc can schedule them appropriately.
>
> Probably also means passing -msse4.2 to gcc while hoping that that
> doesn't enable any #TS-generating instructions (SSE 4.2 is mostly a
> collection of integer instructions).
>
> (H.J., any comments?)
>

I don't think -msse4.2 will generate any SSE instructions unless you
turn on the vectorizer.


-- 
H.J.
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