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Re: {PING] [PATCH] Sign extension elimination
- From: "H. J. Lu" <hjl at lucon dot org>
- To: Leehod Baruch <leehod dot baruch at weizmann dot ac dot il>
- Cc: Mark Mitchell <mark at codesourcery dot com>, Toon Moene <toon at moene dot indiv dot nluug dot nl>, Daniel Berlin <dberlin at dberlin dot org>, Mircea Namolaru <namolaru at il dot ibm dot com>, gcc-patches at gcc dot gnu dot org, leehod at gmail dot com, Roger Sayle <roger at eyesopen dot com>
- Date: Thu, 20 Apr 2006 11:10:53 -0700
- Subject: Re: {PING] [PATCH] Sign extension elimination
- References: <1863.84.108.234.162.1145556496.squirrel@84.108.234.162>
On Thu, Apr 20, 2006 at 09:08:16PM +0300, Leehod Baruch wrote:
> > On Thu, Apr 20, 2006 at 08:53:15PM +0300, Leehod Baruch wrote:
> >> > On Thu, Apr 20, 2006 at 10:23:21AM -0700, Mark Mitchell wrote:
> >> >> H. J. Lu wrote:
> >> >> > On Thu, Apr 20, 2006 at 09:39:23AM -0700, Mark Mitchell wrote:
> >> >> >> I'm not finding this discussion very illuminating.
> >> >> >>
> >> >> >> I'm trying to understand whether the current SEE pass is ready for
> >> >> >> inclusion in the compiler. Roger has approved it on technical
> >> >> merits,
> >> >> >> but HJ has raised the issue that somehow this pass is a bad thing
> >> for
> >> >> >> x86-64.
> >> >> >
> >> >> > The current SEE implemented isn't designed for x86-64 and doesn't
> >> help
> >> >> > x86-64 at all, if it doesn't make it worse on x86-64. But its
> >> >> > infrastructure is needed for future x86-64 SEE work.
> >> >>
> >> >> OK. So, then, there's no problem with incorporating the SEE
> >> >> implementation, and we proceed with that.
> >> >>
> >> >
> >> > Oh, it shouldn't be enabled for a target with any -On unless we can
> >> > demonstrate it does something useful.
> >> >
> >> I guess you referred here to x86-64.
> >
> > Yes. I am curious how it performs for 32bit targets, like x86 or ppc32.
> On ppc32 it is harmless but it doesn't help much either since the number
> of optimization opportunities is very small.
>
In that case, it may not do anything useful for x86 either.
H.J.