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Re: [RFD] Using the 'memory constraint' trick to avoid memory clobber doesn't work
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: David Wohlferd <dw at limegreensocks dot com>, Hans-Peter Nilsson <hp at bitrange dot com>, y dot gribov at samsung dot com, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Gerald Pfeifer <gerald at pfeifer dot com>
- Date: Fri, 14 Nov 2014 03:56:02 -0600
- Subject: Re: [RFD] Using the 'memory constraint' trick to avoid memory clobber doesn't work
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On Thu, Nov 13, 2014 at 01:14:41PM +0100, Richard Biener wrote:
> It might be that RTL alias analysis / CSE give up too early here
> (we don't optimize across asm() on the GIMPLE level at all ... heh).
>
> I didn't look where it gives up (even though appearantly it does).
The cse1 pass doesn't carry the store forward in the "3" case, while it
does in the "4" case. So yes it is just a missed optimisation.
Segher