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Re: [RFC] Fix PR28684
- From: Revital1 Eres <ERES at il dot ibm dot com>
- To: Clint Whaley <whaley at cs dot utsa dot edu>
- Cc: Ayal Zaks <ZAKS at il dot ibm dot com>, Dorit Nuzman <DORIT at il dot ibm dot com>, gcc-patches at gcc dot gnu dot org, rguenther at suse dot de, roger at eyesopen dot com, whaley at cs dot utsa dot edu
- Date: Thu, 16 Nov 2006 17:38:12 +0200
- Subject: Re: [RFC] Fix PR28684
> I wasn't sure if general strength reduction was still controlled by the
> flag, but if it is, we need to mention it, and again the user can
> certify the code as being good in the face of it. I worry a bit about
> strength reduction, as it often is unknown how extreme it can get, and
> in fp, sometimes it can mess with error (though in small ways). For
> replacing 4*X --> X+X+X+X would increase the forward error slightly. Can
> we bound the number of extra flops that strength reduction is allowed to
> Is the strength reduction stuff necessary for vectorization?
I do not think we have cases of strength reduction in the list of
which are allowed by the flag; just reordering. I'll recheck that.