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Re: Inner-loop optimization regression from 3.3 to 3.4
- From: Jan Hubicka <jh at suse dot cz>
- To: Falk Hueffner <falk dot hueffner at student dot uni-tuebingen dot de>
- Cc: Jan Hubicka <jh at suse dot cz>, Richard Henderson <rth at redhat dot com>,Zack Weinberg <zack at codesourcery dot com>, gcc at gcc dot gnu dot org,Jan Hubicka <hubicka at ucw dot cz>
- Date: Sun, 2 Nov 2003 00:19:02 +0100
- Subject: Re: Inner-loop optimization regression from 3.3 to 3.4
- References: <87vfqt66ge.fsf@codesourcery.com> <20031013130323.GY14005@kam.mff.cuni.cz> <87fzhvdxf3.fsf@codesourcery.com> <20031017141002.GF6212@kam.mff.cuni.cz> <20031018201817.GB29612@redhat.com> <20031101113548.GC14974@kam.mff.cuni.cz> <877k2kqcki.fsf@student.uni-tuebingen.de>
> Jan Hubicka <jh@suse.cz> writes:
>
> > + /* Convert (a >= 0) into (~a < 0). */
>
> While we're at it, this is also a pessimization on Alpha, and probably
> elsewhere where one has direct comparisons to registers and a zero
> register.
The conversion is there in order to allow futher combining. Even when
it is not better it should work faster after it happens.
How much slower it is on alpha? (in case setcc is faster then neg, we
need a check)
>
> --
> Falk