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Re: Variable Expansion Optimization
- From: Ayal Zaks <ZAKS at il dot ibm dot com>
- To: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- Cc: Giovanni Bajo <giovannibajo at libero dot it>, Mark Mitchell <mark at codesourcery dot com>, gcc at gcc dot gnu dot org, Mostafa Hagog <MUSTAFA at il dot ibm dot com>
- Date: Mon, 23 Aug 2004 01:41:26 +0300
- Subject: Re: Variable Expansion Optimization
>1) The loop unrolling as a separate optimization should be done on
> rtl level, to avoid unnecessary compile-time overheads (optimizing
> the unrolled loop bodies separately is rarely useful and usually
> just a waste of time). For reasons mentioned by Sebastian (possible
> loss of information during unrolling, mostly), I believe the right
> place for the unrolling optimization would be after the loop-aware
> scheduling passes (SMS), and before rest of scheduling passes and
> register allocation.
Well, SMS could overlap more insns if the loop is unrolled before SMS.
OTOH, SMS generates register-moves (in the absence of rotating registers),
which could be eliminated by further unrolling - after or as a final step
of SMS.
Ayal.