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Re: [RFC] third liveness pass
- From: Richard Henderson <rth at redhat dot com>
- To: Jan Hubicka <jh at suse dot cz>
- Cc: gcc at gcc dot gnu dot org, law at cygnus dot com, gcc-pdo at atrey dot karlin dot mff dot cuni dot cz
- Date: Sun, 26 May 2002 16:38:17 -0700
- Subject: Re: [RFC] third liveness pass
- References: <20020526122147.GM21915@atrey.karlin.mff.cuni.cz>
On Sun, May 26, 2002 at 02:21:47PM +0200, Jan Hubicka wrote:
> But interestingly the only C++ benchamrk, eon shows different figures.
> The savings are about 2.2% in code size and 1.6% performance (*).
Interesting. I wonder if someone with an interest in C++ can
corroborate with "real" applications.
> Similary I think the liveness costs can be made much lower, since
> currently we don't compute bitmaps of local properties, instead re-scan
> every time that can be expensive especially when dead store removal has
> been added.
How can we, when the local property is dependent on which
insns are deleted as dead code?
> Perhaps the dead code removal is better done using DU/UD chains and
> curent ssa-dce code converted to these, but I am not sure how popular
> step this can be.
I wouldn't have a prolem with that at all, if it is faster.
You'd have to rewrite the autoinc portions of life_analysis
at the same time, but it should be fairly straight-forward
to re-implement the existing algorithms with DU/UD chains.