How to check that two ssa registers have the same symbolic value

Zdenek Dvorak rakdver@kam.mff.cuni.cz
Tue May 29 19:27:00 GMT 2007


Hello,

> "Daniel Berlin" <dberlin@dberlin.org> wrote on 29.05.2007 20:05:34:
> 
> >
> > tree level PRE knows it could hoist these things (and they are marked
> > as such), but we simply don't do it because it's not a partial
> > redundancy.
> > IE they are all marked antic at the beginning of the block.
> >
> > I've never bothered to teach it there are other times it might be
> > profitable to move calculations anyway.
> 
> It may be worth to do when PRE is called in its FRE flavor.
> Looks like it always should be helpful for decreasing code size without
> increasing runtime.

in some cases, it might prolong register lifetimes, which in turn may
cause spilling and runtime regressions (or it may not; I believe the
runtime effects would be negligible, but it is hard to tell without
actually trying and measuring it).

Zdenek



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