cfg merge part 19 - gcse tweek
Jan Hubicka
jh@suse.cz
Thu Jun 6 05:45:00 GMT 2002
> > Hi,
> > this is small patch from cfg-branch. It's purpose is to make gcse to drop
> > REG_EQUAL note when it GCSEes out the real computation so the local passes
> > won't lose track of what is going on.
>
> > It helps to avoid negative results of my next GCSE patch to switch it
> > into code hoisting functions (that patch needs liveness that is still
> > discussed), but anyway this has small positive effect.
>
> > Bootstrapped/regtested i386.
> > Honza
>
> > Mon May 27 13:53:16 CEST 2002 Jan Hubicka <jh@suse.cz>
> > * gcse.c (gcse_emit_move_after): New.
> > (pre_delete, hoist_store): Use it.
>
> You delete the check to verify that the change is valid. I don't see any
> code that you have added to check validity before. Worse, instead of
> changing an instruction that is already valid, you generate an ad-hoc
> instruction pattern, altogether ignoring the machine description.
There is code veirfying that the operand can be moved in want_to_gcse_p,
but I see it is not checking whetehr simple reg-reg set works. I guess
it is safe to use emit_move_instructions, as generally it can not have
side effects, since some passes, like reload insert moves at random
places anyway.
I will send a patch tonight.
Honza
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