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Re: RTL sharing tester (for testing)


> Richard Sandiford wrote:
> >If every register in [regno_first, regno_last] was unused, flow would
> >add a REG_UNUSED note for the REG created above.  If only some of those
> >registers were unused, flow would add notes for the individual unused
> >registers.  As I said on IRC yesterday, I'm not convinced the first
> >behaviour was a good idea.  That REG might well be invalid (otherwise
> >why have a SUBREG in the first place?) and it's better not to have
> >invalid registers floating around.
> 
> I agree with everything in your analysis, except possibly this.  If the 
> SUBREG is valid, then I see no way how the REG could be invalid.  Since 
> flow used to do this, I prefer we keep the same behaviour.

I also agree here, in general we should have REGs floating around
subregs valid.  The presence of subreg would be here as a mere retyping
or something.  It should not be that common as we take care to fold away
subregs of hard regs in several places.  (in longer run we might go
further and declare those foldable subregs invalid, not sure if it is
helping much however)

Adding one big coumpound REG_UNUSED/REG_DEAD note for the whole register
IMO should make difference for peephole2 pass that is doing mathching on
them (I am not sure if any of peep2s in existence rely on multiword
hardregs).

The patch seems to be on right track IMHO :)

BTW with the latest round of fixes, PPC is finally in bootstrapland
with sharing enabled.  With clean mainline we have couple of failures in
testsuite, but still an improvement ;)

I also gave that patch testing on i686-linux with sharing checker and it
did pass.

Honza
> 
> 
> Bernd
> -- 
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