Fix twolf -funroll-loops -O3 miscompilation (a semi-latent web.c bug)

[Paolo Bonzini]

Il 15/10/2012 10:13, Steven Bosscher ha scritto:
> > I disagree that it is valid.  At least it is risky to consider it valid,
> > because a pass that simulates liveness might end up doing something
> > wrong because of that note.  If simulation is done backwards, it doesn't
> > even require any interaction with REG_DEAD notes.
> 
> In any case, if web doesn't properly rename the register in the
> REG_EQUAL note (which it doesn't do without my patch) and we declare
> such a note invalid, then we should remove the note. You're right that
> GCC ends up doing something wrong, that's why Honza's test case fails.
> 
> I think we should come to a conclusion of this discussion: Either we
> drop the notes (e.g. by re-computing the DF_NOTE problem after web) or
> we update them, like my patch does. I prefer the patch I proposed
> because it re-instates the behavior GCC had before.

I prefer to declare the notes invalid and drop the notes.

Paolo