Re: [RFA][PR rtl-optimization/70263] Fix creation of new REG_EQUIV notes

[Jeff Law <law at redhat dot com>]

On 03/17/2016 12:23 PM, Bernd Schmidt wrote:
> On 03/17/2016 06:37 PM, Jeff Law wrote:
> > +  bitmap seen_insns;
> >
> > +  seen_insns = BITMAP_ALLOC (NULL);
>
> You could save an allocation here by making this a bitmap_head and using
> bitmap_initialize.
>
> > +      bitmap_set_bit (seen_insns, INSN_UID (insn));
> > +
> >        if (! INSN_P (insn))
> >      continue;
> >
> > @@ -3646,7 +3656,8 @@ update_equiv_regs (void)
> >        && ! find_reg_note (XEXP (reg_equiv[regno].init_insns, 0),
> >                    REG_EQUIV, NULL_RTX)
> >        && ! contains_replace_regs (XEXP (dest, 0))
> > -      && ! pdx_subregs[regno])
> > +      && ! pdx_subregs[regno]
> > +      && ! bitmap_bit_p (seen_insns, INSN_UID (insn)))
>
> This looks odd to me. Isn't this condition always false? Did you want to
> test the init_insn?
And thinking about this a bit more, I can't see how this code was 
correct to begin with -- a linear scan of the insns between init_insn 
and insn does not necessarily correspond to actual control flow during 
execution.

We could have a jump between those points that targets a label that is 
outside those points.  At that target label we might load from DEST.

Hmm....

jeff