Re: ifcvt/crossjump patch: Fix PR 42496, 21803

[Jeff Law <law at redhat dot com>]

 On 07/20/10 14:42, Bernd Schmidt wrote:
> On 04/20/2010 12:05 AM, Eric Botcazou wrote:
> > Bernd Schmidt wrote:
> > > Here's the second part.  This one should help most architectures, not
> > > just the ones with conditional execution.  I've observed it helps on
> > > i686 and arm, with the following being a typical result:
> > >
> > >   .L18:
> > >          ldr     r1, [r2, #4]
> > >          cmp     r1, #34
> > > -       it      hi
> > > -       ldrhi   r3, .L98+12
> > > -       bhi     .L28
> > >          ldr     r3, .L98+12
> > > +       bhi     .L28
> > >          ldrb    r2, [r3, #4]    @ zero_extendqisi2
> > >          cbz     r2, .L29
> > >          ldr     r3, [r3, #8]
> > I'm uncomfortable with this patch because I'm not sure it belongs in ifcvt.c.
> > Conceptually it's a reversed form of cross jumping so it could be implemented
> > more generally in cfgcleanup.c.  And other transformations should already be
> > able to apply this kind of optimizations.  Do you have testcases?
> Here's a new patch.  A testcase is included; as I mentioned before this
> triggers quite frequently.  This is PR44374.
>
> I've moved and reused code from dead_or_predicable for a new function
> can_move_insns_across.  The tests in dead_or_predicable were still
> somewhat ad-hoc, after the patch I believe it's using the exact
> necessary and sufficient conditions for moving code.
>
> Bootstrapped and regression tested on i686-linux.  Ok?
Was this the last version of the patch?  It looks pretty good to me.

jeff