Re: [PATCH 2/5] combine: handle I2 a parallel of two SETs

[Segher Boessenkool <segher at kernel dot crashing dot org>]

On Sat, Nov 15, 2014 at 06:59:23AM -0600, Segher Boessenkool wrote:
> On Fri, Nov 14, 2014 at 08:35:48PM +0100, Bernd Schmidt wrote:
> > On 11/14/2014 08:19 PM, Segher Boessenkool wrote:
> > >+  /* If I2 is a PARALLEL of two SETs of REGs (and perhaps some CLOBBERs),
> > >+     make those two SETs separate I1 and I2 insns, and make an I0 that is
> > >+     the original I1.  */
> > >+  if (i0 == 0
> > >+      && GET_CODE (PATTERN (i2)) == PARALLEL
> > >+      && XVECLEN (PATTERN (i2), 0) >= 2
> > >+      && GET_CODE (XVECEXP (PATTERN (i2), 0, 0)) == SET
> > >+      && GET_CODE (XVECEXP (PATTERN (i2), 0, 1)) == SET
> > >+      && REG_P (SET_DEST (XVECEXP (PATTERN (i2), 0, 0)))
> > >+      && REG_P (SET_DEST (XVECEXP (PATTERN (i2), 0, 1)))
> > >+      && !reg_used_between_p (SET_DEST (XVECEXP (PATTERN (i2), 0, 0)), 
> > >i2, i3)
> > >+      && !reg_used_between_p (SET_DEST (XVECEXP (PATTERN (i2), 0, 1)), 
> > >i2, i3)
> > 
> > Don't we have other code in combine checking the reg_used_between case?

Actually, no, no we don't.

Under the old regime (before adding the regno field to log_links), a
link links a first insn with its earliest successor that uses any of
the regs that first insn sets.  This guarantees that in try_combine
none of the insns between I2 and I3 will use any of the registers set
by I2.

Under the new regime (patches 3 and 4) a link links a first insn with
its earliest successor that uses a particular reg the first insn sets.
For single sets, this is the same as before; but not so for multiple
sets.

There are only two cases where this matters: this patch, and the code
right before it (that never seems to trigger, not on any target; trying
to figure out if that is true, and if so, why).

New patchset is bootstrapping/testing.

Cheers,


Segher