RE: [PATCH]middle-end: don't lower past veclower [PR106063]

[Richard Biener <rguenther@suse.de>]

On Thu, 7 Jul 2022, Tamar Christina wrote:

> > -----Original Message-----
> > From: Richard Biener <rguenther@suse.de>
> > Sent: Thursday, July 7, 2022 8:19 AM
> > To: Tamar Christina <Tamar.Christina@arm.com>
> > Cc: gcc-patches@gcc.gnu.org; nd <nd@arm.com>
> > Subject: Re: [PATCH]middle-end: don't lower past veclower [PR106063]
> > 
> > On Tue, 5 Jul 2022, Tamar Christina wrote:
> > 
> > > Hi All,
> > >
> > > My previous patch can cause a problem if the pattern matches after
> > > veclower as it may replace the construct with a vector sequence which
> > > the target may not directly support.
> > >
> > > As such don't perform the rewriting if after veclower.
> > 
> > Note that when doing the rewriting before veclower to a variant not
> > supported by the target can cause veclower to generate absymal code.  In
> > some cases we are very careful and try to at least preserve code supported
> > by the target over transforming that into a variant not supported.
> > 
> > That said, a better fix would be to check whether the target can perform the
> > new comparison.  Before veclower it would be OK to do the transform
> > nevertheless in case it cannot do the original transform.
> 
> This last statement is somewhat confusing. Did you want me to change it such that
> before veclower the rewrite is always done and after veclowering only if the target
> supports it?
> 
> Or did you want me to never do the rewrite if the target doesn't support it?

I meant before veclower you can do the rewrite if either the rewriting
result is supported by the target OR if the original expression is
_not_ supported by the target.  The latter case might be not too
important to worry doing (it would still canonicalize for those
targets then).  After veclower you can only rewrite under the former
condition.

Richard.

> Thanks,
> Tamar
> 
> > 
> > Richard.
> > 
> > > Bootstrapped Regtested on aarch64-none-linux-gnu, x86_64-pc-linux-gnu
> > > and no issues.
> > >
> > > Ok for master? and backport to GCC 12?
> > >
> > > Thanks,
> > > Tamar
> > >
> > >
> > > gcc/ChangeLog:
> > >
> > > 	PR tree-optimization/106063
> > > 	* match.pd: Do not apply pattern after veclower.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > 	PR tree-optimization/106063
> > > 	* gcc.dg/pr106063.c: New test.
> > >
> > > --- inline copy of patch --
> > > diff --git a/gcc/match.pd b/gcc/match.pd index
> > >
> > 40c09bedadb89dabb6622559a8f69df5384e61fd..ba161892a98756c0278dc40fc
> > 377
> > > d7d0deaacbcf 100644
> > > --- a/gcc/match.pd
> > > +++ b/gcc/match.pd
> > > @@ -6040,7 +6040,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> > >    (simplify
> > >     (cmp (bit_and:c@2 @0 cst@1) integer_zerop)
> > >      (with { tree csts = bitmask_inv_cst_vector_p (@1); }
> > > -     (if (csts && (VECTOR_TYPE_P (TREE_TYPE (@1)) || single_use (@2)))
> > > +     (if (csts && (VECTOR_TYPE_P (TREE_TYPE (@1)) || single_use (@2))
> > > +	  && optimize_vectors_before_lowering_p ())
> > >        (if (TYPE_UNSIGNED (TREE_TYPE (@1)))
> > >         (icmp @0 { csts; })
> > >         (with { tree utype = unsigned_type_for (TREE_TYPE (@1)); }
> > > diff --git a/gcc/testsuite/gcc.dg/pr106063.c
> > > b/gcc/testsuite/gcc.dg/pr106063.c new file mode 100644 index
> > >
> > 0000000000000000000000000000000000000000..b23596724f6bb98c53af2dce77
> > d3
> > > 1509bab10378
> > > --- /dev/null
> > > +++ b/gcc/testsuite/gcc.dg/pr106063.c
> > > @@ -0,0 +1,9 @@
> > > +/* { dg-do compile } */
> > > +/* { dg-options "-O2 -fno-tree-forwprop --disable-tree-evrp" } */
> > > +typedef __int128 __attribute__((__vector_size__ (16))) V;
> > > +
> > > +V
> > > +foo (V v)
> > > +{
> > > +  return (v & (V){15}) == v;
> > > +}
> > >
> > >
> > >
> > >
> > >
> > 
> > --
> > Richard Biener <rguenther@suse.de>
> > SUSE Software Solutions Germany GmbH, Frankenstra
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstra