[PATCH] match.pd: Implement missed optimization (x << c) >> c -> -(x & 1) [PR101955]

[Andrew Pinski]

On Thu, Jul 20, 2023 at 8:17 AM Andrew Pinski <pinskia@gmail.com> wrote:
>
> On Thu, Jul 20, 2023 at 7:47 AM Drew Ross via Gcc-bugs
> <gcc-bugs@gcc.gnu.org> wrote:
> >
> >         PR middle-end/101955
> >
> > gcc/ChangeLog:
> >
> >         * match.pd (x << c) >> c -> -(x & 1): New simplification.
> >
> > gcc/testsuite/ChangeLog:
> >
> >         * gcc.dg/pr101955.c: New test.
> > ---
> >  gcc/match.pd                    |  9 +++++
> >  gcc/testsuite/gcc.dg/pr101955.c | 62 +++++++++++++++++++++++++++++++++
> >  2 files changed, 71 insertions(+)
> >  create mode 100644 gcc/testsuite/gcc.dg/pr101955.c
> >
> > diff --git a/gcc/match.pd b/gcc/match.pd
> > index 8543f777a28..bf63652e80f 100644
> > --- a/gcc/match.pd
> > +++ b/gcc/match.pd
> > @@ -3766,6 +3766,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> >        && (wi::ltu_p (wi::to_wide (@1), element_precision (type))))
> >    (bit_and @0 (rshift { build_minus_one_cst (type); } @1))))
> >
> > +/* Optimize (X << C) >> C where C = precision(type) - 1 and X is signed
> > +   into -(X & 1).  */
> > +(simplify
> > + (rshift (lshift @0 INTEGER_CST@1) @@1)
> > + (if (ANY_INTEGRAL_TYPE_P (type)
> > +      && !TYPE_UNSIGNED (type)
> > +      && wi::eq_p (wi::to_wide (@1), element_precision (type) - 1))
> > +  (negate (bit_and @0 { build_one_cst (type); }))))
>
> I think the lshift does not need to be in the same type but could be
> in the unsigned type so you should add a nop_convert? operand there
> That is:
> (simplify
>  (rshift (nop_convert? (lshift @0 INTEGER_CST@1)) @@1)
> ...
>  (negate (bit_and (convert @0) { build_one_cst (type); }))))
>
> Note I see you use INTEGER_CST and then ANY_INTEGRAL_TYPE_P. If you
> are going to support vectors, you should use uniform_integer_cst_p
> instead of INTEGER_CST and then use uniform_integer_cst_p to get the
> constant.

Note I just noticed you sent the patch to gcc-bugs@, it really should
go to gcc-patches@ .

Thanks,
Andrew

>
> Thanks,
> Andrew
>
>
> > +
> >  /* Optimize x >> x into 0 */
> >  (simplify
> >   (rshift @0 @0)
> > diff --git a/gcc/testsuite/gcc.dg/pr101955.c b/gcc/testsuite/gcc.dg/pr101955.c
> > new file mode 100644
> > index 00000000000..0e233269e21
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/pr101955.c
> > @@ -0,0 +1,62 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2 -fdump-tree-dse1 -Wno-psabi" } */
> > +
> > +typedef int v4si __attribute__((vector_size(16)));
> > +
> > +__attribute__((noipa)) int
> > +t1 (int x)
> > +{
> > +  return (x << 31) >> 31;
> > +}
> > +
> > +__attribute__((noipa)) int
> > +t2 (int x)
> > +{
> > +  int y = x << 31;
> > +  int z = y >> 31;
> > +  return z;
> > +}
> > +
> > +__attribute__((noipa)) int
> > +t3 (int x)
> > +{
> > +  int w = 31;
> > +  int y = x << w;
> > +  int z = y >> w;
> > +  return z;
> > +}
> > +
> > +__attribute__((noipa)) long long
> > +t4 (long long x)
> > +{
> > +  return (x << 63) >> 63;
> > +}
> > +
> > +__attribute__((noipa)) long long
> > +t5 (long long x)
> > +{
> > +  long long y = x << 63;
> > +  long long z = y >> 63;
> > +  return z;
> > +}
> > +
> > +__attribute__((noipa)) long long
> > +t6 (long long x)
> > +{
> > +  int w = 63;
> > +  long long y = x << w;
> > +  long long z = y >> w;
> > +  return z;
> > +}
> > +
> > +__attribute__((noipa)) v4si
> > +t7 (v4si x)
> > +{
> > +  return (x << 31) >> 31;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-not " >> " "dse1" } } */
> > +/* { dg-final { scan-tree-dump-not " << " "dse1" } } */
> > +/* { dg-final { scan-tree-dump-times " -" 7 "dse1" } } */
> > +/* { dg-final { scan-tree-dump-times " & " 7 "dse1" } } */
> > +
> > --
> > 2.39.3
> >