Re: [PATCH v2] match.pd: rewrite select to branchless expression

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Dec 1, 2022 at 7:57 PM Michael Collison <collison@rivosinc.com> wrote:
>
> Richard,
>
> Can you submit this patch for me while I sort out git write access?

Done.  I had to apply the patch manually - in future please make sure
to send patches that can be applied with git am.

Thanks,
Richard.

> On 11/18/22 07:57, Richard Biener wrote:
> > On Fri, Nov 11, 2022 at 3:28 AM Michael Collison <collison@rivosinc.com> wrote:
> >> This patches transforms ((x & 0x1) == 0) ? y : z <op> y -into
> >> (-(typeof(y))(x & 0x1) & z) <op> y, where op is a '^' or a '|'. It also
> >> transforms (cond (and (x , 0x1) != 0), (z op y), y ) into (-(and (x ,
> >> 0x1)) & z ) op y.
> >>
> >> Matching this patterns allows GCC to generate branchless code for one of
> >> the functions in coremark.
> >>
> >> Bootstrapped and tested on x86 and RISC-V. Okay?
> > OK.
> >
> > Thanks,
> > Richard.
> >
> >> Michael.
> >>
> >> 2022-11-10  Michael Collison  <collison@rivosinc.com>
> >>
> >>       * match.pd ((x & 0x1) == 0) ? y : z <op> y
> >>       -> (-(typeof(y))(x & 0x1) & z) <op> y.
> >>
> >> 2022-11-10  Michael Collison <collison@rivosinc.com>
> >>
> >>       * gcc.dg/tree-ssa/branchless-cond.c: New test.
> >>
> >> ---
> >>
> >> Changes in v2:
> >>
> >> - Rewrite comment to use C syntax
> >>
> >> - Guard against 1-bit types
> >>
> >> - Simplify pattern by using zero_one_valued_p
> >>
> >>    gcc/match.pd                                  | 24 +++++++++++++++++
> >>    .../gcc.dg/tree-ssa/branchless-cond.c         | 26 +++++++++++++++++++
> >>    2 files changed, 50 insertions(+)
> >>    create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/branchless-cond.c
> >>
> >> diff --git a/gcc/match.pd b/gcc/match.pd
> >> index 194ba8f5188..258531e9046 100644
> >> --- a/gcc/match.pd
> >> +++ b/gcc/match.pd
> >> @@ -3486,6 +3486,30 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> >>      (cond (le @0 integer_zerop@1) (negate@2 @0) integer_zerop@1)
> >>      (max @2 @1))
> >>
> >> +/* ((x & 0x1) == 0) ? y : z <op> y -> (-(typeof(y))(x & 0x1) & z) <op> y */
> >> +(for op (bit_xor bit_ior)
> >> + (simplify
> >> +  (cond (eq zero_one_valued_p@0
> >> +            integer_zerop)
> >> +        @1
> >> +        (op:c @2 @1))
> >> +  (if (INTEGRAL_TYPE_P (type)
> >> +       && TYPE_PRECISION (type) > 1
> >> +       && (INTEGRAL_TYPE_P (TREE_TYPE (@0))))
> >> +       (op (bit_and (negate (convert:type @0)) @2) @1))))
> >> +
> >> +/* ((x & 0x1) == 0) ? z <op> y : y -> (-(typeof(y))(x & 0x1) & z) <op> y */
> >> +(for op (bit_xor bit_ior)
> >> + (simplify
> >> +  (cond (ne zero_one_valued_p@0
> >> +            integer_zerop)
> >> +       (op:c @2 @1)
> >> +        @1)
> >> +  (if (INTEGRAL_TYPE_P (type)
> >> +       && TYPE_PRECISION (type) > 1
> >> +       && (INTEGRAL_TYPE_P (TREE_TYPE (@0))))
> >> +       (op (bit_and (negate (convert:type @0)) @2) @1))))
> >> +
> >>    /* Simplifications of shift and rotates.  */
> >>
> >>    (for rotate (lrotate rrotate)
> >> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/branchless-cond.c b/gcc/testsuite/gcc.dg/tree-ssa/branchless-cond.c
> >> new file mode 100644
> >> index 00000000000..68087ae6568
> >> --- /dev/null
> >> +++ b/gcc/testsuite/gcc.dg/tree-ssa/branchless-cond.c
> >> @@ -0,0 +1,26 @@
> >> +/* { dg-do compile } */
> >> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> >> +
> >> +int f1(unsigned int x, unsigned int y, unsigned int z)
> >> +{
> >> +  return ((x & 1) == 0) ? y : z ^ y;
> >> +}
> >> +
> >> +int f2(unsigned int x, unsigned int y, unsigned int z)
> >> +{
> >> +  return ((x & 1) != 0) ? z ^ y : y;
> >> +}
> >> +
> >> +int f3(unsigned int x, unsigned int y, unsigned int z)
> >> +{
> >> +  return ((x & 1) == 0) ? y : z | y;
> >> +}
> >> +
> >> +int f4(unsigned int x, unsigned int y, unsigned int z)
> >> +{
> >> +  return ((x & 1) != 0) ? z | y : y;
> >> +}
> >> +
> >> +/* { dg-final { scan-tree-dump-times " -" 4 "optimized" } } */
> >> +/* { dg-final { scan-tree-dump-times " & " 8 "optimized" } } */
> >> +/* { dg-final { scan-tree-dump-not "if" "optimized" } } */
> >> --
> >> 2.34.1
> >>