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

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

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
>