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On 02/12/24 2:20 pm, Surya Kumari Jangala wrote:
> I have incorporated review comments in this patch.
>
> Regards,
> Surya
>
>
> rs6000: Inefficient vector splat of small V2DI constants [PR107757]
>
> On P8, for vector splat of double word constants, specifically -1 and 1,
> gcc generates inefficient code. For -1, gcc generates two instructions
> (vspltisw and vupkhsw) whereas only one instruction (vspltisw) is
> sufficient. For constant 1, gcc generates a load of the constant from
> .rodata instead of the instructions vspltisw and vupkhsw.
>
> The routine vspltisw_vupkhsw_constant_p() returns true if the constant
> can be synthesized with instructions vspltisw and vupkhsw. However, for
> constant 1, this routine returns false.
>
> For constant -1, this routine returns true. Vector splat of -1 can be
> done with only one instruction, i.e., vspltisw. We do not need two
> instructions. Hence this routine should return false for -1.
>
> With this patch, gcc generates only one instruction (vspltisw)
> for -1. And for constant 1, this patch generates two instructions
> (vspltisw and vupkhsw).
>
> 2024-11-20 Surya Kumari Jangala <jskum...@linux.ibm.com>
>
> gcc/
> PR target/107757
> * config/rs6000/rs6000.cc (vspltisw_vupkhsw_constant_p):
> Return false for -1 and return true for 1.
>
> gcc/testsuite/
> PR target/107757
> * gcc.target/powerpc/pr107757-1.c: New.
> * gcc.target/powerpc/pr107757-2.c: New.
> ---
> gcc/config/rs6000/rs6000.cc | 2 +-
> gcc/testsuite/gcc.target/powerpc/pr107757-1.c | 14 ++++++++++++++
> gcc/testsuite/gcc.target/powerpc/pr107757-2.c | 13 +++++++++++++
> 3 files changed, 28 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.target/powerpc/pr107757-1.c
> create mode 100644 gcc/testsuite/gcc.target/powerpc/pr107757-2.c
>
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index 02a2f1152db..d0c528f4d5f 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -6652,7 +6652,7 @@ vspltisw_vupkhsw_constant_p (rtx op, machine_mode mode,
> int *constant_ptr)
> return false;
>
> value = INTVAL (elt);
> - if (value == 0 || value == 1
> + if (value == 0 || value == -1
> || !EASY_VECTOR_15 (value))
> return false;
>
> diff --git a/gcc/testsuite/gcc.target/powerpc/pr107757-1.c
> b/gcc/testsuite/gcc.target/powerpc/pr107757-1.c
> new file mode 100644
> index 00000000000..49076fba255
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/pr107757-1.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-mdejagnu-cpu=power8 -O2" } */
> +/* { dg-require-effective-target powerpc_vsx } */
> +/* { dg-final { scan-assembler {\mvspltisw\M} } } */
> +/* { dg-final { scan-assembler {\mvupkhsw\M} } } */
> +/* { dg-final { scan-assembler-not {\mlvx\M} } } */
> +
> +#include <altivec.h>
> +
> +vector long long
> +foo ()
> +{
> + return vec_splats (1LL);
> +}
> diff --git a/gcc/testsuite/gcc.target/powerpc/pr107757-2.c
> b/gcc/testsuite/gcc.target/powerpc/pr107757-2.c
> new file mode 100644
> index 00000000000..4955696f11d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/pr107757-2.c
> @@ -0,0 +1,13 @@
> +/* { dg-do compile } */
> +/* { dg-options "-mdejagnu-cpu=power8 -O2" } */
> +/* { dg-require-effective-target powerpc_vsx } */
> +/* { dg-final { scan-assembler {\mvspltisw\M} } } */
> +/* { dg-final { scan-assembler-not {\mvupkhsw\M} } } */
> +
> +#include <altivec.h>
> +
> +vector long long
> +foo ()
> +{
> + return vec_splats (~0LL);
> +}
