On Fri, Jul 16, 2021 at 1:30 AM H.J. Lu via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> In a single SET, all bits of the source YMM/ZMM register are zero when
>
> 1. The source is contant zero.
> 2. The source YMM/ZMM operand are defined from contant zero.
>
> and we don't set AVX_U128_DIRTY.
>
> gcc/
>
> PR target/101456
> * config/i386/i386.c (ix86_avx_u128_mode_needed): Don't set
> AVX_U128_DIRTY when all bits are zero.
>
> gcc/testsuite/
>
> PR target/101456
> * gcc.target/i386/pr101456-1.c: New test.
> ---
> gcc/config/i386/i386.c | 47 ++++++++++++++++++++++
> gcc/testsuite/gcc.target/i386/pr101456-1.c | 28 +++++++++++++
> 2 files changed, 75 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/i386/pr101456-1.c
>
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index cff26909292..c2b06934053 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -14129,6 +14129,53 @@ ix86_avx_u128_mode_needed (rtx_insn *insn)
> return AVX_U128_CLEAN;
> }
>
> + rtx set = single_set (insn);
> + if (set)
> + {
> + rtx dest = SET_DEST (set);
> + rtx src = SET_SRC (set);
> + if (ix86_check_avx_upper_register (dest))
> + {
> + /* It is not dirty if the source is known zero. */
> + if (standard_sse_constant_p (src, GET_MODE (dest)) == 1)
> + return AVX_U128_ANY;
> + else
> + return AVX_U128_DIRTY;
> + }
> + else if (ix86_check_avx_upper_register (src))
> + {
> + /* Check for the source operand with all DEFs from constant
> + zero. */
> + df_ref def = DF_REG_DEF_CHAIN (REGNO (src));
> + if (!def)
> + return AVX_U128_DIRTY;
> +
> + for (; def; def = DF_REF_NEXT_REG (def))
> + if (DF_REF_REG_DEF_P (def)
> + && !DF_REF_IS_ARTIFICIAL (def))
> + {
> + rtx_insn *def_insn = DF_REF_INSN (def);
> + set = single_set (def_insn);
> + if (!set)
> + return AVX_U128_DIRTY;
> +
> + dest = SET_DEST (set);
> + if (ix86_check_avx_upper_register (dest))
> + {
> + src = SET_SRC (set);
> + /* It is dirty if the source operand isn't constant
> + zero. */
> + if (standard_sse_constant_p (src, GET_MODE (dest))
> + != 1)
> + return AVX_U128_DIRTY;
> + }
> + }
> +
> + /* It is not dirty only if all sources are known zero. */
> + return AVX_U128_ANY;
> + }
> + }
> +
> /* Require DIRTY mode if a 256bit or 512bit AVX register is referenced.
> Hardware changes state only when a 256bit register is written to,
> but we need to prevent the compiler from moving optimal insertion
> diff --git a/gcc/testsuite/gcc.target/i386/pr101456-1.c
> b/gcc/testsuite/gcc.target/i386/pr101456-1.c
> new file mode 100644
> index 00000000000..6a0f6ccd756
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr101456-1.c
> @@ -0,0 +1,28 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -march=skylake" } */
> +
> +#include <x86intrin.h>
> +
> +extern __m256 x1;
> +extern __m256d x2;
> +extern __m256i x3;
> +
> +void
> +foo1 (void)
> +{
> + x1 = _mm256_setzero_ps ();
> +}
> +
> +void
> +foo2 (void)
> +{
> + x2 = _mm256_setzero_pd ();
> +}
> +
> +void
> +foo3 (void)
> +{
> + x3 = _mm256_setzero_si256 ();
> +}
> +
> +/* { dg-final { scan-assembler-not "vzeroupper" } } */
> --
> 2.31.1
>
LGTM.
--
BR,
Hongtao
