On Tue, Oct 8, 2024 at 3:24 PM Levy Hsu <ad...@levyhsu.com> wrote:
>
> Bootstrapped and tested on x86_64-linux-gnu, OK for trunk?
Ok.
>
> gcc/ChangeLog:
>
> * config/i386/i386.md: Rewrite insn truncsfbf2.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/i386/truncsfbf-1.c: New test.
> * gcc.target/i386/truncsfbf-2.c: New test.
> ---
> gcc/config/i386/i386.md | 16 ++---
> gcc/testsuite/gcc.target/i386/truncsfbf-1.c | 9 +++
> gcc/testsuite/gcc.target/i386/truncsfbf-2.c | 65 +++++++++++++++++++++
> 3 files changed, 83 insertions(+), 7 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/i386/truncsfbf-1.c
> create mode 100644 gcc/testsuite/gcc.target/i386/truncsfbf-2.c
>
> diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
> index 9c2a0aa6112..d3fee0968d8 100644
> --- a/gcc/config/i386/i386.md
> +++ b/gcc/config/i386/i386.md
> @@ -5672,16 +5672,18 @@
> (set_attr "mode" "HF")])
>
> (define_insn "truncsfbf2"
> - [(set (match_operand:BF 0 "register_operand" "=x, v")
> + [(set (match_operand:BF 0 "register_operand" "=x,x,v,Yv")
> (float_truncate:BF
> - (match_operand:SF 1 "register_operand" "x,v")))]
> - "((TARGET_AVX512BF16 && TARGET_AVX512VL) || TARGET_AVXNECONVERT)
> - && !HONOR_NANS (BFmode) && flag_unsafe_math_optimizations"
> + (match_operand:SF 1 "register_operand" "0,x,v,Yv")))]
> + "TARGET_SSE2 && flag_unsafe_math_optimizations && !HONOR_NANS (BFmode)"
> "@
> + psrld\t{$16, %0|%0, 16}
> %{vex%} vcvtneps2bf16\t{%1, %0|%0, %1}
> - vcvtneps2bf16\t{%1, %0|%0, %1}"
> - [(set_attr "isa" "avxneconvert,avx512bf16vl")
> - (set_attr "prefix" "vex,evex")])
> + vcvtneps2bf16\t{%1, %0|%0, %1}
> + vpsrld\t{$16, %1, %0|%0, %1, 16}"
> + [(set_attr "isa" "noavx,avxneconvert,avx512bf16vl,avx")
> + (set_attr "prefix" "orig,vex,evex,vex")
> + (set_attr "type" "sseishft1,ssecvt,ssecvt,sseishft1")])
>
> ;; Signed conversion to DImode.
>
> diff --git a/gcc/testsuite/gcc.target/i386/truncsfbf-1.c
> b/gcc/testsuite/gcc.target/i386/truncsfbf-1.c
> new file mode 100644
> index 00000000000..dd3ff8a50b4
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/truncsfbf-1.c
> @@ -0,0 +1,9 @@
> +/* { dg-do compile } */
> +/* { dg-options "-msse2 -O2 -ffast-math" } */
> +/* { dg-final { scan-assembler-times "psrld" 1 } } */
> +
> +__bf16
> +foo (float a)
> +{
> + return a;
> +}
> diff --git a/gcc/testsuite/gcc.target/i386/truncsfbf-2.c
> b/gcc/testsuite/gcc.target/i386/truncsfbf-2.c
> new file mode 100644
> index 00000000000..f4952f88fc9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/truncsfbf-2.c
> @@ -0,0 +1,65 @@
> +/* { dg-do run } */
> +/* { dg-options "-msse2 -O2 -ffast-math" } */
> +
> +#include <stdlib.h>
> +#include <stdint.h>
> +#include <string.h>
> +#include <math.h>
> +
> +__bf16
> +foo (float a)
> +{
> + return a;
> +}
> +
> +static __bf16
> +CALC (float *a)
> +{
> + uint32_t bits;
> + memcpy (&bits, a, sizeof (bits));
> + bits >>= 16;
> + uint16_t bfloat16_bits = (uint16_t) bits;
> + __bf16 bf16;
> + memcpy (&bf16, &bfloat16_bits, sizeof (bf16));
> + return bf16;
> +}
> +
> +int
> +main (void)
> +{
> + float test_values[] = { 0.0f, -0.0f, 1.0f, -1.0f, 0.5f, -0.5f, 1000.0f,
> -1000.0f,
> + 3.1415926f, -3.1415926f, 1e-8f, -1e-8f,
> + 1.0e+38f, -1.0e+38f, 1.0e-38f, -1.0e-38f };
> + size_t num_values = sizeof (test_values) / sizeof (test_values[0]);
> +
> + for (size_t i = 0; i < num_values; ++i)
> + {
> + float original = test_values[i];
> + __bf16 hw_bf16 = foo (original);
> + __bf16 sw_bf16 = CALC (&original);
> +
> + /* Verify psrld $16, %0 == %0 >> 16 */
> + if (memcmp (&hw_bf16, &sw_bf16, sizeof (__bf16)) != 0)
> + abort ();
> +
> + /* Reconstruct the float value from the __bf16 bits */
> + uint16_t bf16_bits;
> + memcpy (&bf16_bits, &hw_bf16, sizeof (bf16_bits));
> + uint32_t reconstructed_bits = ((uint32_t) bf16_bits) << 16;
> + float converted;
> + memcpy (&converted, &reconstructed_bits, sizeof (converted));
> +
> + float diff = fabsf (original - converted);
> +
> + /* Expected Maximum Precision Loss */
> + uint32_t orig_bits;
> + memcpy (&orig_bits, &original, sizeof (orig_bits));
> + int exponent = ((orig_bits >> 23) & 0xFF) - 127;
> + float expected_loss = (exponent == -127)
> + ? ldexpf (1.0f, -126 - 7)
> + : ldexpf (1.0f, exponent - 7);
> + if (diff > expected_loss)
> + abort ();
> + }
> + return 0;
> +}
> --
> 2.31.1
>
--
BR,
Hongtao
