On Mon, Jun 26, 2023 at 4:54 PM liuhongt <hongtao....@intel.com> wrote:
>
> __bfloat16 is redefined from typedef short to real __bf16 since GCC
> V13. The patch issues an warning for potential silent implicit
> conversion between __bf16 and short where users may only expect a
> data movement.
>
> To avoid too many false positive, warning is only under
> TARGET_AVX512BF16.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}
> Ok for trunk?
Ready to install.
>
> gcc/ChangeLog:
>
> * config/i386/i386.cc (ix86_invalid_conversion): New function.
> (TARGET_INVALID_CONVERSION): Define as
> ix86_invalid_conversion.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/i386/bf16_short_warn.c: New test.
> ---
> gcc/config/i386/i386.cc | 32 +++++++++++++++++++
> .../gcc.target/i386/bf16_short_warn.c | 17 ++++++++++
> 2 files changed, 49 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/i386/bf16_short_warn.c
>
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index 0761965344b..dc02eac6203 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -22718,6 +22718,35 @@ x86_emit_floatuns (rtx operands[2])
>
> emit_label (donelab);
> }
> +
> +/* Return the diagnostic message string if conversion from FROMTYPE to
> + TOTYPE is not allowed, NULL otherwise.
> + Currently it's used to warn for silent implicit conversion between __bf16
> + and short, since __bfloat16 is refined as real __bf16 instead of short
> + since GCC13. */
> +
> +static const char *
> +ix86_invalid_conversion (const_tree fromtype, const_tree totype)
> +{
> + if (element_mode (fromtype) != element_mode (totype)
> + && (TARGET_AVX512BF16 || TARGET_AVXNECONVERT))
> + {
> + /* Warn for silent implicit conversion where user may expect
> + a bitcast. */
> + if ((TYPE_MODE (fromtype) == BFmode
> + && TYPE_MODE (totype) == HImode)
> + || (TYPE_MODE (totype) == BFmode
> + && TYPE_MODE (fromtype) == HImode))
> + warning (0, "%<__bfloat16%> is redefined from typedef %<short%> "
> + "to real %<__bf16%> since GCC V13, be careful of "
> + "implicit conversion between %<__bf16%> and %<short%>; "
> + "a explicit bitcast may be needed here");
> + }
> +
> + /* Conversion allowed. */
> + return NULL;
> +}
> +
>
> /* Target hook for scalar_mode_supported_p. */
> static bool
> @@ -25009,6 +25038,9 @@ ix86_run_selftests (void)
> # define TARGET_MERGE_DECL_ATTRIBUTES merge_dllimport_decl_attributes
> #endif
>
> +#undef TARGET_INVALID_CONVERSION
> +#define TARGET_INVALID_CONVERSION ix86_invalid_conversion
> +
> #undef TARGET_COMP_TYPE_ATTRIBUTES
> #define TARGET_COMP_TYPE_ATTRIBUTES ix86_comp_type_attributes
>
> diff --git a/gcc/testsuite/gcc.target/i386/bf16_short_warn.c
> b/gcc/testsuite/gcc.target/i386/bf16_short_warn.c
> new file mode 100644
> index 00000000000..3e47a815200
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/bf16_short_warn.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +#include<immintrin.h>
> +typedef struct {
> +short payload;
> +} BFloat16;
> +
> +__attribute__((target("avx512vl,avx512bf16")))
> +BFloat16 tobf16_avx512(float f)
> +{
> + BFloat16 r;
> + __m128bh m = _mm_cvtneps_pbh(_mm_set_ss(f));
> + r.payload = m[0]; /* { dg-warning " be careful of implicit conversion
> between '__bf16' and 'short'" } */
> + return r;
> +}
> +
> --
> 2.39.1.388.g2fc9e9ca3c
>
--
BR,
Hongtao
