RE: [PATCH] i386: Fix up -Wuninitialized warnings in avx512erintrin.h [PR105593]

[Liu, Hongtao via Gcc-patches]

> -----Original Message-----
> From: Jakub Jelinek <ja...@redhat.com>
> Sent: Tuesday, January 31, 2023 4:09 PM
> To: Liu, Hongtao <hongtao....@intel.com>; Uros Bizjak <ubiz...@gmail.com>
> Cc: gcc-patches@gcc.gnu.org
> Subject: [PATCH] i386: Fix up -Wuninitialized warnings in avx512erintrin.h
> [PR105593]
> 
> Hi!
> 
> As reported in the PR, there are some -Wuninitialized warnings in
> avx512erintrin.h.  One can see that by compiling sse-23.c testcase with -
> Wuninitialized (or when actually using those intrinsics).
> Those 6 spots use an uninitialized variable and pass it as one of the argument
> to a builtin with constant mask -1, because there is no unmasked builtin.  It 
> is
> true that expansion of those builtins into RTL will see mask is all ones and
> ignore the unneeded argument, but -Wuninitialized is diagnosed on GIMPLE
> and on GIMPLE these builtins are just builtin calls.
> avx512fintrin.h and other headers use in these cases the _mm*_undefined_*
> () intrinsics, like:
>   return (__m512i) __builtin_ia32_psrav8di_mask ((__v8di) __X,
>                                                  (__v8di) __Y,
>                                                  (__v8di)
>                                                  _mm512_undefined_epi32 (),
>                                                  (__mmask8) -1); etc. and the 
> following patch does
> the same for avx512erintrin.h.
> With the recent changes in C++ FE and the _mm*_undefined_* intrinsics, we
> don't emit -Wuninitialized warnings for those (previously we didn't just in C
> due to self-initialization).  Of course we could also just self-initialize 
> these
> uninitialized vars and add the #pragma GCC diagnostic dances around it, but
> using the intrinsics is consistent with the rest and IMHO cleaner.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok, thanks.
> 
> 2023-01-31  Jakub Jelinek  <ja...@redhat.com>
> 
>       PR c++/105593
>       * config/i386/avx512erintrin.h (_mm512_exp2a23_round_pd,
>       _mm512_exp2a23_round_ps, _mm512_rcp28_round_pd,
> _mm512_rcp28_round_ps,
>       _mm512_rsqrt28_round_pd, _mm512_rsqrt28_round_ps): Use
>       _mm512_undefined_pd () or _mm512_undefined_ps () instead of
> using
>       uninitialized automatic variable __W.
> 
>       * gcc.target/i386/sse-23.c: Add -Wuninitialized to dg-options.
> 
> --- gcc/config/i386/avx512erintrin.h.jj       2023-01-16 11:52:15.944736113
> +0100
> +++ gcc/config/i386/avx512erintrin.h  2023-01-30 20:53:08.057769691
> +0100
> @@ -51,9 +51,8 @@ extern __inline __m512d  __attribute__
> ((__gnu_inline__, __always_inline__, __artificial__))
> _mm512_exp2a23_round_pd (__m512d __A, int __R)  {
> -  __m512d __W;
>    return (__m512d) __builtin_ia32_exp2pd_mask ((__v8df) __A,
> -                                            (__v8df) __W,
> +                                            (__v8df) _mm512_undefined_pd
> (),
>                                              (__mmask8) -1, __R);
>  }
> 
> @@ -79,9 +78,8 @@ extern __inline __m512  __attribute__
> ((__gnu_inline__, __always_inline__, __artificial__))
> _mm512_exp2a23_round_ps (__m512 __A, int __R)  {
> -  __m512 __W;
>    return (__m512) __builtin_ia32_exp2ps_mask ((__v16sf) __A,
> -                                           (__v16sf) __W,
> +                                           (__v16sf) _mm512_undefined_ps
> (),
>                                             (__mmask16) -1, __R);
>  }
> 
> @@ -107,9 +105,8 @@ extern __inline __m512d  __attribute__
> ((__gnu_inline__, __always_inline__, __artificial__))
> _mm512_rcp28_round_pd (__m512d __A, int __R)  {
> -  __m512d __W;
>    return (__m512d) __builtin_ia32_rcp28pd_mask ((__v8df) __A,
> -                                             (__v8df) __W,
> +                                             (__v8df)
> _mm512_undefined_pd (),
>                                               (__mmask8) -1, __R);
>  }
> 
> @@ -135,9 +132,8 @@ extern __inline __m512  __attribute__
> ((__gnu_inline__, __always_inline__, __artificial__))
> _mm512_rcp28_round_ps (__m512 __A, int __R)  {
> -  __m512 __W;
>    return (__m512) __builtin_ia32_rcp28ps_mask ((__v16sf) __A,
> -                                            (__v16sf) __W,
> +                                            (__v16sf) _mm512_undefined_ps
> (),
>                                              (__mmask16) -1, __R);
>  }
> 
> @@ -229,9 +225,8 @@ extern __inline __m512d  __attribute__
> ((__gnu_inline__, __always_inline__, __artificial__))
> _mm512_rsqrt28_round_pd (__m512d __A, int __R)  {
> -  __m512d __W;
>    return (__m512d) __builtin_ia32_rsqrt28pd_mask ((__v8df) __A,
> -                                               (__v8df) __W,
> +                                               (__v8df)
> _mm512_undefined_pd (),
>                                                 (__mmask8) -1, __R);
>  }
> 
> @@ -257,9 +252,8 @@ extern __inline __m512  __attribute__
> ((__gnu_inline__, __always_inline__, __artificial__))
> _mm512_rsqrt28_round_ps (__m512 __A, int __R)  {
> -  __m512 __W;
>    return (__m512) __builtin_ia32_rsqrt28ps_mask ((__v16sf) __A,
> -                                              (__v16sf) __W,
> +                                              (__v16sf)
> _mm512_undefined_ps (),
>                                                (__mmask16) -1, __R);
>  }
> 
> --- gcc/testsuite/gcc.target/i386/sse-23.c.jj 2022-11-07
> 10:30:42.831628746 +0100
> +++ gcc/testsuite/gcc.target/i386/sse-23.c    2023-01-30
> 20:48:28.858838817 +0100
> @@ -1,5 +1,5 @@
>  /* { dg-do compile } */
> -/* { dg-options "-O2 -Werror-implicit-function-declaration -march=k8" } */
> +/* { dg-options "-O2 -Werror-implicit-function-declaration
> +-Wuninitialized -march=k8" } */
>  /* { dg-add-options bind_pic_locally } */
> 
>  #include <mm_malloc.h>
> 
>       Jakub