[RTL/fwprop] Allow propagations from inner loop to outer loop.

  Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
Ok for trunk.

gcc/ChangeLog:

	PR rtl/103750
	* cfgloop.h (loop_contains_p): New function.
	* fwprop.c (forward_propagate_into): Allow propagations from
	inner loop to outer loop.

gcc/testsuite/ChangeLog:

	* g++.target/i386/pr103750-fwprop-1.C: New test.
---
 gcc/cfgloop.h                                 | 12 +++++++++
 gcc/fwprop.c                                  |  7 +++--
 .../g++.target/i386/pr103750-fwprop-1.C       | 26 +++++++++++++++++++
 3 files changed, 43 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.target/i386/pr103750-fwprop-1.C
  

On Wed, Jan 5, 2022 at 6:39 AM liuhongt via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> Ok for trunk.
>
> gcc/ChangeLog:
>
>         PR rtl/103750
>         * cfgloop.h (loop_contains_p): New function.
>         * fwprop.c (forward_propagate_into): Allow propagations from
>         inner loop to outer loop.
>
> gcc/testsuite/ChangeLog:
>
>         * g++.target/i386/pr103750-fwprop-1.C: New test.
> ---
>  gcc/cfgloop.h                                 | 12 +++++++++
>  gcc/fwprop.c                                  |  7 +++--
>  .../g++.target/i386/pr103750-fwprop-1.C       | 26 +++++++++++++++++++
>  3 files changed, 43 insertions(+), 2 deletions(-)
>  create mode 100644 gcc/testsuite/g++.target/i386/pr103750-fwprop-1.C
>
> diff --git a/gcc/cfgloop.h b/gcc/cfgloop.h
> index d2714e20cb0..e8fe0cedd5f 100644
> --- a/gcc/cfgloop.h
> +++ b/gcc/cfgloop.h
> @@ -908,6 +908,18 @@ loop_outermost (class loop *loop)
>    return (*loop->superloops)[1];
>  }
>
> +/* Returns true if loop OUTER contains loop INNER.  */

that's flow_loop_nested_p (loop *outer, loop *inner) which
is implemented in O(1).  Note behavior for outer == inner
might be different (didn't check your implementation too hard)

Otherwise looks OK to me.

Thanks,
Richard.

> +static inline bool
> +loop_contains_p (class loop* outer, class loop* inner)
> +{
> +  unsigned n = vec_safe_length (inner->superloops);
> +
> +  for (unsigned i = 0; i != n; i++)
> +    if ((*inner->superloops)[i] == outer)
> +      return true;
> +  return false;
> +}
> +
>  extern void record_niter_bound (class loop *, const widest_int &, bool, bool);
>  extern HOST_WIDE_INT get_estimated_loop_iterations_int (class loop *);
>  extern HOST_WIDE_INT get_max_loop_iterations_int (const class loop *);
> diff --git a/gcc/fwprop.c b/gcc/fwprop.c
> index 2eab4fd4614..aed48e7273f 100644
> --- a/gcc/fwprop.c
> +++ b/gcc/fwprop.c
> @@ -866,10 +866,13 @@ forward_propagate_into (use_info *use, bool reg_prop_only = false)
>    rtx src = SET_SRC (def_set);
>
>    /* Allow propagations into a loop only for reg-to-reg copies, since
> -     replacing one register by another shouldn't increase the cost.  */
> +     replacing one register by another shouldn't increase the cost.
> +     Propagations from inner loop to outer loop should be also ok.  */
>    struct loop *def_loop = def_insn->bb ()->cfg_bb ()->loop_father;
>    struct loop *use_loop = use->bb ()->cfg_bb ()->loop_father;
> -  if ((reg_prop_only || def_loop != use_loop)
> +  if ((reg_prop_only
> +       || (use_loop && def_loop != use_loop
> +          && !loop_contains_p (use_loop, def_loop)))
>        && (!reg_single_def_p (dest) || !reg_single_def_p (src)))
>      return false;
>
> diff --git a/gcc/testsuite/g++.target/i386/pr103750-fwprop-1.C b/gcc/testsuite/g++.target/i386/pr103750-fwprop-1.C
> new file mode 100644
> index 00000000000..26987d307aa
> --- /dev/null
> +++ b/gcc/testsuite/g++.target/i386/pr103750-fwprop-1.C
> @@ -0,0 +1,26 @@
> +/* PR target/103750.  */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -std=c++1y -march=cannonlake -fdump-rtl-fwprop1" } */
> +/* { dg-final { scan-rtl-dump-not "subreg:HI\[ \\\(\]*reg:SI\[^\n]*\n\[^\n]*UNSPEC_TZCNT" "fwprop1" } } */
> +
> +#include<immintrin.h>
> +const char16_t *qustrchr(char16_t *n, char16_t *e, char16_t c) noexcept
> +{
> +  __m256i mch256 = _mm256_set1_epi16(c);
> +  for ( ; n < e; n += 32) {
> +    __m256i data1 = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(n));
> +    __m256i data2 = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(n) + 1);
> +    __mmask16 mask1 = _mm256_cmpeq_epu16_mask(data1, mch256);
> +    __mmask16 mask2 = _mm256_cmpeq_epu16_mask(data2, mch256);
> +    if (_kortestz_mask16_u8(mask1, mask2))
> +      continue;
> +
> +    unsigned idx = _tzcnt_u32(mask1);
> +    if (mask1 == 0) {
> +      idx = __tzcnt_u16(mask2);
> +      n += 16;
> +    }
> +    return n + idx;
> +  }
> +  return e;
> +}
> --
> 2.18.1
>