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

[Richard Biener <richard.guenther@gmail.com>]

On January 6, 2022 7:51:48 AM GMT+01:00, liuhongt <hongtao.liu@intel.com> wrote:
>> 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)
>>
>Thanks, it seems flow_loop_nested_p assume outer and inner not to be
>NULL. So I add some conditions to check NULL which is considered as an outer
> loop of any other loop.

Huh, loop_father should never be NULL. Maybe when fwprop is run after RTL loop opts you instead want to add a check for current_loops or alternelatively initialize loops in fwprop. 

>
>
>gcc/ChangeLog:
>
>	PR rtl/103750
>	* 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/fwprop.c                                  |  7 +++--
> .../g++.target/i386/pr103750-fwprop-1.C       | 26 +++++++++++++++++++
> 2 files changed, 31 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/g++.target/i386/pr103750-fwprop-1.C
>
>diff --git a/gcc/fwprop.c b/gcc/fwprop.c
>index 2eab4fd4614..af2e9d1c189 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
>+	   &&(!def_loop || !flow_loop_nested_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;
>+}