[gcc r12-6342] Allow propagations from inner loop to outer loop.

[gcc r12-6342] Allow propagations from inner loop to outer loop.

[hongtao Liu]

https://gcc.gnu.org/g:e7a7dbb5ca5dd69689f1a462ba7620180acfe8b0

commit r12-6342-ge7a7dbb5ca5dd69689f1a462ba7620180acfe8b0
Author: liuhongt <hongtao.liu@intel.com>
Date:   Mon Dec 20 11:13:38 2021 +0800

    Allow propagations from inner loop to outer loop.
    
    NULL is considered as an outer loop of any other loop.
    
    gcc/ChangeLog:
    
            PR rtl-optimization/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.

Diff:
---
 build.log                                         |  0
 gcc/fwprop.c                                      |  7 ++++--
 gcc/testsuite/g++.target/i386/pr103750-fwprop-1.C | 26 +++++++++++++++++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/build.log b/build.log
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/gcc/fwprop.c b/gcc/fwprop.c
index 2eab4fd4614..3acb552f62f 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 also be 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
+       || (def_loop != use_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;
+}