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

[liuhongt via Gcc-patches]

> 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.



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;
+}
-- 
2.18.1