[Bug tree-optimization/90579] [8/9/10 Regression] Huge store forward stall due to vectorizer

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90579

--- Comment #7 from Hongtao.liu <crazylht at gmail dot com> ---
Transform second loop as 

diff --git a/loop.c b/loop.c
index feea9ea..81a3ea6 100644
--- a/loop.c
+++ b/loop.c
@@ -9,6 +9,6 @@ loop (int k, double x)
   for (i=0;i<6;i++)
     r[i] = x * a[i + k];
   for (i=0;i<6;i++)
-    t+=r[5-i];
+    t+=r[i]; -------- using ascending order, align with former loop.
   return t;
 }
}

Can avoid store forward stalls.

Before loop transform:

loop_avx256: 3710992
loop       : 671995
loop_avx128: 650882

After loop transform:

loop_avx256: 661386
loop       : 652932
loop_avx128: 568710