This shows reassoc is harmful even with len == 3.
Pushed.
PR tree-optimization/120687
* gcc.dg/vect/pr120687-3.c: New testcase.
---
gcc/testsuite/gcc.dg/vect/pr120687-3.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/vect/pr120687-3.c
diff --git a/gcc/testsuite/gcc.dg/vect/pr120687-3.c
b/gcc/testsuite/gcc.dg/vect/pr120687-3.c
new file mode 100644
index 00000000000..f20a66a6223
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr120687-3.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_double } */
+/* { dg-additional-options "-ffast-math" } */
+
+float
+frd (float *p, float *lastone)
+{
+ float sum = 0;
+ for (; p <= lastone; p += 2)
+ sum += p[0] + p[1];
+ return sum;
+}
+
+/* { dg-final { scan-tree-dump "reduction: detected reduction chain" "vect" }
} */
+/* { dg-final { scan-tree-dump-not "SLP discovery of reduction chain failed"
"vect" } } */
+/* { dg-final { scan-tree-dump "optimized: loop vectorized" "vect" } } */
--
2.43.0
