tree-optimization/121768 - bogus double reduction detected

The following changes how we detect double reductions, in particular
not setting vect_double_reduction_def on the outer PHIs when the inner
loop doesn't satisfy double reduction constraints.  It also simplifies
the setup a bit by not having to detect wheter we process an inner
loop of a double reduction.

	PR tree-optimization/121768
	* tree-vect-loop.cc (vect_inner_phi_in_double_reduction_p): Remove.
	(vect_analyze_scalar_cycles_1): Analyze inner loops of
	double reductions immediately and only mark fully recognized
	double reductions.  Skip already analyzed inner loops.
	(vect_is_simple_reduction): Change double_reduc from a flag
	to an output of the inner loop PHI and to whether we are
	processing an inner loop of a double reduction.

	* gcc.dg/vect/pr121768.c: New testcase.

1 files changed, 15 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/vect/pr121768.c b/gcc/testsuite/gcc.dg/vect/pr121768.c
new file mode 100644
index 0000000..b302f79
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr121768.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fno-tree-dce -fno-inline" } */
+
+int a, b, c;
+char d(char p) { return p; }
+int main () {
+  while (c) {
+    for (b = 2; b; b--) {
+      int *g = &a;
+      *g = d((d(*g) >= 128) | b);
+    }
+    c--;
+  }
+  return 0;
+}