tree-optimization/116879 - failure to recognize non-empty latch

When we relaxed the vectorizers constraint on loop structure verifying
the emptiness of the latch became too lose as can be seen in the case
for PR116879 where the latch effectively contains two basic-blocks
which one being an unmerged forwarder that's not empty.

	PR tree-optimization/116879
	* tree-vect-loop.cc (vect_analyze_loop_form): Scan all
	blocks that form the latch.

	* gcc.dg/pr116879.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/pr116879.c b/gcc/testsuite/gcc.dg/pr116879.c
new file mode 100644 (file)
index 0000000..73ddb2b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr116879.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-vectorize -fallow-store-data-races -fno-tree-ch -ftree-loop-distribution" } */
+
+static int b;
+int *a, c, *d = &c;
+int main() {
+  int e = 0;
+  for (; e < 8; e = (char)(e + 1)) {
+    int *f = &b, g[8], h = 0;
+    for (; h < 8; h++)
+      g[h] = 0;
+    --*f != (*d = g[0] || a);
+  }
+  return 0;
+}

diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 5cd4bdb32e040d83d4ceadaaf94187823f6cf070..0ce1bf8ebbacc541acdb718234570f544ca913e9 100644 (file)
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -1851,10 +1851,17 @@ vect_analyze_loop_form (class loop *loop, vect_loop_form_info *info)
                                   " too many incoming edges.\n");
 
   /* We assume that the latch is empty.  */
-  if (!empty_block_p (loop->latch)
-      || !gimple_seq_empty_p (phi_nodes (loop->latch)))
-    return opt_result::failure_at (vect_location,
-                                  "not vectorized: latch block not empty.\n");
+  basic_block latch = loop->latch;
+  do
+    {
+      if (!empty_block_p (latch)
+         || !gimple_seq_empty_p (phi_nodes (latch)))
+       return opt_result::failure_at (vect_location,
+                                      "not vectorized: latch block not "
+                                      "empty.\n");
+      latch = single_pred (latch);
+    }
+  while (single_succ_p (latch));
 
   /* Make sure there is no abnormal exit.  */
   auto_vec<edge> exits = get_loop_exit_edges (loop);