[PATCH] Fix PR78413

[Bill Schmidt]

Hi,

The if-conversion patch for PR77848 missed a case where an outer loop
should not be versioned for vectorization; this was caught by an assert
in tests recorded in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78413.
This patch fixes the problem by ensuring that both inner and outer loop
latches have a single predecessor before versioning an outer loop.

Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no
regressions.  Is this ok for trunk?

Thanks,
Bill


[gcc]

2016-11-18  Bill Schmidt  <wschm...@linux.vnet.ibm.com>

        PR tree-optimization/78413
        * tree-if-conv.c (versionable_outer_loop_p): Require that both
        inner and outer loop latches have single predecessors.

[gcc/testsuite]

2016-11-18  Bill Schmidt  <wschm...@linux.vnet.ibm.com>

        PR tree-optimization/78413
        * gcc.dg/tree-ssa/pr78413.c: New test.


Index: gcc/testsuite/gcc.dg/tree-ssa/pr78413.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr78413.c     (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr78413.c     (working copy)
@@ -0,0 +1,35 @@
+/* PR78413.  These previously failed in tree if-conversion due to a loop
+   latch with multiple predecessors that the code did not anticipate.  */
+/* { dg-do compile } */
+/* { dg-options "-O3 -ffast-math" } */
+
+extern long long int llrint(double x);
+int a;
+double b;
+__attribute__((cold)) void decode_init() {
+  int c, d = 0;
+  for (; d < 12; d++) {
+    if (d)
+      b = 0;
+    c = 0;
+    for (; c < 6; c++)
+      a = b ? llrint(b) : 0;
+  }
+}
+
+struct S {
+  _Bool bo;
+};
+int a, bb, c, d;
+void fn1() {
+  do
+    do
+      do {
+       struct S *e = (struct S *)1;
+       do
+         bb = a / (e->bo ? 2 : 1);
+       while (bb);
+      } while (0);
+    while (d);
+  while (c);
+}
Index: gcc/tree-if-conv.c
===================================================================
--- gcc/tree-if-conv.c  (revision 242551)
+++ gcc/tree-if-conv.c  (working copy)
@@ -2575,6 +2575,8 @@ version_loop_for_if_conversion (struct loop *loop)
     - The loop has a single exit.
     - The loop header has a single successor, which is the inner
       loop header.
+    - Each of the inner and outer loop latches have a single
+      predecessor.
     - The loop exit block has a single predecessor, which is the
       inner loop's exit block.  */
 
@@ -2586,7 +2588,9 @@ versionable_outer_loop_p (struct loop *loop)
       || loop->inner->next
       || !single_exit (loop)
       || !single_succ_p (loop->header)
-      || single_succ (loop->header) != loop->inner->header)
+      || single_succ (loop->header) != loop->inner->header
+      || !single_pred_p (loop->latch)
+      || !single_pred_p (loop->inner->latch))
     return false;
   
   basic_block outer_exit = single_pred (loop->latch);