re PR tree-optimization/85284 (Loop miscompilation starting with r238367)

2018-04-09  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/85284
	* tree-ssa-loop-niter.c (number_of_iterations_exit_assumptions):
	Only use the niter constraining form of simple_iv when the exit
	is always executed.

	* gcc.dg/torture/pr85284.c: New testcase.

From-SVN: r259234

gcc/ChangeLog

+2018-04-09  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/85284
+	* tree-ssa-loop-niter.c (number_of_iterations_exit_assumptions):
+	Only use the niter constraining form of simple_iv when the exit
+	is always executed.
+
 2018-04-09  Tom de Vries  <tom@codesourcery.com>
 
 	PR target/84041

gcc/testsuite/ChangeLog

+2018-04-09  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/85284
+	* gcc.dg/torture/pr85284.c: New testcase.
+
 2018-04-09  Andrey Belevantsev  <abel@ispras.ru>
 
 	PR rtl-optimization/80463

gcc/testsuite/gcc.dg/torture/pr85284.c

+/* { dg-do run } */
+
+static int p[48], v;
+
+int
+main ()
+{
+  p[32] = 1;
+  for (int i = 48; i--;)
+    {
+      if (!p[i])
+	continue;
+      if ((i & 7) > 2)
+	break;
+      v = i & 1;
+    }
+  if (v != 0)
+    __builtin_abort ();
+  return 0;
+}

gcc/tree-ssa-loop-niter.c

@@ -2356,11 +2356,11 @@ number_of_iterations_exit_assumptions (struct loop *loop, edge exit,
 
   tree iv0_niters = NULL_TREE;
   if (!simple_iv_with_niters (loop, loop_containing_stmt (stmt),
-			      op0, &iv0, &iv0_niters, false))
+			      op0, &iv0, safe ? &iv0_niters : NULL, false))
     return false;
   tree iv1_niters = NULL_TREE;
   if (!simple_iv_with_niters (loop, loop_containing_stmt (stmt),
-			      op1, &iv1, &iv1_niters, false))
+			      op1, &iv1, safe ? &iv1_niters : NULL, false))
     return false;
   /* Give up on complicated case.  */
   if (iv0_niters && iv1_niters)