tree-optimization/97627 - Avoid computing niters for fake edges

This avoids computing niters information for fake edges.

2021-01-29  Bin Cheng  <bin.cheng@linux.alibaba.com>
	    Richard Biener  <rguenther@suse.de>

	PR tree-optimization/97627
	* tree-ssa-loop-niter.c (number_of_iterations_exit_assumptions):
	Do not analyze fake edges.

	* g++.dg/pr97627.C: New testcase.

gcc/testsuite/g++.dg/pr97627.C

@@ -0,0 +1,44 @@
+/* PR tree-optimization/97627.  */
+/* { dg-do run } */
+
+struct S { unsigned short x, y; } m = { 1, 0 };
+
+__attribute__((noipa)) void
+baz (int x, int y)
+{
+  if (x != 0 || y != 1)
+    __builtin_abort ();
+}
+
+__attribute__((noipa)) void
+bar ()
+{
+  throw 1;
+}
+
+void
+foo ()
+{
+  while (1)
+    {
+      int a = m.x + 1;
+      int b = m.y + 1;
+      for (int c = 0; c < a; c++)
+	for (int d = 0; d < b; d++)
+	  baz (d, b);
+      bar ();
+    }
+}
+
+int
+main ()
+{
+  try
+    {
+      foo ();
+    }
+  catch (int)
+    {
+    }
+  return 0;
+}

gcc/tree-ssa-loop-niter.c

@@ -2407,6 +2407,11 @@ number_of_iterations_exit_assumptions (class loop *loop, edge exit,
   affine_iv iv0, iv1;
   bool safe;
 
+  /* The condition at a fake exit (if it exists) does not control its
+     execution.  */
+  if (exit->flags & EDGE_FAKE)
+    return false;
+
   /* Nothing to analyze if the loop is known to be infinite.  */
   if (loop_constraint_set_p (loop, LOOP_C_INFINITE))
     return false;