re PR tree-optimization/79621 (Missed path isolation opportunity)

	PR tree-optimization/79621
	* gimple-ssa-isolate-paths.c (find_implicit_erroneous_behavior): Ignore
	blocks with edges to themselves.

	PR tree-optimization/79621
	* gcc.c-torture/compile/pr79621.c: New test.

From-SVN: r245637

gcc/ChangeLog

+2017-02-21 Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/79621
+	* gimple-ssa-isolate-paths.c (find_implicit_erroneous_behavior): Ignore
+	blocks with edges to themselves.
+
 2017-02-21  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/79633

gcc/gimple-ssa-isolate-paths.c

@@ -35,6 +35,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-ssa.h"
 #include "cfgloop.h"
 #include "tree-cfg.h"
+#include "cfganal.h"
 #include "intl.h"
 
 
@@ -352,6 +353,16 @@ find_implicit_erroneous_behavior (void)
       if (has_abnormal_or_eh_outgoing_edge_p (bb))
 	continue;
 
+
+      /* If BB has an edge to itself, then duplication of BB below
+	 could result in reallocation of BB's PHI nodes.   If that happens
+	 then the loop below over the PHIs would use the old PHI and
+	 thus invalid information.  We don't have a good way to know
+	 if a PHI has been reallocated, so just avoid isolation in
+	 this case.  */
+      if (find_edge (bb, bb))
+	continue;
+
       /* First look for a PHI which sets a pointer to NULL and which
  	 is then dereferenced within BB.  This is somewhat overly
 	 conservative, but probably catches most of the interesting

gcc/testsuite/ChangeLog

+2017-02-21  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/79621
+	* gcc.c-torture/compile/pr79621.c: New test.
+
 2017-02-21  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/79655

gcc/testsuite/gcc.c-torture/compile/pr79621.c

+int b5;
+
+void
+h6 (int zb, int e7)
+{
+  while (b5 > 0)
+    {
+      int gv;
+
+      for (gv = 1; gv < 4; ++gv)
+        {
+          ((zb != 0) ? b5 : gv) && (b5 /= e7);
+          zb = 0;
+        }
+      e7 = 0;
+    }
+}
+