[PATCH] Fix PR79034

[Richard Biener <rguenther at suse dot de>]

I am testing the following patch to fix another case where call
shrink-wrapping fails to update PHIs properly.  The previous fix
missed the case where the destination contained a degenerate PHI
thus we can simply propagate those out.

Bootstrap and regtest running on x86_64-unknown-linux-gnu (for trunk
where the testcase doesn't show the latent issue).  I'll backport
later.

Richard.

2016-01-10  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/79034
	* tree-call-cdce.c (shrink_wrap_one_built_in_call_with_conds):
	Propagate out degenerate PHIs in the joiner.

	* g++.dg/torture/pr79034.C: New testcase.

Index: gcc/tree-call-cdce.c
===================================================================
--- gcc/tree-call-cdce.c	(revision 244260)
+++ gcc/tree-call-cdce.c	(working copy)
@@ -805,7 +805,18 @@ shrink_wrap_one_built_in_call_with_conds
       if (EDGE_COUNT (join_tgt_in_edge_from_call->dest->preds) > 1)
 	join_tgt_bb = split_edge (join_tgt_in_edge_from_call);
       else
-	join_tgt_bb = join_tgt_in_edge_from_call->dest;
+	{
+	  join_tgt_bb = join_tgt_in_edge_from_call->dest;
+	  /* We may have degenerate PHIs in the destination.  Propagate
+	     those out.  */
+	  for (gphi_iterator i = gsi_start_phis (join_tgt_bb); !gsi_end_p (i);)
+	    {
+	      gphi *phi = i.phi ();
+	      replace_uses_by (gimple_phi_result (phi),
+			       gimple_phi_arg_def (phi, 0));
+	      remove_phi_node (&i, true);
+	    }
+	}
     }
   else
     {
Index: gcc/testsuite/g++.dg/torture/pr79034.C
===================================================================
--- gcc/testsuite/g++.dg/torture/pr79034.C	(nonexistent)
+++ gcc/testsuite/g++.dg/torture/pr79034.C	(working copy)
@@ -0,0 +1,52 @@
+/* { dg-do compile } */
+
+extern "C" {
+    float sqrtf(float);
+}
+
+class T {
+public:
+    float floats[1];
+
+    inline float length() const {
+	return sqrtf(floats[0]);
+    }
+};
+
+void destruct(void *);
+
+class Container {
+
+    T Ts[1];
+
+public:
+    ~Container() {
+	destruct((void *)Ts);
+    }
+
+    T& operator[](int n) {
+	return Ts[0];
+    }
+};
+
+void fill(Container&);
+
+void doit()
+{
+  Container data;
+  float max = 10;
+
+  int i, j, k;
+
+  for (i = 0; i < 10; i++) {
+      for (j = 1; j < 10; j++) {
+	  if (max < 5)
+	    break;
+	  fill( data);
+	  max = data[0].length();
+	  for (k = 1; k < j; k++) {
+	      max = 5;
+	  }
+      }
+  }
+}