diff --git a/gcc/testsuite/gcc.dg/pr106519.c b/gcc/testsuite/gcc.dg/pr106519.c
new file mode 100644
index 0000000000000000000000000000000000000000..3d4662d8a02c6501560abb71ac53320f093620d8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr106519.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+
+int bytestart, bytemem_0_0, modlookup_l_p;
+
+void
+modlookup_l() {
+  long j;
+  while (modlookup_l_p)
+    while (bytestart && j && bytemem_0_0)
+      j = j + 1;
+}
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index a8e55e040649e17f83a2fc3340e368cf9c4c5e70..1c4942b5b5c18732a8b18789c04e2685437404dd 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -268,7 +268,8 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 	  continue;
 	}
       else if (EDGE_SUCC (bb1, 0)->dest == EDGE_SUCC (bb2, 0)->dest
-	       && !empty_block_p (bb1))
+	       && !empty_block_p (bb1)
+	       && single_succ_p (bb1) && single_succ_p (bb2))
 	diamond_p = true;
       else
 	continue;
@@ -311,6 +312,12 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 	    for (gsi = gsi_start (phis); !gsi_end_p (gsi); gsi_next (&gsi))
 	      {
 		phi = as_a <gphi *> (gsi_stmt (gsi));
+
+		/* A diamond must continue to the same destination node, otherwise
+		   by definition it's not a diamond.  */
+		if (diamond_p && e1->dest != e2->dest)
+		  continue;
+
 		arg0 = gimple_phi_arg_def (phi, e1->dest_idx);
 		arg1 = gimple_phi_arg_def (phi, e2->dest_idx);
 		if (value_replacement (bb, bb1, e1, e2, phi, arg0, arg1) == 2)
@@ -329,12 +336,15 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 	  if (!phi)
 	    continue;
 
-	  arg0 = gimple_phi_arg_def (phi, e1->dest_idx);
-	  arg1 = gimple_phi_arg_def (phi, e2->dest_idx);
+	  /* A diamond must continue to the same destination node, otherwise
+	     by definition it's not a diamond.  */
+	  if (diamond_p && e1->dest != e2->dest)
+	    continue;
 
 	  /* Something is wrong if we cannot find the arguments in the PHI
 	     node.  */
-	  gcc_assert (arg0 != NULL_TREE && arg1 != NULL_TREE);
+	  arg0 = gimple_phi_arg_def (phi, e1->dest_idx);
+	  arg1 = gimple_phi_arg_def (phi, e2->dest_idx);
 
 	  gphi *newphi;
 	  if (single_pred_p (bb1)