re PR debug/42234 (internal compiler error: verify_ssa failed)

	PR debug/42234
	* tree-ssa-dom.c (degenerate_phi_result): Check for NULL phi
	argument earlier.

From-SVN: r155025

gcc/ChangeLog

+2009-12-06  Richard Henderson  <rth@redhat.com>
+
+	PR debug/42234
+	* tree-ssa-dom.c (degenerate_phi_result): Check for NULL phi
+	argument earlier.
+
 2009-12-06  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
 
 	* doc/install.texi: Document MPC is required.

gcc/testsuite/gcc.c-torture/compile/pr42234.c

+/* { dg-options "-g" } */
+
+void
+foo (int x)
+{
+  struct S { int s; } d = { 1 };
+  unsigned int e = 1;
+  if (x)
+    e = x && d.s;
+  else
+    for (e = 0; e <= 3; e--)
+      ;
+  e++;
+}

gcc/tree-ssa-dom.c

@@ -2396,6 +2396,8 @@ degenerate_phi_result (gimple phi)
 
       if (arg == lhs)
 	continue;
+      else if (!arg)
+	break;
       else if (!val)
 	val = arg;
       else if (arg == val)
@@ -2403,7 +2405,7 @@ degenerate_phi_result (gimple phi)
       /* We bring in some of operand_equal_p not only to speed things
 	 up, but also to avoid crashing when dereferencing the type of
 	 a released SSA name.  */
-      else if (!arg || TREE_CODE (val) != TREE_CODE (arg)
+      else if (TREE_CODE (val) != TREE_CODE (arg)
 	       || TREE_CODE (val) == SSA_NAME
 	       || !operand_equal_p (arg, val, 0))
 	break;