Fix PR23511

[Sebastian Pop]

This patch fixes tree-optimization/23511.  Bootstrapped and tested on
i686-linux.  Committed.

        * tree-ssa-loop-niter.c (infer_loop_bounds_from_undefined): Don't 
        handle cases where TYPE_MIN_VALUE or TYPE_MAX_VALUE are NULL_TREE.

Index: tree-ssa-loop-niter.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-ssa-loop-niter.c,v
retrieving revision 2.39
diff -d -u -p -r2.39 tree-ssa-loop-niter.c
--- tree-ssa-loop-niter.c       21 Aug 2005 10:48:19 -0000      2.39
+++ tree-ssa-loop-niter.c       23 Aug 2005 08:13:05 -0000
@@ -1460,7 +1460,9 @@ infer_loop_bounds_from_undefined (struct
                    if (init == NULL_TREE
                        || step == NULL_TREE
                        || TREE_CODE (init) != INTEGER_CST
-                       || TREE_CODE (step) != INTEGER_CST)
+                       || TREE_CODE (step) != INTEGER_CST
+                       || TYPE_MIN_VALUE (type) == NULL_TREE
+                       || TYPE_MAX_VALUE (type) == NULL_TREE)
                      break;
 
                    utype = unsigned_type_for (type);