PR c++/60760 - arithmetic on null pointers should not be allowed in constant
PR c++/71091 - constexpr reference bound to a null pointer dereference

gcc/cp/ChangeLog:

	PR c++/60760
	PR c++/71091
        * constexpr.c (cxx_eval_binary_expression): Reject invalid expressions
        involving null pointers.
        (cxx_eval_component_reference): Reject null pointer dereferences.
        (cxx_eval_indirect_ref): Reject indirecting through null pointers.
        (cxx_eval_constant_expression): Reject invalid expressions involving
        null pointers.

gcc/testsuite/ChangeLog:

	PR c++/60760
	PR c++/71091
	* g++.dg/cpp0x/constexpr-cast.C: New test.
        * g++.dg/cpp0x/constexpr-nullptr-2.C: New test.
        * g++.dg/cpp1y/constexpr-sfinae.C: Correct.
        * g++.dg/ubsan/pr63956.C: Correct.

From-SVN: r238909