* tree-ssa-ccp.c (latticevalue): Add UNKNOWN_VAL.
	(substitute_and_fold): Propigate into VUSE operands when possible.
	(visit_phi_node): Handle UNKNOWN_VAL latticevalue.
	(cp_lattice_meet): Handle merging of latticevalues when
	UNKNOWN_VAL is present.
	(visit_stmt): Visit assignments with V_MUST_DEFs.
	(visit_assignment): Gather ccp information for V_MUST_DEF operands.
	(ccp_fold): Deal with RHS' that are constant and virtual.
	(evaluate_stmt): Handle UNKNOWN_VAL likely values.
	(dump_lattice_value): Dump UNKNOWN_VAL latticevalues.
	(initialize): Mark statements with V_MUST_DEFs as VARYING only if the
	V_MUST_DEF operand is VARYING. Fix comment and include VOPS when
	computing immediate uses.
	(set_lattice_value): Disallow a UNKNOWN_VAL->UNDEFINED state
	transition.
	(replace_vuse_in): New function.
	(likely_value): Add check of vuse operands.
	(get_default_value): Set the default value of virtually defined
	variables to UKNOWN_VAL instead of VARYING.

testsuite:

	* gcc.dg/tree-ssa/20040721-1.c: New test.

From-SVN: r85055