* Makefile.in (OBJS): Add gimple-ssa-isolate-paths.o
	* common.opt (-fisolate-erroneous-paths): Add option and
	documentation.
	* gimple-ssa-isolate-paths.c: New file.
	* gimple.c (check_loadstore): New function.
	(infer_nonnull_range): Moved into gimple.c from tree-vrp.c
	Verify OP is in the argument list and the argument corresponding
	to OP is a pointer type.  Use operand_equal_p rather than
	pointer equality when testing if OP is on the nonnull list.
	Use check_loadstore rather than count_ptr_derefs.  Handle
	GIMPLE_RETURN statements.
	* tree-vrp.c (infer_nonnull_range): Remove.
	* gimple.h (infer_nonnull_range): Declare.
	* opts.c (default_options_table): Add
	* OPT_fisolate_erroneous_paths.
	* passes.def: Add pass_isolate_erroneous_paths.
	* timevar.def (TV_ISOLATE_ERRONEOUS_PATHS): New timevar.
	* tree-pass.h (make_pass_isolate_erroneous_paths): Declare.
	* tree-ssa.c (struct count_ptr_d): Remove.
	(count_ptr_derefs, count_uses_and_derefs): Remove.
	* tree-ssa.h (count_uses_and_derefs): Remove.

	* gcc.dg/pr38984.c: Add -fno-isolate-erroneous-paths.
	* gcc.dg/tree-ssa/isolate-1.c: New test.
	* gcc.dg/tree-ssa/isolate-2.c: New test.
	* gcc.dg/tree-ssa/isolate-3.c: New test.
	* gcc.dg/tree-ssa/isolate-4.c: New test.

From-SVN: r204414