re PR tree-optimization/82434 (-fstore-merging does not work reliably.)

re PR tree-optimization/82434 (-fstore-merging does not work reliably.)

	PR tree-optimization/82434
	* fold-const.h (can_native_encode_type_p,
	can_native_encode_string_p): Remove.
	* fold-const.c (native_encode_int): Formatting fixes.  If ptr is NULL,
	don't encode anything, just return what would be otherwise returned.
	(native_encode_fixed, native_encode_complex, native_encode_vector):
	Likewise.
	(native_encode_string): Likewise.  Inline by hand
	can_native_encode_string_p.
	(can_native_encode_type_p): Remove.
	(can_native_encode_string_p): Remove.
	* tree-vect-stmts.c (vectorizable_store): Instead of testing just
	STRING_CSTs using can_native_encode_string_p, test all
	CONSTANT_CLASS_P values using native_encode_expr with NULL ptr.
	* gimple-ssa-store-merging.c (encode_tree_to_bitpos): Remove last
	argument from native_encode_expr.
	(rhs_valid_for_store_merging_p): Use native_encode_expr with NULL ptr.
	(pass_store_merging::execute): Don't unnecessarily look for 3 stmts,
	but just 2.

	* gcc.dg/store_merging_9.c: New test.

From-SVN: r253483