x86: Enable 256 move by pieces for ALDERLAKE machine.

gcc/ChangeLog:

	* config/i386/x86-tune.def
	(X86_TUNE_AVX256_MOVE_BY_PIECES): Add alderlake.
	(X86_TUNE_AVX256_STORE_BY_PIECES): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pieces-memset-50.c: New test.
2 files changed