sse.md ("mov<mode>_internal"): Use <sseinsnmode> mode attribute for TARGET_AVX512VL.

sse.md ("mov<mode>_internal"): Use <sseinsnmode> mode attribute for TARGET_AVX512VL.

/gcc
        * config/i386/sse.md ("mov<mode>_internal"): Use <sseinsnmode>
	mode attribute for TARGET_AVX512VL.

	* config/i386/i386.opt (mprefer-avx256): New option.
	* config/i386/i386.c (ix86_target_string): Add -mprefer-avx256
	to flag_opts.
	(ix86_preferred_simd_mode): Return 256-bit AVX modes
	for TARGET_PREFER_AVX256.
	* doc/invoke.texi (x86 Options): Document -mprefer-avx256.

/testsuite

        * gcc.target/i386/avx512f-constant-set.c: New test.

	* g++.dg/ext/pr57362.C: Test __attribute__((target("prefer-avx256"))).
	* gcc.target/i386/avx512f-prefer.c: New test.

From-SVN: r253089