Optimize multiplication for V8QI,V16QI,V32QI under TARGET_AVX512BW.

Optimize multiplication for V8QI,V16QI,V32QI under TARGET_AVX512BW.

2020-06-13   Hongtao Liu  <hongtao.liu@intel.com>

gcc/ChangeLog:
	PR target/95488
	* config/i386/i386-expand.c (ix86_expand_vecmul_qihi): New
	function.
	* config/i386/i386-protos.h (ix86_expand_vecmul_qihi): Declare.
	* config/i386/sse.md (mul<mode>3): Drop mask_name since
	there's no real simd int8 multiplication instruction with
	mask. Also optimize it under TARGET_AVX512BW.
	(mulv8qi3): New expander.

gcc/testsuite/ChangeLog:
	* gcc.target/i386/avx512bw-pr95488-1.c: New test.
	* gcc.target/i386/avx512bw-pr95488-2.c: Ditto.
	* gcc.target/i386/avx512vl-pr95488-1.c: Ditto.
	* gcc.target/i386/avx512vl-pr95488-2.c: Ditto.