i386: Fix some -mavx512vl -mno-avx512bw bugs [PR99321]

i386: Fix some -mavx512vl -mno-avx512bw bugs [PR99321]

As I wrote in the mail with the previous PR99321 fix, we have various
bugs where we emit instructions that need avx512bw and avx512vl
ISAs when compiling with -mavx512vl -mno-avx512bw.

Without the following patch, the attached testcase fails with:
/tmp/ccW4PsfG.s: Assembler messages:
/tmp/ccW4PsfG.s:9: Error: unsupported instruction `vpaddb'
/tmp/ccW4PsfG.s:20: Error: unsupported instruction `vpaddb'
/tmp/ccW4PsfG.s:31: Error: unsupported instruction `vpaddw'
/tmp/ccW4PsfG.s:42: Error: unsupported instruction `vpaddw'
/tmp/ccW4PsfG.s:53: Error: unsupported instruction `vpsubb'
/tmp/ccW4PsfG.s:64: Error: unsupported instruction `vpsubb'
/tmp/ccW4PsfG.s:75: Error: unsupported instruction `vpsubw'
/tmp/ccW4PsfG.s:86: Error: unsupported instruction `vpsubw'
/tmp/ccW4PsfG.s:97: Error: unsupported instruction `vpmullw'
/tmp/ccW4PsfG.s:108: Error: unsupported instruction `vpmullw'
/tmp/ccW4PsfG.s:133: Error: unsupported instruction `vpminub'
/tmp/ccW4PsfG.s:144: Error: unsupported instruction `vpminuw'
/tmp/ccW4PsfG.s:155: Error: unsupported instruction `vpminuw'
/tmp/ccW4PsfG.s:166: Error: unsupported instruction `vpminsb'
/tmp/ccW4PsfG.s:177: Error: unsupported instruction `vpminsb'
/tmp/ccW4PsfG.s:202: Error: unsupported instruction `vpminsw'
/tmp/ccW4PsfG.s:227: Error: unsupported instruction `vpmaxub'
/tmp/ccW4PsfG.s:238: Error: unsupported instruction `vpmaxuw'
/tmp/ccW4PsfG.s:249: Error: unsupported instruction `vpmaxuw'
/tmp/ccW4PsfG.s:260: Error: unsupported instruction `vpmaxsb'
/tmp/ccW4PsfG.s:271: Error: unsupported instruction `vpmaxsb'
/tmp/ccW4PsfG.s:296: Error: unsupported instruction `vpmaxsw'

We already have Yw constraint which is equivalent to v for
-mavx512bw -mavx512vl and to nothing otherwise, per discussions
this patch changes it to stand for x otherwise.  As it is an
undocumented internal constraint, hopefully it won't affect
any inline asm in the wild.
For the instructions that need both we need to use Yw and
v for modes that don't need that.

2021-03-07  Jakub Jelinek  <jakub@redhat.com>

	PR target/99321
	* config/i386/constraints.md (Yw): Use SSE_REGS if TARGET_SSE
	but TARGET_AVX512BW or TARGET_AVX512VL is not set.  Adjust description
	and comment.
	* config/i386/sse.md (v_Yw): New define_mode_attr.
	(*<insn><mode>3, *mul<mode>3<mask_name>, *avx2_<code><mode>3,
	*sse4_1_<code><mode>3<mask_name>): Use <v_Yw> instead of v
	in constraints.
	* config/i386/mmx.md (mmx_pshufw_1, *vec_dupv4hi): Use Yw instead of
	xYw in constraints.

	* lib/target-supports.exp
	(check_effective_target_assembler_march_noavx512bw): New effective
	target.
	* gcc.target/i386/avx512vl-pr99321-1.c: New test.