Combine vpcmpuw + zero_extend to vpcmpuw.

Combine vpcmpuw + zero_extend to vpcmpuw.

vcmp{ps,ph,pd} and vpcmp{,u}{b,w,d,q} implicitly clear the upper bits
of dest.

gcc/ChangeLog:

	PR target/103750
	* config/i386/sse.md
	(*<avx512>_cmp<V48H_AVX512VL:mode>3_zero_extend<SWI248x:mode>):
	New pre_reload define_insn_and_split.
	(*<avx512>_cmp<VI12_AVX512VL:mode>3_zero_extend<SWI248x:mode>):
	Ditto.
	(*<avx512>_ucmp<VI12_AVX512VL:mode>3_zero_extend<SWI248x:mode>):
	Ditto.
	(*<avx512>_ucmp<VI48_AVX512VL:mode>3_zero_extend<SWI248x:mode>):
	Ditto.
	(*<avx512>_cmp<V48H_AVX512VL:mode>3_zero_extend<SWI248x:mode>_2):
	Ditto.
	(*<avx512>_cmp<VI12_AVX512VL:mode>3_zero_extend<SWI248x:mode>_2):
	Ditto.
	(*<avx512>_ucmp<VI12_AVX512VL:mode>3_zero_extend<SWI248x:mode>_2):
	Ditto.
	(*<avx512>_ucmp<VI48_AVX512VL:mode>3_zero_extend<SWI248x:mode>_2):
	Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx512bw-pr103750-1.c: New test.
	* gcc.target/i386/avx512bw-pr103750-2.c: New test.
	* gcc.target/i386/avx512f-pr103750-1.c: New test.
	* gcc.target/i386/avx512f-pr103750-2.c: New test.
	* gcc.target/i386/avx512fp16-pr103750-1.c: New test.
	* gcc.target/i386/avx512fp16-pr103750-2.c: New test.