i386: Simplify {,v}ph{add,sub{,s}{w,d} insn patterns [PR94460]

i386: Simplify {,v}ph{add,sub{,s}{w,d} insn patterns [PR94460]

As mentioned in the previous PR94460 patch, the RTL patterns look too
large/complicated, we can simplify them by just performing two 2 arg
permutations to move the arguments into the right spots and then just
doing the plus/minus (or signed saturation version thereof).

2020-05-05  Jakub Jelinek  <jakub@redhat.com>

	PR target/94460
	* config/i386/sse.md (avx2_ph<plusminus_mnemonic>wv16hi3,
	ssse3_ph<plusminus_mnemonic>wv8hi3, ssse3_ph<plusminus_mnemonic>wv4hi3,
	avx2_ph<plusminus_mnemonic>dv8si3, ssse3_ph<plusminus_mnemonic>dv4si3,
	ssse3_ph<plusminus_mnemonic>dv2si3): Simplify RTL patterns.