i386, expand: Optimize also 256-bit and 512-bit permutatations as vpmovzx if possible...

i386, expand: Optimize also 256-bit and 512-bit permutatations as vpmovzx if possible [PR95905]

The following patch implements what I've talked about, i.e. to no longer
force operands of vec_perm_const into registers in the generic code, but let
each of the (currently 8) targets force it into registers individually,
giving the targets better control on if it does that and when and allowing
them to do something special with some particular operands.
And then defines the define_insn_and_split for the 256-bit and 512-bit
permutations into vpmovzx* (only the bw, wd and dq cases, in theory we could
add define_insn_and_split patterns also for the bd, bq and wq).

2021-01-13  Jakub Jelinek  <jakub@redhat.com>

	PR target/95905
	* optabs.c (expand_vec_perm_const): Don't force v0 and v1 into
	registers before calling targetm.vectorize.vec_perm_const, only after
	that.
	* config/i386/i386-expand.c (ix86_vectorize_vec_perm_const): Handle
	two argument permutation when one operand is zero vector and only
	after that force operands into registers.
	* config/i386/sse.md (*avx2_zero_extendv16qiv16hi2_1): New
	define_insn_and_split pattern.
	(*avx512bw_zero_extendv32qiv32hi2_1): Likewise.
	(*avx512f_zero_extendv16hiv16si2_1): Likewise.
	(*avx2_zero_extendv8hiv8si2_1): Likewise.
	(*avx512f_zero_extendv8siv8di2_1): Likewise.
	(*avx2_zero_extendv4siv4di2_1): Likewise.
	* config/mips/mips.c (mips_vectorize_vec_perm_const): Force operands
	into registers.
	* config/arm/arm.c (arm_vectorize_vec_perm_const): Likewise.
	* config/sparc/sparc.c (sparc_vectorize_vec_perm_const): Likewise.
	* config/ia64/ia64.c (ia64_vectorize_vec_perm_const): Likewise.
	* config/aarch64/aarch64.c (aarch64_vectorize_vec_perm_const): Likewise.
	* config/rs6000/rs6000.c (rs6000_vectorize_vec_perm_const): Likewise.
	* config/gcn/gcn.c (gcn_vectorize_vec_perm_const): Likewise.  Use std::swap.

	* gcc.target/i386/pr95905-2.c: Use scan-assembler-times instead of
	scan-assembler.  Add tests with zero vector as first __builtin_shuffle
	operand.
	* gcc.target/i386/pr95905-3.c: New test.
	* gcc.target/i386/pr95905-4.c: New test.