x86/AVX512: improve generated code for mask-to-vector-register conversions

x86/AVX512: improve generated code for mask-to-vector-register conversions

Conversion of comparison results to full vectors does, when VPMOVM2* are
unavailable, not require any intermediate VMOVDQ{A,U}*: Simply use
embedded masking on VPTERNLOG* right away, which is available with
AVX512F (while VPMOVM2{D,Q} are available only with AVX512DQ).

Note that the chosen immediate is only one of many possible ones; I was
trying to make the insn here distinguishable from the pre-existing uses
of vpternlog.

gcc/
2019-07-23  Jan Beulich  <jbeulich@suse.com>

	* config/i386/sse.md (<avx512>_cvtmask2<ssemodesuffix><mode>):
	Require only AVX512F.
	(*<avx512>_cvtmask2<ssemodesuffix><mode>): Likewise.  Add
	alternative expanding to vpternlog.

From-SVN: r273719