i386: Add missing vector zero/sign extend expanders [PR92658]

i386: Add missing vector zero/sign extend expanders [PR92658]

2020-05-19  Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog:
	PR target/92658
	* config/i386/sse.md (<code>v16qiv16hi2): New expander.
	(<code>v32qiv32hi2): Ditto.
	(<code>v8qiv8hi2): Ditto.
	(<code>v16qiv16si2): Ditto.
	(<code>v8qiv8si2): Ditto.
	(<code>v4qiv4si2): Ditto.
	(<code>v16hiv16si2): Ditto.
	(<code>v8hiv8si2): Ditto.
	(<code>v4hiv4si2): Ditto.
	(<code>v8qiv8di2): Ditto.
	(<code>v4qiv4di2): Ditto.
	(<code>v2qiv2di2): Ditto.
	(<code>v8hiv8di2): Ditto.
	(<code>v4hiv4di2): Ditto.
	(<code>v2hiv2di2): Ditto.
	(<code>v8siv8di2): Ditto.
	(<code>v4siv4di2): Ditto.
	(<code>v2siv2di2): Ditto.

gcc/testsuite/ChangeLog:
	PR target/92658
	* gcc.target/i386/pr92658-sse4.c: New test.
	* gcc.target/i386/pr92658-avx2.c: New test.
	* gcc.target/i386/pr92658-avx512bw.c: New test.