x86: Encode 256-bit/512-bit VEX/EVEX insns with 128-bit VEX
Since all AVX512 processors support AVX, we can encode 256-bit/512-bit
VEX/EVEX vector register clearing instructions with 128-bit VEX vector
register clearing instructions at -O1.
* config/tc-i386.c (optimize_encoding): Encode 256-bit/512-bit
VEX/EVEX vector register clearing instructions with 128-bit VEX
vector register clearing instructions at -O1.
* doc/c-i386.texi: Update -O1 and -O2 documentation.
* testsuite/gas/i386/i386.exp: Run optimize-1a and
x86-64-optimize-2a.
* testsuite/gas/i386/optimize-1a.d: New file.
* testsuite/gas/i386/x86-64-optimize-2a.d: Likewise.