[Bug bootstrap/85922] New: bootstrapping fails with -O3 because gcc 8.1.0 generates unknown instruction pshufb

[gcc at mailinator dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85922

            Bug ID: 85922
           Summary: bootstrapping fails with -O3 because gcc 8.1.0
                    generates unknown instruction pshufb
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at mailinator dot com
  Target Milestone: ---

On bootstrapping after implementing an hack for #85921 (environment and options
used specified there) bootstrapping failed:

Command issued by make:

/some/userdir/gcc-8.1.0-build/libiberty>
/some/userdir/gcc-8.1.0-build/./prev-gcc/xgcc
-B/some/userdir/gcc-8.1.0-build/./prev-gcc/
-B/some/userdir/i686-pc-linux-gnu/bin/ -B/some/userdir/i686-pc-linux-gnu/bin/
-B/some/userdir/i686-pc-linux-gnu/lib/ -isystem
/some/userdir/i686-pc-linux-gnu/include -isystem
/some/userdir/i686-pc-linux-gnu/sys-include    -c -DHAVE_CONFIG_H -O3
-march=native -gtoggle  -I. -I../../gcc-8.1.0/libiberty/../include  -W -Wall
-Wwrite-strings -Wc++-compat -Wstrict-prototypes -Wshadow=local -pedantic 
-D_GNU_SOURCE ../../gcc-8.1.0/libiberty/sha1.c -o sha1.o

error message:

/tmp/ccuTEPxe.s: Assembler messages:
/tmp/ccuTEPxe.s:3277: Error: no such instruction: `pshufb .LC2,%xmm0'

The same instruction is generated for a lot of other sources, too (as shown by
`make -k BOOT_CFLAGS='-O3 -march=native' CPATH="/some/userdir/include"
bootstrap-lean`

Workaround: compile with -O2 (the default)