[Bug target/68285] New: Assembler error on x86_64-linux-gnu: invalid instruction suffix for `movabs'

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68285

            Bug ID: 68285
           Summary: Assembler error on x86_64-linux-gnu: invalid
                    instruction suffix for `movabs'
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The current gcc trunk generates an assembler error when compiling the following
code on x86_64-linux-gnu at -O1 and above in the 64-bit mode (but not in the
32-bit mode). 

This is a regression from 5.2.x. 


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20151109 (experimental) [trunk revision 230020] (GCC) 
$ 
$ gcc-trunk -m64 -O0 small.c
$ gcc-trunk -m32 -O1 small.c
$ gcc-5.2 -m64 -O1 small.c
$ 
$ gcc-trunk -m64 -O1 small.c
/tmp/ccwczUop.s: Assembler messages:
/tmp/ccwczUop.s:8: Error: invalid instruction suffix for `movabs'
/tmp/ccwczUop.s:18: Error: invalid instruction suffix for `movabs'
$ 
$ cat small.c
struct
{
  volatile int f0;
} a[4194305];

void
fn1 ()
{
  a[4194304].f0;
}

int
main ()
{
  fn1 (); 
  return 0;
}