ssnop for mips

[Ralf Baechle]

On Wed, Jul 18, 2001 at 08:16:00PM -0700, cgd@sibyte.com wrote:

> mrs@windriver.com ("mike stump") writes:
> > 2001-07-18  Mike Stump  <mrs@wrs.com>
> > 
> > 	* mips-opc.c (ssnop): While the documentation makes it seem
> > 	like this instruction is new for MIPS32, it is not, it is needed
> > 	on all ISA levels.
> 
> for some value of 'needed'.  it may have some absolutely different
> 'no-op' meaning on non-MIPS32/MIPS64 processors.
> 
> if i recall correctly, that instruction doesn't inhibit multi-issue.

Ssnop is documented as ``breaks superscalar dispatch''.  See also the
comments in IRIX <sys/asm.h> which I can't paste here for (C) reasons.

> Personally, I don't think it should be enabled if not MIPS32/MIPS64:
> 
> * the behaviour may not be what's expected, and

All CPUs that don't implement ssnop's special semantics will decode it as
sll $zero, $zero, 1 which is obviously harmless.

  Ralf