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Re: {PING] [PATCH] Sign extension elimination

H. J. Lu wrote:
> On Thu, Apr 20, 2006 at 10:23:21AM -0700, Mark Mitchell wrote:
> > 
> > The x86-64 work is probably going to have to wait for 4.3.
> > 
> > >> What is it about the x86-64 instruction set that is so different from
> > >> PowerPC in this regard?  Are any of our other x86 experts concerned
> > >> about this pass?
> > > 
> > > What is so different for x86-64 is all 32bit register moves are
> > > automatically zero extended to 64bit. 
> > 
> > Whereas on other architectures a 32-bit register move is either (a)
> > sign-extending, or (b) leaves the high bits undefined?
> > 
> 
> I would say "leave the high bits unchanged". But Sparc, MIPS, PPC
> experts have to confirm it.

MIPS requires them to be sign-extended for proper operation.


Thiemo
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