{PING] [PATCH] Sign extension elimination

H. J. Lu hjl@lucon.org
Thu Apr 20 17:29:00 GMT 2006


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.


H.J.



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