Redundant instructions in loop optimization for x86-64?

[James E Wilson]

H. J. Lu wrote:
> Is there a way to tell gcc that 32bit zero extension isn't needed for
> x86-64?

It isn't quite that simple.  Sometimes they will be needed.  Sometimes 
they won't.

You might want to look at
     http://gcc.gnu.org/ml/gcc/2004-09/msg00377.html
which is a proposal to add an RTL optimization pass to eliminate 
unnecessary sign/zero extension instructions on targets that support 
both 32-bit and 64-bit code.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com