gcc-2.7 creates faster code than pgcc-1.1.1

[Zack Weinberg]

On Thu, 04 Mar 1999 23:03:58 -0500, David Edelsohn wrote:
>>>>>> Jeffrey A Law writes:
>
>Jeff> True, but I don't believe the loop optimizer is prepared to do that sinc
>e it
>Jeff> doesn't keep track of what bits are active vs what bits are inactive in 
>a 
>Jeff> value.
>
>	GCC is missing a general feature of value propagation which would
>help with a lot of optimizations like this.  Hopefully this infrastructure
>will be added or contributed someday.

For the case I'm interested in, we don't need general value propagation,
only to recognize that we are loading QImode values into a register without
sign extension.  Mode-based range analysis ought to be simpler than full
value propagation.

If we knew how to generate QImode compares, we wouldn't need to clear the
register at all.  That may be something fixable in i386.md, I'm not sure.

zw