find_mem_givs SMALL_REGISTER_CLASSES patch

John Wehle
Sun Jun 28 14:13:00 GMT 1998

> With all the negatives in the above sentences I had to look at the  
> code to understand what you meant :-), but I think you are right.   

I'll have to try and be more positive in the future. :-)

> The Politically Correct Theory is that this should be handled by  
> Richard Henderson's combine-givs patch, but it might be that it  
> doesn't in its full generality (because ix86 address expressions can  
> be quite complicated).

egcs-19980621 with find_mem_givs patch: 105
egcs-19980621 with loop mark 10 patch: 103

> The reason that your patch works is not so  
> much because it's the Right Thing on machines with  
> SMALL_REGISTER_CLASSES but rather that complicated address  
> expressions in ix86 instructions are essentially free.

I'm incline to believe that not recording a giv which is a valid
address * is * the Right Thing to do on a register poor machine if
the other option is to spill registers.  Now if my other option
is to record the giv and * not * spill (important) registers than 
that sounds like a better Right Thing.

Long turn Richard Henderson's patch is probably a more powerful
change.  It certainly would have saved me some time if I had
remembered it.  Thank you (and Richard) for reminding me. :-)

-- John
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