[LLVMdev] PATCH: Use size reduction -- wave2

[Chris Lattner]

On Apr 16, 2008, at 11:25 AM, Dan Gohman wrote:
>> So, my idea is that these changes are performance neutral.

I strongly agree with Dan that we need to measure performance to  
ensure there is no significant performance regression.

>> I hope that this is interesting, but I'd like to ask anybody who is
>> comfortable with performance testing to help provide some hard
>> data :-)
>
> I agree that performance testing is not easy and requires resources,
> but I'm curious what's motivating this project here. My assumption
> has been that no one would likely go to the extreme of inventing a
> mini-language encoded in the least significant bits of pointer
> members in successive structs unless they were pretty desperate for
> performance or scalability.

Ah, this question is easy: it shrinks the Use class by a word, which  
reduces the most popular class in the LLVM IR by 25%.  This directly  
makes all binary operators 8 bytes smaller for example, which is a  
pretty big memory footprint win, and memory footprint translates to  
dcache efficiency as well.

-Chris