[llvm-commits] PATCH: Add a function splitting pass to LLVM which extracts cold regions into their own functions

[Andrew Trick]

On May 5, 2012, at 12:54 AM, Chandler Carruth <chandlerc at gmail.com> wrote:
> I wanted to start the initial review on a pass I've been working on. It's essentially doing hot/cold partitioning, cold region extraction, function splitting, or cold region outlining. Whatever terminology you would like, you get the idea. It's a really simple pass, built entirely out of all the existing infrastructure (some of which I've been cleaning up to let everything fall out this easily).
> 
> While this won't do a whole lot of interesting things on its own, I'm preparing to tweak the inline cost heuristics in a way that will allow this to form the essence of partial inlining. We can run this before inlining, splitting large cold regions of code into separate functions, and then be able to inline the remainder more easily.
> 
> I haven't run benchmarks, and this patch doesn't turn the pass on, I just want to get initial feedback, and get the code into the shape where I can put it in-tree, and then look at turning it on if benchmarks prove positive.

Chandler,

Very nice.

I'm dismayed that you depend on RegionInfo, but it is understandable. We could probably improve RegionInfo to be more efficient and self-contained (no DomFrontier), but I think we'd be much better off dropping RegionInfo and handling SEME regions. AFAIK CodeExtractor can already handle that. Is there any particular reason you need RegionInfo other than finding a connected set of blocks dominated by a cold block? Can FunctionSplitter just find its own regions?

-Andy