[PATCH] D28934: Write a new SSAUpdater

Chandler Carruth via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Fri Jan 20 00:52:36 PST 2017

chandlerc added a comment.

In https://reviews.llvm.org/D28934#651323, @sanjoy wrote:

> I've never really heard people complain about our current `SSAUpdater` (about it being too slow or difficult to use) -- well except in this review :).  Is there a specific problem you're trying to address with this?

When I worked on SROA and SROA had split logic between SSAUpdater and mem2reg, it was definitely confusing and a source of much sorrow... That said, we fixed it by getting rid of SSAUpdater...

But looking at this code and looking at SSAUpdater, I'm at least interested in the simplification. This code doesn't have comments, debug info handling, or the SCC-stuff Danny mentioned, but even if it grows by 3x, by by guess it will still be less than 1/3rd the code of the current SSAUpdater.

I guess the question is can we get the quality up w/o regressing the simplicity. From your description Danny, I'd be interested in the SCC formation bit to get minimal and other properties, and it would need to handle debug info a bit. Not sure if there are any other challenges really.


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