[PATCH] D86673: [StackColoring] Conservatively merge Variable in catch(Variable)

[Xiang Zhang via Phabricator via llvm-commits]

xiangzhangllvm added a comment.

First, I thanks for your careful reviewing.
The windows Exception model has work well for many years, I tend not to change it. If we carefully watch the catch values (e.g. Type * *exp.i), we will find that they usually have a very long life range guarded by lifetime.start and lifetime.end, (usually almost equal with the whole function life range).
This seems that the front/mid ends don't want to do much optimization on this special mechanism, because in their eyes, the back-end optimization should based on the lifetime.start and lifetime.end they generated.
And if we reflected it in the IR, it will bring much complexity into current clear mid end IR, because every function in try block (may contain branch) need to reflected that it may change the catch values (e.g. Type * *exp.i).
I also find that, current "-stackcoloring-lifetime-start-on-first-use" didn't handle the multi-lifetime.start/end case, catch value may has multi-first use. it is make sense to handle the corner case of catch variable in this option.
What's more, current patch is simple and clear, I think it is the most probably easiest way to fix this bug.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86673/new/

https://reviews.llvm.org/D86673