[llvm] [Matrix] Adjust lifetime.ends during multiply fusion. (PR #84914)

[via llvm-commits]

Gerolf-Apple wrote:

Is the potential lifetime extension something you expect rarely? We should discuss this more on sample IR. I'm worried that we don't have good grasp on the trade-off. Another possible short term solution is to suppress fusion in this scenario (but again, I have no sense how frequent the liveends would interfere with fusion).

https://github.com/llvm/llvm-project/pull/84914