[llvm] [AMDGPU] - Fix non-deterministic compile issue (PR #126271)

[David Stuttard via llvm-commits]

dstutt wrote:

> Sounds reasonable, but I don't immediately see anything in #124327 which iterates over `RematDefToLiveInRegions`. How and where does that happen?

There's an iteration over RematDefToLiveInRegions in sinkTriviallyRematInsts - which pre-dates the changes in #124327 
My assumption is that the change enabled more rematerialization - and that's highlighted this pre-existing issue that probably didn't trigger very often before.
Note that we're only seeing the issue on 2 test pipelines out of 10k+ and only for one asic variant.

The resulting code is going to be functionally correct in both cases, so this only gets picked up when we specifically check for non-determinism.


https://github.com/llvm/llvm-project/pull/126271