[llvm] clastb representation in existing IR, and AArch64 codegen (PR #112738)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

Bad TargetLowering API with no use context. SelectionDAGBuilder should directly translate into dag nodes and not be a point of configuration 

https://github.com/llvm/llvm-project/pull/112738