[llvm] AMDGPU/GlobalISel: Lower G_EXTRACT in legalizer (PR #181036)

[via llvm-commits]

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vangthao95 wrote:

I changed it to a hybrid approach, custom lowering with unmerge/merge for easy 32-bit aligned cases and call legalizer helper for the rest. Not sure exactly how to tackle handling unmerge/merge in legalizer helper or if it's worth it since we will have to teach it about subregs.

https://github.com/llvm/llvm-project/pull/181036