[llvm] [AMDGPU] Add writelane and readlane pseudos for SGPR spilling (PR #69923)

[Christudasan Devadasan via llvm-commits]

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@@ -3907,7 +3915,9 @@ bool SIInstrInfo::hasUnwantedEffectsWhenEXECEmpty(const MachineInstr &MI) const
   // However, executing them with EXEC = 0 causes them to operate on undefined
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cdevadas wrote:

You are right. The readlane & writelane instructions shouldn't be here.
Posted https://github.com/llvm/llvm-project/pull/70206.

https://github.com/llvm/llvm-project/pull/69923