[llvm] [PeepholeOptimizer] Add REG_SEQUENCE subregister use folding (PR #205795)

[Matt Arsenault via llvm-commits]

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@@ -1739,6 +1764,119 @@ bool PeepholeOptimizerLegacy::runOnMachineFunction(MachineFunction &MF) {
   return Impl.run(MF);
 }
 
+/// Check if a REG_SEQUENCE subregister use can be safely rewritten to use
+/// the source register directly.
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arsenm wrote:

You can do this fully with existing TargetRegisterInfo functions 

https://github.com/llvm/llvm-project/pull/205795