[llvm] [AMDGPU] Add regbankselect rules for G_ADD/SUB and variants (PR #159860)

[Petar Avramovic via llvm-commits]

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@@ -124,6 +125,7 @@ class RegBankLegalizeHelper {
   void lowerSplitTo32Select(MachineInstr &MI);
   void lowerSplitTo32SExtInReg(MachineInstr &MI);
   void lowerUnpackMinMax(MachineInstr &MI);
+  void lowerV2S16ViaS32Widening(MachineInstr &MI);
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petar-avramovic wrote:

Bad name, need something similar to lowerUnpackMinMax, which is not best name either since it has nothing to do with min and max but with type of extension (Zext or Sext),
Maybe lowerUnpackAExt

https://github.com/llvm/llvm-project/pull/159860