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

[Petar Avramovic via llvm-commits]

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@@ -500,6 +500,27 @@ void RegBankLegalizeHelper::lowerUnpackMinMax(MachineInstr &MI) {
   MI.eraseFromParent();
 }
 
+void RegBankLegalizeHelper::lowerScalarizeV2S16(MachineInstr &MI) {
+  auto Op1 = B.buildUnmerge({SgprRB, S16}, MI.getOperand(1).getReg());
+  auto Hi1 = Op1.getReg(0);
+  auto Lo1 = Op1.getReg(1);
+  auto Op2 = B.buildUnmerge({SgprRB, S16}, MI.getOperand(2).getReg());
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petar-avramovic wrote:

Should check what -global-isel path does, this is not of much use without proper ll test, 

>; TODO: Add test for s_add_v2i16. The current test does not work


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