[llvm] [AMDGPU] Allocate i1 argument to SGPRs (PR #72461)

[Matt Arsenault via llvm-commits]

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@@ -3741,6 +3741,19 @@ AMDGPURegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
     if (!DstBank)
       DstBank = SrcBank;
 
+    // For i1 function arguments, the call of getRegBank() currently gives
+    // incorrect result. We set both src and dst banks to VCCRegBank.
+    if (!MI.getOperand(1).getReg().isVirtual() &&
+        MRI.getType(MI.getOperand(0).getReg()) == LLT::scalar(1)) {
+      DstBank = SrcBank = &AMDGPU::VCCRegBank;
+    }
+
+    // For i1 return value, the dst reg is an SReg but we need to set the reg
+    // bank to VCCRegBank.
+    if (!MI.getOperand(0).getReg().isVirtual() &&
+        SrcBank == &AMDGPU::VCCRegBank)
+      DstBank = SrcBank;
+
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arsenm wrote:

Can you also make this a separate PR (I want 2, one for the RegBankSelect and one for the InstructionSelect parts)

https://github.com/llvm/llvm-project/pull/72461