Eliminate G_TRUNC to S1 SGPR

Author: gandhi56

llvm/lib/Target/AMDGPU/AMDGPURegBankLegalize.cpp

@@ -475,6 +475,21 @@ bool AMDGPURegBankLegalize::runOnMachineFunction(MachineFunction &MF) {
         Combiner.tryCombineCopy(MI);
         continue;
       }
+      if (MI.getOpcode() == AMDGPU::G_TRUNC) {
+        Register Dst = MI.getOperand(0).getReg();
+        Register Src = MI.getOperand(1).getReg();
+        auto *SrcDefMI = MRI.getVRegDef(Src);
+        if (MRI.getType(Dst) != LLT::scalar(1) || !MRI.use_empty(Dst))
+          continue;
+
+        if (SrcDefMI->getOpcode() == AMDGPU::G_UADDO ||
+            SrcDefMI->getOpcode() == AMDGPU::G_USUBO ||
+            SrcDefMI->getOpcode() == AMDGPU::G_UADDE ||
+            SrcDefMI->getOpcode() == AMDGPU::G_USUBE) {
+          MI.eraseFromParent();
+          continue;
+        }
+      }
       if (MI.getOpcode() == AMDGPU::G_ANYEXT) {
         Combiner.tryCombineS1AnyExt(MI);
         continue;