madmixpat update for true16

Author: broxigarchen

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

@@ -3651,6 +3651,10 @@ bool AMDGPUDAGToDAGISel::SelectVOP3PMadMixModsImpl(SDValue In, SDValue &Src,
       // TODO: Should we try to look for neg/abs here?
     }
 
+    // Prevent unnecessary subreg COPY to VGPR_16
+    if (Subtarget->useRealTrue16Insts() && Src.getOpcode() == ISD::TRUNCATE) {
+      Src = Src.getOperand(0);
+    }
     return true;
   }
 

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

@@ -5841,6 +5841,14 @@ AMDGPUInstructionSelector::selectVOP3PMadMixModsImpl(MachineOperand &Root,
       CheckAbsNeg();
     }
 
+    // Since we looked through FPEXT and removed it, we must also remove
+    // G_TRUNC. G_TRUNC to 16-bits would have a destination in RC VGPR_16, which
+    // is not compatible with MadMix instructions
+    Register PeekSrc = Src;
+    if (Subtarget->useRealTrue16Insts() &&
+        mi_match(PeekSrc, *MRI, m_GTrunc(m_Reg(PeekSrc))))
+      Src = PeekSrc;
+
     Matched = true;
   }