diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
@@ -16,7 +16,6 @@
 #include "AMDGPU.h"
 #include "AMDGPUInstrInfo.h"
 #include "AMDGPUMachineFunction.h"
-#include "GCNSubtarget.h"
 #include "SIMachineFunctionInfo.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
@@ -4905,22 +4904,6 @@
   case ISD::INTRINSIC_WO_CHAIN: {
     unsigned IID = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
     switch (IID) {
-    case Intrinsic::amdgcn_mbcnt_lo:
-    case Intrinsic::amdgcn_mbcnt_hi: {
-      const GCNSubtarget &ST =
-          DAG.getMachineFunction().getSubtarget<GCNSubtarget>();
-      // These return at most the (wavefront size - 1) + src1
-      // As long as src1 is an immediate we can calc known bits
-      KnownBits Src1Known = DAG.computeKnownBits(Op.getOperand(2), Depth + 1);
-      unsigned Src1ValBits = Src1Known.countMaxActiveBits();
-      unsigned MaxActiveBits = std::max(Src1ValBits, ST.getWavefrontSizeLog2());
-      // Cater for potential carry
-      MaxActiveBits += Src1ValBits ? 1 : 0;
-      unsigned Size = Op.getValueType().getSizeInBits();
-      if (MaxActiveBits < Size)
-        Known.Zero.setHighBits(Size - MaxActiveBits);
-      break;
-    }
     case Intrinsic::amdgcn_workitem_id_x:
     case Intrinsic::amdgcn_workitem_id_y:
     case Intrinsic::amdgcn_workitem_id_z: {
diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.h b/llvm/lib/Target/AMDGPU/SIISelLowering.h
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.h
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.h
@@ -452,6 +452,10 @@
 
   void finalizeLowering(MachineFunction &MF) const override;
 
+  void computeKnownBitsForTargetNode(const SDValue Op, KnownBits &Known,
+                                     const APInt &DemandedElts,
+                                     const SelectionDAG &DAG,
+                                     unsigned Depth = 0) const override;
   void computeKnownBitsForFrameIndex(int FrameIdx,
                                      KnownBits &Known,
                                      const MachineFunction &MF) const override;
diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -12706,6 +12706,41 @@
   TargetLoweringBase::finalizeLowering(MF);
 }
 
+void SITargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
+                                                     KnownBits &Known,
+                                                     const APInt &DemandedElts,
+                                                     const SelectionDAG &DAG,
+                                                     unsigned Depth) const {
+  Known.resetAll();
+  unsigned Opc = Op.getOpcode();
+  switch (Opc) {
+  case ISD::INTRINSIC_WO_CHAIN: {
+    unsigned IID = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
+    switch (IID) {
+    case Intrinsic::amdgcn_mbcnt_lo:
+    case Intrinsic::amdgcn_mbcnt_hi: {
+      const GCNSubtarget &ST =
+          DAG.getMachineFunction().getSubtarget<GCNSubtarget>();
+      // These return at most the (wavefront size - 1) + src1
+      // As long as src1 is an immediate we can calc known bits
+      KnownBits Src1Known = DAG.computeKnownBits(Op.getOperand(2), Depth + 1);
+      unsigned Src1ValBits = Src1Known.countMaxActiveBits();
+      unsigned MaxActiveBits = std::max(Src1ValBits, ST.getWavefrontSizeLog2());
+      // Cater for potential carry
+      MaxActiveBits += Src1ValBits ? 1 : 0;
+      unsigned Size = Op.getValueType().getSizeInBits();
+      if (MaxActiveBits < Size)
+        Known.Zero.setHighBits(Size - MaxActiveBits);
+      return;
+    }
+    }
+    break;
+  }
+  }
+  return AMDGPUTargetLowering::computeKnownBitsForTargetNode(
+      Op, Known, DemandedElts, DAG, Depth);
+}
+
 void SITargetLowering::computeKnownBitsForFrameIndex(
   const int FI, KnownBits &Known, const MachineFunction &MF) const {
   TargetLowering::computeKnownBitsForFrameIndex(FI, Known, MF);