diff --git a/llvm/include/llvm/CodeGen/GlobalISel/Utils.h b/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
--- a/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
@@ -263,6 +263,8 @@
 Optional<APInt> ConstantFoldBinOp(unsigned Opcode, const Register Op1,
                                   const Register Op2,
                                   const MachineRegisterInfo &MRI);
+Optional<APInt> ConstantFoldUnaryOp(unsigned Opcode, const Register Op1,
+                                    const MachineRegisterInfo &MRI);
 Optional<APFloat> ConstantFoldFPBinOp(unsigned Opcode, const Register Op1,
                                       const Register Op2,
                                       const MachineRegisterInfo &MRI);
@@ -274,6 +276,14 @@
 Optional<MachineInstr *>
 ConstantFoldVectorBinop(unsigned Opcode, const Register Op1, const Register Op2,
                         const MachineRegisterInfo &MRI, MachineIRBuilder &MIB);
+/// Tries to constant fold a vector unary operation with source \p Op.
+/// If successful, returns the G_BUILD_VECTOR representing the folded vector
+/// constant. \p MIB should have an insertion point already set to create new
+/// G_CONSTANT instructions as needed.
+Optional<MachineInstr *>
+ConstantFoldVectorUnaryOp(unsigned Opcode, const Register Op,
+                          const MachineRegisterInfo &MRI,
+                          MachineIRBuilder &MIB);
 
 Optional<APInt> ConstantFoldExtOp(unsigned Opcode, const Register Op1,
                                   uint64_t Imm, const MachineRegisterInfo &MRI);
diff --git a/llvm/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp b/llvm/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp
--- a/llvm/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp
@@ -226,18 +226,18 @@
   case TargetOpcode::G_CTLZ: {
     assert(SrcOps.size() == 1 && "Expected one source");
     assert(DstOps.size() == 1 && "Expected one dest");
-    auto MaybeCsts = ConstantFoldCTLZ(SrcOps[0].getReg(), *getMRI());
-    if (!MaybeCsts)
+    if (SrcOps[0].getLLTTy(*getMRI()).isVector()) {
+      // Try to constant fold vector constants.
+      auto VecCst =
+          ConstantFoldVectorUnaryOp(Opc, SrcOps[0].getReg(), *getMRI(), *this);
+      if (VecCst)
+        return MachineInstrBuilder(getMF(), *VecCst);
       break;
-    if (MaybeCsts->size() == 1)
-      return buildConstant(DstOps[0], (*MaybeCsts)[0]);
-    // This was a vector constant. Build a G_BUILD_VECTOR for them.
-    SmallVector<Register> ConstantRegs;
-    LLT VecTy = DstOps[0].getLLTTy(*getMRI());
-    for (unsigned Cst : *MaybeCsts)
-      ConstantRegs.emplace_back(
-          buildConstant(VecTy.getScalarType(), Cst).getReg(0));
-    return buildBuildVector(DstOps[0], ConstantRegs);
+    }
+    if (Optional<APInt> Cst =
+            ConstantFoldUnaryOp(Opc, SrcOps[0].getReg(), *getMRI()))
+      return buildConstant(DstOps[0], *Cst);
+    break;
   }
   }
   bool CanCopy = checkCopyToDefsPossible(DstOps);
diff --git a/llvm/lib/CodeGen/GlobalISel/Utils.cpp b/llvm/lib/CodeGen/GlobalISel/Utils.cpp
--- a/llvm/lib/CodeGen/GlobalISel/Utils.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/Utils.cpp
@@ -530,6 +530,46 @@
   return None;
 }
 
+Optional<APInt> llvm::ConstantFoldUnaryOp(unsigned Opcode, const Register Op1,
+
+                                          const MachineRegisterInfo &MRI) {
+  Optional<APInt> MaybeCst = getIConstantVRegVal(Op1, MRI);
+  if (!MaybeCst)
+    return None;
+
+  APInt &C = *MaybeCst;
+  switch (Opcode) {
+  default:
+    return None;
+  case TargetOpcode::G_CTLZ:
+    return APInt(C.getBitWidth(), C.countLeadingZeros());
+  }
+}
+
+Optional<MachineInstr *>
+llvm::ConstantFoldVectorUnaryOp(unsigned Opcode, const Register Op,
+                                const MachineRegisterInfo &MRI,
+                                MachineIRBuilder &MIB) {
+  auto *SrcVec = getOpcodeDef<GBuildVector>(Op, MRI);
+  if (!SrcVec)
+    return None;
+
+  const LLT EltTy = MRI.getType(SrcVec->getSourceReg(0));
+
+  SmallVector<Register, 16> FoldedElements;
+  for (unsigned Idx = 0, E = SrcVec->getNumSources(); Idx < E; ++Idx) {
+    auto MaybeCst = ConstantFoldUnaryOp(Opcode, SrcVec->getSourceReg(Idx), MRI);
+    if (!MaybeCst)
+      return None;
+    auto FoldedCstReg = MIB.buildConstant(EltTy, *MaybeCst).getReg(0);
+    FoldedElements.emplace_back(FoldedCstReg);
+  }
+  // Create the new vector constant.
+  auto CstVec =
+      MIB.buildBuildVector(MRI.getType(SrcVec->getReg(0)), FoldedElements);
+  return &*CstVec;
+}
+
 Optional<APFloat> llvm::ConstantFoldFPBinOp(unsigned Opcode, const Register Op1,
                                             const Register Op2,
                                             const MachineRegisterInfo &MRI) {