diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 86de1f3..3f1094e 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -2461,13 +2461,22 @@
       NewOpc = TargetOpcode::G_CTTZ_ZERO_UNDEF;
     }
 
+    unsigned SizeDiff = WideTy.getSizeInBits() - CurTy.getSizeInBits();
+
+    if (MI.getOpcode() == TargetOpcode::G_CTLZ_ZERO_UNDEF) {
+      // An optimization where the result is the CTLZ after the left shift by
+      // (Difference in widety and current ty), that is,
+      // MIBSrc = MIBSrc << (sizeinbits(WideTy) - sizeinbits(CurTy))
+      // Result = ctlz MIBSrc
+      MIBSrc = MIRBuilder.buildShl(WideTy, MIBSrc,
+                                   MIRBuilder.buildConstant(WideTy, SizeDiff));
+    }
+
     // Perform the operation at the larger size.
     auto MIBNewOp = MIRBuilder.buildInstr(NewOpc, {WideTy}, {MIBSrc});
     // This is already the correct result for CTPOP and CTTZs
-    if (MI.getOpcode() == TargetOpcode::G_CTLZ ||
-        MI.getOpcode() == TargetOpcode::G_CTLZ_ZERO_UNDEF) {
+    if (MI.getOpcode() == TargetOpcode::G_CTLZ) {
       // The correct result is NewOp - (Difference in widety and current ty).
-      unsigned SizeDiff = WideTy.getSizeInBits() - CurTy.getSizeInBits();
       MIBNewOp = MIRBuilder.buildSub(
           WideTy, MIBNewOp, MIRBuilder.buildConstant(WideTy, SizeDiff));
     }