Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -439,6 +439,14 @@
     if (match(Op0, m_Neg(m_Value(X))))
       return IC.replaceOperand(II, 0, X);
 
+    // cttz(sext(x)) -> cttz(zext(x))
+    if (match(Op0, m_OneUse(m_SExt(m_Value(X))))) {
+      auto *Zext = IC.Builder.CreateZExt(X, II.getType());
+      auto *CttzZext =
+          IC.Builder.CreateBinaryIntrinsic(Intrinsic::cttz, Zext, Op1);
+      return IC.replaceInstUsesWith(II, CttzZext);
+    }
+
     // Zext doesn't change the number of trailing zeros, so narrow:
     // cttz(zext(x)) -> zext(cttz(x)) if the 'ZeroIsUndef' parameter is 'true'.
     if (match(Op0, m_OneUse(m_ZExt(m_Value(X)))) && match(Op1, m_One())) {
Index: llvm/test/Transforms/InstCombine/cttz.ll
===================================================================
--- llvm/test/Transforms/InstCombine/cttz.ll
+++ llvm/test/Transforms/InstCombine/cttz.ll
@@ -64,9 +64,9 @@
 
 define i32 @cttz_sext_zero_undef(i16 %x) {
 ; CHECK-LABEL: @cttz_sext_zero_undef(
-; CHECK-NEXT:    [[S:%.*]] = sext i16 [[X:%.*]] to i32
-; CHECK-NEXT:    [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 true), !range [[RNG1]]
-; CHECK-NEXT:    ret i32 [[TZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i16 @llvm.cttz.i16(i16 [[X:%.*]], i1 true), !range [[RNG0]]
+; CHECK-NEXT:    [[TMP2:%.*]] = zext i16 [[TMP1]] to i32
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %s = sext i16 %x to i32
   %tz = call i32 @llvm.cttz.i32(i32 %s, i1 true)
@@ -75,11 +75,11 @@
 
 define i32 @cttz_sext_zero_def(i16 %x) {
 ; CHECK-LABEL: @cttz_sext_zero_def(
-; CHECK-NEXT:    [[S:%.*]] = zext i16 [[X:%.*]] to i32
-; CHECK-NEXT:    [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 false), !range [[RNG1]]
-; CHECK-NEXT:    ret i32 [[TZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    [[TMP2:%.*]] = call i32 @llvm.cttz.i32(i32 [[TMP1]], i1 false), !range [[RNG1]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
-  %s = zext i16 %x to i32
+  %s = sext i16 %x to i32
   %tz = call i32 @llvm.cttz.i32(i32 %s, i1 false)
   ret i32 %tz
 }
@@ -99,9 +99,9 @@
 
 define <2 x i64> @cttz_sext_zero_undef_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @cttz_sext_zero_undef_vec(
-; CHECK-NEXT:    [[S:%.*]] = sext <2 x i32> [[X:%.*]] to <2 x i64>
-; CHECK-NEXT:    [[TZ:%.*]] = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[S]], i1 true)
-; CHECK-NEXT:    ret <2 x i64> [[TZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[X:%.*]], i1 true)
+; CHECK-NEXT:    [[TMP2:%.*]] = zext <2 x i32> [[TMP1]] to <2 x i64>
+; CHECK-NEXT:    ret <2 x i64> [[TMP2]]
 ;
   %s = sext <2 x i32> %x to <2 x i64>
   %tz = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> %s, i1 true)
@@ -110,9 +110,9 @@
 
 define <2 x i64> @cttz_sext_zero_def_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @cttz_sext_zero_def_vec(
-; CHECK-NEXT:    [[S:%.*]] = sext <2 x i32> [[X:%.*]] to <2 x i64>
-; CHECK-NEXT:    [[TZ:%.*]] = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[S]], i1 false)
-; CHECK-NEXT:    ret <2 x i64> [[TZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext <2 x i32> [[X:%.*]] to <2 x i64>
+; CHECK-NEXT:    [[TMP2:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[TMP1]], i1 false)
+; CHECK-NEXT:    ret <2 x i64> [[TMP2]]
 ;
   %s = sext <2 x i32> %x to <2 x i64>
   %tz = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> %s, i1 false)