Index: lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1194,10 +1194,21 @@
     return CallInst::Create(F, {X, II.getArgOperand(1)});
   }
 
-  // cttz(-x) -> cttz(x)
-  if (IsTZ && match(Op0, m_Neg(m_Value(X)))) {
-    II.setOperand(0, X);
-    return ⅈ
+  if (IsTZ) {
+    // cttz(-x) -> cttz(x)
+    if (match(Op0, m_Neg(m_Value(X)))) {
+      II.setOperand(0, X);
+      return ⅈ
+    }
+
+    // cttz(abs(x)) -> cttz(x)
+    // cttz(nabs(x)) -> cttz(x)
+    Value *Y;
+    SelectPatternFlavor SPF = matchSelectPattern(Op0, X, Y).Flavor;
+    if (SPF == SPF_ABS || SPF == SPF_NABS) {
+      II.setOperand(0, X);
+      return ⅈ
+    }
   }
 
   KnownBits Known = IC.computeKnownBits(Op0, 0, &II);
Index: test/Transforms/InstCombine/cttz-abs.ll
===================================================================
--- test/Transforms/InstCombine/cttz-abs.ll
+++ test/Transforms/InstCombine/cttz-abs.ll
@@ -3,10 +3,7 @@
 
 define i32 @cttz_abs(i32 %x) {
 ; CHECK-LABEL: @cttz_abs(
-; CHECK-NEXT:    [[C:%.*]] = icmp slt i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[S:%.*]] = sub i32 0, [[X]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[C]], i32 [[S]], i32 [[X]]
-; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[D]], i1 true), !range !0
+; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 true), !range !0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %c = icmp slt i32 %x, 0
@@ -18,10 +15,7 @@
 
 define <2 x i64> @cttz_abs_vec(<2 x i64> %x) {
 ; CHECK-LABEL: @cttz_abs_vec(
-; CHECK-NEXT:    [[C:%.*]] = icmp slt <2 x i64> [[X:%.*]], zeroinitializer
-; CHECK-NEXT:    [[S:%.*]] = sub <2 x i64> zeroinitializer, [[X]]
-; CHECK-NEXT:    [[D:%.*]] = select <2 x i1> [[C]], <2 x i64> [[S]], <2 x i64> [[X]]
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[D]], i1 false)
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[X:%.*]], i1 false)
 ; CHECK-NEXT:    ret <2 x i64> [[R]]
 ;
   %c = icmp slt <2 x i64> %x, zeroinitializer
@@ -35,9 +29,7 @@
 ; CHECK-LABEL: @cttz_abs2(
 ; CHECK-NEXT:    [[C:%.*]] = icmp sgt i32 [[X:%.*]], 0
 ; CHECK-NEXT:    call void @use_cond(i1 [[C]])
-; CHECK-NEXT:    [[S:%.*]] = sub i32 0, [[X]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[C]], i32 [[X]], i32 [[S]]
-; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[D]], i1 true), !range !0
+; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[X]], i1 true), !range !0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %c = icmp sgt i32 %x, 0
@@ -52,9 +44,7 @@
 ; CHECK-LABEL: @cttz_abs3(
 ; CHECK-NEXT:    [[C:%.*]] = icmp sgt i32 [[X:%.*]], -1
 ; CHECK-NEXT:    call void @use_cond(i1 [[C]])
-; CHECK-NEXT:    [[S:%.*]] = sub i32 0, [[X]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[C]], i32 [[X]], i32 [[S]]
-; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[D]], i1 true), !range !0
+; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[X]], i1 true), !range !0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %c = icmp sgt i32 %x, -1
@@ -67,10 +57,7 @@
 
 define i32 @cttz_abs4(i32 %x) {
 ; CHECK-LABEL: @cttz_abs4(
-; CHECK-NEXT:    [[C:%.*]] = icmp slt i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[S:%.*]] = sub i32 0, [[X]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[C]], i32 [[S]], i32 [[X]]
-; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[D]], i1 true), !range !0
+; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 true), !range !0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %c = icmp slt i32 %x, 1
@@ -82,10 +69,7 @@
 
 define i32 @cttz_nabs(i32 %x) {
 ; CHECK-LABEL: @cttz_nabs(
-; CHECK-NEXT:    [[C:%.*]] = icmp slt i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[S:%.*]] = sub i32 0, [[X]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[C]], i32 [[X]], i32 [[S]]
-; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[D]], i1 false), !range !0
+; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 false), !range !0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %c = icmp slt i32 %x, 0
@@ -97,10 +81,7 @@
 
 define <2 x i64> @cttz_nabs_vec(<2 x i64> %x) {
 ; CHECK-LABEL: @cttz_nabs_vec(
-; CHECK-NEXT:    [[C:%.*]] = icmp slt <2 x i64> [[X:%.*]], zeroinitializer
-; CHECK-NEXT:    [[S:%.*]] = sub <2 x i64> zeroinitializer, [[X]]
-; CHECK-NEXT:    [[D:%.*]] = select <2 x i1> [[C]], <2 x i64> [[X]], <2 x i64> [[S]]
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[D]], i1 false)
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[X:%.*]], i1 false)
 ; CHECK-NEXT:    ret <2 x i64> [[R]]
 ;
   %c = icmp slt <2 x i64> %x, zeroinitializer
@@ -112,10 +93,7 @@
 
 define i64 @cttz_abs_64(i64 %x) {
 ; CHECK-LABEL: @cttz_abs_64(
-; CHECK-NEXT:    [[C:%.*]] = icmp slt i64 [[X:%.*]], 0
-; CHECK-NEXT:    [[S:%.*]] = sub i64 0, [[X]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[C]], i64 [[S]], i64 [[X]]
-; CHECK-NEXT:    [[R:%.*]] = call i64 @llvm.cttz.i64(i64 [[D]], i1 false), !range !1
+; CHECK-NEXT:    [[R:%.*]] = call i64 @llvm.cttz.i64(i64 [[X:%.*]], i1 false), !range !1
 ; CHECK-NEXT:    ret i64 [[R]]
 ;
   %c = icmp slt i64 %x, 0
@@ -131,7 +109,7 @@
 ; CHECK-NEXT:    [[S:%.*]] = sub i32 0, [[X]]
 ; CHECK-NEXT:    [[D:%.*]] = select i1 [[C]], i32 [[S]], i32 [[X]]
 ; CHECK-NEXT:    call void @use_abs(i32 [[D]])
-; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[D]], i1 true), !range !0
+; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[X]], i1 true), !range !0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %c = icmp slt i32 %x, 1
@@ -148,7 +126,7 @@
 ; CHECK-NEXT:    [[S:%.*]] = sub i32 0, [[X]]
 ; CHECK-NEXT:    [[D:%.*]] = select i1 [[C]], i32 [[X]], i32 [[S]]
 ; CHECK-NEXT:    call void @use_abs(i32 [[D]])
-; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[D]], i1 true), !range !0
+; CHECK-NEXT:    [[R:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[X]], i1 true), !range !0
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %c = icmp slt i32 %x, 1