Index: lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1194,6 +1194,17 @@
     return CallInst::Create(F, {X, II.getArgOperand(1)});
   }
 
+  // cttz(abs(x)) -> cttz(x)
+  Value *Y;
+  const auto *SI = dyn_cast<SelectInst>(Op0);
+  if (IsTZ && Op0->hasOneUse() && SI) {
+    SelectPatternFlavor SPF = matchSelectPattern(Op0, X, Y).Flavor;
+    if (SPF == SPF_ABS) {
+      II.setOperand(0, X);
+      return &II;
+    }
+  }
+
   KnownBits Known = IC.computeKnownBits(Op0, 0, &II);
 
   // Create a mask for bits above (ctlz) or below (cttz) the first known one.
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 nsw 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
@@ -20,9 +17,7 @@
 ; CHECK-LABEL: @cttz_abs2(
 ; CHECK-NEXT:    [[C:%.*]] = icmp sgt i32 [[X:%.*]], 0
 ; CHECK-NEXT:    call void @use_cond(i1 [[C]])
-; CHECK-NEXT:    [[S:%.*]] = sub nsw 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
@@ -37,9 +32,7 @@
 ; CHECK-LABEL: @cttz_abs3(
 ; CHECK-NEXT:    [[C:%.*]] = icmp sgt i32 [[X:%.*]], -1
 ; CHECK-NEXT:    call void @use_cond(i1 [[C]])
-; CHECK-NEXT:    [[S:%.*]] = sub nsw 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
@@ -52,10 +45,7 @@
 
 define i32 @cttz_abs4(i32 %x) {
 ; CHECK-LABEL: @cttz_abs4(
-; CHECK-NEXT:    [[C:%.*]] = icmp slt i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[S:%.*]] = sub nsw 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
@@ -67,10 +57,7 @@
 
 define i64 @cttz_abs_64(i64 %x) {
 ; CHECK-LABEL: @cttz_abs_64(
-; CHECK-NEXT:    [[C:%.*]] = icmp slt i64 [[X:%.*]], 0
-; CHECK-NEXT:    [[S:%.*]] = sub nsw 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