Index: lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -2689,7 +2689,16 @@
         return DAG.getSetCC(dl, VT, And, DAG.getConstant(0, dl, CTVT), CC);
       }
 
-      // TODO: (ctpop x) == 1 -> x && (x & x-1) == 0 iff ctpop is illegal.
+      // (ctpop x) == 1 ->  (x-1) u< (x & -x)  iff ctpop is illegal.
+      if (Cond == ISD::SETEQ && C1 == 1 &&
+          !isOperationLegalOrCustom(ISD::CTPOP, CTVT)) {
+        SDValue Sub =
+            DAG.getNode(ISD::SUB, dl, CTVT, CTOp, DAG.getConstant(1, dl, CTVT));
+        SDValue Neg =
+            DAG.getNode(ISD::SUB, dl, CTVT, DAG.getConstant(0, dl, CTVT), CTOp);
+        SDValue And = DAG.getNode(ISD::AND, dl, CTVT, CTOp, Neg);
+        return DAG.getSetCC(dl, VT, Sub, And, ISD::SETULT);
+      }
     }
 
     // (zext x) == C --> x == (trunc C)
Index: test/CodeGen/X86/ctpop-combine.ll
===================================================================
--- test/CodeGen/X86/ctpop-combine.ll
+++ test/CodeGen/X86/ctpop-combine.ll
@@ -122,28 +122,13 @@
 ;
 ; NO-POPCOUNT-LABEL: ctpop_eq_one:
 ; NO-POPCOUNT:       # %bb.0:
-; NO-POPCOUNT-NEXT:    movq %rdi, %rax
-; NO-POPCOUNT-NEXT:    shrq %rax
-; NO-POPCOUNT-NEXT:    movabsq $6148914691236517205, %rcx # imm = 0x5555555555555555
-; NO-POPCOUNT-NEXT:    andq %rax, %rcx
-; NO-POPCOUNT-NEXT:    subq %rcx, %rdi
-; NO-POPCOUNT-NEXT:    movabsq $3689348814741910323, %rax # imm = 0x3333333333333333
 ; NO-POPCOUNT-NEXT:    movq %rdi, %rcx
-; NO-POPCOUNT-NEXT:    andq %rax, %rcx
-; NO-POPCOUNT-NEXT:    shrq $2, %rdi
-; NO-POPCOUNT-NEXT:    andq %rax, %rdi
-; NO-POPCOUNT-NEXT:    addq %rcx, %rdi
-; NO-POPCOUNT-NEXT:    movq %rdi, %rax
-; NO-POPCOUNT-NEXT:    shrq $4, %rax
-; NO-POPCOUNT-NEXT:    addq %rdi, %rax
-; NO-POPCOUNT-NEXT:    movabsq $1085102592571150095, %rcx # imm = 0xF0F0F0F0F0F0F0F
-; NO-POPCOUNT-NEXT:    andq %rax, %rcx
-; NO-POPCOUNT-NEXT:    movabsq $72340172838076673, %rdx # imm = 0x101010101010101
-; NO-POPCOUNT-NEXT:    imulq %rcx, %rdx
-; NO-POPCOUNT-NEXT:    shrq $56, %rdx
+; NO-POPCOUNT-NEXT:    negq %rcx
+; NO-POPCOUNT-NEXT:    andq %rdi, %rcx
+; NO-POPCOUNT-NEXT:    decq %rdi
 ; NO-POPCOUNT-NEXT:    xorl %eax, %eax
-; NO-POPCOUNT-NEXT:    cmpq $1, %rdx
-; NO-POPCOUNT-NEXT:    sete %al
+; NO-POPCOUNT-NEXT:    cmpq %rdi, %rcx
+; NO-POPCOUNT-NEXT:    seta %al
 ; NO-POPCOUNT-NEXT:    retq
   %count = tail call i64 @llvm.ctpop.i64(i64 %x)
   %cmp = icmp eq i64 %count, 1