Index: lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -2689,7 +2689,18 @@
         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 && (x & x-1) == 0 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 And = DAG.getNode(ISD::AND, dl, CTVT, CTOp, Sub);
+        SDValue LHS = DAG.getSetCC(dl, VT, CTOp, DAG.getConstant(0, dl, CTVT),
+                                   ISD::SETUGT);
+        SDValue RHS =
+            DAG.getSetCC(dl, VT, And, DAG.getConstant(0, dl, CTVT), ISD::SETEQ);
+        return DAG.getNode(ISD::AND, dl, VT, LHS, RHS);
+      }
     }
 
     // (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
@@ -1,5 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -mtriple=x86_64-unknown -mcpu=corei7 | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-unknown -mcpu=corei7 -mattr=+popcnt | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-unknown -mcpu=corei7 -mattr=-popcnt | FileCheck %s -check-prefix=NO-POPCOUNT
 
 declare i8 @llvm.ctpop.i8(i8) nounwind readnone
 declare i64 @llvm.ctpop.i64(i64) nounwind readnone
@@ -12,6 +13,14 @@
 ; CHECK-NEXT:    testq %rcx, %rdi
 ; CHECK-NEXT:    setne %al
 ; CHECK-NEXT:    retq
+;
+; NO-POPCOUNT-LABEL: test1:
+; NO-POPCOUNT:       # %bb.0:
+; NO-POPCOUNT-NEXT:    leaq -1(%rdi), %rcx
+; NO-POPCOUNT-NEXT:    xorl %eax, %eax
+; NO-POPCOUNT-NEXT:    testq %rcx, %rdi
+; NO-POPCOUNT-NEXT:    setne %al
+; NO-POPCOUNT-NEXT:    retq
   %count = tail call i64 @llvm.ctpop.i64(i64 %x)
   %cast = trunc i64 %count to i32
   %cmp = icmp ugt i32 %cast, 1
@@ -28,6 +37,14 @@
 ; CHECK-NEXT:    testq %rcx, %rdi
 ; CHECK-NEXT:    sete %al
 ; CHECK-NEXT:    retq
+;
+; NO-POPCOUNT-LABEL: test2:
+; NO-POPCOUNT:       # %bb.0:
+; NO-POPCOUNT-NEXT:    leaq -1(%rdi), %rcx
+; NO-POPCOUNT-NEXT:    xorl %eax, %eax
+; NO-POPCOUNT-NEXT:    testq %rcx, %rdi
+; NO-POPCOUNT-NEXT:    sete %al
+; NO-POPCOUNT-NEXT:    retq
   %count = tail call i64 @llvm.ctpop.i64(i64 %x)
   %cmp = icmp ult i64 %count, 2
   %conv = zext i1 %cmp to i32
@@ -43,6 +60,33 @@
 ; CHECK-NEXT:    cmpb $2, %cl
 ; CHECK-NEXT:    setb %al
 ; CHECK-NEXT:    retq
+;
+; NO-POPCOUNT-LABEL: test3:
+; 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:    andb $63, %dl
+; NO-POPCOUNT-NEXT:    xorl %eax, %eax
+; NO-POPCOUNT-NEXT:    cmpb $2, %dl
+; NO-POPCOUNT-NEXT:    setb %al
+; NO-POPCOUNT-NEXT:    retq
   %count = tail call i64 @llvm.ctpop.i64(i64 %x)
   %cast = trunc i64 %count to i6 ; Too small for 0-64
   %cmp = icmp ult i6 %cast, 2
@@ -57,8 +101,53 @@
 ; CHECK-NEXT:    popcntl %edi, %eax
 ; CHECK-NEXT:    # kill: def $al killed $al killed $eax
 ; CHECK-NEXT:    retq
+;
+; NO-POPCOUNT-LABEL: test4:
+; NO-POPCOUNT:       # %bb.0:
+; NO-POPCOUNT-NEXT:    # kill: def $edi killed $edi def $rdi
+; NO-POPCOUNT-NEXT:    andb $127, %dil
+; NO-POPCOUNT-NEXT:    movl %edi, %eax
+; NO-POPCOUNT-NEXT:    shrb %al
+; NO-POPCOUNT-NEXT:    andb $21, %al
+; NO-POPCOUNT-NEXT:    subb %al, %dil
+; NO-POPCOUNT-NEXT:    movl %edi, %eax
+; NO-POPCOUNT-NEXT:    andb $51, %al
+; NO-POPCOUNT-NEXT:    shrb $2, %dil
+; NO-POPCOUNT-NEXT:    andb $51, %dil
+; NO-POPCOUNT-NEXT:    addb %al, %dil
+; NO-POPCOUNT-NEXT:    movl %edi, %eax
+; NO-POPCOUNT-NEXT:    shrb $4, %al
+; NO-POPCOUNT-NEXT:    addl %edi, %eax
+; NO-POPCOUNT-NEXT:    andb $15, %al
+; NO-POPCOUNT-NEXT:    # kill: def $al killed $al killed $eax
+; NO-POPCOUNT-NEXT:    retq
   %x2 = and i8 %x, 127
   %count = tail call i8 @llvm.ctpop.i8(i8 %x2)
   %and = and i8 %count, 7
   ret i8 %and
 }
+
+define i32 @test5(i64 %x) nounwind readnone {
+; CHECK-LABEL: test5:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    popcntq %rdi, %rcx
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    cmpq $1, %rcx
+; CHECK-NEXT:    sete %al
+; CHECK-NEXT:    retq
+;
+; NO-POPCOUNT-LABEL: test5:
+; NO-POPCOUNT:       # %bb.0:
+; NO-POPCOUNT-NEXT:    leaq -1(%rdi), %rax
+; NO-POPCOUNT-NEXT:    testq %rax, %rdi
+; NO-POPCOUNT-NEXT:    sete %al
+; NO-POPCOUNT-NEXT:    testq %rdi, %rdi
+; NO-POPCOUNT-NEXT:    setne %cl
+; NO-POPCOUNT-NEXT:    andb %al, %cl
+; NO-POPCOUNT-NEXT:    movzbl %cl, %eax
+; NO-POPCOUNT-NEXT:    retq
+  %count = tail call i64 @llvm.ctpop.i64(i64 %x)
+  %cmp = icmp eq i64 %count, 1
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}