diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index cf3c467ab64..f42a4d4a82a 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -7831,14 +7831,16 @@ X86TargetLowering::EmitAtomicBit6432WithCustomInserter(MachineInstr *bInstr,
   BuildMI(newMBB, dl, TII->get(X86::PHI), dest2Oper.getReg())
     .addReg(t2).addMBB(thisMBB).addReg(t4).addMBB(newMBB);
 
-  unsigned tt1 = F->getRegInfo().createVirtualRegister(RC);
-  unsigned tt2 = F->getRegInfo().createVirtualRegister(RC);
+  // The subsequent operations should be using the destination registers of
+  //the PHI instructions.
   if (invSrc) {
-    MIB = BuildMI(newMBB, dl, TII->get(NotOpc), tt1).addReg(t1);
-    MIB = BuildMI(newMBB, dl, TII->get(NotOpc), tt2).addReg(t2);
+    t1 = F->getRegInfo().createVirtualRegister(RC);
+    t2 = F->getRegInfo().createVirtualRegister(RC);
+    MIB = BuildMI(newMBB, dl, TII->get(NotOpc), t1).addReg(dest1Oper.getReg());
+    MIB = BuildMI(newMBB, dl, TII->get(NotOpc), t2).addReg(dest2Oper.getReg());
   } else {
-    tt1 = t1;
-    tt2 = t2;
+    t1 = dest1Oper.getReg();
+    t2 = dest2Oper.getReg();
   }
 
   int valArgIndx = lastAddrIndx + 1;
@@ -7852,7 +7854,7 @@ X86TargetLowering::EmitAtomicBit6432WithCustomInserter(MachineInstr *bInstr,
   else
     MIB = BuildMI(newMBB, dl, TII->get(immOpcL), t5);
   if (regOpcL != X86::MOV32rr)
-    MIB.addReg(tt1);
+    MIB.addReg(t1);
   (*MIB).addOperand(*argOpers[valArgIndx]);
   assert(argOpers[valArgIndx + 1]->isReg() ==
          argOpers[valArgIndx]->isReg());
@@ -7863,7 +7865,7 @@ X86TargetLowering::EmitAtomicBit6432WithCustomInserter(MachineInstr *bInstr,
   else
     MIB = BuildMI(newMBB, dl, TII->get(immOpcH), t6);
   if (regOpcH != X86::MOV32rr)
-    MIB.addReg(tt2);
+    MIB.addReg(t2);
   (*MIB).addOperand(*argOpers[valArgIndx + 1]);
 
   MIB = BuildMI(newMBB, dl, TII->get(copyOpc), X86::EAX);
diff --git a/test/CodeGen/X86/2010-01-08-Atomic64Bug.ll b/test/CodeGen/X86/2010-01-08-Atomic64Bug.ll
new file mode 100644
index 00000000000..172e1c73d56
--- /dev/null
+++ b/test/CodeGen/X86/2010-01-08-Atomic64Bug.ll
@@ -0,0 +1,29 @@
+; RUN: llc < %s -mtriple=i386-apple-darwin | FileCheck %s
+; rdar://r7512579
+
+; PHI defs in the atomic loop should be used by the add / adc
+; instructions. They should not be dead.
+
+define void @t(i64* nocapture %p) nounwind ssp {
+entry:
+; CHECK: t:
+; CHECK: movl $1
+; CHECK: movl (%ebp), %eax
+; CHECK: movl 4(%ebp), %edx
+; CHECK: LBB1_1:
+; CHECK-NOT: movl $1
+; CHECK-NOT: movl $0
+; CHECK: addl
+; CHECK: adcl
+; CHECK: lock
+; CHECK: cmpxchg8b
+; CHECK: jne
+  tail call void @llvm.memory.barrier(i1 true, i1 true, i1 true, i1 true, i1 true)
+  %0 = tail call i64 @llvm.atomic.load.add.i64.p0i64(i64* %p, i64 1) ; <i64> [#uses=0]
+  tail call void @llvm.memory.barrier(i1 true, i1 true, i1 true, i1 true, i1 true)
+  ret void
+}
+
+declare void @llvm.memory.barrier(i1, i1, i1, i1, i1) nounwind
+
+declare i64 @llvm.atomic.load.add.i64.p0i64(i64* nocapture, i64) nounwind