Index: llvm/trunk/include/llvm/IR/IntrinsicsPowerPC.td
===================================================================
--- llvm/trunk/include/llvm/IR/IntrinsicsPowerPC.td
+++ llvm/trunk/include/llvm/IR/IntrinsicsPowerPC.td
@@ -1132,4 +1132,6 @@
 
 def int_ppc_ttest : GCCBuiltin<"__builtin_ttest">,
       Intrinsic<[llvm_i64_ty], [], []>;
+
+def int_ppc_cfence : Intrinsic<[], [llvm_anyint_ty], []>;
 }
Index: llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h
===================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h
+++ llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h
@@ -905,6 +905,7 @@
     SDValue LowerINSERT_VECTOR_ELT(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerEXTRACT_VECTOR_ELT(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerINTRINSIC_WO_CHAIN(SDValue Op, SelectionDAG &DAG) const;
+    SDValue LowerINTRINSIC_VOID(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSCALAR_TO_VECTOR(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSIGN_EXTEND_INREG(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerMUL(SDValue Op, SelectionDAG &DAG) const;
Index: llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -410,6 +410,11 @@
   // To handle counter-based loop conditions.
   setOperationAction(ISD::INTRINSIC_W_CHAIN, MVT::i1, Custom);
 
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::i8, Custom);
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::i16, Custom);
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::i32, Custom);
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::Other, Custom);
+
   // Comparisons that require checking two conditions.
   setCondCodeAction(ISD::SETULT, MVT::f32, Expand);
   setCondCodeAction(ISD::SETULT, MVT::f64, Expand);
@@ -8184,6 +8189,26 @@
   return Flags;
 }
 
+SDValue PPCTargetLowering::LowerINTRINSIC_VOID(SDValue Op,
+                                               SelectionDAG &DAG) const {
+  // SelectionDAGBuilder::visitTargetIntrinsic may insert one extra chain to
+  // the beginning of the argument list.
+  int ArgStart = isa<ConstantSDNode>(Op.getOperand(0)) ? 0 : 1;
+  SDLoc DL(Op);
+  switch (cast<ConstantSDNode>(Op.getOperand(ArgStart))->getZExtValue()) {
+  case Intrinsic::ppc_cfence: {
+    assert(Subtarget.isPPC64() && "Only 64-bit is supported for now.");
+    return SDValue(DAG.getMachineNode(PPC::CFENCE8, DL, MVT::Other,
+                                      DAG.getNode(ISD::ANY_EXTEND, DL, MVT::i64,
+                                                  Op.getOperand(ArgStart + 1))),
+                   0);
+  }
+  default:
+    break;
+  }
+  return SDValue();
+}
+
 SDValue PPCTargetLowering::LowerSIGN_EXTEND_INREG(SDValue Op,
                                                   SelectionDAG &DAG) const {
   SDLoc dl(Op);
@@ -8649,6 +8674,9 @@
   // Frame & Return address.
   case ISD::RETURNADDR:         return LowerRETURNADDR(Op, DAG);
   case ISD::FRAMEADDR:          return LowerFRAMEADDR(Op, DAG);
+
+  case ISD::INTRINSIC_VOID:
+    return LowerINTRINSIC_VOID(Op, DAG);
   }
 }
 
@@ -8753,12 +8781,19 @@
 Instruction *PPCTargetLowering::emitTrailingFence(IRBuilder<> &Builder,
                                                   Instruction *Inst,
                                                   AtomicOrdering Ord) const {
-  if (Inst->hasAtomicLoad() && isAcquireOrStronger(Ord))
+  if (Inst->hasAtomicLoad() && isAcquireOrStronger(Ord)) {
+    // See http://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html and
+    // http://www.rdrop.com/users/paulmck/scalability/paper/N2745r.2011.03.04a.html
+    // and http://www.cl.cam.ac.uk/~pes20/cppppc/ for justification.
+    if (isa<LoadInst>(Inst) && Subtarget.isPPC64())
+      return Builder.CreateCall(
+          Intrinsic::getDeclaration(
+              Builder.GetInsertBlock()->getParent()->getParent(),
+              Intrinsic::ppc_cfence, {Inst->getType()}),
+          {Inst});
+    // FIXME: Can use isync for rmw operation.
     return callIntrinsic(Builder, Intrinsic::ppc_lwsync);
-  // FIXME: this is too conservative, a dependent branch + isync is enough.
-  // See http://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html and
-  // http://www.rdrop.com/users/paulmck/scalability/paper/N2745r.2011.03.04a.html
-  // and http://www.cl.cam.ac.uk/~pes20/cppppc/ for justification.
+  }
   return nullptr;
 }
 
Index: llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td
===================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td
+++ llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td
@@ -983,6 +983,10 @@
                         [(set i64:$rD,
                           (PPCldGotTprelL tglobaltlsaddr:$disp, i64:$reg))]>,
                  isPPC64;
+
+let isBarrier = 1, isPseudo = 1, Defs = [CR7], Itinerary = IIC_LdStSync in
+def CFENCE8 : Pseudo<(outs), (ins g8rc:$cr), "#CFENCE8", []>;
+
 def : Pat<(PPCaddTls i64:$in, tglobaltlsaddr:$g),
           (ADD8TLS $in, tglobaltlsaddr:$g)>;
 def ADDIStlsgdHA: Pseudo<(outs g8rc:$rD), (ins g8rc_nox0:$reg, s16imm64:$disp),
Index: llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp
===================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -1873,6 +1873,8 @@
 }
 
 bool PPCInstrInfo::expandPostRAPseudo(MachineInstr &MI) const {
+  auto &MBB = *MI.getParent();
+  auto DL = MI.getDebugLoc();
   switch (MI.getOpcode()) {
   case TargetOpcode::LOAD_STACK_GUARD: {
     assert(Subtarget.isTargetLinux() &&
@@ -1920,6 +1922,17 @@
     MI.setDesc(get(Opcode));
     return true;
   }
+  case PPC::CFENCE8: {
+    auto Val = MI.getOperand(0).getReg();
+    BuildMI(MBB, MI, DL, get(PPC::CMPW), PPC::CR7).addReg(Val).addReg(Val);
+    BuildMI(MBB, MI, DL, get(PPC::CTRL_DEP))
+        .addImm(PPC::PRED_NE_MINUS)
+        .addReg(PPC::CR7)
+        .addImm(1);
+    MI.setDesc(get(PPC::ISYNC));
+    MI.RemoveOperand(0);
+    return true;
+  }
   }
   return false;
 }
Index: llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td
===================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td
+++ llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td
@@ -1223,9 +1223,15 @@
   // FIXME: should be able to write a pattern for PPCcondbranch, but can't use
   // a two-value operand where a dag node expects two operands. :(
   let isCodeGenOnly = 1 in {
-    def BCC : BForm<16, 0, 0, (outs), (ins pred:$cond, condbrtarget:$dst),
-                    "b${cond:cc}${cond:pm} ${cond:reg}, $dst"
-                    /*[(PPCcondbranch crrc:$crS, imm:$opc, bb:$dst)]*/>;
+    class BCC_class : BForm<16, 0, 0, (outs), (ins pred:$cond, condbrtarget:$dst),
+                            "b${cond:cc}${cond:pm} ${cond:reg}, $dst"
+                            /*[(PPCcondbranch crrc:$crS, imm:$opc, bb:$dst)]*/>;
+    def BCC : BCC_class;
+
+    // The same as BCC, except that it's not a terminator. Used for introducing
+    // control flow dependency without creating new blocks.
+    let isTerminator = 0 in def CTRL_DEP : BCC_class;
+
     def BCCA : BForm<16, 1, 0, (outs), (ins pred:$cond, abscondbrtarget:$dst),
                      "b${cond:cc}a${cond:pm} ${cond:reg}, $dst">;
 
Index: llvm/trunk/test/CodeGen/PowerPC/atomic-2.ll
===================================================================
--- llvm/trunk/test/CodeGen/PowerPC/atomic-2.ll
+++ llvm/trunk/test/CodeGen/PowerPC/atomic-2.ll
@@ -108,8 +108,10 @@
 ; CHECK: @atomic_load
   %tmp = load atomic i64, i64* %mem acquire, align 64
 ; CHECK-NOT: ldarx
-; CHECK: ld
-; CHECK: lwsync
+; CHECK: ld [[VAL:[0-9]+]]
+; CHECK: cmpw [[CR:[0-9]+]], [[VAL]], [[VAL]]
+; CHECK: bne- [[CR]], .+4
+; CHECK: isync
   ret i64 %tmp
 }
 
Index: llvm/trunk/test/CodeGen/PowerPC/atomics-indexed.ll
===================================================================
--- llvm/trunk/test/CodeGen/PowerPC/atomics-indexed.ll
+++ llvm/trunk/test/CodeGen/PowerPC/atomics-indexed.ll
@@ -10,16 +10,22 @@
 define i8 @load_x_i8_seq_cst([100000 x i8]* %mem) {
 ; CHECK-LABEL: load_x_i8_seq_cst
 ; CHECK: sync
-; CHECK: lbzx
-; CHECK: lwsync
+; CHECK: lbzx [[VAL:r[0-9]+]]
+; CHECK-PPC32: lwsync
+; CHECK-PPC64: cmpw [[CR:cr[0-9]+]], [[VAL]], [[VAL]]
+; CHECK-PPC64: bne- [[CR]], .+4
+; CHECK-PPC64: isync
   %ptr = getelementptr inbounds [100000 x i8], [100000 x i8]* %mem, i64 0, i64 90000
   %val = load atomic i8, i8* %ptr seq_cst, align 1
   ret i8 %val
 }
 define i16 @load_x_i16_acquire([100000 x i16]* %mem) {
 ; CHECK-LABEL: load_x_i16_acquire
-; CHECK: lhzx
-; CHECK: lwsync
+; CHECK: lhzx [[VAL:r[0-9]+]]
+; CHECK-PPC32: lwsync
+; CHECK-PPC64: cmpw [[CR:cr[0-9]+]], [[VAL]], [[VAL]]
+; CHECK-PPC64: bne- [[CR]], .+4
+; CHECK-PPC64: isync
   %ptr = getelementptr inbounds [100000 x i16], [100000 x i16]* %mem, i64 0, i64 90000
   %val = load atomic i16, i16* %ptr acquire, align 2
   ret i16 %val
Index: llvm/trunk/test/CodeGen/PowerPC/atomics-regression.ll
===================================================================
--- llvm/trunk/test/CodeGen/PowerPC/atomics-regression.ll
+++ llvm/trunk/test/CodeGen/PowerPC/atomics-regression.ll
@@ -23,7 +23,9 @@
 ; PPC64LE-LABEL: test2:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    lbz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i8, i8* %ptr acquire, align 1
   ret i8 %val
@@ -35,7 +37,9 @@
 ; PPC64LE-NEXT:    sync
 ; PPC64LE-NEXT:    ori 2, 2, 0
 ; PPC64LE-NEXT:    lbz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i8, i8* %ptr seq_cst, align 1
   ret i8 %val
@@ -63,7 +67,9 @@
 ; PPC64LE-LABEL: test6:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    lhz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i16, i16* %ptr acquire, align 2
   ret i16 %val
@@ -75,7 +81,9 @@
 ; PPC64LE-NEXT:    sync
 ; PPC64LE-NEXT:    ori 2, 2, 0
 ; PPC64LE-NEXT:    lhz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i16, i16* %ptr seq_cst, align 2
   ret i16 %val
@@ -103,7 +111,9 @@
 ; PPC64LE-LABEL: test10:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    lwz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i32, i32* %ptr acquire, align 4
   ret i32 %val
@@ -115,7 +125,9 @@
 ; PPC64LE-NEXT:    sync
 ; PPC64LE-NEXT:    ori 2, 2, 0
 ; PPC64LE-NEXT:    lwz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i32, i32* %ptr seq_cst, align 4
   ret i32 %val
@@ -143,7 +155,9 @@
 ; PPC64LE-LABEL: test14:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    ld 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i64, i64* %ptr acquire, align 8
   ret i64 %val
@@ -155,7 +169,9 @@
 ; PPC64LE-NEXT:    sync
 ; PPC64LE-NEXT:    ori 2, 2, 0
 ; PPC64LE-NEXT:    ld 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i64, i64* %ptr seq_cst, align 8
   ret i64 %val
@@ -9544,3 +9560,35 @@
   %ret = atomicrmw umin i64* %ptr, i64 %val singlethread seq_cst
   ret i64 %ret
 }
+
+; The second load should never be scheduled before isync.
+define i32 @test_ordering0(i32* %ptr1, i32* %ptr2) {
+; PPC64LE-LABEL: test_ordering0:
+; PPC64LE:       # BB#0:
+; PPC64LE-NEXT:    lwz 4, 0(3)
+; PPC64LE-NEXT:    cmpw 7, 4, 4
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
+; PPC64LE-NEXT:    lwz 3, 0(3)
+; PPC64LE-NEXT:    add 3, 4, 3
+; PPC64LE-NEXT:    blr
+  %val1 = load atomic i32, i32* %ptr1 acquire, align 4
+  %val2 = load i32, i32* %ptr1
+  %add = add i32 %val1, %val2
+  ret i32 %add
+}
+
+; The second store should never be scheduled before isync.
+define i32 @test_ordering1(i32* %ptr1, i32 %val1, i32* %ptr2) {
+; PPC64LE-LABEL: test_ordering1:
+; PPC64LE:       # BB#0:
+; PPC64LE-NEXT:    lwz 3, 0(3)
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
+; PPC64LE-NEXT:    stw 4, 0(5)
+; PPC64LE-NEXT:    blr
+  %val2 = load atomic i32, i32* %ptr1 acquire, align 4
+  store i32 %val1, i32* %ptr2
+  ret i32 %val2
+}
Index: llvm/trunk/test/CodeGen/PowerPC/atomics.ll
===================================================================
--- llvm/trunk/test/CodeGen/PowerPC/atomics.ll
+++ llvm/trunk/test/CodeGen/PowerPC/atomics.ll
@@ -25,9 +25,12 @@
 }
 define i32 @load_i32_acquire(i32* %mem) {
 ; CHECK-LABEL: load_i32_acquire
-; CHECK: lwz
+; CHECK: lwz [[VAL:r[0-9]+]]
   %val = load atomic i32, i32* %mem acquire, align 4
-; CHECK: lwsync
+; CHECK-PPC32: lwsync
+; CHECK-PPC64: cmpw [[CR:cr[0-9]+]], [[VAL]], [[VAL]]
+; CHECK-PPC64: bne- [[CR]], .+4
+; CHECK-PPC64: isync
   ret i32 %val
 }
 define i64 @load_i64_seq_cst(i64* %mem) {
@@ -35,9 +38,12 @@
 ; CHECK: sync
 ; PPC32: __sync_
 ; PPC64-NOT: __sync_
-; PPC64: ld
+; PPC64: ld [[VAL:r[0-9]+]]
   %val = load atomic i64, i64* %mem seq_cst, align 8
-; CHECK: lwsync
+; CHECK-PPC32: lwsync
+; CHECK-PPC64: cmpw [[CR:cr[0-9]+]], [[VAL]], [[VAL]]
+; CHECK-PPC64: bne- [[CR]], .+4
+; CHECK-PPC64: isync
   ret i64 %val
 }