diff --git a/include/clang/AST/Expr.h b/include/clang/AST/Expr.h
index 14c94e7..b9fd02f 100644
--- a/include/clang/AST/Expr.h
+++ b/include/clang/AST/Expr.h
@@ -4410,7 +4410,7 @@
 class AtomicExpr : public Expr {
 public:
   enum AtomicOp { Load, Store, CmpXchgStrong, CmpXchgWeak, Xchg,
-                  Add, Sub, And, Or, Xor };
+                  Add, Sub, And, Or, Xor, Init };
 private:
   enum { PTR, ORDER, VAL1, ORDER_FAIL, VAL2, END_EXPR };
   Stmt* SubExprs[END_EXPR];
@@ -4438,10 +4438,16 @@
     SubExprs[ORDER] = E;
   }
   Expr *getVal1() const {
+    if (Op == Init)
+      return cast<Expr>(SubExprs[ORDER]);
     assert(NumSubExprs >= 3);
     return cast<Expr>(SubExprs[VAL1]);
   }
   void setVal1(Expr *E) {
+    if (Op == Init) {
+      SubExprs[ORDER] = E;
+      return;
+    }
     assert(NumSubExprs >= 3);
     SubExprs[VAL1] = E;
   }
diff --git a/include/clang/AST/OperationKinds.h b/include/clang/AST/OperationKinds.h
index 87ba113..8348033 100644
--- a/include/clang/AST/OperationKinds.h
+++ b/include/clang/AST/OperationKinds.h
@@ -267,7 +267,12 @@
   /// in ARC cause blocks to be copied; this is for cases where that
   /// would not otherwise be guaranteed, such as when casting to a
   /// non-block pointer type.
-  CK_ARCExtendBlockObject
+  CK_ARCExtendBlockObject,
+
+  /// \brief Converts from _Atomic(T) to T.
+  CK_AtomicToNonAtomic,
+  /// \brief Converts from T to _Atomic(T).
+  CK_NonAtomicToAtomic
 };
 
 #define CK_Invalid ((CastKind) -1)
diff --git a/include/clang/Basic/Builtins.def b/include/clang/Basic/Builtins.def
index 6ac2473..5942e53 100644
--- a/include/clang/Basic/Builtins.def
+++ b/include/clang/Basic/Builtins.def
@@ -599,6 +599,7 @@
 BUILTIN(__atomic_fetch_xor, "v.", "t")
 BUILTIN(__atomic_thread_fence, "vi", "n")
 BUILTIN(__atomic_signal_fence, "vi", "n")
+BUILTIN(__atomic_init, "v.", "t")
 BUILTIN(__atomic_is_lock_free, "iz", "n")
 
 // Non-overloaded atomic builtins.
diff --git a/lib/AST/Expr.cpp b/lib/AST/Expr.cpp
index b94a08d..bffcccc 100644
--- a/lib/AST/Expr.cpp
+++ b/lib/AST/Expr.cpp
@@ -1092,6 +1092,8 @@
   case CK_Dependent:
   case CK_LValueToRValue:
   case CK_NoOp:
+  case CK_AtomicToNonAtomic:
+  case CK_NonAtomicToAtomic:
   case CK_PointerToBoolean:
   case CK_IntegralToBoolean:
   case CK_FloatingToBoolean:
@@ -1204,6 +1206,10 @@
     return "ARCReclaimReturnedObject";
   case CK_ARCExtendBlockObject:
     return "ARCCExtendBlockObject";
+  case CK_AtomicToNonAtomic:
+    return "AtomicToNonAtomic";
+  case CK_NonAtomicToAtomic:
+    return "NonAtomicToAtomic";
   }
 
   llvm_unreachable("Unhandled cast kind!");
@@ -2536,6 +2542,18 @@
   case CStyleCastExprClass: {
     const CastExpr *CE = cast<CastExpr>(this);
 
+    // If we're promoting an integer to an _Atomic type then this is constant
+    // if the integer is constant.  We also need to check the converse in case
+    // someone does something like:
+    //
+    // int a = (_Atomic(int))42;
+    //
+    // I doubt anyone would write code like this directly, but it's quite
+    // possible as the result of macro expansions.
+    if (CE->getCastKind() == CK_NonAtomicToAtomic ||
+        CE->getCastKind() == CK_AtomicToNonAtomic)
+      return CE->getSubExpr()->isConstantInitializer(Ctx, false);
+
     // Handle bitcasts of vector constants.
     if (getType()->isVectorType() && CE->getCastKind() == CK_BitCast)
       return CE->getSubExpr()->isConstantInitializer(Ctx, false);
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index ae68e19..89e8ab7 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -2277,6 +2277,8 @@
     default:
       break;
 
+    case CK_AtomicToNonAtomic:
+    case CK_NonAtomicToAtomic:
     case CK_NoOp:
       return StmtVisitorTy::Visit(E->getSubExpr());
 
@@ -4531,6 +4533,8 @@
     return Error(E);
 
   case CK_LValueToRValue:
+  case CK_AtomicToNonAtomic:
+  case CK_NonAtomicToAtomic:
   case CK_NoOp:
     return ExprEvaluatorBaseTy::VisitCastExpr(E);
 
@@ -4997,6 +5001,8 @@
     llvm_unreachable("invalid cast kind for complex value");
 
   case CK_LValueToRValue:
+  case CK_AtomicToNonAtomic:
+  case CK_NonAtomicToAtomic:
   case CK_NoOp:
     return ExprEvaluatorBaseTy::VisitCastExpr(E);
 
@@ -5855,6 +5861,8 @@
     }
     switch (cast<CastExpr>(E)->getCastKind()) {
     case CK_LValueToRValue:
+    case CK_AtomicToNonAtomic:
+    case CK_NonAtomicToAtomic:
     case CK_NoOp:
     case CK_IntegralToBoolean:
     case CK_IntegralCast:
diff --git a/lib/AST/StmtPrinter.cpp b/lib/AST/StmtPrinter.cpp
index 836f192..ecf8ed7 100644
--- a/lib/AST/StmtPrinter.cpp
+++ b/lib/AST/StmtPrinter.cpp
@@ -1052,6 +1052,9 @@
 void StmtPrinter::VisitAtomicExpr(AtomicExpr *Node) {
   const char *Name = 0;
   switch (Node->getOp()) {
+    case AtomicExpr::Init:
+      Name = "__atomic_init(";
+      break;
     case AtomicExpr::Load:
       Name = "__atomic_load(";
       break;
@@ -1094,7 +1097,8 @@
     PrintExpr(Node->getVal2());
     OS << ", ";
   }
-  PrintExpr(Node->getOrder());
+  if (Node->getOp() != AtomicExpr::Init)
+    PrintExpr(Node->getOrder());
   if (Node->isCmpXChg()) {
     OS << ", ";
     PrintExpr(Node->getOrderFail());
diff --git a/lib/CodeGen/CGDecl.cpp b/lib/CodeGen/CGDecl.cpp
index dd7cdb6..7c7501b 100644
--- a/lib/CodeGen/CGDecl.cpp
+++ b/lib/CodeGen/CGDecl.cpp
@@ -494,7 +494,7 @@
     llvm::Value *value = EmitScalarExpr(init);
     if (capturedByInit)
       drillIntoBlockVariable(*this, lvalue, cast<VarDecl>(D));
-    EmitStoreThroughLValue(RValue::get(value), lvalue);
+    EmitStoreThroughLValue(RValue::get(value), lvalue, true);
     return;
   }
 
@@ -535,7 +535,7 @@
 
     // Otherwise just do a simple store.
     else
-      EmitStoreOfScalar(zero, tempLV);
+      EmitStoreOfScalar(zero, tempLV, /* isInitialization */ true);
   }
 
   // Emit the initializer.
@@ -581,19 +581,19 @@
   // both __weak and __strong, but __weak got filtered out above.
   if (accessedByInit && lifetime == Qualifiers::OCL_Strong) {
     llvm::Value *oldValue = EmitLoadOfScalar(lvalue);
-    EmitStoreOfScalar(value, lvalue);
+    EmitStoreOfScalar(value, lvalue, /* isInitialization */ true);
     EmitARCRelease(oldValue, /*precise*/ false);
     return;
   }
 
-  EmitStoreOfScalar(value, lvalue);
+  EmitStoreOfScalar(value, lvalue, /* isInitialization */ true);
 }
 
 /// EmitScalarInit - Initialize the given lvalue with the given object.
 void CodeGenFunction::EmitScalarInit(llvm::Value *init, LValue lvalue) {
   Qualifiers::ObjCLifetime lifetime = lvalue.getObjCLifetime();
   if (!lifetime)
-    return EmitStoreThroughLValue(RValue::get(init), lvalue);
+    return EmitStoreThroughLValue(RValue::get(init), lvalue, true);
 
   switch (lifetime) {
   case Qualifiers::OCL_None:
@@ -617,7 +617,7 @@
     break;
   }
 
-  EmitStoreOfScalar(init, lvalue);
+  EmitStoreOfScalar(init, lvalue, /* isInitialization */ true);
 }
 
 /// canEmitInitWithFewStoresAfterMemset - Decide whether we can emit the
@@ -1045,7 +1045,7 @@
     RValue rvalue = EmitReferenceBindingToExpr(init, D);
     if (capturedByInit)
       drillIntoBlockVariable(*this, lvalue, cast<VarDecl>(D));
-    EmitStoreThroughLValue(rvalue, lvalue);
+    EmitStoreThroughLValue(rvalue, lvalue, true);
   } else if (!hasAggregateLLVMType(type)) {
     EmitScalarInit(init, D, lvalue, capturedByInit);
   } else if (type->isAnyComplexType()) {
@@ -1505,7 +1505,7 @@
     if (doStore) {
       LValue lv = MakeAddrLValue(DeclPtr, Ty,
                                  getContext().getDeclAlign(&D));
-      EmitStoreOfScalar(Arg, lv);
+      EmitStoreOfScalar(Arg, lv, /* isInitialization */ true);
     }
   }
 
diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp
index c6ba65c..43ab116 100644
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -764,6 +764,9 @@
     Load->setAlignment(Alignment);
   if (TBAAInfo)
     CGM.DecorateInstruction(Load, TBAAInfo);
+  // If this is an atomic type, all normal reads must be atomic
+  if (Ty->isAtomicType())
+    Load->setAtomic(llvm::SequentiallyConsistent);
 
   return EmitFromMemory(Load, Ty);
 }
@@ -800,7 +803,8 @@
 void CodeGenFunction::EmitStoreOfScalar(llvm::Value *Value, llvm::Value *Addr,
                                         bool Volatile, unsigned Alignment,
                                         QualType Ty,
-                                        llvm::MDNode *TBAAInfo) {
+                                        llvm::MDNode *TBAAInfo,
+                                        bool isInit) {
   Value = EmitToMemory(Value, Ty);
   
   llvm::StoreInst *Store = Builder.CreateStore(Value, Addr, Volatile);
@@ -808,12 +812,15 @@
     Store->setAlignment(Alignment);
   if (TBAAInfo)
     CGM.DecorateInstruction(Store, TBAAInfo);
+  if (!isInit && Ty->isAtomicType())
+    Store->setAtomic(llvm::SequentiallyConsistent);
 }
 
-void CodeGenFunction::EmitStoreOfScalar(llvm::Value *value, LValue lvalue) {
+void CodeGenFunction::EmitStoreOfScalar(llvm::Value *value, LValue lvalue,
+    bool isInit) {
   EmitStoreOfScalar(value, lvalue.getAddress(), lvalue.isVolatile(),
                     lvalue.getAlignment().getQuantity(), lvalue.getType(),
-                    lvalue.getTBAAInfo());
+                    lvalue.getTBAAInfo(), isInit);
 }
 
 /// EmitLoadOfLValue - Given an expression that represents a value lvalue, this
@@ -961,7 +968,7 @@
 /// EmitStoreThroughLValue - Store the specified rvalue into the specified
 /// lvalue, where both are guaranteed to the have the same type, and that type
 /// is 'Ty'.
-void CodeGenFunction::EmitStoreThroughLValue(RValue Src, LValue Dst) {
+void CodeGenFunction::EmitStoreThroughLValue(RValue Src, LValue Dst, bool isInit) {
   if (!Dst.isSimple()) {
     if (Dst.isVectorElt()) {
       // Read/modify/write the vector, inserting the new element.
@@ -1041,7 +1048,7 @@
   }
 
   assert(Src.isScalar() && "Can't emit an agg store with this method");
-  EmitStoreOfScalar(Src.getScalarVal(), Dst);
+  EmitStoreOfScalar(Src.getScalarVal(), Dst, isInit);
 }
 
 void CodeGenFunction::EmitStoreThroughBitfieldLValue(RValue Src, LValue Dst,
@@ -2052,6 +2059,11 @@
 
   case CK_Dependent:
     llvm_unreachable("dependent cast kind in IR gen!");
+ 
+  // These two casts are currently treated as no-ops, although they could
+  // potentially be real operations depending on the target's ABI.
+  case CK_NonAtomicToAtomic:
+  case CK_AtomicToNonAtomic:
 
   case CK_NoOp:
   case CK_LValueToRValue:
@@ -2541,6 +2553,7 @@
     case AtomicExpr::CmpXchgWeak:
     case AtomicExpr::CmpXchgStrong:
     case AtomicExpr::Store:
+    case AtomicExpr::Init:
     case AtomicExpr::Load:  assert(0 && "Already handled!");
     case AtomicExpr::Add:   Op = llvm::AtomicRMWInst::Add;  break;
     case AtomicExpr::Sub:   Op = llvm::AtomicRMWInst::Sub;  break;
@@ -2588,8 +2601,20 @@
       getContext().getTargetInfo().getMaxAtomicInlineWidth();
   bool UseLibcall = (Size != Align || Size > MaxInlineWidth);
 
+
+
   llvm::Value *Ptr, *Order, *OrderFail = 0, *Val1 = 0, *Val2 = 0;
   Ptr = EmitScalarExpr(E->getPtr());
+
+  if (E->getOp() == AtomicExpr::Init) {
+    assert(!Dest && "Init does not return a value");
+    Val1 = EmitScalarExpr(E->getVal1());
+    llvm::StoreInst *Store = Builder.CreateStore(Val1, Ptr);
+    Store->setAlignment(Size);
+    Store->setVolatile(E->isVolatile());
+    return RValue::get(0);
+  }
+
   Order = EmitScalarExpr(E->getOrder());
   if (E->isCmpXChg()) {
     Val1 = EmitScalarExpr(E->getVal1());
@@ -2703,7 +2728,7 @@
       // enforce that in general.
       break; 
     }
-    if (E->getOp() == AtomicExpr::Store)
+    if (E->getOp() == AtomicExpr::Store || E->getOp() == AtomicExpr::Init)
       return RValue::get(0);
     return ConvertTempToRValue(*this, E->getType(), OrigDest);
   }
diff --git a/lib/CodeGen/CGExprAgg.cpp b/lib/CodeGen/CGExprAgg.cpp
index 47984af..fbcdcc0 100644
--- a/lib/CodeGen/CGExprAgg.cpp
+++ b/lib/CodeGen/CGExprAgg.cpp
@@ -337,6 +337,8 @@
 
   case CK_LValueToRValue: // hope for downstream optimization
   case CK_NoOp:
+  case CK_AtomicToNonAtomic:
+  case CK_NonAtomicToAtomic:
   case CK_UserDefinedConversion:
   case CK_ConstructorConversion:
     assert(CGF.getContext().hasSameUnqualifiedType(E->getSubExpr()->getType(),
diff --git a/lib/CodeGen/CGExprComplex.cpp b/lib/CodeGen/CGExprComplex.cpp
index d58db67..b4b1b1d 100644
--- a/lib/CodeGen/CGExprComplex.cpp
+++ b/lib/CodeGen/CGExprComplex.cpp
@@ -358,6 +358,10 @@
   switch (CK) {
   case CK_Dependent: llvm_unreachable("dependent cast kind in IR gen!");
 
+  // Atomic to non-atomic casts may be more than a no-op for some platforms and
+  // for some types.
+  case CK_AtomicToNonAtomic:
+  case CK_NonAtomicToAtomic:
   case CK_NoOp:
   case CK_LValueToRValue:
   case CK_UserDefinedConversion:
diff --git a/lib/CodeGen/CGExprConstant.cpp b/lib/CodeGen/CGExprConstant.cpp
index f27586d..789d863 100644
--- a/lib/CodeGen/CGExprConstant.cpp
+++ b/lib/CodeGen/CGExprConstant.cpp
@@ -624,6 +624,8 @@
       return CGM.getCXXABI().EmitMemberPointerConversion(C, E);
 
     case CK_LValueToRValue:
+    case CK_AtomicToNonAtomic:
+    case CK_NonAtomicToAtomic:
     case CK_NoOp:
       return C;
 
diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index c2aec36..8087c3b 100644
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -1064,6 +1064,8 @@
     Value *Src = Visit(const_cast<Expr*>(E));
     return Builder.CreateBitCast(Src, ConvertType(DestTy));
   }
+  case CK_AtomicToNonAtomic:
+  case CK_NonAtomicToAtomic:
   case CK_NoOp:
   case CK_UserDefinedConversion:
     return Visit(const_cast<Expr*>(E));
@@ -1293,9 +1295,21 @@
   QualType type = E->getSubExpr()->getType();
   llvm::Value *value = EmitLoadOfLValue(LV);
   llvm::Value *input = value;
+  llvm::PHINode *atomicPHI = 0;
 
   int amount = (isInc ? 1 : -1);
 
+  if (const AtomicType *atomicTy = type->getAs<AtomicType>()) {
+    llvm::BasicBlock *startBB = Builder.GetInsertBlock();
+    llvm::BasicBlock *opBB = CGF.createBasicBlock("atomic_op", CGF.CurFn);
+    Builder.CreateBr(opBB);
+    Builder.SetInsertPoint(opBB);
+    atomicPHI = Builder.CreatePHI(value->getType(), 2);
+    atomicPHI->addIncoming(value, startBB);
+    type = atomicTy->getValueType();
+    value = atomicPHI;
+  }
+
   // Special case of integer increment that we have to check first: bool++.
   // Due to promotion rules, we get:
   //   bool++ -> bool = bool + 1
@@ -1415,6 +1429,18 @@
       value = Builder.CreateInBoundsGEP(value, sizeValue, "incdec.objptr");
     value = Builder.CreateBitCast(value, input->getType());
   }
+  
+  if (atomicPHI) {
+    llvm::BasicBlock *opBB = Builder.GetInsertBlock();
+    llvm::BasicBlock *contBB = CGF.createBasicBlock("atomic_cont", CGF.CurFn);
+    llvm::Value *old = Builder.CreateAtomicCmpXchg(LV.getAddress(), atomicPHI,
+        value, llvm::SequentiallyConsistent);
+    atomicPHI->addIncoming(old, opBB);
+    llvm::Value *success = Builder.CreateICmpEQ(old, atomicPHI);
+    Builder.CreateCondBr(success, contBB, opBB);
+    Builder.SetInsertPoint(contBB);
+    return isPre ? value : input;
+  }
 
   // Store the updated result through the lvalue.
   if (LV.isBitField())
@@ -1670,12 +1696,38 @@
   OpInfo.LHS = EmitLoadOfLValue(LHSLV);
   OpInfo.LHS = EmitScalarConversion(OpInfo.LHS, LHSTy,
                                     E->getComputationLHSType());
+
+  llvm::PHINode *atomicPHI = 0;
+  if (const AtomicType *atomicTy = OpInfo.Ty->getAs<AtomicType>()) {
+    // FIXME: For floating point types, we should be saving and restoring the
+    // floating point environment in the loop.
+    llvm::BasicBlock *startBB = Builder.GetInsertBlock();
+    llvm::BasicBlock *opBB = CGF.createBasicBlock("atomic_op", CGF.CurFn);
+    Builder.CreateBr(opBB);
+    Builder.SetInsertPoint(opBB);
+    atomicPHI = Builder.CreatePHI(OpInfo.LHS->getType(), 2);
+    atomicPHI->addIncoming(OpInfo.LHS, startBB);
+    OpInfo.Ty = atomicTy->getValueType();
+    OpInfo.LHS = atomicPHI;
+  }
   
   // Expand the binary operator.
   Result = (this->*Func)(OpInfo);
   
   // Convert the result back to the LHS type.
   Result = EmitScalarConversion(Result, E->getComputationResultType(), LHSTy);
+
+  if (atomicPHI) {
+    llvm::BasicBlock *opBB = Builder.GetInsertBlock();
+    llvm::BasicBlock *contBB = CGF.createBasicBlock("atomic_cont", CGF.CurFn);
+    llvm::Value *old = Builder.CreateAtomicCmpXchg(LHSLV.getAddress(), atomicPHI,
+        Result, llvm::SequentiallyConsistent);
+    atomicPHI->addIncoming(old, opBB);
+    llvm::Value *success = Builder.CreateICmpEQ(old, atomicPHI);
+    Builder.CreateCondBr(success, contBB, opBB);
+    Builder.SetInsertPoint(contBB);
+    return LHSLV;
+  }
   
   // Store the result value into the LHS lvalue. Bit-fields are handled
   // specially because the result is altered by the store, i.e., [C99 6.5.16p1]
diff --git a/lib/CodeGen/CodeGenFunction.h b/lib/CodeGen/CodeGenFunction.h
index e55732a..0c13951 100644
--- a/lib/CodeGen/CodeGenFunction.h
+++ b/lib/CodeGen/CodeGenFunction.h
@@ -2029,13 +2029,14 @@
   /// the LLVM value representation.
   void EmitStoreOfScalar(llvm::Value *Value, llvm::Value *Addr,
                          bool Volatile, unsigned Alignment, QualType Ty,
-                         llvm::MDNode *TBAAInfo = 0);
+                         llvm::MDNode *TBAAInfo = 0, bool isInit=false);
 
   /// EmitStoreOfScalar - Store a scalar value to an address, taking
   /// care to appropriately convert from the memory representation to
   /// the LLVM value representation.  The l-value must be a simple
-  /// l-value.
-  void EmitStoreOfScalar(llvm::Value *value, LValue lvalue);
+  /// l-value.  The isInit flag indicates whether this is an initialization.
+  /// If so, atomic qualifiers are ignored and the store is always non-atomic.
+  void EmitStoreOfScalar(llvm::Value *value, LValue lvalue, bool isInit=false);
 
   /// EmitLoadOfLValue - Given an expression that represents a value lvalue,
   /// this method emits the address of the lvalue, then loads the result as an
@@ -2047,7 +2048,7 @@
   /// EmitStoreThroughLValue - Store the specified rvalue into the specified
   /// lvalue, where both are guaranteed to the have the same type, and that type
   /// is 'Ty'.
-  void EmitStoreThroughLValue(RValue Src, LValue Dst);
+  void EmitStoreThroughLValue(RValue Src, LValue Dst, bool isInit=false);
   void EmitStoreThroughExtVectorComponentLValue(RValue Src, LValue Dst);
 
   /// EmitStoreThroughLValue - Store Src into Dst with same constraints as
diff --git a/lib/Frontend/InitPreprocessor.cpp b/lib/Frontend/InitPreprocessor.cpp
index c736ca3..93c9989 100644
--- a/lib/Frontend/InitPreprocessor.cpp
+++ b/lib/Frontend/InitPreprocessor.cpp
@@ -325,6 +325,14 @@
   Builder.defineMacro("__GNUC__", "4");
   Builder.defineMacro("__GXX_ABI_VERSION", "1002");
 
+  // Define macros for the C11 / C++11 memory orderings
+  Builder.defineMacro("__ATOMIC_RELAXED", "0");
+  Builder.defineMacro("__ATOMIC_CONSUME", "1");
+  Builder.defineMacro("__ATOMIC_ACQUIRE", "2");
+  Builder.defineMacro("__ATOMIC_RELEASE", "3");
+  Builder.defineMacro("__ATOMIC_ACQ_REL", "4");
+  Builder.defineMacro("__ATOMIC_SEQ_CST", "5");
+
   // As sad as it is, enough software depends on the __VERSION__ for version
   // checks that it is necessary to report 4.2.1 (the base GCC version we claim
   // compatibility with) first.
diff --git a/lib/Lex/PPMacroExpansion.cpp b/lib/Lex/PPMacroExpansion.cpp
index 76962e4..73efb4d 100644
--- a/lib/Lex/PPMacroExpansion.cpp
+++ b/lib/Lex/PPMacroExpansion.cpp
@@ -626,12 +626,14 @@
            .Case("arc_cf_code_audited", true)
            // C11 features
            .Case("c_alignas", LangOpts.C11)
+           .Case("c_atomic", LangOpts.C11)
            .Case("c_generic_selections", LangOpts.C11)
            .Case("c_static_assert", LangOpts.C11)
            // C++0x features
            .Case("cxx_access_control_sfinae", LangOpts.CPlusPlus0x)
            .Case("cxx_alias_templates", LangOpts.CPlusPlus0x)
            .Case("cxx_alignas", LangOpts.CPlusPlus0x)
+           .Case("cxx_atomic", LangOpts.CPlusPlus0x)
            .Case("cxx_attributes", LangOpts.CPlusPlus0x)
            .Case("cxx_auto_type", LangOpts.CPlusPlus0x)
          //.Case("cxx_constexpr", false);
@@ -724,9 +726,11 @@
   return llvm::StringSwitch<bool>(II->getName())
            // C11 features supported by other languages as extensions.
            .Case("c_alignas", true)
+           .Case("c_atomic", true)
            .Case("c_generic_selections", true)
            .Case("c_static_assert", true)
            // C++0x features supported by other languages as extensions.
+           .Case("cxx_atomic", LangOpts.CPlusPlus)
            .Case("cxx_deleted_functions", LangOpts.CPlusPlus)
            .Case("cxx_explicit_conversions", LangOpts.CPlusPlus)
            .Case("cxx_inline_namespaces", LangOpts.CPlusPlus)
diff --git a/lib/Sema/SemaCast.cpp b/lib/Sema/SemaCast.cpp
index 2c7611d..fe7667e 100644
--- a/lib/Sema/SemaCast.cpp
+++ b/lib/Sema/SemaCast.cpp
@@ -1897,6 +1897,11 @@
   if (SrcExpr.isInvalid())
     return;
   QualType SrcType = SrcExpr.get()->getType();
+
+  // You can cast an _Atomic(T) to anything you can cast a T to.
+  if (const AtomicType *AtomicSrcType = SrcType->getAs<AtomicType>())
+    SrcType = AtomicSrcType->getValueType();
+
   assert(!SrcType->isPlaceholderType());
 
   if (Self.RequireCompleteType(OpRange.getBegin(), DestType,
diff --git a/lib/Sema/SemaChecking.cpp b/lib/Sema/SemaChecking.cpp
index 90ad037..77c5717 100644
--- a/lib/Sema/SemaChecking.cpp
+++ b/lib/Sema/SemaChecking.cpp
@@ -277,6 +277,8 @@
     return SemaAtomicOpsOverloaded(move(TheCallResult), AtomicExpr::Load);
   case Builtin::BI__atomic_store:
     return SemaAtomicOpsOverloaded(move(TheCallResult), AtomicExpr::Store);
+  case Builtin::BI__atomic_init:
+    return SemaAtomicOpsOverloaded(move(TheCallResult), AtomicExpr::Init);
   case Builtin::BI__atomic_exchange:
     return SemaAtomicOpsOverloaded(move(TheCallResult), AtomicExpr::Xchg);
   case Builtin::BI__atomic_compare_exchange_strong:
@@ -538,6 +540,8 @@
     NumVals = 2;
     NumOrders = 2;
   }
+  if (Op == AtomicExpr::Init)
+    NumOrders = 0;
 
   if (TheCall->getNumArgs() < NumVals+NumOrders+1) {
     Diag(TheCall->getLocEnd(), diag::err_typecheck_call_too_few_args)
@@ -600,7 +604,7 @@
   }
 
   QualType ResultType = ValType;
-  if (Op == AtomicExpr::Store)
+  if (Op == AtomicExpr::Store || Op == AtomicExpr::Init)
     ResultType = Context.VoidTy;
   else if (Op == AtomicExpr::CmpXchgWeak || Op == AtomicExpr::CmpXchgStrong)
     ResultType = Context.BoolTy;
@@ -641,6 +645,8 @@
   SubExprs.push_back(Ptr);
   if (Op == AtomicExpr::Load) {
     SubExprs.push_back(TheCall->getArg(1)); // Order
+  } else if (Op == AtomicExpr::Init) {
+    SubExprs.push_back(TheCall->getArg(1)); // Val1
   } else if (Op != AtomicExpr::CmpXchgWeak && Op != AtomicExpr::CmpXchgStrong) {
     SubExprs.push_back(TheCall->getArg(2)); // Order
     SubExprs.push_back(TheCall->getArg(1)); // Val1
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 39161ea..5baf143 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -4066,6 +4066,11 @@
   // pointers.  Everything else should be possible.
 
   QualType SrcTy = Src.get()->getType();
+  if (const AtomicType *SrcAtomicTy = SrcTy->getAs<AtomicType>())
+    SrcTy = SrcAtomicTy->getValueType();
+  if (const AtomicType *DestAtomicTy = DestTy->getAs<AtomicType>())
+    DestTy = DestAtomicTy->getValueType();
+
   if (Context.hasSameUnqualifiedType(SrcTy, DestTy))
     return CK_NoOp;
 
@@ -5358,9 +5363,6 @@
   LHSType = Context.getCanonicalType(LHSType).getUnqualifiedType();
   RHSType = Context.getCanonicalType(RHSType).getUnqualifiedType();
 
-  // We can't do assignment from/to atomics yet.
-  if (LHSType->isAtomicType())
-    return Incompatible;
 
   // Common case: no conversion required.
   if (LHSType == RHSType) {
@@ -5368,6 +5370,21 @@
     return Compatible;
   }
 
+  if (const AtomicType *AtomicTy = dyn_cast<AtomicType>(LHSType)) {
+    if (AtomicTy->getValueType() == RHSType) {
+      Kind = CK_NonAtomicToAtomic;
+      return Compatible;
+    }
+  }
+
+  if (const AtomicType *AtomicTy = dyn_cast<AtomicType>(RHSType)) {
+    if (AtomicTy->getValueType() == LHSType) {
+      Kind = CK_AtomicToNonAtomic;
+      return Compatible;
+    }
+  }
+
+
   // If the left-hand side is a reference type, then we are in a
   // (rare!) case where we've allowed the use of references in C,
   // e.g., as a parameter type in a built-in function. In this case,
@@ -5906,9 +5923,15 @@
   if (LHS.isInvalid() || RHS.isInvalid())
     return QualType();
 
+
   if (!LHS.get()->getType()->isArithmeticType() ||
-      !RHS.get()->getType()->isArithmeticType())
+      !RHS.get()->getType()->isArithmeticType()) {
+    if (IsCompAssign &&
+        LHS.get()->getType()->isAtomicType() &&
+        RHS.get()->getType()->isArithmeticType())
+      return compType;
     return InvalidOperands(Loc, LHS, RHS);
+  }
 
   // Check for division by zero.
   if (IsDiv &&
@@ -6134,6 +6157,12 @@
     return compType;
   }
 
+  if (LHS.get()->getType()->isAtomicType() &&
+      RHS.get()->getType()->isArithmeticType()) {
+    *CompLHSTy = LHS.get()->getType();
+    return compType;
+  }
+
   // Put any potential pointer into PExp
   Expr* PExp = LHS.get(), *IExp = RHS.get();
   if (IExp->getType()->isAnyPointerType())
@@ -6194,6 +6223,12 @@
     return compType;
   }
 
+  if (LHS.get()->getType()->isAtomicType() &&
+      RHS.get()->getType()->isArithmeticType()) {
+    *CompLHSTy = LHS.get()->getType();
+    return compType;
+  }
+
   // Either ptr - int   or   ptr - ptr.
   if (LHS.get()->getType()->isAnyPointerType()) {
     QualType lpointee = LHS.get()->getType()->getPointeeType();
@@ -7290,6 +7325,12 @@
     return S.Context.DependentTy;
 
   QualType ResType = Op->getType();
+  // Atomic types can be used for increment / decrement where the non-atomic
+  // versions can, so ignore the _Atomic() specifier for the purpose of
+  // checking.
+  if (const AtomicType *ResAtomicType = ResType->getAs<AtomicType>())
+    ResType = ResAtomicType->getValueType();
+
   assert(!ResType.isNull() && "no type for increment/decrement expression");
 
   if (S.getLangOptions().CPlusPlus && ResType->isBooleanType()) {
diff --git a/lib/StaticAnalyzer/Core/ExprEngineC.cpp b/lib/StaticAnalyzer/Core/ExprEngineC.cpp
index b3c5802..1ac35f0 100644
--- a/lib/StaticAnalyzer/Core/ExprEngineC.cpp
+++ b/lib/StaticAnalyzer/Core/ExprEngineC.cpp
@@ -218,6 +218,11 @@
       case CK_ARCConsumeObject:
       case CK_ARCReclaimReturnedObject:
       case CK_ARCExtendBlockObject: // Fall-through.
+        // The analyser can ignore atomic casts for now, although some future
+        // checkers may want to make certain that you're not modifying the same
+        // value through atomic and nonatomic pointers.
+      case CK_AtomicToNonAtomic:
+      case CK_NonAtomicToAtomic:
         // True no-ops.
       case CK_NoOp:
       case CK_FunctionToPointerDecay: {
diff --git a/test/CodeGen/atomic_init.c b/test/CodeGen/atomic_init.c
new file mode 100644
index 0000000..243eb60
--- /dev/null
+++ b/test/CodeGen/atomic_init.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s
+
+// Check that no atomic operations are used in any initialisation of _Atomic
+// types.  
+
+_Atomic(int) i = 42;
+
+void foo()
+{
+  _Atomic(int) j = 12; // CHECK: store 
+                       // CHECK-NOT: atomic
+  __atomic_init(&j, 42); // CHECK: store 
+                         // CHECK-NOT: atomic
+}
diff --git a/test/CodeGen/atomic_ops.c b/test/CodeGen/atomic_ops.c
new file mode 100644
index 0000000..9a18c9e
--- /dev/null
+++ b/test/CodeGen/atomic_ops.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s
+
+void foo(void)
+{
+  _Atomic(int) i = 0;
+  // Check that multiply / divides on atomics produce a cmpxchg loop
+  i *= 2; // CHECK: cmpxchg
+  i /= 2; // CHECK: cmpxchg
+  // These should be emitting atomicrmw instructions, but they aren't yet
+  i += 2; // CHECK: cmpxchg
+  i -= 2; // CHECK: cmpxchg
+  i++; // CHECK: cmpxchg
+  i--; // CHECK: cmpxchg
+}
diff --git a/test/Lexer/has_feature_c1x.c b/test/Lexer/has_feature_c1x.c
index a502f16..c9a5f56 100644
--- a/test/Lexer/has_feature_c1x.c
+++ b/test/Lexer/has_feature_c1x.c
@@ -1,6 +1,15 @@
 // RUN: %clang_cc1 -E -std=c1x %s -o - | FileCheck --check-prefix=CHECK-1X %s
 // RUN: %clang_cc1 -E %s -o - | FileCheck --check-prefix=CHECK-NO-1X %s
 
+#if __has_feature(c_atomic)
+int has_atomic();
+#else
+int no_atomic();
+#endif
+
+// CHECK-1X: has_atomic
+// CHECK-NO-1X: no_atomic
+
 #if __has_feature(c_static_assert)
 int has_static_assert();
 #else
diff --git a/test/Lexer/has_feature_cxx0x.cpp b/test/Lexer/has_feature_cxx0x.cpp
index a22cf64..f02f103 100644
--- a/test/Lexer/has_feature_cxx0x.cpp
+++ b/test/Lexer/has_feature_cxx0x.cpp
@@ -1,6 +1,15 @@
 // RUN: %clang_cc1 -E -std=c++11 %s -o - | FileCheck --check-prefix=CHECK-0X %s
 // RUN: %clang_cc1 -E %s -o - | FileCheck --check-prefix=CHECK-NO-0X %s
 
+#if __has_feature(cxx_atomic)
+int has_atomic();
+#else
+int no_atomic();
+#endif
+
+// CHECK-0X: has_atomic
+// CHECK-NO-0X: no_atomic
+
 #if __has_feature(cxx_lambdas)
 int has_lambdas();
 #else