diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index 46d0f57..9ca6e4a 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -87,6 +87,7 @@
     void CheckDynamicCast();
     void CheckCXXCStyleCast(bool FunctionalCast, bool ListInitialization);
     void CheckCStyleCast();
+    void CheckBuiltinBitCast();
 
     void updatePartOfExplicitCastFlags(CastExpr *CE) {
       // Walk down from the CE to the OrigSrcExpr, and mark all immediate
@@ -331,6 +332,38 @@
   }
 }
 
+ExprResult Sema::ActOnBuiltinBitCastExpr(SourceLocation KWLoc, Declarator &D,
+                                         ExprResult Operand,
+                                         SourceLocation RParenLoc) {
+  assert(!D.isInvalidType());
+
+  TypeSourceInfo *TInfo = GetTypeForDeclaratorCast(D, Operand.get()->getType());
+  if (D.isInvalidType())
+    return ExprError();
+
+  return BuildBuiltinBitCastExpr(KWLoc, TInfo, Operand.get(), RParenLoc);
+}
+
+ExprResult Sema::BuildBuiltinBitCastExpr(SourceLocation KWLoc,
+                                         TypeSourceInfo *TSI, Expr *Operand,
+                                         SourceLocation RParenLoc) {
+  CastOperation Op(*this, TSI->getType(), Operand);
+  Op.OpRange = SourceRange(KWLoc, RParenLoc);
+  TypeLoc TL = TSI->getTypeLoc();
+  Op.DestRange = SourceRange(TL.getBeginLoc(), TL.getEndLoc());
+
+  if (!Operand->isTypeDependent() && !TSI->getType()->isDependentType()) {
+    Op.CheckBuiltinBitCast();
+    if (Op.SrcExpr.isInvalid())
+      return ExprError();
+  }
+
+  BuiltinBitCastExpr *BCE =
+      new (Context) BuiltinBitCastExpr(Op.ResultType, Op.ValueKind, Op.Kind,
+                                       Op.SrcExpr.get(), TSI, KWLoc, RParenLoc);
+  return Op.complete(BCE);
+}
+
 /// Try to diagnose a failed overloaded cast.  Returns true if
 /// diagnostics were emitted.
 static bool tryDiagnoseOverloadedCast(Sema &S, CastType CT,
@@ -2764,6 +2797,43 @@
     checkCastAlign();
 }
 
+void CastOperation::CheckBuiltinBitCast() {
+  QualType SrcType = SrcExpr.get()->getType();
+  if (SrcExpr.get()->isRValue())
+    SrcExpr = Self.CreateMaterializeTemporaryExpr(SrcType, SrcExpr.get(),
+                                                  /*IsLValueReference=*/false);
+
+  CharUnits DestSize = Self.Context.getTypeSizeInChars(DestType);
+  CharUnits SourceSize = Self.Context.getTypeSizeInChars(SrcType);
+  if (DestSize != SourceSize) {
+    Self.Diag(OpRange.getBegin(), diag::err_bit_cast_type_size_mismatch)
+        << (int)SourceSize.getQuantity() << (int)DestSize.getQuantity();
+    SrcExpr = ExprError();
+    return;
+  }
+
+  if (!DestType.isTriviallyCopyableType(Self.Context)) {
+    Self.Diag(OpRange.getBegin(), diag::err_bit_cast_non_trivially_copyable)
+        << 1;
+    SrcExpr = ExprError();
+    return;
+  }
+
+  if (!SrcType.isTriviallyCopyableType(Self.Context)) {
+    Self.Diag(OpRange.getBegin(), diag::err_bit_cast_non_trivially_copyable)
+        << 0;
+    SrcExpr = ExprError();
+    return;
+  }
+
+  if (Self.Context.hasSameUnqualifiedType(DestType, SrcType)) {
+    Kind = CK_NoOp;
+    return;
+  }
+
+  Kind = CK_LValueToRValueBitCast;
+}
+
 /// DiagnoseCastQual - Warn whenever casts discards a qualifiers, be it either
 /// const, volatile or both.
 static void DiagnoseCastQual(Sema &Self, const ExprResult &SrcExpr,