Index: include/clang/AST/Expr.h
===================================================================
--- include/clang/AST/Expr.h
+++ include/clang/AST/Expr.h
@@ -537,6 +537,13 @@
   bool isConstantInitializer(ASTContext &Ctx, bool ForRef,
                              const Expr **Culprit = nullptr) const;
 
+  enum SideEffectsKind {
+    SE_NoSideEffects,          ///< Strictly evaluate the expression.
+    SE_AllowUndefinedBehavior, ///< Allow UB that we can give a value, but not
+                               ///< arbitrary unmodeled side effects.
+    SE_AllowSideEffects        ///< Allow any unmodeled side effect.
+  };
+
   /// EvalStatus is a struct with detailed info about an evaluation in progress.
   struct EvalStatus {
     /// Whether the evaluated expression has side effects.
@@ -565,6 +572,11 @@
     bool hasSideEffects() const {
       return HasSideEffects;
     }
+
+    bool hasUnacceptableSideEffect(SideEffectsKind SEK) {
+      return (SEK < SE_AllowSideEffects && HasSideEffects) ||
+             (SEK < SE_AllowUndefinedBehavior && HasUndefinedBehavior);
+    }
   };
 
   /// EvalResult is a struct with detailed info about an evaluated expression.
@@ -591,13 +603,6 @@
   /// side-effects.
   bool EvaluateAsBooleanCondition(bool &Result, const ASTContext &Ctx) const;
 
-  enum SideEffectsKind {
-    SE_NoSideEffects,          ///< Strictly evaluate the expression.
-    SE_AllowUndefinedBehavior, ///< Allow UB that we can give a value, but not
-                               ///< arbitrary unmodeled side effects.
-    SE_AllowSideEffects        ///< Allow any unmodeled side effect.
-  };
-
   /// EvaluateAsInt - Return true if this is a constant which we can fold and
   /// convert to an integer, using any crazy technique that we want to.
   bool EvaluateAsInt(llvm::APSInt &Result, const ASTContext &Ctx,
Index: lib/AST/ExprConstant.cpp
===================================================================
--- lib/AST/ExprConstant.cpp
+++ lib/AST/ExprConstant.cpp
@@ -10312,12 +10312,6 @@
          HandleConversionToBool(Scratch.Val, Result);
 }
 
-static bool hasUnacceptableSideEffect(Expr::EvalStatus &Result,
-                                      Expr::SideEffectsKind SEK) {
-  return (SEK < Expr::SE_AllowSideEffects && Result.HasSideEffects) ||
-         (SEK < Expr::SE_AllowUndefinedBehavior && Result.HasUndefinedBehavior);
-}
-
 bool Expr::EvaluateAsInt(APSInt &Result, const ASTContext &Ctx,
                          SideEffectsKind AllowSideEffects) const {
   if (!getType()->isIntegralOrEnumerationType())
@@ -10325,7 +10319,7 @@
 
   EvalResult ExprResult;
   if (!EvaluateAsRValue(ExprResult, Ctx) || !ExprResult.Val.isInt() ||
-      hasUnacceptableSideEffect(ExprResult, AllowSideEffects))
+      ExprResult.hasUnacceptableSideEffect(AllowSideEffects))
     return false;
 
   Result = ExprResult.Val.getInt();
@@ -10339,7 +10333,7 @@
 
   EvalResult ExprResult;
   if (!EvaluateAsRValue(ExprResult, Ctx) || !ExprResult.Val.isFloat() ||
-      hasUnacceptableSideEffect(ExprResult, AllowSideEffects))
+      ExprResult.hasUnacceptableSideEffect(AllowSideEffects))
     return false;
 
   Result = ExprResult.Val.getFloat();
@@ -10417,7 +10411,7 @@
 bool Expr::isEvaluatable(const ASTContext &Ctx, SideEffectsKind SEK) const {
   EvalResult Result;
   return EvaluateAsRValue(Result, Ctx) &&
-         !hasUnacceptableSideEffect(Result, SEK);
+         !Result.hasUnacceptableSideEffect(SEK);
 }
 
 APSInt Expr::EvaluateKnownConstInt(const ASTContext &Ctx,
Index: lib/CodeGen/CGExprConstant.cpp
===================================================================
--- lib/CodeGen/CGExprConstant.cpp
+++ lib/CodeGen/CGExprConstant.cpp
@@ -1392,20 +1392,40 @@
   return type;
 }
 
+/// Checks if the specified initializer is equivalent to zero initialization.
+static bool isZeroInitializer(ConstantEmitter &CE, const Expr *Init) {
+  if (auto *E = dyn_cast_or_null<CXXConstructExpr>(Init)) {
+    CXXConstructorDecl *CD = E->getConstructor();
+    return CD->isDefaultConstructor() && CD->isTrivial();
+  }
+
+  if (auto *IL = dyn_cast_or_null<InitListExpr>(Init)) {
+    for (auto I : IL->inits())
+      if (!isZeroInitializer(CE, I))
+        return false;
+    if (const Expr *Filler = IL->getArrayFiller())
+      return isZeroInitializer(CE, Filler);
+    return true;
+  }
+
+  QualType InitTy = Init->getType();
+  if (InitTy->isIntegralOrEnumerationType() || InitTy->isPointerType()) {
+    Expr::EvalResult Result;
+    if (Init->EvaluateAsRValue(Result, CE.CGM.getContext()) &&
+        !Result.hasUnacceptableSideEffect(Expr::SE_NoSideEffects))
+      return (Result.Val.isInt() && Result.Val.getInt().isNullValue()) ||
+             (Result.Val.isLValue() && Result.Val.isNullPointer());
+  }
+
+  return false;
+}
+
 llvm::Constant *ConstantEmitter::tryEmitPrivateForVarInit(const VarDecl &D) {
   // Make a quick check if variable can be default NULL initialized
   // and avoid going through rest of code which may do, for c++11,
   // initialization of memory to all NULLs.
-  if (!D.hasLocalStorage()) {
-    QualType Ty = CGM.getContext().getBaseElementType(D.getType());
-    if (Ty->isRecordType())
-      if (const CXXConstructExpr *E =
-          dyn_cast_or_null<CXXConstructExpr>(D.getInit())) {
-        const CXXConstructorDecl *CD = E->getConstructor();
-        if (CD->isTrivial() && CD->isDefaultConstructor())
-          return CGM.EmitNullConstant(D.getType());
-      }
-  }
+  if (!D.hasLocalStorage() && isZeroInitializer(*this, D.getInit()))
+    return CGM.EmitNullConstant(D.getType());
 
   QualType destType = D.getType();
 
Index: test/CodeGen/const-init.c
===================================================================
--- test/CodeGen/const-init.c
+++ test/CodeGen/const-init.c
@@ -167,7 +167,7 @@
     int : 1;
     int x;
   } a = {};
-  // CHECK: @g30.a = internal global %struct.anon.1 <{ i8 undef, i32 0 }>, align 1
+  // CHECK: @g30.a = internal global %struct.anon.1 zeroinitializer, align 1
 #pragma pack()
 }
 
Index: test/CodeGen/designated-initializers.c
===================================================================
--- test/CodeGen/designated-initializers.c
+++ test/CodeGen/designated-initializers.c
@@ -8,7 +8,7 @@
 // CHECK: @u = global %union.anon zeroinitializer
 union { int i; float f; } u = { };
 
-// CHECK: @u2 = global { i32, [4 x i8] } { i32 0, [4 x i8] undef }
+// CHECK: @u2 = global %union.anon.0 zeroinitializer
 union { int i; double f; } u2 = { };
 
 // CHECK: @u3 = global  %union.anon.1 zeroinitializer
Index: test/CodeGen/union-init2.c
===================================================================
--- test/CodeGen/union-init2.c
+++ test/CodeGen/union-init2.c
@@ -5,7 +5,7 @@
 union x {long long b;union x* a;} r = {.a = &r};
 
 
-// CHECK: global { [3 x i8], [5 x i8] } { [3 x i8] zeroinitializer, [5 x i8] undef }
+// CHECK: global %union.z zeroinitializer
 union z {
   char a[3];
   long long b;
Index: test/CodeGenCXX/cxx11-initializer-aggregate.cpp
===================================================================
--- test/CodeGenCXX/cxx11-initializer-aggregate.cpp
+++ test/CodeGenCXX/cxx11-initializer-aggregate.cpp
@@ -51,3 +51,30 @@
   // meaningful.
   B b[30] = {};
 }
+
+namespace ZeroInit {
+  enum { Zero, One };
+  constexpr int zero() { return 0; }
+  constexpr int *null() { return nullptr; }
+  struct Filler {
+    int x;
+    Filler();
+  };
+  struct S1 {
+    int x;
+  };
+
+  // These declarations, if implemented elementwise, require huge
+  // amout of memory and compiler time.
+  unsigned char data_1[1024 * 1024 * 1024 * 2u] = { 0 };
+  unsigned char data_2[1024 * 1024 * 1024 * 2u] = { Zero };
+  unsigned char data_3[1024][1024][1024] = {{{0}}};
+  unsigned char data_4[1024 * 1024 * 1024 * 2u] = { zero() };
+  int *data_5[1024 * 1024 * 512] = { nullptr };
+  int *data_6[1024 * 1024 * 512] = { null() };
+  struct S1 data_7[1024 * 1024 * 512] = {{0}};
+
+  // This variable must be initialized elementwise.
+  Filler data_e1[1024] = {};
+  // CHECK: getelementptr inbounds {{.*}} @_ZN8ZeroInit7data_e1E
+}
Index: test/CodeGenCXX/cxx1z-initializer-aggregate.cpp
===================================================================
--- test/CodeGenCXX/cxx1z-initializer-aggregate.cpp
+++ test/CodeGenCXX/cxx1z-initializer-aggregate.cpp
@@ -17,14 +17,14 @@
 
   C c1 = {};
   C c2 = {1};
-  // CHECK: @_ZN8Constant2c1E = global { i8 } zeroinitializer, align 1
+  // CHECK: @_ZN8Constant2c1E = global %"struct.Constant::C" zeroinitializer, align 1
   // CHECK: @_ZN8Constant2c2E = global { i8 } { i8 1 }, align 1
 
   // Test packing bases into tail padding.
   D d1 = {};
   D d2 = {1, 2, 3};
   D d3 = {1};
-  // CHECK: @_ZN8Constant2d1E = global { i32, i8, i8 } zeroinitializer, align 4
+  // CHECK: @_ZN8Constant2d1E = global %"struct.Constant::D" zeroinitializer, align 4
   // CHECK: @_ZN8Constant2d2E = global { i32, i8, i8 } { i32 1, i8 2, i8 3 }, align 4
   // CHECK: @_ZN8Constant2d3E = global { i32, i8, i8 } { i32 1, i8 0, i8 0 }, align 4
 
Index: test/SemaCXX/large-array-init.cpp
===================================================================
--- test/SemaCXX/large-array-init.cpp
+++ test/SemaCXX/large-array-init.cpp
@@ -1,10 +0,0 @@
-// RUN: %clang_cc1 -S -o %t.ll -mllvm -debug-only=exprconstant %s 2>&1 | \
-// RUN:     FileCheck %s
-// REQUIRES: asserts
-
-struct S { int i; };
-
-static struct S arr[100000000] = {{ 0 }};
-// CHECK: The number of elements to initialize: 1.
-
-struct S *foo() { return arr; }