Index: lib/CodeGen/CGExprAgg.cpp
===================================================================
--- lib/CodeGen/CGExprAgg.cpp
+++ lib/CodeGen/CGExprAgg.cpp
@@ -14,6 +14,7 @@
 #include "CodeGenFunction.h"
 #include "CGObjCRuntime.h"
 #include "CodeGenModule.h"
+#include "ConstantEmitter.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclTemplate.h"
@@ -85,7 +86,7 @@
   void EmitMoveFromReturnSlot(const Expr *E, RValue Src);
 
   void EmitArrayInit(Address DestPtr, llvm::ArrayType *AType,
-                     QualType elementType, InitListExpr *E);
+                     QualType ArrayQTy, InitListExpr *E);
 
   AggValueSlot::NeedsGCBarriers_t needsGC(QualType T) {
     if (CGF.getLangOpts().getGC() && TypeRequiresGCollection(T))
@@ -394,12 +395,15 @@
 
 /// \brief Emit initialization of an array from an initializer list.
 void AggExprEmitter::EmitArrayInit(Address DestPtr, llvm::ArrayType *AType,
-                                   QualType elementType, InitListExpr *E) {
+                                   QualType ArrayQTy, InitListExpr *E) {
   uint64_t NumInitElements = E->getNumInits();
 
   uint64_t NumArrayElements = AType->getNumElements();
   assert(NumInitElements <= NumArrayElements);
 
+  QualType elementType =
+      CGF.getContext().getAsArrayType(ArrayQTy)->getElementType();
+
   // DestPtr is an array*.  Construct an elementType* by drilling
   // down a level.
   llvm::Value *zero = llvm::ConstantInt::get(CGF.SizeTy, 0);
@@ -411,6 +415,29 @@
   CharUnits elementAlign =
     DestPtr.getAlignment().alignmentOfArrayElement(elementSize);
 
+  // Consider initializing the array by copying from a global. For this to be
+  // more efficient than per-element initialization, the number of the elements
+  // with explicit initializers should be large enough.
+  if (NumInitElements > 8 &&
+      elementType.isTriviallyCopyableType(CGF.getContext())) {
+    CodeGen::CodeGenModule &CGM = CGF.CGM;
+    ConstantEmitter Emitter(CGM);
+    LangAS AS = ArrayQTy.getAddressSpace();
+    if (llvm::Constant *C = Emitter.tryEmitForInitializer(E, AS, ArrayQTy)) {
+      auto GV = new llvm::GlobalVariable(
+          CGM.getModule(), C->getType(),
+          CGM.isTypeConstant(ArrayQTy, /* ExcludeCtorDtor= */ true),
+          llvm::GlobalValue::PrivateLinkage, C, "constinit",
+          /* InsertBefore= */ nullptr, llvm::GlobalVariable::NotThreadLocal,
+          CGM.getContext().getTargetAddressSpace(AS));
+      Emitter.finalize(GV);
+      CharUnits Align = CGM.getContext().getTypeAlignInChars(ArrayQTy);
+      GV->setAlignment(Align.getQuantity());
+      EmitFinalDestCopy(ArrayQTy, CGF.MakeAddrLValue(GV, ArrayQTy, Align));
+      return;
+    }
+  }
+
   // Exception safety requires us to destroy all the
   // already-constructed members if an initializer throws.
   // For that, we'll need an EH cleanup.
@@ -1158,11 +1185,8 @@
 
   // Handle initialization of an array.
   if (E->getType()->isArrayType()) {
-    QualType elementType =
-        CGF.getContext().getAsArrayType(E->getType())->getElementType();
-
     auto AType = cast<llvm::ArrayType>(Dest.getAddress().getElementType());
-    EmitArrayInit(Dest.getAddress(), AType, elementType, E);
+    EmitArrayInit(Dest.getAddress(), AType, E->getType(), E);
     return;
   }
 
Index: test/CodeGen/init.c
===================================================================
--- test/CodeGen/init.c
+++ test/CodeGen/init.c
@@ -8,8 +8,9 @@
 // CHECK-DAG: %struct.M = type { [2 x %struct.I] }
 // CHECK-DAG: %struct.I = type { [3 x i32] }
 
-// CHECK: [1 x %struct.M] [%struct.M { [2 x %struct.I] [%struct.I { [3 x i32] [i32 4, i32 4, i32 0] }, %struct.I { [3 x i32] [i32 4, i32 4, i32 5] }] }],
-// CHECK: [2 x [3 x i32]] {{[[][[]}}3 x i32] [i32 2222, i32 2222, i32 0], [3 x i32] [i32 2222, i32 2222, i32 3333]],
+// CHECK-DAG: [1 x %struct.M] [%struct.M { [2 x %struct.I] [%struct.I { [3 x i32] [i32 4, i32 4, i32 0] }, %struct.I { [3 x i32] [i32 4, i32 4, i32 5] }] }],
+// CHECK-DAG: [2 x [3 x i32]] {{[[][[]}}3 x i32] [i32 2222, i32 2222, i32 0], [3 x i32] [i32 2222, i32 2222, i32 3333]],
+// CHECK-DAG: [[INIT14:.*]] = private global [16 x i32] [i32 0, i32 0, i32 0, i32 0, i32 0, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 0, i32 0, i32 0, i32 0], align 4
 
 void f1() {
   // Scalars in braces.
@@ -33,8 +34,8 @@
 }
 
 // Constants
-// CHECK: @g3 = constant i32 10
-// CHECK: @f4.g4 = internal constant i32 12
+// CHECK-DAG: @g3 = constant i32 10
+// CHECK-DAG: @f4.g4 = internal constant i32 12
 const int g3 = 10;
 int f4() {
   static const int g4 = 12;
@@ -61,7 +62,7 @@
 
 
 
-// CHECK: @test7 = global{{.*}}{ i32 0, [4 x i8] c"bar\00" }
+// CHECK-DAG: @test7 = global{{.*}}{ i32 0, [4 x i8] c"bar\00" }
 // PR8217
 struct a7 {
   int  b;
@@ -151,3 +152,15 @@
   // CHECK: memcpy{{.*}}getelementptr inbounds ([3 x i8], [3 x i8]* @
   bar((char[3]) {""});
 }
+
+// Test that we initialize large member arrays by copying from a global and not
+// with a series of stores.
+struct S14 { int a[16]; };
+
+void test14(struct S14 *s14) {
+// CHECK-LABEL: @test14
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 {{.*}}, i8* align 4 {{.*}} [[INIT14]] {{.*}}, i32 64, i1 false)
+// CHECK-NOT: store
+// CHECK: ret void
+  *s14 = (struct S14) { { [5 ... 11] = 17 } };
+}