Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -2290,17 +2290,17 @@
 /// as a constant.
 ///
 /// If ExcludeCtor is true, the duration when the object's constructor runs
-/// will not be considered. The caller will need to verify that the object is
-/// not written to during its construction.
+/// will not be considered (unless trivial). The caller will need to verify that
+/// the object is not written to during its construction.
 bool CodeGenModule::isTypeConstant(QualType Ty, bool ExcludeCtor) {
   if (!Ty.isConstant(Context) && !Ty->isReferenceType())
     return false;
 
   if (Context.getLangOpts().CPlusPlus) {
-    if (const CXXRecordDecl *Record
-          = Context.getBaseElementType(Ty)->getAsCXXRecordDecl())
-      return ExcludeCtor && !Record->hasMutableFields() &&
-             Record->hasTrivialDestructor();
+    if (const CXXRecordDecl *Record =
+            Context.getBaseElementType(Ty)->getAsCXXRecordDecl())
+      return (ExcludeCtor || Record->hasTrivialDefaultConstructor()) &&
+             !Record->hasMutableFields() && Record->hasTrivialDestructor();
   }
 
   return true;
@@ -2372,7 +2372,7 @@
 
   auto *GV = new llvm::GlobalVariable(
       getModule(), Ty->getElementType(), false,
-      llvm::GlobalValue::ExternalLinkage, nullptr, MangledName, nullptr,
+      llvm::GlobalVariable::ExternalLinkage, nullptr, MangledName, nullptr,
       llvm::GlobalVariable::NotThreadLocal, TargetAddrSpace);
 
   // If we already created a global with the same mangled name (but different
@@ -2428,6 +2428,29 @@
         D->getType().isConstant(Context) &&
         isExternallyVisible(D->getLinkageAndVisibility().getLinkage()))
       GV->setSection(".cp.rodata");
+
+    // Check if we a have a const declaration with an initializer, we may be
+    // able to emit it as available_externally to expose it's value to the
+    // optimizer.
+    if (GV->hasExternalLinkage() && GV->isConstant() && !GV->hasInitializer() &&
+        !D->hasDefinition() && D->hasInit()) {
+      bool HasMutableField = false;
+      if (Context.getLangOpts().CPlusPlus) {
+        if (const CXXRecordDecl *Record =
+                Context.getBaseElementType(D->getType())->getAsCXXRecordDecl())
+          HasMutableField = Record->hasMutableFields();
+      }
+
+      if (D->getType().isConstQualified() &&
+          !HasMutableField & !D->isInline() && !D->hasAttr<DLLImportAttr>()) {
+        const VarDecl *InitDecl;
+        const Expr *InitExpr = D->getAnyInitializer(InitDecl);
+        if (InitExpr) {
+          GV->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);
+          GV->setInitializer(EmitConstantInit(*InitDecl));
+        }
+      }
+    }
   }
 
   auto ExpectedAS =
Index: clang/test/CodeGenCXX/cxx11-extern-constexpr.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/cxx11-extern-constexpr.cpp
@@ -0,0 +1,48 @@
+// RUN: %clang_cc1 -std=c++11 %s -emit-llvm -o - -triple x86_64-linux-gnu | FileCheck %s --check-prefix=CHECK --check-prefix=CXX11
+// RUN: %clang_cc1 -std=c++1z %s -emit-llvm -o - -triple x86_64-linux-gnu | FileCheck %s --check-prefix=CHECK --check-prefix=CXX17
+
+struct Bar {
+  int b;
+};
+
+struct MutableBar {
+  mutable int b;
+};
+
+struct Foo {
+  // CXX11: @_ZN3Foo21ConstexprStaticMemberE = available_externally constant i32 42,
+  // CXX17: @_ZN3Foo21ConstexprStaticMemberE = linkonce_odr constant i32 42,
+  static constexpr int ConstexprStaticMember = 42;
+  // CHECK: @_ZN3Foo17ConstStaticMemberE = available_externally constant i32 43,
+  static const int ConstStaticMember = 43;
+
+  // CXX11: @_ZN3Foo23ConstStaticStructMemberE = available_externally constant %struct.Bar { i32 44 },
+  // CXX17: @_ZN3Foo23ConstStaticStructMemberE = linkonce_odr constant %struct.Bar { i32 44 },
+  static constexpr Bar ConstStaticStructMember = {44};
+
+  // CXX11: @_ZN3Foo34ConstexprStaticMutableStructMemberE = external global %struct.MutableBar,
+  // CXX17: @_ZN3Foo34ConstexprStaticMutableStructMemberE = linkonce_odr global %struct.MutableBar { i32 45 },
+  static constexpr MutableBar ConstexprStaticMutableStructMember = {45};
+};
+// CHECK: @_ZL15ConstStaticexpr = internal constant i32 46,
+static constexpr int ConstStaticexpr = 46;
+// CHECK: @_ZL9ConstExpr = internal constant i32 46, align 4
+static const int ConstExpr = 46;
+
+// CHECK: @_ZL21ConstexprStaticStruct = internal constant %struct.Bar { i32 47 },
+static constexpr Bar ConstexprStaticStruct = {47};
+
+// CHECK: @_ZL28ConstexprStaticMutableStruct = internal global %struct.MutableBar { i32 48 },
+static constexpr MutableBar ConstexprStaticMutableStruct = {48};
+
+void use(const int &);
+void foo() {
+  use(Foo::ConstexprStaticMember);
+  use(Foo::ConstStaticMember);
+  use(Foo::ConstStaticStructMember.b);
+  use(Foo::ConstexprStaticMutableStructMember.b);
+  use(ConstStaticexpr);
+  use(ConstExpr);
+  use(ConstexprStaticStruct.b);
+  use(ConstexprStaticMutableStruct.b);
+}