AST: Support constant folding of variables of const pointer type.

lib/AST/ExprConstant.cpp

if (!Frame) {
           if (Info.getLangOpts().CPlusPlus) {
             Info.Diag(E, diag::note_constexpr_ltor_non_const_int, 1) << VD;
             Info.Note(VD->getLocation(), diag::note_declared_at);
           } else {
             Info.Diag(E);
           }
           return CompleteObject();
         }
-      } else if (BaseType->isFloatingType() && BaseType.isConstQualified()) {
-        // We support folding of const floating-point types, in order to make
-        // static const data members of such types (supported as an extension)
-        // more useful.
+      } else if ((BaseType->isFloatingType() || BaseType->isPointerType()) &&
+                 BaseType.isConstQualified()) {
+        // We support folding of const floating-point and pointer types, in
+        // order to make static const data members of such types (supported as
+        // an extension) more useful.
         if (Info.getLangOpts().CPlusPlus11) {
           Info.CCEDiag(E, diag::note_constexpr_ltor_non_constexpr, 1) << VD;
           Info.Note(VD->getLocation(), diag::note_declared_at);
         } else {
           Info.CCEDiag(E);
         }
       } else {
         // FIXME: Allow folding of values of any literal type in all languages.

test/CodeGenCXX/global-init.cpp

 
 struct C { void *field; };
 
 struct D { ~D(); };
 
 // CHECK: @__dso_handle = external global i8
 // CHECK: @c = global %struct.C zeroinitializer, align 8
 
-// It's okay if we ever implement the IR-generation optimization to remove this.
-// CHECK: @_ZN5test3L3varE = internal constant i8* getelementptr inbounds ([7 x i8], [7 x i8]* 
+// CHECK: @[[STR:.*]] = private unnamed_addr constant [7 x i8] c"string\00"
 
 // PR6205: The casts should not require global initializers
 // CHECK: @_ZN6PR59741cE = external global %"struct.PR5974::C"
 // CHECK: @_ZN6PR59741aE = global %"struct.PR5974::A"* getelementptr inbounds (%"struct.PR5974::C", %"struct.PR5974::C"* @_ZN6PR59741cE, i32 0, i32 0)
 // CHECK: @_ZN6PR59741bE = global %"struct.PR5974::B"* bitcast (i8* getelementptr (i8, i8* bitcast (%"struct.PR5974::C"* @_ZN6PR59741cE to i8*), i64 4) to %"struct.PR5974::B"*), align 8
 
 // CHECK: call void @_ZN1AC1Ev(%struct.A* @a)
 // CHECK: call i32 @__cxa_atexit(void (i8*)* bitcast (void (%struct.A*)* @_ZN1AD1Ev to void (i8*)*), i8* getelementptr inbounds (%struct.A, %struct.A* @a, i32 0, i32 0), i8* @__dso_handle)
namespace test2 {
   A a;
 // CHECK: call void @_ZN5test29allocatorC1Ev(
 // CHECK: invoke void @_ZN5test21AC1ERKNS_9allocatorE(
 // CHECK: call void @_ZN5test29allocatorD1Ev(
 // CHECK: call i32 @__cxa_atexit({{.*}} @_ZN5test21AD1Ev {{.*}} @_ZN5test21aE
 }
 
 namespace test3 {
-  // Tested at the beginning of the file.
   const char * const var = "string";
   extern const char * const var;
 
+  // CHECK: ret i8* getelementptr inbounds ([7 x i8], [7 x i8]* @[[STR]], i32 0, i32 0)
   const char *test() { return var; }
 }
 
 namespace test4 {
   struct A {
     A();
   };
   extern int foo();