Enhance Clang to start instantiating static data member definitions

within class templates when they are necessary to complete the type of
the member. The canonical example is code like:

  template <typename T> struct S {
    static const int arr[];
    static const int x;
    static int f();
  };

  template <typename T> const int S<T>::arr[] = { 1, 2, 3 };
  template <typename T> const int S<T>::x = sizeof(arr) / sizeof(arr[0]);
  template <typename T> int S<T>::f() { return x; }

  int x = S<int>::f();

We need to instantiate S<T>::arr's definition to pick up its initializer
and complete the array type. This involves new code to specially handle
completing the type of an expression where the type alone is
insufficient. It also requires *updating* the expression with the newly
completed type. Fortunately, all the other infrastructure is already in
Clang to do the instantiation, do the completion, and prune out the
unused bits of code that result from this instantiation.

This addresses the initial bug in PR10001, and will be a step to
fleshing out other cases where we need to work harder to complete an
expression's type. Who knew we still had missing C++03 "features"?

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@132172 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 30 insertions, 0 deletions

diff --git a/test/CodeGenCXX/template-instantiation.cpp b/test/CodeGenCXX/template-instantiation.cpp
index 635e1d2099..cc30af0aba 100644
--- a/test/CodeGenCXX/template-instantiation.cpp
+++ b/test/CodeGenCXX/template-instantiation.cpp
@@ -1,9 +1,15 @@
 // RUN: %clang_cc1 %s -O1 -triple=x86_64-apple-darwin10 -emit-llvm -o - | FileCheck %s
 
+// CHECK: @_ZN7PR100011xE = global
+// CHECK-NOT: @_ZN7PR100014kBarE = external global i32
+//
 // CHECK-NOT: @_ZTVN5test118stdio_sync_filebufIwEE = constant
 // CHECK-NOT: _ZTVN5test315basic_fstreamXXIcEE
 // CHECK: @_ZTVN5test018stdio_sync_filebufIwEE = unnamed_addr constant
 
+// CHECK: @_ZN7PR100011SIiE3arrE = weak_odr global [3 x i32]
+// CHECK-NOT: @_ZN7PR100011SIiE3arr2E = weak_odr global [3 x i32]A
+
 // CHECK-NOT: _ZTVN5test31SIiEE
 // CHECK-NOT: _ZTSN5test31SIiEE
 
@@ -122,3 +128,27 @@ class B {
 // CHECK-NOT: _ZN6PR85051AILi0EE1B1fEv
 template class A<0>;
 }
+
+// Ensure that when instantiating initializers for static data members to
+// complete their type in an unevaluated context, we *do* emit initializers with
+// side-effects, but *don't* emit initializers and variables which are otherwise
+// unused in the program.
+namespace PR10001 {
+  template <typename T> struct S {
+    static const int arr[];
+    static const int arr2[];
+    static const int x, y;
+    static int f();
+  };
+
+  extern int foo();
+  extern int kBar;
+
+  template <typename T> const int S<T>::arr[] = { 1, 2, foo() }; // possible side effects
+  template <typename T> const int S<T>::arr2[] = { 1, 2, kBar }; // no side effects
+  template <typename T> const int S<T>::x = sizeof(arr) / sizeof(arr[0]);
+  template <typename T> const int S<T>::y = sizeof(arr2) / sizeof(arr2[0]);
+  template <typename T> int S<T>::f() { return x + y; }
+
+  int x = S<int>::f();
+}