[MS] Don't statically initialize dllimport member function pointers

Summary:
r306137 made dllimport pointers to member functions non-constant. This
is correct because a load must be executed to resolve any dllimported
data. However, r306137 did not account for the use of dllimport member
function pointers used as template arguments.

This change re-lands r306137 with a template instantiation fix.

This fixes PR33570.

Reviewers: rnk, majnemer

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D34714

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@307446 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 548a1e24f8..0c0c861e5d 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -1665,6 +1665,19 @@ static bool CheckLValueConstantExpression(EvalInfo &Info, SourceLocation Loc,
   return true;
 }
 
+/// Member pointers are constant expressions unless they point to a
+/// non-virtual dllimport member function.
+static bool CheckMemberPointerConstantExpression(EvalInfo &Info,
+                                                 SourceLocation Loc,
+                                                 QualType Type,
+                                                 const APValue &Value) {
+  const ValueDecl *Member = Value.getMemberPointerDecl();
+  const auto *FD = dyn_cast_or_null<CXXMethodDecl>(Member);
+  if (!FD)
+    return true;
+  return FD->isVirtual() || !FD->hasAttr<DLLImportAttr>();
+}
+
 /// Check that this core constant expression is of literal type, and if not,
 /// produce an appropriate diagnostic.
 static bool CheckLiteralType(EvalInfo &Info, const Expr *E,
@@ -1757,6 +1770,9 @@ static bool CheckConstantExpression(EvalInfo &Info, SourceLocation DiagLoc,
     return CheckLValueConstantExpression(Info, DiagLoc, Type, LVal);
   }
 
+  if (Value.isMemberPointer())
+    return CheckMemberPointerConstantExpression(Info, DiagLoc, Type, Value);
+
   // Everything else is fine.
   return true;
 }