From 060f1d33e896224c26b056e56eae24cadde71671 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Sun, 26 Aug 2018 09:17:49 +0000
Subject: [PATCH] Avoid specializing a variadic member template in a way that
 seems to not agree with MSVC.

There isn't actually a need for specialization here as we can write the
code generically and just have a test that will fold away as a constant.

llvm-svn: 340700
---
 lib/Support/ItaniumManglingCanonicalizer.cpp | 28 +++++++++-----------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/lib/Support/ItaniumManglingCanonicalizer.cpp b/lib/Support/ItaniumManglingCanonicalizer.cpp
index 7023305774e..ca63c6d1c7d 100644
--- a/lib/Support/ItaniumManglingCanonicalizer.cpp
+++ b/lib/Support/ItaniumManglingCanonicalizer.cpp
@@ -104,8 +104,19 @@ class FoldingNodeAllocator {
 public:
   void reset() {}
 
-  template<typename T, typename ...Args>
-  std::pair<Node*, bool> getOrCreateNode(bool CreateNewNodes, Args &&...As) {
+  template <typename T, typename... Args>
+  std::pair<Node *, bool> getOrCreateNode(bool CreateNewNodes, Args &&... As) {
+    // FIXME: Don't canonicalize forward template references for now, because
+    // they contain state (the resolved template node) that's not known at their
+    // point of creation.
+    if (std::is_same<T, ForwardTemplateReference>::value) {
+      // Note that we don't use if-constexpr here and so we must still write
+      // this code in a generic form.
+      return {new (RawAlloc.Allocate(sizeof(T), alignof(T)))
+                  T(std::forward<Args>(As)...),
+              true};
+    }
+
     llvm::FoldingSetNodeID ID;
     profileCtor(ID, NodeKind<T>::Kind, As...);
 
@@ -136,19 +147,6 @@ public:
   }
 };
 
-// FIXME: Don't canonicalize forward template references for now, because they
-// contain state (the resolved template node) that's not known at their point
-// of creation.
-template<>
-std::pair<Node *, bool>
-FoldingNodeAllocator::getOrCreateNode<ForwardTemplateReference>(bool,
-                                                                size_t &Index) {
-  return {new (RawAlloc.Allocate(sizeof(ForwardTemplateReference),
-                                 alignof(ForwardTemplateReference)))
-              ForwardTemplateReference(Index),
-          true};
-}
-
 class CanonicalizerAllocator : public FoldingNodeAllocator {
   Node *MostRecentlyCreated = nullptr;
   Node *TrackedNode = nullptr;