From 178be5db99d47508fb39c39aad2eae1080ba4b7a Mon Sep 17 00:00:00 2001
From: Reid Kleckner <rnk@google.com>
Date: Tue, 10 Jan 2017 00:26:56 +0000
Subject: [PATCH] Fix MSVC build of AlignedCharArrayUnion

Use constexpr recursion for alignof like we do for sizeof. Seems to work
with Clang and MSVC. Also, don't recurse twice to avoid slowdowns in
compilers that don't memoize constexpr results (Clang).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291514 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Support/AlignOf.h | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/include/llvm/Support/AlignOf.h b/include/llvm/Support/AlignOf.h
index 5fda901a100..e1e304f4c1a 100644
--- a/include/llvm/Support/AlignOf.h
+++ b/include/llvm/Support/AlignOf.h
@@ -107,20 +107,18 @@ LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
 // Once these are the baselines for LLVM, we can use std::aligned_union instead.
 
 namespace detail {
-template <typename... Ts> class AlignerImpl;
+template <typename T1> constexpr size_t aligner() { return alignof(T1); }
 
-template <typename T1, typename... Ts>
-class AlignerImpl<T1, Ts...> : AlignerImpl<Ts...> {
-  T1 t;
-  AlignerImpl() = delete;
-};
-
-template <> class AlignerImpl<> { AlignerImpl() = delete; };
+template <typename T1, typename T2, typename... Ts> constexpr size_t aligner() {
+  size_t rest = aligner<T2, Ts...>();
+  return (alignof(T1) > rest) ? alignof(T1) : rest;
+}
 
 template <typename T1> constexpr size_t sizer() { return sizeof(T1); }
 
 template <typename T1, typename T2, typename... Ts> constexpr size_t sizer() {
-  return (sizeof(T1) > sizer<T2, Ts...>()) ? sizeof(T1) : sizer<T2, Ts...>();
+  size_t rest = sizer<T2, Ts...>();
+  return (sizeof(T1) > rest) ? sizeof(T1) : rest;
 }
 } // end namespace detail
 
@@ -132,7 +130,7 @@ template <typename T1, typename T2, typename... Ts> constexpr size_t sizer() {
 /// a placement new of any of these types.
 template <typename... Ts>
 struct AlignedCharArrayUnion
-    : llvm::AlignedCharArray<alignof(llvm::detail::AlignerImpl<Ts...>),
+    : llvm::AlignedCharArray<detail::aligner<Ts...>(),
                              detail::sizer<Ts...>()> {};
 } // end namespace llvm
 
-- 
2.49.0