2 files changed, 52 insertions, 5 deletions

diff --git a/llvm/include/llvm/Support/AlignOf.h b/llvm/include/llvm/Support/AlignOf.h
index 07da02d063c..5268c8d1698 100644
--- a/llvm/include/llvm/Support/AlignOf.h
+++ b/llvm/include/llvm/Support/AlignOf.h
@@ -17,9 +17,15 @@
 
 #include "llvm/Support/Compiler.h"
 #include <cstddef>
+#include <type_traits>
 
 namespace llvm {
-template <typename T>
+
+namespace detail {
+
+// For everything other than an abstract class we can calulate alignment by
+// building a class with a single character and a member of the given type.
+template <typename T, bool = std::is_abstract<T>::value>
 struct AlignmentCalcImpl {
   char x;
 #if defined(_MSC_VER)
@@ -35,6 +41,25 @@ private:
   AlignmentCalcImpl() {} // Never instantiate.
 };
 
+// Abstract base class helper, this will have the minimal alignment and size
+// for any abstract class. We don't even define its destructor because this
+// type should never be used in a way that requires it.
+struct AlignmentCalcImplBase {
+  virtual ~AlignmentCalcImplBase() = 0;
+};
+
+// When we have an abstract class type, specialize the alignment computation
+// engine to create another abstract class that derives from both an empty
+// abstract base class and the provided type. This has the same effect as the
+// above except that it handles the fact that we can't actually create a member
+// of type T.
+template <typename T>
+struct AlignmentCalcImpl<T, true> : AlignmentCalcImplBase, T {
+  virtual ~AlignmentCalcImpl() = 0;
+};
+
+} // End detail namespace.
+
 /// AlignOf - A templated class that contains an enum value representing
 ///  the alignment of the template argument.  For example,
 ///  AlignOf<int>::Alignment represents the alignment of type "int".  The
@@ -50,11 +75,13 @@ struct AlignOf {
   //   llvm::AlignOf<Y>::<anonymous>' [-Wenum-compare]
   // by using constexpr instead of enum.
   // (except on MSVC, since it doesn't support constexpr yet).
-  static constexpr unsigned Alignment =
-      static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T));
+  static constexpr unsigned Alignment = static_cast<unsigned int>(
+      sizeof(detail::AlignmentCalcImpl<T>) - sizeof(T));
 #else
-  enum { Alignment =
-         static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)) };
+  enum {
+    Alignment = static_cast<unsigned int>(sizeof(detail::AlignmentCalcImpl<T>) -
+                                          sizeof(T))
+  };
 #endif
   enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 };
   enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 };
diff --git a/llvm/unittests/Support/AlignOfTest.cpp b/llvm/unittests/Support/AlignOfTest.cpp
index e0859fc747f..be208f7d28e 100644
--- a/llvm/unittests/Support/AlignOfTest.cpp
+++ b/llvm/unittests/Support/AlignOfTest.cpp
@@ -89,6 +89,22 @@ V6::~V6() {}
 V7::~V7() {}
 V8::~V8() {}
 
+struct Abstract1 {
+  virtual ~Abstract1() {}
+  virtual void method() = 0;
+
+  char c;
+};
+
+struct Abstract2 : Abstract1 {
+  virtual ~Abstract2() {}
+  double d;
+};
+
+struct Final final : Abstract2 {
+  void method() override {}
+};
+
 // Ensure alignment is a compile-time constant.
 char LLVM_ATTRIBUTE_UNUSED test_arr1
   [AlignOf<char>::Alignment > 0]
@@ -174,6 +190,10 @@ TEST(AlignOfTest, BasicAlignmentInvariants) {
   EXPECT_LE(alignOf<V1>(),     alignOf<V6>());
   EXPECT_LE(alignOf<V1>(),     alignOf<V7>());
   EXPECT_LE(alignOf<V1>(),     alignOf<V8>());
+
+  EXPECT_LE(alignOf<char>(), alignOf<Abstract1>());
+  EXPECT_LE(alignOf<double>(), alignOf<Abstract2>());
+  EXPECT_LE(alignOf<Abstract2>(), alignOf<Final>());
 }
 
 TEST(AlignOfTest, BasicAlignedArray) {