[llvm] 7d9a162 - [ADT] Allow IsSizeLessThanThresholdT for incomplete types. NFC

[Yevgeny Rouban via llvm-commits]

Author: Yevgeny Rouban
Date: 2020-08-21T11:01:57+07:00
New Revision: 7d9a16241fdd800a394e5cb4ecdf76f6bb8c9d9f

URL: https://github.com/llvm/llvm-project/commit/7d9a16241fdd800a394e5cb4ecdf76f6bb8c9d9f
DIFF: https://github.com/llvm/llvm-project/commit/7d9a16241fdd800a394e5cb4ecdf76f6bb8c9d9f.diff

LOG: [ADT] Allow IsSizeLessThanThresholdT for incomplete types. NFC

If the type T is incomplete then sizeof(T) results in C++ compilation error at line:
  static constexpr bool value = sizeof(T) <= (2 * sizeof(void *));

This patch allows incomplete types in parameters of function. Example:
  using SomeFunc = void(SomeIncompleteType &);
  llvm::unique_function<SomeFuncType> SomeFunc;

Reviewers: DaniilSuchkov, vvereschaka

Differential Revision: https://reviews.llvm.org/D81554

Added: 
    

Modified: 
    llvm/include/llvm/ADT/FunctionExtras.h

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/ADT/FunctionExtras.h b/llvm/include/llvm/ADT/FunctionExtras.h
index 4c75e4d2547b..7f8fb103f148 100644
--- a/llvm/include/llvm/ADT/FunctionExtras.h
+++ b/llvm/include/llvm/ADT/FunctionExtras.h
@@ -64,12 +64,12 @@ template <typename ReturnT, typename... ParamTs> class UniqueFunctionBase {
 protected:
   static constexpr size_t InlineStorageSize = sizeof(void *) * 3;
 
-  // MSVC has a bug and ICEs if we give it a particular dependent value
-  // expression as part of the `std::conditional` below. To work around this,
-  // we build that into a template struct's constexpr bool.
-  template <typename T> struct IsSizeLessThanThresholdT {
-    static constexpr bool value = sizeof(T) <= (2 * sizeof(void *));
-  };
+  template <typename T, class = void>
+  struct IsSizeLessThanThresholdT : std::false_type {};
+
+  template <typename T>
+  struct IsSizeLessThanThresholdT<
+      T, std::enable_if_t<sizeof(T) <= 2 * sizeof(void *)>> : std::true_type {};
 
   // Provide a type function to map parameters that won't observe extra copies
   // or moves and which are small enough to likely pass in register to values