[NFC] Make Optional<T> trivially copyable when T is trivially copyable

This is a follow-up to r354246 and a reimplementation of https://reviews.llvm.org/D57097?id=186600
that should not trigger any UB thanks to the use of an union.

This may still be subject to the problem solved by std::launder, but I'm unsure how it interacts whith union.
/me plans to revert if this triggers any relevant bot failure. At least this validates in Release mode with
clang 6.0.1 and gcc 4.8.5.

llvm-svn: 354264

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/OptionalTest.cpp b/llvm/unittests/ADT/OptionalTest.cpp
index 98adaccca96..1f26c101183 100644
--- a/llvm/unittests/ADT/OptionalTest.cpp
+++ b/llvm/unittests/ADT/OptionalTest.cpp
@@ -14,8 +14,15 @@
 
 #include <array>
 
+
 using namespace llvm;
 
+static_assert(is_trivially_copyable<Optional<int>>::value,
+          "trivially copyable");
+
+static_assert(is_trivially_copyable<Optional<std::array<int, 3>>>::value,
+              "trivially copyable");
+
 namespace {
 
 struct NonDefaultConstructible {
@@ -45,6 +52,10 @@ unsigned NonDefaultConstructible::CopyConstructions = 0;
 unsigned NonDefaultConstructible::Destructions = 0;
 unsigned NonDefaultConstructible::CopyAssignments = 0;
 
+static_assert(
+      !is_trivially_copyable<Optional<NonDefaultConstructible>>::value,
+      "not trivially copyable");
+
 // Test fixture
 class OptionalTest : public testing::Test {
 };
@@ -203,6 +214,10 @@ struct MultiArgConstructor {
 };
 unsigned MultiArgConstructor::Destructions = 0;
 
+static_assert(
+  !is_trivially_copyable<Optional<MultiArgConstructor>>::value,
+  "not trivially copyable");
+
 TEST_F(OptionalTest, Emplace) {
   MultiArgConstructor::ResetCounts();
   Optional<MultiArgConstructor> A;
@@ -250,6 +265,9 @@ unsigned MoveOnly::MoveConstructions = 0;
 unsigned MoveOnly::Destructions = 0;
 unsigned MoveOnly::MoveAssignments = 0;
 
+static_assert(!is_trivially_copyable<Optional<MoveOnly>>::value,
+              "not trivially copyable");
+
 TEST_F(OptionalTest, MoveOnlyNull) {
   MoveOnly::ResetCounts();
   Optional<MoveOnly> O;
@@ -351,6 +369,9 @@ private:
 unsigned Immovable::Constructions = 0;
 unsigned Immovable::Destructions = 0;
 
+static_assert(!is_trivially_copyable<Optional<Immovable>>::value,
+              "not trivially copyable");
+
 TEST_F(OptionalTest, ImmovableEmplace) {
   Optional<Immovable> A;
   Immovable::ResetCounts();