Make llvm::Optional<T> trivially copyable when T is trivially copyable

This is an ever-recurring issue (see https://bugs.llvm.org/show_bug.cgi?id=39427 and https://bugs.llvm.org/show_bug.cgi?id=35978)
but I believe that thanks to https://reviews.llvm.org/D54472 we can now ship a decent implementation of this.

Basically the fact that llvm::is_trivially_copyable has a consistent behavior across compilers should prevent any ABI issue,
and using in-place new instead of memcpy should keep compiler bugs away.

Differential Revision: https://reviews.llvm.org/D57097

llvm-svn: 353927

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/OptionalTest.cpp b/llvm/unittests/ADT/OptionalTest.cpp
index 9d6d5d29fe0..8d49b3dc22a 100644
--- a/llvm/unittests/ADT/OptionalTest.cpp
+++ b/llvm/unittests/ADT/OptionalTest.cpp
@@ -16,6 +16,12 @@ using namespace llvm;
 
 namespace {
 
+static_assert(llvm::is_trivially_copyable<Optional<int>>::value,
+              "trivially copyable");
+
+static_assert(llvm::is_trivially_copyable<Optional<std::array<int, 3>>>::value,
+              "trivially copyable");
+
 struct NonDefaultConstructible {
   static unsigned CopyConstructions;
   static unsigned Destructions;
@@ -43,6 +49,10 @@ unsigned NonDefaultConstructible::CopyConstructions = 0;
 unsigned NonDefaultConstructible::Destructions = 0;
 unsigned NonDefaultConstructible::CopyAssignments = 0;
 
+static_assert(
+    !llvm::is_trivially_copyable<Optional<NonDefaultConstructible>>::value,
+    "not trivially copyable");
+
 // Test fixture
 class OptionalTest : public testing::Test {
 };
@@ -201,6 +211,10 @@ struct MultiArgConstructor {
 };
 unsigned MultiArgConstructor::Destructions = 0;
 
+static_assert(
+    !llvm::is_trivially_copyable<Optional<MultiArgConstructor>>::value,
+    "not trivially copyable");
+
 TEST_F(OptionalTest, Emplace) {
   MultiArgConstructor::ResetCounts();
   Optional<MultiArgConstructor> A;
@@ -248,6 +262,9 @@ unsigned MoveOnly::MoveConstructions = 0;
 unsigned MoveOnly::Destructions = 0;
 unsigned MoveOnly::MoveAssignments = 0;
 
+static_assert(!llvm::is_trivially_copyable<Optional<MoveOnly>>::value,
+              "not trivially copyable");
+
 TEST_F(OptionalTest, MoveOnlyNull) {
   MoveOnly::ResetCounts();
   Optional<MoveOnly> O;
@@ -349,6 +366,9 @@ private:
 unsigned Immovable::Constructions = 0;
 unsigned Immovable::Destructions = 0;
 
+static_assert(!llvm::is_trivially_copyable<Optional<Immovable>>::value,
+              "not trivially copyable");
+
 TEST_F(OptionalTest, ImmovableEmplace) {
   Optional<Immovable> A;
   Immovable::ResetCounts();