From fd015e4488fefe110be947cd9624de95d0d85ad7 Mon Sep 17 00:00:00 2001
From: Serge Guelton <sguelton@redhat.com>
Date: Thu, 14 Feb 2019 19:17:00 +0000
Subject: [PATCH] Recommit Optional specialization for trivially copyable types

Unfortunately the original code gets misscompiled by GCC (at least 8.1),
this is a tentative workaround using std::memcpy instead of inplace new
for trivially copyable types. I'll revert if it breaks.

Original revision: https://reviews.llvm.org/D57097


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354051 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/ADT/Optional.h    | 43 ++++++++++++++++++++++++++++++++++
 unittests/ADT/OptionalTest.cpp | 20 ++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/include/llvm/ADT/Optional.h b/include/llvm/ADT/Optional.h
index 25a3185064f..c628df9d711 100644
--- a/include/llvm/ADT/Optional.h
+++ b/include/llvm/ADT/Optional.h
@@ -21,6 +21,7 @@
 #include "llvm/Support/type_traits.h"
 #include <algorithm>
 #include <cassert>
+#include <cstring>
 #include <new>
 #include <utility>
 
@@ -109,6 +110,48 @@ template <typename T, bool = is_trivially_copyable<T>::value> struct OptionalSto
   }
 };
 
+template <typename T> struct OptionalStorage<T, true> {
+  AlignedCharArrayUnion<T> storage;
+  bool hasVal = false;
+
+  OptionalStorage() = default;
+
+  OptionalStorage(const T &y) : hasVal(true) { new (storage.buffer) T(y); }
+  OptionalStorage(const OptionalStorage &O) = default;
+  OptionalStorage(T &&y) : hasVal(true) {
+    std::memcpy(storage.buffer, reinterpret_cast<char*>(&y), sizeof(T));
+  }
+
+  OptionalStorage(OptionalStorage &&O) = default;
+
+  OptionalStorage &operator=(T &&y) {
+    hasVal = true;
+    std::memcpy(storage.buffer, reinterpret_cast<char*>(&y), sizeof(T));
+    return *this;
+  }
+  OptionalStorage &operator=(OptionalStorage &&O) = default;
+
+  OptionalStorage &operator=(const T &y) {
+    hasVal = true;
+    std::memcpy(storage.buffer, reinterpret_cast<char const*>(&y), sizeof(T));
+    return *this;
+  }
+  OptionalStorage &operator=(const OptionalStorage &O) = default;
+
+  ~OptionalStorage() = default;
+
+  T *getPointer() {
+    assert(hasVal);
+    return reinterpret_cast<T *>(storage.buffer);
+  }
+  const T *getPointer() const {
+    assert(hasVal);
+    return reinterpret_cast<const T *>(storage.buffer);
+  }
+
+  void reset() { hasVal = false; }
+};
+
 } // namespace optional_detail
 
 template <typename T> class Optional {
diff --git a/unittests/ADT/OptionalTest.cpp b/unittests/ADT/OptionalTest.cpp
index 98adaccca96..c39b6727cd5 100644
--- a/unittests/ADT/OptionalTest.cpp
+++ b/unittests/ADT/OptionalTest.cpp
@@ -18,6 +18,12 @@ 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;
@@ -45,6 +51,10 @@ 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 {
 };
@@ -203,6 +213,10 @@ 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;
@@ -250,6 +264,9 @@ 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;
@@ -351,6 +368,9 @@ 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();
-- 
2.50.1