From 1c1448984d43f1f02c0235d35ebe8460c9b57afd Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Fri, 2 Mar 2012 10:56:40 +0000
Subject: [PATCH] Simplify the pair optimization. Rather than using complex
 type traits, just ensure that the number of bytes in the pair is the sum of
 the bytes in each side of the pair. As long as thats true, there are no extra
 bytes that might be padding.

Also add a few tests that previously would have slipped through the
checking. The more accurate checking mechanism catches these and ensures
they are handled conservatively correctly.

Thanks to Duncan for prodding me to do this right and more simply.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151891 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/ADT/Hashing.h         |  4 ++--
 include/llvm/Support/type_traits.h | 18 ------------------
 unittests/ADT/HashingTest.cpp      | 20 ++++++++++++++++++++
 3 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/include/llvm/ADT/Hashing.h b/include/llvm/ADT/Hashing.h
index 1b0e66947b2..7fbe5bb0ca2 100644
--- a/include/llvm/ADT/Hashing.h
+++ b/include/llvm/ADT/Hashing.h
@@ -357,8 +357,8 @@ template <typename T> struct is_hashable_data
 template <typename T, typename U> struct is_hashable_data<std::pair<T, U> >
   : integral_constant<bool, (is_hashable_data<T>::value &&
                              is_hashable_data<U>::value &&
-                             !is_alignment_padded<std::pair<T, U> >::value &&
-                             !is_pod_pair_padded<T, U>::value)> {};
+                             (sizeof(T) + sizeof(U)) ==
+                              sizeof(std::pair<T, U>))> {};
 
 /// \brief Helper to get the hashable data representation for a type.
 /// This variant is enabled when the type itself can be used.
diff --git a/include/llvm/Support/type_traits.h b/include/llvm/Support/type_traits.h
index a10d83ca5e0..85d90b17f17 100644
--- a/include/llvm/Support/type_traits.h
+++ b/include/llvm/Support/type_traits.h
@@ -126,24 +126,6 @@ struct is_integral : is_integral_impl<T> {};
 template <typename T> struct is_pointer : false_type {};
 template <typename T> struct is_pointer<T*> : true_type {};
 
-/// \brief Metafunction to compute whether a type requires alignment padding.
-/// When true, an object of this type will have padding bytes inside its
-/// 'sizeof' bytes.
-template <typename T> class is_alignment_padded {
-  struct pod_size_tester { T t; char c; };
-public:
-  enum { value = offsetof(pod_size_tester, c) != sizeof(T) };
-};
-
-/// \brief Metafunction to determine whether an adjacent pair of two types will
-/// require padding between them due to alignment.
-template <typename T, typename U> class is_pod_pair_padded {
-  struct pod_pair { T t; U u; };
-  struct pod_char_pair { T t; char c; };
-public:
-  enum { value = offsetof(pod_pair, u) != offsetof(pod_char_pair, c) };
-};
-
   
 // enable_if_c - Enable/disable a template based on a metafunction
 template<bool Cond, typename T = void>
diff --git a/unittests/ADT/HashingTest.cpp b/unittests/ADT/HashingTest.cpp
index a12cf90e274..449b6afae23 100644
--- a/unittests/ADT/HashingTest.cpp
+++ b/unittests/ADT/HashingTest.cpp
@@ -42,6 +42,16 @@ using namespace llvm;
 
 namespace {
 
+struct NonPOD {
+  uint64_t x, y;
+  NonPOD(uint64_t x, uint64_t y) : x(x), y(y) {}
+  ~NonPOD() {}
+  friend hash_code hash_value(const NonPOD &obj) {
+    return hash_combine(obj.x, obj.y);
+  }
+};
+
+
 TEST(HashingTest, HashValueBasicTest) {
   int x = 42, y = 43, c = 'x';
   void *p = 0;
@@ -73,6 +83,16 @@ TEST(HashingTest, HashValueBasicTest) {
             hash_value(std::make_pair(42, std::make_pair(43, 44))));
   EXPECT_EQ(hash_value(std::make_pair(42, std::make_pair(43, 44))),
             hash_value(std::make_pair(std::make_pair(42, 43), 44)));
+
+  // Ensure that pairs which have padding bytes *inside* them don't get treated
+  // this way.
+  EXPECT_EQ(hash_combine('0', hash_combine(1ull, '2')),
+            hash_value(std::make_pair('0', std::make_pair(1ull, '2'))));
+
+  // Ensure that non-POD pairs don't explode the traits used.
+  NonPOD obj1(1, 2), obj2(3, 4), obj3(5, 6);
+  EXPECT_EQ(hash_combine(obj1, hash_combine(obj2, obj3)),
+            hash_value(std::make_pair(obj1, std::make_pair(obj2, obj3))));
 }
 
 template <typename T, size_t N> T *begin(T (&arr)[N]) { return arr; }
-- 
2.34.1