Add ALIGNAS and ALIGNOF macros to ensure proper alignment of StaticMemorySingletonTraits

base/memory/aligned_memory_unittest.cc

Index: base/memory/aligned_memory_unittest.cc
diff --git a/base/memory/aligned_memory_unittest.cc b/base/memory/aligned_memory_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c52f02ebab48403eb8a4709c690124b41bc25941
--- /dev/null
+++ b/base/memory/aligned_memory_unittest.cc
@@ -0,0 +1,51 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/memory/aligned_memory.h"
+#include "base/memory/scoped_ptr.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+#define EXPECT_ALIGNED(ptr, align) \
+    EXPECT_EQ(reinterpret_cast<intptr_t>(ptr) & (align - 1), 0)
+
+namespace {
+
+using base::RawAlignedMemory;
+using base::AlignedMemory;
+
+TEST(AlignedMemoryTest, StaticAlignment) {
+  static RawAlignedMemory<8, 8> raw8;
+  static RawAlignedMemory<8, 16> raw16;
+  static RawAlignedMemory<8, 256> raw256;
+  static RawAlignedMemory<8, 4096> raw4096;
+
+  EXPECT_EQ(ALIGNOF(raw8), 8u);
+  EXPECT_EQ(ALIGNOF(raw16), 16u);
+  EXPECT_EQ(ALIGNOF(raw256), 256u);
+  EXPECT_EQ(ALIGNOF(raw4096), 4096u);
+
+  EXPECT_ALIGNED(raw8.data_, 8);
+  EXPECT_ALIGNED(raw16.data_, 16);
+  EXPECT_ALIGNED(raw256.data_, 256);
+  EXPECT_ALIGNED(raw4096.data_, 4096);
+}
+
+TEST(AlignedMemoryTest, StackAlignment) {
+  RawAlignedMemory<8, 8> raw8;

[Sigurður Ásgeirsson, 2012/02/22 15:31:32]

nice - do you know if is there a cost to this? I assume the compiler needs to
align the stack/frame pointer to the max alignment used in a function - does
that cause fallout in e.g. stack unwinding for crash reports? 
(I'm only curious, not suggesting any measurement or code changes).

[jbates, 2012/02/22 19:37:15]

I'm not sure. It must already happen to a certain extent for base types of
alignment 1, 2, 4, or 8 bytes (or 16 if we count vector types such as __m128).
Seems like the only cost would be padding in the stack frame.

+  RawAlignedMemory<8, 16> raw16;
+  RawAlignedMemory<8, 256> raw256;
+  RawAlignedMemory<8, 4096> raw4096;
+
+  EXPECT_EQ(ALIGNOF(raw8), 8u);
+  EXPECT_EQ(ALIGNOF(raw16), 16u);
+  EXPECT_EQ(ALIGNOF(raw256), 256u);
+  EXPECT_EQ(ALIGNOF(raw4096), 4096u);
+
+  EXPECT_ALIGNED(raw8.data_, 8);
+  EXPECT_ALIGNED(raw16.data_, 16);
+  EXPECT_ALIGNED(raw256.data_, 256);
+  EXPECT_ALIGNED(raw4096.data_, 4096);
+}
+
+}  // namespace