7 files changed, 149 insertions, 0 deletions
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 4787b857110..d5a0eea4d59 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -122,6 +122,7 @@ def InitializerOverrides : DiagGroup<"initializer-overrides">;
 def NonNull : DiagGroup<"nonnull">;
 def : DiagGroup<"nonportable-cfstrings">;
 def NonVirtualDtor : DiagGroup<"non-virtual-dtor">;
+def OveralignedType : DiagGroup<"over-aligned">;
 def : DiagGroup<"old-style-cast">;
 def : DiagGroup<"old-style-definition">;
 def OutOfLineDeclaration : DiagGroup<"out-of-line-declaration">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 87522e5eb39..dec27e07375 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4024,6 +4024,11 @@ def note_hidden_overloaded_virtual_declared_here : Note<
 def warn_using_directive_in_header : Warning<
   "using namespace directive in global context in header">,
   InGroup<HeaderHygiene>, DefaultIgnore;
+def warn_overaligned_type : Warning<
+  "type %0 requires %1 bytes of alignment and the default allocator only "
+  "guarantees %2 bytes">,
+  InGroup<OveralignedType>, DefaultIgnore;
+def note_overaligned_type : Note<"over-aligned here">;
 
 def err_conditional_void_nonvoid : Error<
   "%select{left|right}1 operand to ? is void, but %select{right|left}1 operand "
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index bea0954c6f0..919ef06957c 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -20,6 +20,7 @@
 #include "clang/Sema/Scope.h"
 #include "clang/Sema/TemplateDeduction.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/CharUnits.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/ExprCXX.h"
@@ -1104,6 +1105,21 @@ Sema::BuildCXXNew(SourceLocation StartLoc, bool UseGlobal,
       PlaceArgs = &AllPlaceArgs[0];
   }
 
+  // Warn if the type is over-aligned and is being allocated by global operator
+  // new.
+  if (OperatorNew &&
+      (OperatorNew->isImplicit() ||
+       getSourceManager().isInSystemHeader(OperatorNew->getLocStart()))) {
+    if (unsigned Align = Context.getPreferredTypeAlign(AllocType.getTypePtr())){
+      unsigned SuitableAlign = Context.getTargetInfo().getSuitableAlign();
+      if (Align > SuitableAlign)
+        Diag(StartLoc, diag::warn_overaligned_type)
+            << AllocType
+            << unsigned(Align / Context.getCharWidth())
+            << unsigned(SuitableAlign / Context.getCharWidth());
+    }
+  }
+
   bool Init = ConstructorLParen.isValid();
   // --- Choosing a constructor ---
   CXXConstructorDecl *Constructor = 0;
diff --git a/clang/test/SemaCXX/Inputs/warn-new-overaligned-3.h b/clang/test/SemaCXX/Inputs/warn-new-overaligned-3.h
new file mode 100644
index 00000000000..024acc299fe
--- /dev/null
+++ b/clang/test/SemaCXX/Inputs/warn-new-overaligned-3.h
@@ -0,0 +1,12 @@
+#pragma GCC system_header
+
+// This header file pretends to be <new> from the system library, for the
+// purpose of the over-aligned warnings test.
+
+void* operator new(unsigned long) {
+  return 0;
+}
+void* operator new[](unsigned long) {
+  return 0;
+}
+
diff --git a/clang/test/SemaCXX/warn-new-overaligned-2.cpp b/clang/test/SemaCXX/warn-new-overaligned-2.cpp
new file mode 100644
index 00000000000..0a7643956db
--- /dev/null
+++ b/clang/test/SemaCXX/warn-new-overaligned-2.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -Wover-aligned -verify %s
+
+// This test verifies that we don't warn when the global operator new is
+// overridden. That's why we can't merge this with the other test file.
+
+void* operator new(unsigned long);
+void* operator new[](unsigned long);
+
+struct Test {
+  template <typename T>
+  struct SeparateCacheLines {
+    T data;
+  } __attribute__((aligned(256)));
+
+  SeparateCacheLines<int> high_contention_data[10];
+};
+
+void helper() {
+  Test t;
+  new Test;
+  new Test[10];
+}
diff --git a/clang/test/SemaCXX/warn-new-overaligned-3.cpp b/clang/test/SemaCXX/warn-new-overaligned-3.cpp
new file mode 100644
index 00000000000..f3b0cb7dd18
--- /dev/null
+++ b/clang/test/SemaCXX/warn-new-overaligned-3.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -Wover-aligned %s -isystem %S/Inputs -verify
+
+// This test ensures that we still get the warning even if we #include <new>
+// where the header here simulates <new>.
+#include <warn-new-overaligned-3.h>
+
+struct Test {
+  template <typename T>
+  struct SeparateCacheLines {
+    T data;
+  } __attribute__((aligned(256)));
+
+  SeparateCacheLines<int> high_contention_data[10];
+};
+
+void helper() {
+  Test t;
+  new Test;  // expected-warning {{type 'Test' requires 256 bytes of alignment and the default allocator only guarantees}}
+  new Test[10];  // expected-warning {{type 'Test' requires 256 bytes of alignment and the default allocator only guarantees}}
+}
diff --git a/clang/test/SemaCXX/warn-new-overaligned.cpp b/clang/test/SemaCXX/warn-new-overaligned.cpp
new file mode 100644
index 00000000000..6ebae8b513a
--- /dev/null
+++ b/clang/test/SemaCXX/warn-new-overaligned.cpp
@@ -0,0 +1,73 @@
+// RUN: %clang_cc1 -Wover-aligned -verify %s
+
+namespace test1 {
+struct Test {
+  template <typename T>
+  struct SeparateCacheLines {
+    T data;
+  } __attribute__((aligned(256)));
+
+  SeparateCacheLines<int> high_contention_data[10];
+};
+
+void helper() {
+  Test t;
+  new Test;  // expected-warning {{type 'test1::Test' requires 256 bytes of alignment and the default allocator only guarantees}}
+  new Test[10];  // expected-warning {{type 'test1::Test' requires 256 bytes of alignment and the default allocator only guarantees}}
+}
+}
+
+namespace test2 {
+class Test {
+  typedef int __attribute__((aligned(256))) aligned_int;
+  aligned_int high_contention_data[10];
+};
+
+void helper() {
+  Test t;
+  new Test;  // expected-warning {{type 'test2::Test' requires 256 bytes of alignment and the default allocator only guarantees}}
+  new Test[10];  // expected-warning {{type 'test2::Test' requires 256 bytes of alignment and the default allocator only guarantees}}
+}
+}
+
+namespace test3 {
+struct Test {
+  template <typename T>
+  struct SeparateCacheLines {
+    T data;
+  } __attribute__((aligned(256)));
+
+  void* operator new(unsigned long) {
+    return 0;
+  }
+
+  SeparateCacheLines<int> high_contention_data[10];
+};
+
+void helper() {
+  Test t;
+  new Test;
+  new Test[10];  // expected-warning {{type 'test3::Test' requires 256 bytes of alignment and the default allocator only guarantees}}
+}
+}
+
+namespace test4 {
+struct Test {
+  template <typename T>
+  struct SeparateCacheLines {
+    T data;
+  } __attribute__((aligned(256)));
+
+  void* operator new[](unsigned long) {
+    return 0;
+  }
+
+  SeparateCacheLines<int> high_contention_data[10];
+};
+
+void helper() {
+  Test t;
+  new Test;  // expected-warning {{type 'test4::Test' requires 256 bytes of alignment and the default allocator only guarantees}}
+  new Test[10];
+}
+}