Add modernize-use-default check to clang-tidy.

Summary:
Add a check that replaces empty bodies of special member functions with '= default;'.
For now, it is only implemented for the default constructor and the destructor, which are the easier cases.
The copy-constructor and the copy-assignment operator cases will be implemented later.

I applied this check to the llvm code base and found 627 warnings (385 in llvm, 9 in compiler-rt, 220 in clang and 13 in clang-tools-extra).
Applying the fixes didn't break any build or test, it only caused a -Wpedantic warning in lib/Target/Mips/MipsOptionRecord.h:33 becaused it replaced
virtual ~MipsOptionRecord(){}; to virtual ~MipsOptionRecord()= default;;

Reviewers: klimek

Subscribers: george.burgess.iv, Eugene.Zelenko, alexfh, cfe-commits

Differential Revision: http://reviews.llvm.org/D13871

llvm-svn: 250897

2 files changed, 28 insertions, 0 deletions

diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index d1dda8ecdb2..a2e4de29135 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -55,6 +55,7 @@ List of clang-tidy Checks
    modernize-replace-auto-ptr
    modernize-shrink-to-fit
    modernize-use-auto
+   modernize-use-default
    modernize-use-nullptr
    modernize-use-override
    readability-braces-around-statements
diff --git a/clang-tools-extra/docs/clang-tidy/checks/modernize-use-default.rst b/clang-tools-extra/docs/clang-tidy/checks/modernize-use-default.rst
new file mode 100644
index 00000000000..c52cf89b918
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/modernize-use-default.rst
@@ -0,0 +1,27 @@
+modernize-use-default
+=====================
+
+This check replaces default bodies of special member functions with ``=
+default;``.  The explicitly defaulted function declarations enable more
+opportunities in optimization, because the compiler might treat explicitly
+defaulted functions as trivial.
+
+.. code-block:: c++
+
+  struct A {
+    A() {}
+    ~A();
+  };
+  A::~A() {}
+
+  // becomes
+
+  struct A {
+    A() = default;
+    ~A();
+  };
+  A::~A() = default;
+
+.. note::
+  Copy-constructor, copy-assignment operator, move-constructor and
+  move-assignment operator are not supported yet.