[Cxx1z] Implement Lambda Capture of *this by Value as [=,*this] (P0018R3)

Implement lambda capture of *this by copy.
For e.g.:
struct A {

  int d = 10;
  auto foo() { return [*this] (auto a) mutable { d+=a; return d; }; }

};

auto L = A{}.foo(); // A{}'s lifetime is gone.

// Below is still ok, because *this was captured by value.
assert(L(10) == 20);
assert(L(100) == 120);

If the capture was implicit, or [this] (i.e. *this was captured by reference), this code would be otherwise undefined.

Implementation Strategy:
  - amend the parser to accept *this in the lambda introducer
  - add a new king of capture LCK_StarThis
  - teach Sema::CheckCXXThisCapture to handle by copy captures of the
    enclosing object (i.e. *this)
  - when CheckCXXThisCapture does capture by copy, the corresponding 
    initializer expression for the closure's data member 
    direct-initializes it thus making a copy of '*this'.
  - in codegen, when assigning to CXXThisValue, if *this was captured by 
    copy, make sure it points to the corresponding field member, and
    not, unlike when captured by reference, what the field member points
    to.
  - mark feature as implemented in svn

Much gratitude to Richard Smith for his carefully illuminating reviews!   


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@263921 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 1 deletions

diff --git a/include/clang/Basic/Lambda.h b/include/clang/Basic/Lambda.h
index e676e726dd..1c19f1dcc8 100644
--- a/include/clang/Basic/Lambda.h
+++ b/include/clang/Basic/Lambda.h
@@ -32,7 +32,8 @@ enum LambdaCaptureDefault {
 /// by reference.  C++1y also allows "init-capture", where the initializer
 /// is an expression.
 enum LambdaCaptureKind {
-  LCK_This,   ///< Capturing the \c this pointer
+  LCK_This,   ///< Capturing the \c *this object by reference
+  LCK_StarThis, /// < Capturing the \c *this object by copy
   LCK_ByCopy, ///< Capturing by copy (a.k.a., by value)
   LCK_ByRef,  ///< Capturing by reference
   LCK_VLAType ///< Capturing variable-length array type