[clang][Interp] Support LambdaThisCaptures

Differential Revision: https://reviews.llvm.org/D154262

Author: tbaederr

clang/lib/AST/Interp/ByteCodeEmitter.cpp

@@ -64,8 +64,8 @@ ByteCodeEmitter::compileFunc(const FunctionDecl *FuncDecl) {
         this->LambdaCaptures[Cap.first] = {
             Offset, Cap.second->getType()->isReferenceType()};
       }
-      // FIXME: LambdaThisCapture
-      (void)LTC;
+      if (LTC)
+        this->LambdaThisCapture = R->getField(LTC)->Offset;
     }
   }
 

clang/lib/AST/Interp/ByteCodeEmitter.h

@@ -67,7 +67,8 @@ class ByteCodeEmitter {
   llvm::DenseMap<const ParmVarDecl *, ParamOffset> Params;
   /// Lambda captures.
   llvm::DenseMap<const ValueDecl *, ParamOffset> LambdaCaptures;
-  unsigned LambdaThisCapture;
+  /// Offset of the This parameter in a lambda record.
+  unsigned LambdaThisCapture = 0;
   /// Local descriptors.
   llvm::SmallVector<SmallVector<Local, 8>, 2> Descriptors;
 

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -2305,6 +2305,10 @@ template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitCXXThisExpr(const CXXThisExpr *E) {
   if (DiscardResult)
     return true;
+
+  if (this->LambdaThisCapture > 0)
+    return this->emitGetThisFieldPtr(this->LambdaThisCapture, E);
+
   return this->emitThis(E);
 }
 

clang/lib/AST/Interp/EvalEmitter.h

@@ -73,7 +73,8 @@ class EvalEmitter : public SourceMapper {
   llvm::DenseMap<const ParmVarDecl *, ParamOffset> Params;
   /// Lambda captures.
   llvm::DenseMap<const ValueDecl *, ParamOffset> LambdaCaptures;
-  unsigned LambdaThisCapture;
+  /// Offset of the This parameter in a lambda record.
+  unsigned LambdaThisCapture = 0;
   /// Local descriptors.
   llvm::SmallVector<SmallVector<Local, 8>, 2> Descriptors;
 

clang/test/AST/Interp/lambda.cpp

@@ -179,3 +179,24 @@ namespace LambdasAsParams {
   }
   static_assert(heh() == 1.0);
 }
+
+namespace ThisCapture {
+  class Foo {
+  public:
+    int b = 32;
+    int a;
+
+    constexpr Foo() : a([this](){ return b + 1;}()) {}
+
+    constexpr int Aplus2() const {
+      auto F = [this]() {
+        return a + 2;
+      };
+
+      return F();
+    }
+  };
+  constexpr Foo F;
+  static_assert(F.a == 33, "");
+  static_assert(F.Aplus2() == (33 + 2), "");
+}