[clang][Interp] LambdaThisCaptures

[tbaeder]

Summary

Fix a FIXME from an earlier commit.

[tbaeder]

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[aaron.ballman]

LGTM aside from a request for some comments.

clang/lib/AST/Interp/ByteCodeEmitter.h

70–71

Some comments explaining what this member represents would be helpful.

clang/lib/AST/Interp/EvalEmitter.h

76–77

Comments would also help here.

clang/lib/AST/Interp/ByteCodeEmitter.h

protected:
 
   /// Callback for local registration.
   Local createLocal(Descriptor *D);
 
   /// Parameter indices.
   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;
 
 private:
   /// Current compilation context.
   Context &Ctx;
   /// Program to link to.
   Program &P;

clang/lib/AST/Interp/ByteCodeEmitter.cpp

if (isLambdaCallOperator(MD)) {
 
       MD->getParent()->getCaptureFields(LC, LTC);
 
       for (auto Cap : LC) {
         unsigned Offset = R->getField(Cap.second)->Offset;
         this->LambdaCaptures[Cap.first] = {
             Offset, Cap.second->getType()->isReferenceType()};
       }
-      // FIXME: LambdaThisCapture
-      (void)LTC;
+      if (LTC)
+        this->LambdaThisCapture = R->getField(LTC)->Offset;
     }
   }
 
   // Assign descriptors to all parameters.
   // Composite objects are lowered to pointers.
   for (const ParmVarDecl *PD : FuncDecl->parameters()) {
     std::optional<PrimType> T = Ctx.classify(PD->getType());
     PrimType PT = T.value_or(PT_Ptr);

clang/lib/AST/Interp/ByteCodeExprGen.cpp

bool ByteCodeExprGen<Emitter>::VisitGNUNullExpr(const GNUNullExpr *E) {
   PrimType T = classifyPrim(E->getType());
   return this->emitZero(T, E);
 }
 
 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);
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitUnaryOperator(const UnaryOperator *E) {
   const Expr *SubExpr = E->getSubExpr();
   std::optional<PrimType> T = classify(SubExpr->getType());
 

clang/lib/AST/Interp/EvalEmitter.h

protected:
   SourceInfo getSource(const Function *F, CodePtr PC) const override {
     return (F && F->hasBody()) ? F->getSource(PC) : CurrentSource;
   }
 
   /// Parameter indices.
   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;
 
 private:
   /// Current compilation context.
   Context &Ctx;
   /// Current program.
   Program &P;

clang/test/AST/Interp/lambda.cpp

constexpr float heh() {
     auto a = []() {
       return 1.0;
     };
 
     return static_cast<float>(a());
   }
   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), "");
+}