[clang][bytecode] Remove InterpFrame::IsBottom flag (#159279)

The bottom frame is the one without a parent. No need to save that
information separately.

Author: tbaederr

clang/lib/AST/ByteCode/InterpFrame.cpp

@@ -24,13 +24,13 @@ using namespace clang::interp;
 
 InterpFrame::InterpFrame(InterpState &S)
     : Caller(nullptr), S(S), Depth(0), Func(nullptr), RetPC(CodePtr()),
-      ArgSize(0), Args(nullptr), FrameOffset(0), IsBottom(true) {}
+      ArgSize(0), Args(nullptr), FrameOffset(0) {}
 
 InterpFrame::InterpFrame(InterpState &S, const Function *Func,
                          InterpFrame *Caller, CodePtr RetPC, unsigned ArgSize)
     : Caller(Caller), S(S), Depth(Caller ? Caller->Depth + 1 : 0), Func(Func),
       RetPC(RetPC), ArgSize(ArgSize), Args(static_cast<char *>(S.Stk.top())),
-      FrameOffset(S.Stk.size()), IsBottom(!Caller) {
+      FrameOffset(S.Stk.size()) {
   if (!Func)
     return;
 

clang/lib/AST/ByteCode/InterpFrame.h

@@ -129,7 +129,7 @@ class InterpFrame final : public Frame {
 
   bool isStdFunction() const;
 
-  bool isBottomFrame() const { return IsBottom; }
+  bool isBottomFrame() const { return !Caller; }
 
   void dump() const { dump(llvm::errs(), 0); }
   void dump(llvm::raw_ostream &OS, unsigned Indent = 0) const;
@@ -179,7 +179,6 @@ class InterpFrame final : public Frame {
   const size_t FrameOffset;
   /// Mapping from arg offsets to their argument blocks.
   llvm::DenseMap<unsigned, std::unique_ptr<char[]>> Params;
-  bool IsBottom = false;
 };
 
 } // namespace interp