[clang] [clang][bytecode] Remove `InterpFrame::ThisPointerOffset` (PR #202322)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/202322

Replace it with a `uint8_t` representing some bool flags about the function. This reduces the size of a frame from 88 to 80 bytes.

>From 3aa88a9ef2b44e0ac59db6f59b3d31abf3336ee1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Mon, 8 Jun 2026 13:09:37 +0200
Subject: [PATCH] FuncFlags

---
 clang/lib/AST/ByteCode/InterpFrame.cpp | 10 ++++------
 clang/lib/AST/ByteCode/InterpFrame.h   | 13 +++++++++----
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/clang/lib/AST/ByteCode/InterpFrame.cpp b/clang/lib/AST/ByteCode/InterpFrame.cpp
index 9c9318fe0e55a..98bd897445cad 100644
--- a/clang/lib/AST/ByteCode/InterpFrame.cpp
+++ b/clang/lib/AST/ByteCode/InterpFrame.cpp
@@ -35,6 +35,10 @@ InterpFrame::InterpFrame(InterpState &S, const Function *Func,
 
   if (!Func)
     return;
+
+  FuncFlags |= Func->hasRVO() * HasRVOFlag;
+  FuncFlags |= Func->hasThisPointer() * HasThisFlag;
+
   // Initialize argument blocks.
   for (unsigned I = 0, N = Func->getNumWrittenParams(); I != N; ++I)
     new (argBlock(I)) Block(S.EvalID, Func->getParamDescriptor(I).Desc);
@@ -61,12 +65,6 @@ InterpFrame::InterpFrame(InterpState &S, const Function *Func, CodePtr RetPC,
   // If the fuction has a This pointer, that one is next.
   // Then follow the actual arguments (but those are handled
   // in getParamPointer()).
-  if (Func->hasRVO()) {
-    // RVO pointer offset is always 0.
-  }
-
-  if (Func->hasThisPointer())
-    ThisPointerOffset = Func->hasRVO() ? sizeof(Pointer) : 0;
 }
 
 InterpFrame::~InterpFrame() {
diff --git a/clang/lib/AST/ByteCode/InterpFrame.h b/clang/lib/AST/ByteCode/InterpFrame.h
index 7dbf58c23fd5c..64bbb87d7a6fe 100644
--- a/clang/lib/AST/ByteCode/InterpFrame.h
+++ b/clang/lib/AST/ByteCode/InterpFrame.h
@@ -127,13 +127,13 @@ class InterpFrame final : public Frame {
   /// Returns a pointer to an argument - lazily creates a block.
   Pointer getParamPointer(unsigned Offset);
 
-  bool hasThisPointer() const { return Func && Func->hasThisPointer(); }
+  bool hasThisPointer() const { return FuncFlags & HasThisFlag; }
 
   /// Returns the 'this' pointer.
   const Pointer &getThis() const {
     assert(hasThisPointer());
     assert(!isBottomFrame());
-    return stackRef<Pointer>(ThisPointerOffset);
+    return stackRef<Pointer>((FuncFlags & HasRVOFlag) ? sizeof(Pointer) : 0);
   }
 
   /// Returns the RVO pointer, if the Function has one.
@@ -169,6 +169,9 @@ class InterpFrame final : public Frame {
   void dump(llvm::raw_ostream &OS, unsigned Indent = 0) const;
 
 private:
+  static constexpr uint8_t HasRVOFlag = 1u << 0u;
+  static constexpr uint8_t HasThisFlag = 1u << 1u;
+
   /// Returns an original argument from the stack.
   template <typename T> const T &stackRef(unsigned Offset) const {
     assert(Args);
@@ -215,8 +218,6 @@ class InterpFrame final : public Frame {
   unsigned Depth;
   /// Reference to the function being executed.
   const Function *Func;
-  /// Offset of the instance pointer. Use with stackRef<>().
-  unsigned ThisPointerOffset;
   /// Return address.
   CodePtr RetPC;
   /// The size of all the arguments.
@@ -228,6 +229,10 @@ class InterpFrame final : public Frame {
 
 public:
   unsigned MSVCConstexprAllowed = 0;
+
+private:
+  /// Relevant flags about the function.
+  uint8_t FuncFlags = 0;
 };
 
 } // namespace interp