[clang] [clang][bytecode] Keep a list of initializing blocks in InterpState (PR #148120)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/148120

So we can know what blocks we're currently running constructors or destructors for.

>From 047fa0e0bc313548227c724b5b32ce862199f301 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Thu, 10 Jul 2025 20:46:52 +0200
Subject: [PATCH] [clang][bytecode] Keep a list of initializing blocks in
 InterpState

So we can know what blocks we're currently running constructors or
destructors for.
---
 clang/lib/AST/ByteCode/Interp.cpp    | 43 ++++++++++++++--------------
 clang/lib/AST/ByteCode/InterpState.h |  4 +++
 2 files changed, 25 insertions(+), 22 deletions(-)

diff --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index be77657acabcc..18b84fa48fb1d 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/clang/lib/AST/ByteCode/Interp.cpp
@@ -576,23 +576,14 @@ bool CheckConst(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
   if (!Ptr.isConst() || Ptr.isMutable())
     return true;
 
-  // The This pointer is writable in constructors and destructors,
-  // even if isConst() returns true.
-  // TODO(perf): We could be hitting this code path quite a lot in complex
-  // constructors. Is there a better way to do this?
-  if (S.Current->getFunction()) {
-    for (const InterpFrame *Frame = S.Current; Frame; Frame = Frame->Caller) {
-      if (const Function *Func = Frame->getFunction();
-          Func && (Func->isConstructor() || Func->isDestructor()) &&
-          Ptr.block() == Frame->getThis().block()) {
-        return true;
-      }
-    }
-  }
-
   if (!Ptr.isBlockPointer())
     return false;
 
+  // The This pointer is writable in constructors and destructors,
+  // even if isConst() returns true.
+  if (llvm::find(S.InitializingBlocks, Ptr.block()))
+    return true;
+
   const QualType Ty = Ptr.getType();
   const SourceInfo &Loc = S.Current->getSource(OpPC);
   S.FFDiag(Loc, diag::note_constexpr_modify_const_type) << Ty;
@@ -1524,6 +1515,9 @@ bool Call(InterpState &S, CodePtr OpPC, const Function *Func,
       return false;
     if (Func->isDestructor() && !CheckDestructor(S, OpPC, ThisPtr))
       return false;
+
+    if (Func->isConstructor() || Func->isDestructor())
+      S.InitializingBlocks.push_back(ThisPtr.block());
   }
 
   if (!Func->isFullyCompiled())
@@ -1550,16 +1544,21 @@ bool Call(InterpState &S, CodePtr OpPC, const Function *Func,
   // Note that we cannot assert(CallResult.hasValue()) here since
   // Ret() above only sets the APValue if the curent frame doesn't
   // have a caller set.
-  if (Interpret(S)) {
-    NewFrame.release(); // Frame was delete'd already.
-    assert(S.Current == FrameBefore);
-    return true;
+  bool Success = Interpret(S);
+  // Remove initializing  block again.
+  if (Func->isConstructor() || Func->isDestructor())
+    S.InitializingBlocks.pop_back();
+
+  if (!Success) {
+    // Interpreting the function failed somehow. Reset to
+    // previous state.
+    S.Current = FrameBefore;
+    return false;
   }
 
-  // Interpreting the function failed somehow. Reset to
-  // previous state.
-  S.Current = FrameBefore;
-  return false;
+  NewFrame.release(); // Frame was delete'd already.
+  assert(S.Current == FrameBefore);
+  return true;
 }
 
 bool CallVirt(InterpState &S, CodePtr OpPC, const Function *Func,
diff --git a/clang/lib/AST/ByteCode/InterpState.h b/clang/lib/AST/ByteCode/InterpState.h
index 08765561985e2..861e4c38049ab 100644
--- a/clang/lib/AST/ByteCode/InterpState.h
+++ b/clang/lib/AST/ByteCode/InterpState.h
@@ -190,6 +190,10 @@ class InterpState final : public State, public SourceMapper {
       std::pair<const Expr *, const LifetimeExtendedTemporaryDecl *>>
       SeenGlobalTemporaries;
 
+  /// List of blocks we're currently running either constructors or destructors
+  /// for.
+  llvm::SmallVector<const Block *> InitializingBlocks;
+
   mutable llvm::BumpPtrAllocator Allocator;
 };