[clang] [clang][bytecode] Fix a crash with explicit this parameters (PR #177154)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr updated https://github.com/llvm/llvm-project/pull/177154

>From 0c105af8b293b6cafe0a5ba0325cca4febf13784 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Wed, 21 Jan 2026 13:34:58 +0100
Subject: [PATCH] [clang][bytecode] Fix a crash with explicit this parameters

Fixes https://github.com/llvm/llvm-project/issues/177133
---
 clang/lib/AST/ByteCode/InterpFrame.cpp |  7 ++++---
 clang/test/AST/ByteCode/cxx26.cpp      | 17 +++++++++++++++++
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/clang/lib/AST/ByteCode/InterpFrame.cpp b/clang/lib/AST/ByteCode/InterpFrame.cpp
index 5d645feb5579d..b92dfbe0b1138 100644
--- a/clang/lib/AST/ByteCode/InterpFrame.cpp
+++ b/clang/lib/AST/ByteCode/InterpFrame.cpp
@@ -152,7 +152,7 @@ static bool shouldSkipInBacktrace(const Function *F) {
 
 void InterpFrame::describe(llvm::raw_ostream &OS) const {
   // For lambda static invokers, we would just print __invoke().
-  if (const auto *F = getFunction(); F && shouldSkipInBacktrace(F))
+  if (Func && shouldSkipInBacktrace(Func))
     return;
 
   const Expr *CallExpr = Caller->getExpr(getRetPC());
@@ -189,13 +189,14 @@ void InterpFrame::describe(llvm::raw_ostream &OS) const {
   unsigned Off = 0;
 
   Off += Func->hasRVO() ? primSize(PT_Ptr) : 0;
-  Off += Func->hasThisPointer() ? primSize(PT_Ptr) : 0;
+  Off += (Func->hasThisPointer() && !Func->isThisPointerExplicit())
+             ? primSize(PT_Ptr)
+             : 0;
 
   llvm::ListSeparator Comma;
   for (unsigned I = 0, N = F->getNumParams(); I < N; ++I) {
     OS << Comma;
     QualType Ty = F->getParamDecl(I)->getType();
-
     PrimType PrimTy = S.Ctx.classify(Ty).value_or(PT_Ptr);
 
     TYPE_SWITCH(PrimTy, print(OS, stackRef<T>(Off), S.getASTContext(), Ty));
diff --git a/clang/test/AST/ByteCode/cxx26.cpp b/clang/test/AST/ByteCode/cxx26.cpp
index 64461ee9e12cd..acab347963923 100644
--- a/clang/test/AST/ByteCode/cxx26.cpp
+++ b/clang/test/AST/ByteCode/cxx26.cpp
@@ -45,3 +45,20 @@ constexpr int a = 12;
 constexpr const int *b = &a;
 constexpr int *f = (int*)(void*)b;
 static_assert(*f == 12);
+
+namespace ExplicitThisInBacktrace {
+  struct S {
+    constexpr void foo(this const S& self) {
+      throw; // both-note {{not valid in a constant expression}}
+    }
+  };
+
+  constexpr bool test() {
+    S s;
+    s.foo(); // both-note {{in call to}}
+    return true;
+  }
+
+  static_assert(test()); // both-error {{not an integral constant expression}} \
+                         // both-note {{in call to}}
+}