[clang] [clang][bytecode] Don't call getIndex() on one-past-end pointers (PR #155173)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr updated https://github.com/llvm/llvm-project/pull/155173

>From 448ee9a9b416b3c78d6134bc649f6a4b2e4b2391 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Sun, 24 Aug 2025 16:47:01 +0200
Subject: [PATCH] [clang][bytecode] Don't call getIndex() on one-past-end
 pointers

That doesn't work.

Fixes #152903
---
 clang/lib/AST/ByteCode/Interp.cpp | 4 ++--
 clang/test/AST/ByteCode/cxx11.cpp | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index 796c24e9071ec..d4525c8288c68 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/clang/lib/AST/ByteCode/Interp.cpp
@@ -2117,8 +2117,8 @@ bool DiagTypeid(InterpState &S, CodePtr OpPC) {
 
 bool arePotentiallyOverlappingStringLiterals(const Pointer &LHS,
                                              const Pointer &RHS) {
-  unsigned LHSOffset = LHS.getIndex();
-  unsigned RHSOffset = RHS.getIndex();
+  unsigned LHSOffset = LHS.isOnePastEnd() ? LHS.getNumElems() : LHS.getIndex();
+  unsigned RHSOffset = RHS.isOnePastEnd() ? RHS.getNumElems() : RHS.getIndex();
   unsigned LHSLength = (LHS.getNumElems() - 1) * LHS.elemSize();
   unsigned RHSLength = (RHS.getNumElems() - 1) * RHS.elemSize();
 
diff --git a/clang/test/AST/ByteCode/cxx11.cpp b/clang/test/AST/ByteCode/cxx11.cpp
index 08caca03b8056..72bc7622eb6d8 100644
--- a/clang/test/AST/ByteCode/cxx11.cpp
+++ b/clang/test/AST/ByteCode/cxx11.cpp
@@ -287,6 +287,8 @@ namespace OverlappingStrings {
   constexpr bool may_overlap_4 = &"xfoo"[1] == &"xfoo"[1]; // both-error {{}} both-note {{addresses of potentially overlapping literals}}
 
 
+  /// Used to crash.
+  const bool x = &"ab"[0] == &"ba"[3];
 
 }