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

That doesn't work.

Fixes #152903

Author: tbaederr

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();
 

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];
 
 }