[PATCH] D151760: [Demangle] fix deref of std::string_view::end()

[Nick Desaulniers via Phabricator via llvm-commits]

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In D148546 <https://reviews.llvm.org/D148546>, I replaced much of the use of llvm::StringView w/
std::string_view.  There's one important semantic difference between the
two:

In most STL containers, end() returns an iterator that refers to one
past the end of the container. But llvm::StringView::end() refers to the
last element.

Expressions such as `&*my_std_string_view.end()` produce the failed
assertion:

  include/c++/v1/__iterator/bounded_iter.h:93: assertion
  __in_bounds(__current_) failed: __bounded_iter::operator*: Attempt to
  dereference an out-of-range iterator

This was caught when copying the recent downstream changes back upstream
in D148566 <https://reviews.llvm.org/D148566>, and is reproducible via:

  $ libcxx/utils/ci/run-buildbot generic-debug-mode

when compiled with clang and clang++. The correct way to get the same
value as before without dereferencing invalid iterators is to prefer
`&*my_std_string_view.rbegin() + 1`.

Fix this downstream so that I might copy it back upstream in D148566 <https://reviews.llvm.org/D148566>.

The other instance of `&*my_std_string_view.end()` that I introduced in
D148546 <https://reviews.llvm.org/D148546> has been fixed already in D149061 <https://reviews.llvm.org/D149061>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D151760

Files:
  llvm/include/llvm/Demangle/ItaniumDemangle.h


Index: llvm/include/llvm/Demangle/ItaniumDemangle.h
===================================================================
--- llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -3715,7 +3715,7 @@
       std::string_view Proto;
       {
         ScopedOverride<const char *> SaveFirst(First, &*ProtoSourceName.begin()),
-            SaveLast(Last, &*ProtoSourceName.end());
+            SaveLast(Last, &*ProtoSourceName.rbegin() + 1);
         Proto = parseBareSourceName();
       }
       if (Proto.empty())


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