message: Asking result_t for an out-of-bound src is not fatal.
  Summary:
  Similar to an earlier issue, it is possible for a result not to populate values
  at a source index if they are not reachable, but it should not be an error to
  request them.
diff: @@ -47,11 +47,11 @@ result_t::src_range result_t::matching(location_t l,
  // const_cast is required because `insns` holds `IRInstruction*` keys, but
  // `find` will not mutate the `insn` passed in, despite the cast.
  auto srcs = insns->find(const_cast<IRInstruction*>(insn));
  - if (srcs == insns->end()) {
  + if (srcs == insns->end() || ix >= srcs->second.size()) {
  return src_range::empty();
  }
  - auto& src = srcs->second.at(ix);
  + auto& src = srcs->second[ix];
  return src_range{src.cbegin(), src.cend()};
  }
  