message: Avoid one redundant call to IsReachable.
diff: @@ -350,12 +350,13 @@ void MultiOutputFusion::UpdateReachability(
  if (skip != nullptr && skip(instr)) {
  continue;
  }
  - if (reachability_->IsReachable(instr2, instr) &&
  - reachability_->IsReachable(instr1, instr)) {
  + bool instr2_instr = reachability_->IsReachable(instr2, instr);
  + bool instr1_instr = reachability_->IsReachable(instr1, instr);
  + if (instr2_instr && instr1_instr) {
  // If a candidate was already reachable by both, no update needed.
  continue;
  }
  - if (reachability_->IsReachable(instr2, instr)) {
  + if (instr2_instr) {
  reachability_->FastSetReachabilityToUnion({instr, instr1}, instr);
  }
  if (reachability_->IsReachable(instr1, instr)) {
  