message: [XLA] Check that operands(i) is requesting an in-range operand.
  Previously we'd silently return out-of-bounds memory.
diff: @@ -1624,12 +1624,12 @@ const HloInstruction* HloInstruction::LatestNonGteAncestor() const {
  }
  const HloInstruction* HloInstruction::operand(int64 i) const {
  - return operands_[i];
  + return operands_.at(i);
  }
  HloInstruction* HloInstruction::mutable_operand(int64 i) {
  CHECK(operands_[i] != nullptr);
  - return operands_[i];
  + return operands_.at(i);
  }
  int64 HloInstruction::operand_index(const HloInstruction* target) const {
  