message: Remove overly-conservative CHECK in rematerialization. The CHECK verified
  that the memory use tracker used in remat matched expectations, but the
  expectation was not always correct in the case of dead values.
diff: @@ -811,24 +811,6 @@ bool MemoryUsageTracker::Check() const {
  CHECK_EQ(buffer.unfinished_user_count, unfinished_uses)
  << "Incorrect unplaced use count for " << buffer.ToString();
  }
  -
  - // Verify live set size against memory_usage_.
  - int64 live_size = 0;
  - for (const Buffer& buffer : buffers_) {
  - // The while instruction reuses its input buffers as output buffers so
  - // don't double count its buffers if it is currently executing.
  - if (IsCurrentlyLive(buffer.id) &&
  - !(buffer.defining_instruction == in_progress_item_ &&
  - in_progress_item_->instruction->opcode() == HloOpcode::kWhile)) {
  - live_size += AllocatedSize(buffer.id);
  - }
  - }
  - CHECK(live_size == memory_usage_)
  - << "Live set size " << live_size << " is not same as memory usage "
  - << memory_usage_
  - << ". This could happen if some nodes defined in the "
  - "computation are not being used/executed.";
  -
  return true;
  }
  