message: [XLA:GPU] [NFC] Clarify the precondition for the fast reduction emitter
diff: @@ -226,6 +226,11 @@ bool IsReductionFromOrToContiguousDimensions(const HloInstruction& reduce) {
  dims_to_keep.push_back(dim);
  }
  }
  +
  + // We support fast codegen for three cases:
  + // 1) Row reduction: (K, R)
  + // 2) Column reduction: (K, R, K)
  + // 3) "Batched" row reduction: (R, K, R)
  if (!LayoutUtil::AreDimensionsConsecutive(input->shape().layout(),
  dims_to_keep) &&
  !LayoutUtil::AreDimensionsConsecutive(input->shape().layout(),
  