message: Clarify comments describing propagation algorithm
diff: @@ -1222,13 +1222,13 @@ Status AutoMixedPrecisionImpl::Optimize() {
  // 2) Add nodes to the black_set iff they are numerically-dangerous (aka
  // "blacklist" ops) or they are on a forward path from a blacklist node to
  // a black/gray node (including the node at the end of the path) through
  - // zero or more numerically-safe ops (aka "clearlist" ops).
  + // non-numerically-dangerous ops (aka "greylist" and "clearlist" ops).
  // This is done to prevent numerically-dangerous ops and their downstream
  // effects from being changed to fp16, which would risk breaking the
  // numerical accuracy of the model.
  - // 3) For all remaining nodes that are not considered dangerous (aka
  - // "greylist" and clearlist ops), find those that are between (i.e., both
  - // upstream and downstream of) white nodes, and add them to the white_set.
  + // 3) For all remaining nodes that are not considered dangerous (greylist
  + // and clearlist ops), find those that are between (i.e., both upstream
  + // and downstream of) white nodes, and add them to the white_set.
  // This is done to avoid unnecessary casts between whitelist ops.
  // 4) For all remaining clearlist nodes, add them to the white_set if they are
  // connected to a node in the white_set via other clearlist nodes.
  @@ -1335,7 +1335,7 @@ void AutoMixedPrecisionImpl::AddWhitelistOps(
  // Adds nodes to black_set iff they are on the blacklist or they are on a
  // forward path from a blacklist node to a black/gray node (including the node
  -// at the end of the path) through zero or more clear nodes.
  +// at the end of the path) through clear and gray nodes.
  // E.g., black -> gray -> clear -> gray -> clear -> white -> gray
  // becomes: black -> black -> black -> black -> clear -> white -> gray.
  void AutoMixedPrecisionImpl::PropagateBlackFwdThroughClearAndGray(
  