tree 94837a6293297f33ef727e4bd263bc4407504aca
parent 5670d048c0f88af9976b5505c7853b23dd06770d
author Nicholas Nethercote <nnethercote@mozilla.com> 1568686104 +1000
committer Nicholas Nethercote <nnethercote@mozilla.com> 1568698349 +1000

Move a `Node`'s parent into the descendents list.

`Node` has an optional parent and a list of other descendents. Most of
the time the parent is treated the same as the other descendents --
error-handling is the exception -- and chaining them together for
iteration has a non-trivial cost.

This commit changes the representation. There is now a single list of
descendants, and a boolean flag that indicates if there is a parent (in
which case it is first descendent). This representation encodes the same
information, in a way that is less idiomatic but cheaper to iterate over
for the common case where the parent doesn't need special treatment.

As a result, some benchmark workloads are up to 2% faster.