Previously, every expression/statement type was responsible for
pruning or clearing the store-cache when branches were involved. This
was difficult to reason about and easy to get wrong, particularly if
the details are not fresh in your mind.
Now, `writeLabel` takes care of the details for you. Pass in the
location of the branch(es) which use the label, and the proper cache
updating behavior will occur automatically.
Some of the label enum types are not strictly necessary and exist for
the benefit of a reader. Specifically:
- `kBranchlessBlock` and `kBranchIsOnPreviousLine` are synonyms
- `kBranchIsBelow` and `kBranchesOnBothSides` are also synonyms
The hope is that extra enum names will be easier for a reader to
follow, versus fewer but very-verbose enum names (like
`kBranchIsBelowOrOnBothSides`).
This change earned some very minor switch-related dividends. Previously,
every label in a switch was treated as a forward-branch, but in fact,
the very first label in a switch is privileged. This is because we are
branching from the previous line, and the store cache is trustworthy in
this case. (Versus "branching from above," where the store cache needs
to be pruned before it can be trusted.)
Change-Id: I38b539069c22be9f0777b632f60f0eab2409d687
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/531540
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
fce87a43e6