Previously, the base `ExpressionInfo` class contained four fields:
- `type`: the type of the expression.
- `ifTrue`: a flow model describing the state of the program after the
expression is evaluated, assuming the expression evaluates to
`true`.
- `ifFalse`: a flow model describing the state of the program after
the expression is evaluated, assuming the expression evaluates to
`false`.
- `after`: a flow model describing the state of the prorgam after the
expression is evaluated, making no assumptions about what value the
expression evaluates to.
The `after` field was largely redundant, since it tracked the same
information as `FlowAnalysisImpl._current`. In fact, flow analysis
contained a substantial amount of code to copy from
`ExpressionInfo.after` to `FlowAnalysisImpl._current`, or vice versa,
in order to keep the two in sync.
The one exception was in `FlowAnalysisImpl.conditional_end`, which is
called at the end of visiting a conditional expression (`e1 ? e2 :
e3`): it joined the `after` flow models from `e2` and `e3` in order to
determine the state of the program after the conditional expression
completes. To preserve this behavior, a small amount of extra
accounting logic had to be added to the handling of conditional
expressions, to keep track of these flow models. (`e2.after` is now
stored in `_ConditionalContext.thenModel`, and `e3.after` comes from
the state of `_current` at the time of entry into
`FlowAnalysisImpl.conditional_end`).
Change-Id: I46e771f8b029550d43a5fe50366177f189a6a91d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/388081
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Kallen Tu <kallentu@google.com>
Paul Berry
38c08f919d