Alexander Markov
742850f9cc
Previously, TFA was building a summary for the comparison
'v == null' assuming type of 'v' is Null on the true branch.
As a result, after joining data flow Null contaminates value of 'v'
further down:
v0 = ...
t1 = IsNull(v0) // Condition
t2 = Null // On true branch
t3 = NarrowNotNull(v0) // On false branch
v1 = Join(t2, t3) // This value is nullable even if v0 was not.
...
use(v1)
This change adds a condition to the Null value so it is evaluated to
Empty type if original value turns out to be non-nullable:
t1 = IsNull(v0)
t2 = Move(Null) {t1} // Empty if t1 is false.
t3 = NarrowNotNull(v0)
v1 = Join(t2, t3)
TEST=pkg/vm/testcases/transformations/type_flow/transformer/regress_59845.dart
Fixes https://github.com/dart-lang/sdk/issues/59845
Change-Id: I0f78e31f9eaf6507cc78e393de2fc12a9cf29f4a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/403200
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>