9a3420f1d4
Previously, flow analysis used a hack to make it easy to generate "why
not promoted" messages when the user tried to promote a non-promotable
field: it treated all field accesses as stable for the purpose of
assigning SSA nodes, but avoided promoting non-promotable fields by
setting the `_Reference.isPromotable` flag to `false`. So, for
instance, in the following code, both subexpressions `c.i` got
assigned the same SSA node, even though there's no guarantee that
`C.x` will return the same value each time it's invoked.
class C {
int? get i => ...;
}
f(C c) {
if (c.i != null) {
var i = c.i; // Inferred type `int?`
}
}
This mostly worked, since the SSA node assigned by flow analysis is
only used for promotion, and promotion is disabled for non-promotable
fields. However, it broke when the field in question was used as the
target of a cascade, because fields within cascades always had their
`_Reference.isPromotable` flag set to `true` regardless of whether the
corresponding cascade target is promotable. For example:
class C {
D? get d => ...;
}
class D {
final E? _e;
...
}
class E {
m() { ... }
}
f(C c) {
(c.d)
.._e!.m() // OK; promotes _e
.._e.m(); // OK; _e is promoted now
(c.d)
.._e.m(); // OOPS, _e is still promoted; it shouldn't be
}
See
`tests/language/inference_update_2/cascaded_field_promotion_unstable_target_test.dart`
for a more detailed example.
This CL removes the hack; now, when a non-promotable property is
accessed more than once, flow analysis assignes a different SSA node
for each access. As a result, the `_Reference.isPromotable` is not
needed, because non-promotable fields simply never have the chance to
be promoted (since every field access gets a separate SSA node, so
type checking one field access has no effect on others).
To preserve the ability to generate "why not promoted" messages, the
`_PropertySsaNode` class now contains a `previousSsaNode` pointer,
which links together the separate SSA nodes allocated for
non-promotable properties, so that they form a linked list. The "why
not promoted" logic traverses this list to figure out which promotions
*would* have occurred if the property had been promotable.
In order to make it efficient to create this linked list, the
`SsaNode` class also had to acquire a `_nonPromotableProperties` map,
which records the SSA node that was allocated the last time each
property was accessed.
Fixes https://github.com/dart-lang/sdk/issues/52728.
Change-Id: I16a7b27f77c309bdccce86195a53398e32e8f75d
Bug: https://github.com/dart-lang/sdk/issues/52728
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/318745
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
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| .dart_tool | ||
| .github | ||
| benchmarks | ||
| build | ||
| docs | ||
| pkg | ||
| runtime | ||
| samples | ||
| sdk | ||
| tests | ||
| third_party | ||
| tools | ||
| utils | ||
| .clang-format | ||
| .gitattributes | ||
| .gitconfig | ||
| .gitignore | ||
| .gn | ||
| .mailmap | ||
| .style.yapf | ||
| .vpython | ||
| AUTHORS | ||
| BUILD.gn | ||
| CHANGELOG.md | ||
| codereview.settings | ||
| CONTRIBUTING.md | ||
| DEPS | ||
| LICENSE | ||
| OWNERS | ||
| PATENT_GRANT | ||
| PRESUBMIT.py | ||
| README.dart-sdk | ||
| README.md | ||
| sdk.code-workspace | ||
| sdk_args.gni | ||
| SECURITY.md | ||
| WATCHLISTS | ||
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