commit c6fe9e21f005537ecfff947a0e5dbab129a17c26
author Vyacheslav Egorov <vegorov@google.com> Tue Nov 16 12:48:52 2021 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> Tue Nov 16 12:48:52 2021 +0000
tree 54d5554b2e1a5d19c5d18d4821b4f71d660b70eb
parent a643e537fb84e54c1c80d15651fba415fbb8c284

[vm/compiler] Avoid invalid code motion

In Dart doing a type check against one value can constrain the type
of another value in an indirect fashion. This possibility needs to be
taken into account when inserting Redefinitions to inhibit the code
motion. This CL addresses two previously ignored situations:

* Given a generic container `C<T> c` which holds a value `T v` doing a
type check against `c` might narrow the type of `v`.
* Given two generic classes `C<T>` and `H<T>`, doing a type-check
against an instance of type `C<X> c` might narrow the type of an
unrelated instance of `H<X> v` within the same scope.

The second situation is currently limited to a situation when we do an
invocation on `this` and the target of the call has constrained generic
parameter (e.g. because the target of the call is in the subclass which
instantiates the base class with a more specific type
`class C_ extends C<int>`). Calls on `this` are special because
they are allowed to bypass argument type checks which are
usually performed due to covariance.

In both cases we need to ensure that all uses of `v` which are
using narrowed type are pinned to stay within the true successor
of the type-check against `c`.

Previously we would only insert redefinitions for the value that is
being type checked, but this is not enough and this CL tries to
address the newly discovered cases:

* When replacing loads in load optimizer we must ensure that
if replaced load was dependant on the redefinition (and thus
was pinned) the replacement is similarly pinned (if the type of the
load might have been narrowed). If neccessary we must insert a
redefinition for the loaded value itself.
* When performing inlining of calls on `this` we must insert
redefinitions for all parameters that might have their types
narrowed.
* When replacing phis which have redefinitions as all inputs.

Fixes https://github.com/flutter/flutter/issues/91370
Fixes https://github.com/dart-lang/sdk/issues/43652

TEST=vm/dart{,_2}/flutter_regress_91370_il_test

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-product-x64-try,vm-kernel-precomp-linux-release-x64-try
Change-Id: I89c1f165615dd827102e9f6af90365af7d8f32b2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/219241
Commit-Queue: Slava Egorov <vegorov@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>