Put extra guardrails for J2CLOpts. #6171
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The patch puts a new guardrail that will only hoist the field
if it is initialized with the owner class.
The constant hoisting optimization in J2CL pass relies on the
assumption that clinit that will initialize the field will be
executed before the read of the field. That means the field
that is optiized is within the same class:
class Foo {
public static final Object field = new Object();
}
Although it is possible to observe the initial value, that is
not intention of the developer (which the point of the
optimization).
However can also see a similar pattern in following:
class Foo {
public static Object field;
}
class Zoo {
static {
Foo.field = new Object();
}
}
Currently the pass also optimizes it as well since the field
is only initialized once and by a clinit. However Zoo clinit
is not guaranteed to be run before Foo.field access so it is
less safe to speculate on the intention of the developer here
hence it is not worth the risk.
FWIW, we haven't seen this issue. But this is something we
are also guarding in Closure Compiler so I decided it is
worthwhile to do here as well.
kripken
reviewed
Dec 12, 2023
Co-authored-by: Alon Zakai <alonzakai@gmail.com>
Co-authored-by: Alon Zakai <alonzakai@gmail.com>
Co-authored-by: Alon Zakai <alonzakai@gmail.com>
kripken
approved these changes
Dec 12, 2023
radekdoulik
pushed a commit
to dotnet/binaryen
that referenced
this pull request
Jul 12, 2024
The patch puts a new guardrail that will only hoist the field
if it is initialized with the owner class.
The constant hoisting optimization in J2CL pass relies on the
assumption that clinit that will initialize the field will be
executed before the read of the field. That means the field
that is optimized is within the same class:
class Foo {
public static final Object field = new Object();
}
Although it is possible to observe the initial value, that is
not intention of the developer (which the point of the
optimization).
However can also see a similar pattern in following:
class Foo {
public static Object field;
}
class Zoo {
static {
Foo.field = new Object();
}
}
Currently the pass also optimizes it as well since the field
is only initialized once and by a clinit. However Zoo clinit
is not guaranteed to be run before Foo.field access so it is
less safe to speculate on the intention of the developer here
hence it is not worth the risk.
FWIW, we haven't seen this issue. But this is something we
are also guarding in Closure Compiler so I decided it is
worthwhile to do here as well.
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The patch puts a new guardrail that will only hoist the field if it is initialized with the owner class.
The constant hoisting optimization in J2CL pass relies on the assumption that clinit that will initialize the field will be executed before the read of the field. That means the field that is optiized is within the same class:
class Foo {
public static final Object field = new Object();
}
Although it is possible to observe the initial value, that is not intention of the developer (which the point of the optimization).
However can also see a similar pattern in following:
class Foo {
public static Object field;
}
class Zoo {
static {
Foo.field = new Object();
}
}
Currently the pass also optimizes it as well since the field is only initialized once and by a clinit. However Zoo clinit is not guaranteed to be run before Foo.field access so it is less safe to speculate on the intention of the developer here hence it is not worth the risk.
FWIW, we haven't seen this issue. But this is something we are also guarding in Closure Compiler so I decided it is worthwhile to do here as well.