[2/n][vm-rewrite][Move] Update runtime value representation to support global references. #21066
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external-crates/move/crates/move-vm-runtime/src/execution/values/values_impl.rs
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| // XXX/TODO(vm-rewrite): Remove this and replace with proper value dirtying. | ||
| #[derive(Debug)] | ||
| pub struct FixedSizeVec(Box<[Value]>); | ||
| pub struct GlobalFingerprint(Option<String>); |
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Maybe add a deprecated note here so we remember to come back and fix it?
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…t global references.
This updates the VM value representation to support global values, and
"fingerprinting" of the global values so that they can be properly
dirtied at the end of execution.
**IMPORTANT**:
Additional work is needed to make the fingerprinting of global values
actually something we'd want to use in prod, but the underlying logic of
what a fingerprint is, and how it is computed has been abstracted away
into a newtype so we can update this fairly easily hopefully.
**Semantic changes**:
This changes the semantics of execution around global values. Previously
a global value would always be counted as mutated if the reference was
written, even with the same value. In the implementation here this is no
longer the case -- if the value is the same at time of read and the
conclusion of execution, the value will not be viewed as mutated. As an
example of a program that would exhibit this change in behavior:
```move
module 0x42::a;
public struct X has key, store {
id: UID,
x: u64,
}
public fun update1(x: &mut UID) {
let s: &mut X = dynamic_field::borrow_mut(x, 0);
assert!(s.x == 10);
s.x = 11;
s.x = 12;
s.x = 10;
}
public fun update2(x: &mut UID) {
let s: &mut X = dynamic_field::borrow_mut(x, 0);
assert!(s.x == 10);
s.x = 10;
}
```
In the previous semantics, the borrowed dynamic field would show as a
mutated output of the transaction, in the new semantics it will not show
up as mutated as extensionally the value was unchanged.
NB: The code in the PR may not be working as future PRs will build on top of
this.
… support global references.
…tion to support global references.
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This updates the VM value representation to support global values, and "fingerprinting" of the global values so that they can be properly dirtied at the end of execution.
IMPORTANT
Additional work is needed to make the fingerprinting of global values actually something we'd want to use in prod, but the underlying logic of what a fingerprint is, and how it is computed has been abstracted away into a newtype so we can update this fairly easily hopefully.
Semantic changes
This changes the semantics of execution around global values. Previously a global value would always be counted as mutated if the reference was written, even with the same value. In the implementation here this is no longer the case -- if the value is the same at time of read and the conclusion of execution, the value will not be viewed as mutated. As an example of a program that would exhibit this change in behavior:
In the previous semantics, the borrowed dynamic field would show as a mutated output of the transaction, in the new semantics it will not show up as mutated as extensionally the value was unchanged.
Note however, that for
move_fromandmove_tooperations, we always view this as a dirtying operation. Eventually this logic for global value dirtying will be moved out and will be tracked in the object runtime, but for now we use this implementation to unblock the adapter updates.NB: The code in the PR may not be working as future PRs will build on top of this.