[compiler][rewrite] Represent scope dependencies with value blocks #32099

mofeiZ · 2025-01-16T16:37:43Z

(needs cleanup)

Scopes no longer store a flat list of their dependencies. Instead:
- Scope terminals are effectively a goto for scope dependency instructions (represented as value blocks that terminate with a goto scopeBlock for HIR and a series of ReactiveInstructions for ReactiveIR)
- Scopes themselves store dependencies: Array<Place>, which refer to temporaries written to by scope dependency instructions

Next steps:

new pass to dedupe scope dependency instructions after all dependency and scope pruning passes, effectively 'hoisting' dependencies out
more complex dependencies (unary ops like Boolean or Not, binary ops like !== or logical operators)

Stack created with Sapling. Best reviewed with ReviewStack.

josephsavona

i did a quick skim through, this is just some early feedback

josephsavona · 2025-01-21T18:56:34Z

compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts

@@ -3414,7 +3413,7 @@ function lowerExpressionToTemporary(
  return lowerValueToTemporary(builder, value);
 }

-function lowerValueToTemporary(
+export function lowerValueToTemporary(


not used outside this file, remove the export?

This is used in propagateScopeDependencies, which creates new instructions / temporaries for scope dependency blocks

josephsavona · 2025-01-21T18:59:10Z

compiler/packages/babel-plugin-react-compiler/src/HIR/Environment.ts

@@ -902,6 +904,7 @@ export class Environment {
      this.#moduleTypes.set(REANIMATED_MODULE_NAME, reanimatedModuleType);
    }

+    this.parentFunction = parentFunction;


nit: splitting changes like this into a separate PR would make it easier to review and focus on the core dependency changes

josephsavona · 2025-01-21T19:05:07Z

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/PromoteUsedTemporaries.ts

I have not processed the changes here deeply, but my first instinct is to wonder why this pass should have to change at all?

Since we're now representing scope dependencies with value blocks + a list of Places, two things need to change:

Promoting unnamed Identifiers referenced by scope dependencies now requires explicitly traversing the value blocks (see this.visitBlock(scopeBlock.dependencyInstructions, ...)

We now also need to perform some form of DCE -- after pruning passes, some instructions within scopeBlock.dependencyInstructions no longer correspond to real dependencies. Concretely, we need to figure out which base Identifiers should be excluded for promotion.
Note that this isn't an issue for codegen as ReactiveScopeBlock.dependencyInstructions always contains non-named, non-null lvalues (which simply stores into a Temporaries: Map<Identifier, babel.t.Expression> sidemap for later inlining

Small patch to pass aliased context values into `Object|ArrayExpression`s --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32093). * #32099 * #32104 * #32098 * #32097 * #32096 * #32095 * #32094 * __->__ #32093

See test fixture --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32094). * #32099 * #32104 * #32098 * #32097 * #32096 * #32095 * __->__ #32094 * #32093

See test fixture --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32095). * #32099 * #32104 * #32098 * #32097 * #32096 * __->__ #32095 * #32094 * #32093

mofeiZ · 2025-02-14T23:12:38Z

compiler/packages/babel-plugin-react-compiler/src/HIR/CollectHoistablePropertyLoads.ts

+  getOrCreateIdentifier(
+    identifier: Identifier,
+    reactive: boolean,
+  ): PropertyPathNode {


Note that we now need to track reactivity, as we're creating new instructions to represent dependencies

mofeiZ · 2025-02-15T01:02:33Z

Synced offline with @josephsavona, I'm going to hold off on landing this until after:

We do a meta sync to check that this rewrite doesn't produce code / bailout changes
I put up a poc for deduping dependencies and other hoistable instructions (e.g. ===, bool, etc)

…ns (#32096) LoweredFunction dependencies were exclusively used for dependency extraction (in `propagateScopeDeps`). Now that we have a `propagateScopeDepsHIR` that recursively traverses into nested functions, we can delete `dependencies` and their associated synthetic `LoadLocal`/`PropertyLoad` instructions. [Internal snapshot diff](https://www.internalfb.com/phabricator/paste/view/P1716950202) for this change shows ~.2% of files changed. I [read through ~60 of the changed files](https://www.internalfb.com/phabricator/paste/view/P1733074307) - most changes are due to better outlining (due to better DCE) - a few changes in memo inference are due to changed ordering ``` // source arr.map(() => contextVar.inner); // previous instructions $0 = LoadLocal arr $1 = $0.map // Below instructions are synthetic $2 = LoadLocal contextVar $3 = $2.inner $4 = Function deps=$3 context=contextVar { ... } ``` - a few changes are effectively bugfixes (see `aliased-nested-scope-fn-expr`) --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32096). * #32099 * #32286 * #32104 * #32098 * #32097 * __->__ #32096

(needs cleanup) - Scopes no longer store a flat list of their dependencies. Instead: - Scope terminals are effectively a `goto` for scope dependency instructions (represented as value blocks that terminate with a `goto scopeBlock` for HIR and a series of ReactiveInstructions for ReactiveIR) - Scopes themselves store `dependencies: Array<Place>`, which refer to temporaries written to by scope dependency instructions Next steps: - new pass to dedupe scope dependency instructions after all dependency and scope pruning passes, effectively 'hoisting' dependencies out - more complex dependencies (unary ops like `Boolean` or `Not`, binary ops like `!==` or logical operators)

Inferred effect dependencies now include optional chains. This is a temporary solution while #32099 and its followups are worked on. Ideally, we should model reactive scope dependencies in the IR similarly to `ComputeIR` -- dependencies should be hoisted and all references rewritten to use the hoisted dependencies. (will add more test cases)

Inferred effect dependencies now include optional chains. This is a temporary solution while #32099 and its followups are worked on. Ideally, we should model reactive scope dependencies in the IR similarly to `ComputeIR` -- dependencies should be hoisted and all references rewritten to use the hoisted dependencies. `

When collecting scope dependencies, mark each dependency with `reactive: true | false`. This prepares for later PRs #33326 and #32099 which rewrite scope dependencies into instructions. Note that some reactive objects may have non-reactive properties, but we do not currently track this. Technically, state[0] is reactive and state[1] is not. Currently, both would be marked as reactive. ```js const state = useState(); ```

Inferred effect dependencies now include optional chains. This is a temporary solution while #32099 and its followups are worked on. Ideally, we should model reactive scope dependencies in the IR similarly to `ComputeIR` -- dependencies should be hoisted and all references rewritten to use the hoisted dependencies. `

When collecting scope dependencies, mark each dependency with `reactive: true | false`. This prepares for later PRs #33326 and #32099 which rewrite scope dependencies into instructions. Note that some reactive objects may have non-reactive properties, but we do not currently track this. Technically, state[0] is reactive and state[1] is not. Currently, both would be marked as reactive. ```js const state = useState(); ```

When collecting scope dependencies, mark each dependency with `reactive: true | false`. This prepares for later PRs #33326 and #32099 which rewrite scope dependencies into instructions. Note that some reactive objects may have non-reactive properties, but we do not currently track this. Technically, state[0] is reactive and state[1] is not. Currently, both would be marked as reactive. ```js const state = useState(); ``` --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/33325). * #33326 * __->__ #33325 * #32286

…33326) Inferred effect dependencies now include optional chains. This is a temporary solution while #32099 and its followups are worked on. Ideally, we should model reactive scope dependencies in the IR similarly to `ComputeIR` -- dependencies should be hoisted and all references rewritten to use the hoisted dependencies. ` --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/33326). * __->__ #33326 * #33325 * #32286

…33326) Inferred effect dependencies now include optional chains. This is a temporary solution while #32099 and its followups are worked on. Ideally, we should model reactive scope dependencies in the IR similarly to `ComputeIR` -- dependencies should be hoisted and all references rewritten to use the hoisted dependencies. ` --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/33326). * __->__ #33326 * #33325 * #32286 DiffTrain build for [0d07288](0d07288)

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[compiler] Clean up deadcode: DeriveMinimalDeps (non-hir fork) #32104

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[compiler] Represent array accesses with PropertyLoad #32287

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[compiler] Prepare HIRBuilder to be used by later passes #32286

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[compiler] Prepare HIRBuilder to be used by later passes

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[compiler] Inferred effect dependencies now include optional chains #33326

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[compiler] Add reactive flag on scope dependencies #33325

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[compiler][rewrite] Represent scope dependencies with value blocks #32099

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