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[compiler] Prevent overriding a derivationEntry on effect mutation and instead update typeOfValue and fix infinite loops #34967

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[compiler] Prevent overriding a derivationEntry on effect mutation and instead update typeOfValue and fix infinite loops #34967

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74 changes: 59 additions & 15 deletions .../babel-plugin-react-compiler/src/Validation/ValidateNoDerivedComputationsInEffects_exp.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,43 @@ type ValidationContext = {
class DerivationCache {
hasChanges: boolean = false;
cache: Map<IdentifierId, DerivationMetadata> = new Map();
private previousCache: Map<IdentifierId, DerivationMetadata> | null = null;

takeSnapshot(): void {
this.previousCache = new Map();
for (const [key, value] of this.cache.entries()) {
this.previousCache.set(key, {
place: value.place,
sourcesIds: new Set(value.sourcesIds),
typeOfValue: value.typeOfValue,
});
}
}

checkForChanges(): void {
if (this.previousCache === null) {
this.hasChanges = true;
return;
}

for (const [key, value] of this.cache.entries()) {
const previousValue = this.previousCache.get(key);
if (
previousValue === undefined ||
!this.isDerivationEqual(previousValue, value)
) {
this.hasChanges = true;
return;
}
}

if (this.cache.size !== this.previousCache.size) {
this.hasChanges = true;
return;
}

this.hasChanges = false;
}

snapshot(): boolean {
const hasChanges = this.hasChanges;
Expand Down Expand Up @@ -92,14 +129,7 @@ class DerivationCache {
newValue.sourcesIds.add(derivedVar.identifier.id);
}

const existingValue = this.cache.get(derivedVar.identifier.id);
if (
existingValue === undefined ||
!this.isDerivationEqual(existingValue, newValue)
) {
this.cache.set(derivedVar.identifier.id, newValue);
this.hasChanges = true;
}
this.cache.set(derivedVar.identifier.id, newValue);
}

private isDerivationEqual(
Expand Down Expand Up @@ -175,7 +205,6 @@ export function validateNoDerivedComputationsInEffects_exp(
sourcesIds: new Set([param.identifier.id]),
typeOfValue: 'fromProps',
});
context.derivationCache.hasChanges = true;
}
}
} else if (fn.fnType === 'Component') {
Expand All @@ -186,19 +215,21 @@ export function validateNoDerivedComputationsInEffects_exp(
sourcesIds: new Set([props.identifier.id]),
typeOfValue: 'fromProps',
});
context.derivationCache.hasChanges = true;
}
}

let isFirstPass = true;
do {
context.derivationCache.takeSnapshot();

for (const block of fn.body.blocks.values()) {
recordPhiDerivations(block, context);
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@mofeiZ mofeiZ Oct 28, 2025

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Hmm what's the reasoning for moving when we record phis? A block's phis often defines values used by the block so we may find that the derivation cache is missing values when processing instructions with this change.

In the below example, we want to call recordPhiDerivations to insert x@2 into the context. Then, when we walk over the instructions of the fallthrough block (LoadLocal x@2, Call doSomething), we can read the proper typeOfValue from context

let x = thing1; // x@0
if (cond) {
  x = {}; // x@1
}
// x@2 = phi(x@0, x@1)
doSomething(x) // <- references x@2

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@jorge-cab jorge-cab Oct 28, 2025

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Oh, my bad, I moved it when debugging the infinite loop. I'll move it back

for (const instr of block.instructions) {
recordInstructionDerivations(instr, context, isFirstPass);
}
}

context.derivationCache.checkForChanges();
isFirstPass = false;
} while (context.derivationCache.snapshot());

Expand Down Expand Up @@ -331,11 +362,24 @@ function recordInstructionDerivations(
case Effect.ConditionallyMutateIterator:
case Effect.Mutate: {
if (isMutable(instr, operand)) {
context.derivationCache.addDerivationEntry(
operand,
sources,
typeOfValue,
);
if (context.derivationCache.cache.has(operand.identifier.id)) {
const operandMetadata = context.derivationCache.cache.get(
operand.identifier.id,
);

if (operandMetadata !== undefined) {
operandMetadata.typeOfValue = joinValue(
typeOfValue,
operandMetadata.typeOfValue,
);
}
} else {
context.derivationCache.addDerivationEntry(
operand,
sources,
typeOfValue,
);
}
}
break;
}
Expand Down
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