Refactoring of Generator DAG to Generator Tree. (#2434)

Summary:
Release notes: None

To avoid all kinds of serialization issues, generators should form
a tree, and not a DAG. This is an attempt to establish that.
Pull Request resolved: https://github.com/facebook/prepack/pull/2434

Differential Revision: D9887684

Pulled By: NTillmann

fbshipit-source-id: c11c50c56dcd6eff02bd03448756bf79f6e2c820

src/serializer/GeneratorTree.js

@@ -13,14 +13,13 @@ import invariant from "../invariant.js";
 import { FunctionValue, ObjectValue } from "../values/index.js";
 import { Generator } from "../utils/generator.js";
 
-// This class maintains a DAG containing all generators known so far,
+// This class maintains a tree containing all generators known so far,
 // and information about the most specific generator that created any
 // particular object.
-// New sub-DAGs are added in chunks, at the beginning for the global generator,
+// New sub-trees are added in chunks, at the beginning for the global generator,
 // and every time the visitor handles another additional function.
-// NOTE: The serializer can only properly handle Generator trees, not actual DAGs.
+export class GeneratorTree {
-export class GeneratorDAG {
+  parents: Map<Generator, Generator | FunctionValue | "GLOBAL">;
-  parents: Map<Generator, Array<Generator | FunctionValue | "GLOBAL">>;
   createdObjects: Map<ObjectValue, Generator>;
 
   constructor() {
@@ -28,16 +27,10 @@ export class GeneratorDAG {
     this.createdObjects = new Map();
   }
 
-  // DAG TODO: This function is dubious in the presence of actual dags.
   getParent(generator: Generator): Generator | FunctionValue | "GLOBAL" {
-    let a = this.parents.get(generator);
+    let parent = this.parents.get(generator);
-    invariant(a !== undefined && a.length >= 1);
+    invariant(parent !== undefined);
-    return a[0];
+    return parent;
-  }
-
-  isParent(parent: Generator | FunctionValue | "GLOBAL", generator: Generator): boolean {
-    let a = this.parents.get(generator);
-    return a !== undefined && a.includes(parent);
   }
 
   getCreator(value: ObjectValue): Generator | void {
@@ -49,9 +42,8 @@ export class GeneratorDAG {
   }
 
   _add(parent: Generator | FunctionValue | "GLOBAL", generator: Generator): void {
-    let a = this.parents.get(generator);
+    invariant(!this.parents.has(generator));
-    if (a === undefined) this.parents.set(generator, (a = []));
+    this.parents.set(generator, parent);
-    if (!a.includes(parent)) a.push(parent);
     let effects = generator.effectsToApply;
     if (effects !== undefined) {
       invariant(parent instanceof FunctionValue);

src/serializer/LazyObjectsSerializer.js

@@ -24,7 +24,7 @@ import { ResidualHeapSerializer } from "./ResidualHeapSerializer.js";
 import { getOrDefault } from "./utils.js";
 import type { ResidualOptimizedFunctions } from "./ResidualOptimizedFunctions";
 import type { Referentializer } from "./Referentializer.js";
-import { GeneratorDAG } from "./GeneratorDAG.js";
+import { GeneratorTree } from "./GeneratorTree.js";
 
 const LAZY_OBJECTS_SERIALIZER_BODY_TYPE = "LazyObjectInitializer";
 
@@ -49,7 +49,7 @@ export class LazyObjectsSerializer extends ResidualHeapSerializer {
     options: SerializerOptions,
     additionalFunctionValuesAndEffects: Map<FunctionValue, AdditionalFunctionEffects>,
     referentializer: Referentializer,
-    generatorDAG: GeneratorDAG,
+    generatorTree: GeneratorTree,
     residualOptimizedFunctions: ResidualOptimizedFunctions
   ) {
     super(
@@ -62,7 +62,7 @@ export class LazyObjectsSerializer extends ResidualHeapSerializer {
       options,
       additionalFunctionValuesAndEffects,
       referentializer,
-      generatorDAG,
+      generatorTree,
       residualOptimizedFunctions
     );
 

src/serializer/ResidualHeapSerializer.js

@@ -81,7 +81,7 @@ import { ResidualReactElementSerializer } from "./ResidualReactElementSerializer
 import type { Binding } from "../environment.js";
 import { GlobalEnvironmentRecord, DeclarativeEnvironmentRecord } from "../environment.js";
 import type { Referentializer } from "./Referentializer.js";
-import { GeneratorDAG } from "./GeneratorDAG.js";
+import { GeneratorTree } from "./GeneratorTree.js";
 import { type Replacement, getReplacement } from "./ResidualFunctionInstantiator.js";
 import { describeValue } from "../utils.js";
 import { getAsPropertyNameExpression } from "../utils/babelhelpers.js";
@@ -123,7 +123,7 @@ export class ResidualHeapSerializer {
     options: SerializerOptions,
     additionalFunctionValuesAndEffects: Map<FunctionValue, AdditionalFunctionEffects>,
     referentializer: Referentializer,
-    generatorDAG: GeneratorDAG,
+    generatorTree: GeneratorTree,
     residualOptimizedFunctions: ResidualOptimizedFunctions
   ) {
     this.realm = realm;
@@ -215,7 +215,7 @@ export class ResidualHeapSerializer {
     this.rewrittenAdditionalFunctions = new Map();
     this.declarativeEnvironmentRecordsBindings = residualHeapInfo.declarativeEnvironmentRecordsBindings;
     this.globalBindings = residualHeapInfo.globalBindings;
-    this.generatorDAG = generatorDAG;
+    this.generatorTree = generatorTree;
     this.conditionalFeasibility = residualHeapInfo.conditionalFeasibility;
     this.additionalFunctionGenerators = new Map();
     this.declaredGlobalLets = new Map();
@@ -274,7 +274,7 @@ export class ResidualHeapSerializer {
   // TODO: revisit this and fix additional functions to be capable of delaying initializations
   additionalFunctionValueNestedFunctions: Set<FunctionValue>;
 
-  generatorDAG: GeneratorDAG;
+  generatorTree: GeneratorTree;
   conditionalFeasibility: Map<AbstractValue, { t: boolean, f: boolean }>;
   additionalGeneratorRoots: Map<Generator, Set<ObjectValue>>;
 
@@ -888,7 +888,7 @@ export class ResidualHeapSerializer {
       generators = generators.filter(generator => {
         let s = generator;
         while (s instanceof Generator) {
-          s = this.generatorDAG.getParent(s);
+          s = this.generatorTree.getParent(s);
         }
         return s === "GLOBAL";
       });
@@ -904,7 +904,7 @@ export class ResidualHeapSerializer {
     }
 
     const getGeneratorParent = g => {
-      let s = this.generatorDAG.getParent(g);
+      let s = this.generatorTree.getParent(g);
       return s instanceof Generator ? s : undefined;
     };
     // This value is referenced from more than one generator.
@@ -2132,7 +2132,7 @@ export class ResidualHeapSerializer {
 
   _annotateGeneratorStatements(generator: Generator, statements: Array<BabelNodeStatement>): void {
     let comment = `generator "${generator.getName()}"`;
-    let parent = this.generatorDAG.getParent(generator);
+    let parent = this.generatorTree.getParent(generator);
     if (parent instanceof Generator) {
       comment = `${comment} with parent "${parent.getName()}"`;
     } else if (parent instanceof FunctionValue) {
@@ -2574,7 +2574,7 @@ export class ResidualHeapSerializer {
     for (let s of scopes)
       if (s instanceof Generator) {
         let text = "";
-        for (; s instanceof Generator; s = this.generatorDAG.getParent(s)) text += "=>" + s.getName();
+        for (; s instanceof Generator; s = this.generatorTree.getParent(s)) text += "=>" + s.getName();
         console.log(`      ${text}`);
       } else {
         invariant(s instanceof FunctionValue);

src/serializer/ResidualHeapVisitor.js

@@ -65,7 +65,7 @@ import {
 import { createPathConditions, Environment, To } from "../singletons.js";
 import { isReactElement, isReactPropsObject, valueIsReactLibraryObject } from "../react/utils.js";
 import { ResidualReactElementVisitor } from "./ResidualReactElementVisitor.js";
-import { GeneratorDAG } from "./GeneratorDAG.js";
+import { GeneratorTree } from "./GeneratorTree.js";
 import { PropertyDescriptor, AbstractJoinedDescriptor } from "../descriptors.js";
 
 type BindingState = {|
@@ -113,7 +113,7 @@ export class ResidualHeapVisitor {
     this.globalEnvironmentRecord = environment;
     this.additionalGeneratorRoots = new Map();
     this.residualReactElementVisitor = new ResidualReactElementVisitor(this.realm, this);
-    this.generatorDAG = new GeneratorDAG();
+    this.generatorTree = new GeneratorTree();
   }
 
   realm: Realm;
@@ -142,7 +142,7 @@ export class ResidualHeapVisitor {
   classMethodInstances: Map<FunctionValue, ClassMethodInstance>;
   // Parents will always be a generator, optimized function value or "GLOBAL"
   additionalGeneratorRoots: Map<Generator, Set<ObjectValue>>;
-  generatorDAG: GeneratorDAG;
+  generatorTree: GeneratorTree;
   globalEnvironmentRecord: GlobalEnvironmentRecord;
   residualReactElementVisitor: ResidualReactElementVisitor;
 
@@ -151,13 +151,13 @@ export class ResidualHeapVisitor {
   _getCommonScope(): FunctionValue | Generator {
     let s = this.scope;
     while (true) {
-      if (s instanceof Generator) s = this.generatorDAG.getParent(s);
+      if (s instanceof Generator) s = this.generatorTree.getParent(s);
       else if (s instanceof FunctionValue) {
         // Did we find an additional function?
         if (this.additionalFunctionValuesAndEffects.has(s)) return s;
 
         // Did the function itself get created by a generator we can chase?
-        s = this.generatorDAG.getCreator(s) || "GLOBAL";
+        s = this.generatorTree.getCreator(s) || "GLOBAL";
       } else {
         invariant(s === "GLOBAL");
         let generator = this.globalGenerator;
@@ -179,7 +179,7 @@ export class ResidualHeapVisitor {
   // created --- this causes the value later to be serialized in its
   // creation scope, ensuring that the value has the right creation / life time.
   _registerAdditionalRoot(value: ObjectValue): void {
-    let creationGenerator = this.generatorDAG.getCreator(value) || this.globalGenerator;
+    let creationGenerator = this.generatorTree.getCreator(value) || this.globalGenerator;
 
     let additionalFunction = this._getAdditionalFunctionOfScope() || "GLOBAL";
     let targetAdditionalFunction;
@@ -188,7 +188,7 @@ export class ResidualHeapVisitor {
     } else {
       let s = creationGenerator;
       while (s instanceof Generator) {
-        s = this.generatorDAG.getParent(s);
+        s = this.generatorTree.getParent(s);
         invariant(s !== undefined);
       }
       invariant(s === "GLOBAL" || s instanceof FunctionValue);
@@ -206,7 +206,7 @@ export class ResidualHeapVisitor {
       additionalFVEffects.additionalRoots.add(value);
 
       this._visitInUnrelatedScope(creationGenerator, value);
-      usageScope = this.generatorDAG.getCreator(value) || this.globalGenerator;
+      usageScope = this.generatorTree.getCreator(value) || this.globalGenerator;
     }
 
     usageScope = this.scope;
@@ -215,7 +215,7 @@ export class ResidualHeapVisitor {
       // applying effects; if so, store additional information that the serializer
       // can use to proactive serialize such objects from within the right generator
       let anyRelevantEffects = false;
-      for (let g = usageScope; g instanceof Generator; g = this.generatorDAG.getParent(g)) {
+      for (let g = usageScope; g instanceof Generator; g = this.generatorTree.getParent(g)) {
         if (g === creationGenerator) {
           if (anyRelevantEffects) {
             let s = this.additionalGeneratorRoots.get(g);
@@ -1098,7 +1098,7 @@ export class ResidualHeapVisitor {
       if (this.preProcessValue(val)) this.visitValueProxy(val);
       this.postProcessValue(val);
     } else if (val instanceof FunctionValue) {
-      let creationGenerator = this.generatorDAG.getCreator(val) || this.globalGenerator;
+      let creationGenerator = this.generatorTree.getCreator(val) || this.globalGenerator;
 
       // 1. Visit function in its creation scope
       this._enqueueWithUnrelatedScope(creationGenerator, () => {
@@ -1132,7 +1132,7 @@ export class ResidualHeapVisitor {
     let callbacks = {
       visitEquivalentValue: this.visitEquivalentValue.bind(this),
       visitGenerator: (generator, parent) => {
-        invariant(this.generatorDAG.isParent(parent, generator));
+        invariant(this.generatorTree.getParent(generator) === parent);
         this.visitGenerator(generator, additionalFunctionInfo);
       },
       canOmit: (value: Value): boolean => {
@@ -1282,7 +1282,7 @@ export class ResidualHeapVisitor {
       this.additionalFunctionValueInfos.set(functionValue, additionalFunctionInfo);
 
       let effectsGenerator = additionalEffects.generator;
-      this.generatorDAG.add(functionValue, effectsGenerator);
+      this.generatorTree.add(functionValue, effectsGenerator);
       this.visitGenerator(effectsGenerator, additionalFunctionInfo);
     };
 
@@ -1294,7 +1294,7 @@ export class ResidualHeapVisitor {
   }
 
   visitRoots(): void {
-    this.generatorDAG.add("GLOBAL", this.globalGenerator);
+    this.generatorTree.add("GLOBAL", this.globalGenerator);
     this.visitGenerator(this.globalGenerator);
     for (let moduleValue of this.modules.initializedModules.values()) this.visitValue(moduleValue);
 
@@ -1316,7 +1316,7 @@ export class ResidualHeapVisitor {
       let expected = 0;
       for (let { scope, action } of this.delayedActions) {
         let generator;
-        if (scope instanceof FunctionValue) generator = this.generatorDAG.getCreator(scope) || this.globalGenerator;
+        if (scope instanceof FunctionValue) generator = this.generatorTree.getCreator(scope) || this.globalGenerator;
         else if (scope === "GLOBAL") generator = this.globalGenerator;
         else {
           invariant(scope instanceof Generator);
@@ -1370,10 +1370,10 @@ export class ResidualHeapVisitor {
               info.nestedEffectsRunners.push(runGeneratorAction);
               runGeneratorAction = undefined;
             }
-            s = this.generatorDAG.getParent(s);
+            s = this.generatorTree.getParent(s);
           } else if (s instanceof FunctionValue) {
             invariant(this.additionalFunctionValuesAndEffects.has(s));
-            s = this.generatorDAG.getCreator(s) || "GLOBAL";
+            s = this.generatorTree.getCreator(s) || "GLOBAL";
           }
           invariant(s instanceof Generator || s instanceof FunctionValue || s === "GLOBAL");
         }

src/serializer/ResidualOptimizedFunctions.js

@@ -12,7 +12,7 @@
 import { FunctionValue } from "../values/index.js";
 import type { AdditionalFunctionEffects } from "./types";
 import invariant from "../invariant.js";
-import { GeneratorDAG } from "./GeneratorDAG";
+import { GeneratorTree } from "./GeneratorTree";
 import type { Scope } from "./types.js";
 import { FunctionEnvironmentRecord } from "../environment";
 import type { Value } from "../values/index";
@@ -20,16 +20,16 @@ import { Generator } from "../utils/generator";
 
 export class ResidualOptimizedFunctions {
   constructor(
-    generatorDAG: GeneratorDAG,
+    generatorTree: GeneratorTree,
     optimizedFunctionsAndEffects: Map<FunctionValue, AdditionalFunctionEffects>,
     residualValues: Map<Value, Set<Scope>>
   ) {
-    this._generatorDAG = generatorDAG;
+    this._generatorTree = generatorTree;
     this._optimizedFunctionsAndEffects = optimizedFunctionsAndEffects;
     this._residualValues = residualValues;
   }
 
-  _generatorDAG: GeneratorDAG;
+  _generatorTree: GeneratorTree;
   _optimizedFunctionsAndEffects: Map<FunctionValue, AdditionalFunctionEffects>;
   _residualValues: Map<Value, Set<Scope>>;
 
@@ -80,7 +80,7 @@ export class ResidualOptimizedFunctions {
     for (let scope of scopes) {
       let s = scope;
       while (s instanceof Generator) {
-        s = this._generatorDAG.getParent(s);
+        s = this._generatorTree.getParent(s);
       }
       if (s === "GLOBAL") return undefined;
       invariant(s instanceof FunctionValue);

src/serializer/serializer.js

@@ -193,7 +193,7 @@ export class Serializer {
         if (this.realm.react.verbose) {
           this.logger.logInformation(`Visiting evaluated nodes...`);
         }
-        let [residualHeapInfo, generatorDAG, inspector] = (() => {
+        let [residualHeapInfo, generatorTree, inspector] = (() => {
           let residualHeapVisitor = new ResidualHeapVisitor(
             this.realm,
             this.logger,
@@ -201,12 +201,12 @@ export class Serializer {
             additionalFunctionValuesAndEffects
           );
           statistics.deepTraversal.measure(() => residualHeapVisitor.visitRoots());
-          return [residualHeapVisitor.toInfo(), residualHeapVisitor.generatorDAG, residualHeapVisitor.inspector];
+          return [residualHeapVisitor.toInfo(), residualHeapVisitor.generatorTree, residualHeapVisitor.inspector];
         })();
         if (this.logger.hasErrors()) return undefined;
 
         let residualOptimizedFunctions = new ResidualOptimizedFunctions(
-          generatorDAG,
+          generatorTree,
           additionalFunctionValuesAndEffects,
           residualHeapInfo.values
         );
@@ -270,7 +270,7 @@ export class Serializer {
               this.options,
               additionalFunctionValuesAndEffects,
               referentializer,
-              generatorDAG,
+              generatorTree,
               residualOptimizedFunctions
             ).serialize();
           });
@@ -293,7 +293,7 @@ export class Serializer {
             this.options,
             additionalFunctionValuesAndEffects,
             referentializer,
-            generatorDAG,
+            generatorTree,
             residualOptimizedFunctions
           ).serialize()
         );