[compiler] Delete LoweredFunction.dependencies and hoisted instructions

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`)

Author: mofeiZ

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

@@ -7,7 +7,6 @@
 
 import {NodePath, Scope} from '@babel/traverse';
 import * as t from '@babel/types';
-import {Expression} from '@babel/types';
 import invariant from 'invariant';
 import {
   CompilerError,
@@ -75,7 +74,7 @@ export function lower(
   parent: NodePath<t.Function> | null = null,
 ): Result<HIRFunction, CompilerError> {
   const builder = new HIRBuilder(env, parent ?? func, bindings, capturedRefs);
-  const context: Array<Place> = [];
+  const context: HIRFunction['context'] = [];
 
   for (const ref of capturedRefs ?? []) {
     context.push({
@@ -3378,7 +3377,7 @@ function lowerFunction(
   >,
 ): LoweredFunction | null {
   const componentScope: Scope = builder.parentFunction.scope;
-  const captured = gatherCapturedDeps(builder, expr, componentScope);
+  const capturedContext = gatherCapturedContext(expr, componentScope);
 
   /*
    * TODO(gsn): In the future, we could only pass in the context identifiers
@@ -3392,7 +3391,7 @@ function lowerFunction(
     expr,
     builder.environment,
     builder.bindings,
-    [...builder.context, ...captured.identifiers],
+    [...builder.context, ...capturedContext],
     builder.parentFunction,
   );
   let loweredFunc: HIRFunction;
@@ -3405,7 +3404,6 @@ function lowerFunction(
   loweredFunc = lowering.unwrap();
   return {
     func: loweredFunc,
-    dependencies: captured.refs,
   };
 }
 
@@ -4079,14 +4077,6 @@ function lowerAssignment(
   }
 }
 
-function isValidDependency(path: NodePath<t.MemberExpression>): boolean {
-  const parent: NodePath<t.Node> = path.parentPath;
-  return (
-    !path.node.computed &&
-    !(parent.isCallExpression() && parent.get('callee') === path)
-  );
-}
-
 function captureScopes({from, to}: {from: Scope; to: Scope}): Set<Scope> {
   let scopes: Set<Scope> = new Set();
   while (from) {
@@ -4101,19 +4091,16 @@ function captureScopes({from, to}: {from: Scope; to: Scope}): Set<Scope> {
   return scopes;
 }
 
-function gatherCapturedDeps(
-  builder: HIRBuilder,
+function gatherCapturedContext(
   fn: NodePath<
     | t.FunctionExpression
     | t.ArrowFunctionExpression
     | t.FunctionDeclaration
     | t.ObjectMethod
   >,
   componentScope: Scope,
-): {identifiers: Array<t.Identifier>; refs: Array<Place>} {
-  const capturedIds: Map<t.Identifier, number> = new Map();
-  const capturedRefs: Set<Place> = new Set();
-  const seenPaths: Set<string> = new Set();
+): Array<t.Identifier> {
+  const capturedIds = new Set<t.Identifier>();
 
   /*
    * Capture all the scopes from the parent of this function up to and including
@@ -4124,33 +4111,11 @@ function gatherCapturedDeps(
     to: componentScope,
   });
 
-  function addCapturedId(bindingIdentifier: t.Identifier): number {
-    if (!capturedIds.has(bindingIdentifier)) {
-      const index = capturedIds.size;
-      capturedIds.set(bindingIdentifier, index);
-      return index;
-    } else {
-      return capturedIds.get(bindingIdentifier)!;
-    }
-  }
-
   function handleMaybeDependency(
-    path:
-      | NodePath<t.MemberExpression>
-      | NodePath<t.Identifier>
-      | NodePath<t.JSXOpeningElement>,
+    path: NodePath<t.Identifier> | NodePath<t.JSXOpeningElement>,
   ): void {
     // Base context variable to depend on
     let baseIdentifier: NodePath<t.Identifier> | NodePath<t.JSXIdentifier>;
-    /*
-     * Base expression to depend on, which (for now) may contain non side-effectful
-     * member expressions
-     */
-    let dependency:
-      | NodePath<t.MemberExpression>
-      | NodePath<t.JSXMemberExpression>
-      | NodePath<t.Identifier>
-      | NodePath<t.JSXIdentifier>;
     if (path.isJSXOpeningElement()) {
       const name = path.get('name');
       if (!(name.isJSXMemberExpression() || name.isJSXIdentifier())) {
@@ -4166,115 +4131,20 @@ function gatherCapturedDeps(
         'Invalid logic in gatherCapturedDeps',
       );
       baseIdentifier = current;
-
-      /*
-       * Get the expression to depend on, which may involve PropertyLoads
-       * for member expressions
-       */
-      let currentDep:
-        | NodePath<t.JSXMemberExpression>
-        | NodePath<t.Identifier>
-        | NodePath<t.JSXIdentifier> = baseIdentifier;
-
-      while (true) {
-        const nextDep: null | NodePath<t.Node> = currentDep.parentPath;
-        if (nextDep && nextDep.isJSXMemberExpression()) {
-          currentDep = nextDep;
-        } else {
-          break;
-        }
-      }
-      dependency = currentDep;
-    } else if (path.isMemberExpression()) {
-      // Calculate baseIdentifier
-      let currentId: NodePath<Expression> = path;
-      while (currentId.isMemberExpression()) {
-        currentId = currentId.get('object');
-      }
-      if (!currentId.isIdentifier()) {
-        return;
-      }
-      baseIdentifier = currentId;
-
-      /*
-       * Get the expression to depend on, which may involve PropertyLoads
-       * for member expressions
-       */
-      let currentDep:
-        | NodePath<t.MemberExpression>
-        | NodePath<t.Identifier>
-        | NodePath<t.JSXIdentifier> = baseIdentifier;
-
-      while (true) {
-        const nextDep: null | NodePath<t.Node> = currentDep.parentPath;
-        if (
-          nextDep &&
-          nextDep.isMemberExpression() &&
-          isValidDependency(nextDep)
-        ) {
-          currentDep = nextDep;
-        } else {
-          break;
-        }
-      }
-
-      dependency = currentDep;
     } else {
       baseIdentifier = path;
-      dependency = path;
     }
 
     /*
      * Skip dependency path, as we already tried to recursively add it (+ all subexpressions)
      * as a dependency.
      */
-    dependency.skip();
+    path.skip();
 
     // Add the base identifier binding as a dependency.
     const binding = baseIdentifier.scope.getBinding(baseIdentifier.node.name);
-    if (binding === undefined || !pureScopes.has(binding.scope)) {
-      return;
-    }
-    const idKey = String(addCapturedId(binding.identifier));
-
-    // Add the expression (potentially a memberexpr path) as a dependency.
-    let exprKey = idKey;
-    if (dependency.isMemberExpression()) {
-      let pathTokens = [];
-      let current: NodePath<Expression> = dependency;
-      while (current.isMemberExpression()) {
-        const property = current.get('property') as NodePath<t.Identifier>;
-        pathTokens.push(property.node.name);
-        current = current.get('object');
-      }
-
-      exprKey += '.' + pathTokens.reverse().join('.');
-    } else if (dependency.isJSXMemberExpression()) {
-      let pathTokens = [];
-      let current: NodePath<t.JSXMemberExpression | t.JSXIdentifier> =
-        dependency;
-      while (current.isJSXMemberExpression()) {
-        const property = current.get('property');
-        pathTokens.push(property.node.name);
-        current = current.get('object');
-      }
-    }
-
-    if (!seenPaths.has(exprKey)) {
-      let loweredDep: Place;
-      if (dependency.isJSXIdentifier()) {
-        loweredDep = lowerValueToTemporary(builder, {
-          kind: 'LoadLocal',
-          place: lowerIdentifier(builder, dependency),
-          loc: path.node.loc ?? GeneratedSource,
-        });
-      } else if (dependency.isJSXMemberExpression()) {
-        loweredDep = lowerJsxMemberExpression(builder, dependency);
-      } else {
-        loweredDep = lowerExpressionToTemporary(builder, dependency);
-      }
-      capturedRefs.add(loweredDep);
-      seenPaths.add(exprKey);
+    if (binding !== undefined && pureScopes.has(binding.scope)) {
+      capturedIds.add(binding.identifier);
     }
   }
 
@@ -4305,13 +4175,13 @@ function gatherCapturedDeps(
         return;
       } else if (path.isJSXElement()) {
         handleMaybeDependency(path.get('openingElement'));
-      } else if (path.isMemberExpression() || path.isIdentifier()) {
+      } else if (path.isIdentifier()) {
         handleMaybeDependency(path);
       }
     },
   });
 
-  return {identifiers: [...capturedIds.keys()], refs: [...capturedRefs]};
+  return [...capturedIds.keys()];
 }
 
 function notNull<T>(value: T | null): value is T {

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

@@ -131,15 +131,7 @@ function collectHoistablePropertyLoadsImpl(
   fn: HIRFunction,
   context: CollectHoistablePropertyLoadsContext,
 ): ReadonlyMap<BlockId, BlockInfo> {
-  const functionExpressionLoads = collectFunctionExpressionFakeLoads(fn);
-  const actuallyEvaluatedTemporaries = new Map(
-    [...context.temporaries].filter(([id]) => !functionExpressionLoads.has(id)),
-  );
-
-  const nodes = collectNonNullsInBlocks(fn, {
-    ...context,
-    temporaries: actuallyEvaluatedTemporaries,
-  });
+  const nodes = collectNonNullsInBlocks(fn, context);
   propagateNonNull(fn, nodes, context.registry);
 
   if (DEBUG_PRINT) {
@@ -598,30 +590,3 @@ function reduceMaybeOptionalChains(
     }
   } while (changed);
 }
-
-function collectFunctionExpressionFakeLoads(
-  fn: HIRFunction,
-): Set<IdentifierId> {
-  const sources = new Map<IdentifierId, IdentifierId>();
-  const functionExpressionReferences = new Set<IdentifierId>();
-
-  for (const [_, block] of fn.body.blocks) {
-    for (const {lvalue, value} of block.instructions) {
-      if (
-        value.kind === 'FunctionExpression' ||
-        value.kind === 'ObjectMethod'
-      ) {
-        for (const reference of value.loweredFunc.dependencies) {
-          let curr: IdentifierId | undefined = reference.identifier.id;
-          while (curr != null) {
-            functionExpressionReferences.add(curr);
-            curr = sources.get(curr);
-          }
-        }
-      } else if (value.kind === 'PropertyLoad') {
-        sources.set(lvalue.identifier.id, value.object.identifier.id);
-      }
-    }
-  }
-  return functionExpressionReferences;
-}

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

@@ -245,8 +245,6 @@ const EnvironmentConfigSchema = z.object({
    */
   enableUseTypeAnnotations: z.boolean().default(false),
 
-  enableFunctionDependencyRewrite: z.boolean().default(true),
-
   /**
    * Enables inference of optional dependency chains. Without this flag
    * a property chain such as `props?.items?.foo` will infer as a dep on

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

@@ -722,7 +722,6 @@ export type ObjectProperty = {
 };
 
 export type LoweredFunction = {
-  dependencies: Array<Place>;
   func: HIRFunction;
 };
 

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

@@ -148,6 +148,14 @@ function collectScopeInfo(fn: HIRFunction): ScopeInfo {
     const scope = place.identifier.scope;
     if (scope != null) {
       placeScopes.set(place, scope);
+      /**
+       * Record both mutating and non-mutating scopes to merge scopes with
+       * still-mutating values with inner scopes that alias those values
+       * (see `nonmutating-capture-in-unsplittable-memo-block`)
+       *
+       * Note that this isn't perfect, as it also leads to merging of mutating
+       * scopes with JSX single-instruction scopes (see `mutation-within-jsx`)
+       */
       if (scope.range.start !== scope.range.end) {
         getOrInsertDefault(scopeStarts, scope.range.start, new Set()).add(
           scope,
@@ -254,7 +262,7 @@ function visitPlace(
    * of the stack to the mutated outer scope.
    */
   const placeScope = getPlaceScope(id, place);
-  if (placeScope != null && isMutable({id} as any, place)) {
+  if (placeScope != null && isMutable({id}, place)) {
     const placeScopeIdx = activeScopes.indexOf(placeScope);
     if (placeScopeIdx !== -1 && placeScopeIdx !== activeScopes.length - 1) {
       joined.union([placeScope, ...activeScopes.slice(placeScopeIdx + 1)]);
@@ -275,6 +283,13 @@ function getOverlappingReactiveScopes(
     for (const instr of block.instructions) {
       visitInstructionId(instr.id, context, state);
       for (const place of eachInstructionOperand(instr)) {
+        if (
+          (instr.value.kind === 'FunctionExpression' ||
+            instr.value.kind === 'ObjectMethod') &&
+          place.identifier.type.kind === 'Primitive'
+        ) {
+          continue;
+        }
         visitPlace(instr.id, place, state);
       }
       for (const place of eachInstructionLValue(instr)) {

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

@@ -538,9 +538,6 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
         .split('\n')
         .map(line => `      ${line}`)
         .join('\n');
-      const deps = instrValue.loweredFunc.dependencies
-        .map(dep => printPlace(dep))
-        .join(',');
       const context = instrValue.loweredFunc.func.context
         .map(dep => printPlace(dep))
         .join(',');
@@ -557,7 +554,7 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
           })
           .join(', ') ?? '';
       const type = printType(instrValue.loweredFunc.func.returnType).trim();
-      value = `${kind} ${name} @deps[${deps}] @context[${context}] @effects[${effects}]${type !== '' ? ` return${type}` : ''}:\n${fn}`;
+      value = `${kind} ${name} @context[${context}] @effects[${effects}]${type !== '' ? ` return${type}` : ''}:\n${fn}`;
       break;
     }
     case 'TaggedTemplateExpression': {

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

@@ -738,9 +738,8 @@ function collectDependencies(
       }
       for (const instr of block.instructions) {
         if (
-          fn.env.config.enableFunctionDependencyRewrite &&
-          (instr.value.kind === 'FunctionExpression' ||
-            instr.value.kind === 'ObjectMethod')
+          instr.value.kind === 'FunctionExpression' ||
+          instr.value.kind === 'ObjectMethod'
         ) {
           context.declare(instr.lvalue.identifier, {
             id: instr.id,