pruneableValue() — react Function Reference

Source Code

compiler/packages/babel-plugin-react-compiler/src/Optimization/DeadCodeElimination.ts lines 278–408

function pruneableValue(value: InstructionValue, state: State): boolean {
  switch (value.kind) {
    case 'DeclareLocal': {
      // Declarations are pruneable only if the named variable is never read later
      return !state.isIdOrNameUsed(value.lvalue.place.identifier);
    }
    case 'StoreLocal': {
      if (value.lvalue.kind === InstructionKind.Reassign) {
        // Reassignments can be pruned if the specific instance being assigned is never read
        return !state.isIdUsed(value.lvalue.place.identifier);
      }
      // Declarations are pruneable only if the named variable is never read later
      return !state.isIdOrNameUsed(value.lvalue.place.identifier);
    }
    case 'Destructure': {
      let isIdOrNameUsed = false;
      let isIdUsed = false;
      for (const place of eachPatternOperand(value.lvalue.pattern)) {
        if (state.isIdUsed(place.identifier)) {
          isIdOrNameUsed = true;
          isIdUsed = true;
        } else if (state.isIdOrNameUsed(place.identifier)) {
          isIdOrNameUsed = true;
        }
      }
      if (value.lvalue.kind === InstructionKind.Reassign) {
        // Reassignments can be pruned if the specific instance being assigned is never read
        return !isIdUsed;
      } else {
        // Otherwise pruneable only if none of the identifiers are read from later
        return !isIdOrNameUsed;
      }
    }
    case 'PostfixUpdate':
    case 'PrefixUpdate': {
      // Updates are pruneable if the specific instance instance being assigned is never read
      return !state.isIdUsed(value.lvalue.identifier);
    }
    case 'Debugger': {
      // explicitly retain debugger statements to not break debugging workflows
      return false;
    }
    case 'CallExpression':
    case 'MethodCall': {
      if (state.env.outputMode === 'ssr') {
        const calleee =
          value.kind === 'CallExpression' ? value.callee : value.property;
        const hookKind = getHookKind(state.env, calleee.identifier);
        switch (hookKind) {
          case 'useState':
          case 'useReducer':
          case 'useRef': {
            // unused refs can be removed
            return true;
          }
        }
      }
      return false;
    }
    case 'Await':
    case 'ComputedDelete':
    case 'ComputedStore':
    case 'PropertyDelete':
    case 'PropertyStore':
    case 'StoreGlobal': {
      /*
       * Mutating instructions are not safe to prune.
       * TODO: we could be more precise and make this conditional on whether
       * any arguments are actually modified
       */
      return false;
    }
    case 'NewExpression':
    case 'UnsupportedNode':
    case 'TaggedTemplateExpression': {
      // Potentially safe to prune, since they should just be creating new values
      return false;
    }
    case 'GetIterator':
    case 'NextPropertyOf':
    case 'IteratorNext': {