webpack/lib/optimize/RemoveParentModulesPlugin.js

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

const { STAGE_BASIC } = require("../OptimizationStages");

/** @typedef {import("../Chunk")} Chunk */
/** @typedef {import("../ChunkGroup")} ChunkGroup */
/** @typedef {import("../Compiler")} Compiler */
/** @typedef {import("../Module")} Module */

/**
 * Intersects multiple masks represented as bigints
 * @param {bigint[]} masks The module masks to intersect
 * @returns {bigint} The intersection of all masks
 */
function intersectMasks(masks) {
	let result = masks[0];
	for (let i = masks.length - 1; i >= 1; i--) {
		result &= masks[i];
	}
	return result;
}

const ZERO_BIGINT = BigInt(0);
const ONE_BIGINT = BigInt(1);
const THIRTY_TWO_BIGINT = BigInt(32);

/**
 * Parses the module mask and returns the modules represented by it
 * @param {bigint} mask the module mask
 * @param {Module[]} ordinalModules the modules in the order they were added to the mask (LSB is index 0)
 * @returns {Generator<Module>} the modules represented by the mask
 */
function* getModulesFromMask(mask, ordinalModules) {
	let offset = 31;
	while (mask !== ZERO_BIGINT) {
		// Consider the last 32 bits, since that's what Math.clz32 can handle
		let last32 = Number(BigInt.asUintN(32, mask));
		while (last32 > 0) {
			const last = Math.clz32(last32);
			// The number of trailing zeros is the number trimmed off the input mask + 31 - the number of leading zeros
			// The 32 is baked into the initial value of offset
			const moduleIndex = offset - last;
			// The number of trailing zeros is the index into the array generated by getOrCreateModuleMask
			const module = ordinalModules[moduleIndex];
			yield module;
			// Remove the matched module from the mask
			// Since we can only count leading zeros, not trailing, we can't just downshift the mask
			last32 &= ~(1 << (31 - last));
		}

		// Remove the processed chunk from the mask
		mask >>= THIRTY_TWO_BIGINT;
		offset += 32;
	}
}

const PLUGIN_NAME = "RemoveParentModulesPlugin";

class RemoveParentModulesPlugin {
	/**
	 * @param {Compiler} compiler the compiler
	 * @returns {void}
	 */
	apply(compiler) {
		compiler.hooks.compilation.tap(PLUGIN_NAME, compilation => {
			/**
			 * @param {Iterable<Chunk>} chunks the chunks
			 * @param {ChunkGroup[]} chunkGroups the chunk groups
			 */
			const handler = (chunks, chunkGroups) => {
				const chunkGraph = compilation.chunkGraph;
				const queue = new Set();
				const availableModulesMap = new WeakMap();

				let nextModuleMask = ONE_BIGINT;
				const maskByModule = new WeakMap();
				/** @type {Module[]} */
				const ordinalModules = [];

				/**
				 * Gets or creates a unique mask for a module
				 * @param {Module} mod the module to get the mask for
				 * @returns {bigint} the module mask to uniquely identify the module
				 */
				const getOrCreateModuleMask = mod => {
					let id = maskByModule.get(mod);
					if (id === undefined) {
						id = nextModuleMask;
						ordinalModules.push(mod);
						maskByModule.set(mod, id);
						nextModuleMask <<= ONE_BIGINT;
					}
					return id;
				};

				// Initialize masks by chunk and by chunk group for quicker comparisons
				const chunkMasks = new WeakMap();
				for (const chunk of chunks) {
					let mask = ZERO_BIGINT;
					for (const m of chunkGraph.getChunkModulesIterable(chunk)) {
						const id = getOrCreateModuleMask(m);
						mask |= id;
					}
					chunkMasks.set(chunk, mask);
				}

				const chunkGroupMasks = new WeakMap();
				for (const chunkGroup of chunkGroups) {
					let mask = ZERO_BIGINT;
					for (const chunk of chunkGroup.chunks) {
						const chunkMask = chunkMasks.get(chunk);
						if (chunkMask !== undefined) {
							mask |= chunkMask;
						}
					}
					chunkGroupMasks.set(chunkGroup, mask);
				}

				for (const chunkGroup of compilation.entrypoints.values()) {
					// initialize available modules for chunks without parents
					availableModulesMap.set(chunkGroup, ZERO_BIGINT);
					for (const child of chunkGroup.childrenIterable) {
						queue.add(child);
					}
				}
				for (const chunkGroup of compilation.asyncEntrypoints) {
					// initialize available modules for chunks without parents
					availableModulesMap.set(chunkGroup, ZERO_BIGINT);
					for (const child of chunkGroup.childrenIterable) {
						queue.add(child);
					}
				}

				for (const chunkGroup of queue) {
					let availableModulesMask = availableModulesMap.get(chunkGroup);
					let changed = false;
					for (const parent of chunkGroup.parentsIterable) {
						const availableModulesInParent = availableModulesMap.get(parent);
						if (availableModulesInParent !== undefined) {
							const parentMask =
								availableModulesInParent | chunkGroupMasks.get(parent);
							// If we know the available modules in parent: process these
							if (availableModulesMask === undefined) {
								// if we have not own info yet: create new entry
								availableModulesMask = parentMask;
								changed = true;
							} else {
								const newMask = availableModulesMask & parentMask;
								if (newMask !== availableModulesMask) {
									changed = true;
									availableModulesMask = newMask;
								}
							}
						}
					}

					if (changed) {
						availableModulesMap.set(chunkGroup, availableModulesMask);
						// if something changed: enqueue our children
						for (const child of chunkGroup.childrenIterable) {
							// Push the child to the end of the queue
							queue.delete(child);
							queue.add(child);
						}
					}
				}

				// now we have available modules for every chunk
				for (const chunk of chunks) {
					const chunkMask = chunkMasks.get(chunk);
					if (chunkMask === undefined) continue; // No info about this chunk

					const availableModulesSets = Array.from(
						chunk.groupsIterable,
						chunkGroup => availableModulesMap.get(chunkGroup)
					);
					if (availableModulesSets.includes(undefined)) continue; // No info about this chunk group

					const availableModulesMask = intersectMasks(availableModulesSets);
					const toRemoveMask = chunkMask & availableModulesMask;
					if (toRemoveMask !== ZERO_BIGINT) {
						for (const module of getModulesFromMask(
							toRemoveMask,
							ordinalModules
						)) {
							chunkGraph.disconnectChunkAndModule(chunk, module);
						}
					}
				}
			};
			compilation.hooks.optimizeChunks.tap(
				{
					name: PLUGIN_NAME,
					stage: STAGE_BASIC
				},
				handler
			);
		});
	}
}
module.exports = RemoveParentModulesPlugin;