Remove job from build keys. Saves encoding and decoding the jobs.

The runtime of the following (in release build) went from 2.27 minutes to 2.29 seconds (notice the change in units!!!)
// RUN: %{python} -c 'for i in range(500001): print("-DTEST5_" + str(i))' > %t.5.resp
// RUN: not %target-swiftc_driver %s @%t.5.resp -Xfrontend -debug-crash-immediately 2>&1

Author: cltnschlosser

Sources/SwiftDriver/Execution/JobExecutor.swift

@@ -118,8 +118,11 @@ public final class JobExecutor {
   /// The context required during job execution.
   struct Context {
 
-    /// This contains mapping from an output to the job that produces that output.
-    let producerMap: [VirtualPath: Job]
+    /// This contains mapping from an output to the index(in the jobs array) of the job that produces that output.
+    let producerMap: [VirtualPath: Int]
+
+    /// All the jobs being executed.
+    let jobs: [Job]
 
     /// The resolver for argument template.
     let argsResolver: ArgsResolver
@@ -152,14 +155,16 @@ public final class JobExecutor {
       argsResolver: ArgsResolver,
       env: [String: String],
       fileSystem: FileSystem,
-      producerMap: [VirtualPath: Job],
+      producerMap: [VirtualPath: Int],
+      jobs: [Job],
       executorDelegate: JobExecutorDelegate,
       jobQueue: OperationQueue,
       processSet: ProcessSet?,
       forceResponseFiles: Bool,
       recordedInputModificationDates: [TypedVirtualPath: Date]
     ) {
       self.producerMap = producerMap
+      self.jobs = jobs
       self.argsResolver = argsResolver
       self.env = env
       self.fileSystem = fileSystem
@@ -217,7 +222,7 @@ public final class JobExecutor {
     let delegate = JobExecutorBuildDelegate(context)
     let engine = LLBuildEngine(delegate: delegate)
 
-    let result = try engine.build(key: ExecuteAllJobsRule.RuleKey(jobs: jobs))
+    let result = try engine.build(key: ExecuteAllJobsRule.RuleKey())
 
     // Throw the stub error the build didn't finish successfully.
     if !result.success {
@@ -227,11 +232,11 @@ public final class JobExecutor {
 
   /// Create the context required during the execution.
   func createContext(_ jobs: [Job], env: [String: String], fileSystem: FileSystem) -> Context {
-    var producerMap: [VirtualPath: Job] = [:]
-    for job in jobs {
+    var producerMap: [VirtualPath: Int] = [:]
+    for (index, job) in jobs.enumerated() {
       for output in job.outputs {
         assert(!producerMap.keys.contains(output.file), "multiple producers for output \(output): \(job) \(producerMap[output.file]!)")
-        producerMap[output.file] = job
+        producerMap[output.file] = index
       }
     }
 
@@ -244,6 +249,7 @@ public final class JobExecutor {
       env: env,
       fileSystem: fileSystem,
       producerMap: producerMap,
+      jobs: jobs,
       executorDelegate: executorDelegate,
       jobQueue: jobQueue,
       processSet: processSet,
@@ -264,7 +270,7 @@ struct JobExecutorBuildDelegate: LLBuildEngineDelegate {
   func lookupRule(rule: String, key: Key) -> Rule {
     switch rule {
     case ExecuteAllJobsRule.ruleName:
-      return ExecuteAllJobsRule(key, fileSystem: context.fileSystem)
+      return ExecuteAllJobsRule(key, jobs: context.jobs, fileSystem: context.fileSystem)
     case ExecuteJobRule.ruleName:
       return ExecuteJobRule(key, context: context)
     default:
@@ -294,26 +300,26 @@ class ExecuteAllJobsRule: LLBuildRule {
   struct RuleKey: LLBuildKey {
     typealias BuildValue = DriverBuildValue
     typealias BuildRule = ExecuteAllJobsRule
-
-    let jobs: [Job]
   }
 
   override class var ruleName: String { "\(ExecuteAllJobsRule.self)" }
 
   private let key: RuleKey
+  private let jobs: [Job]
 
   /// True if any of the inputs had any error.
   private var allInputsSucceeded: Bool = true
 
-  init(_ key: Key, fileSystem: FileSystem) {
+  init(_ key: Key, jobs: [Job], fileSystem: FileSystem) {
     self.key = RuleKey(key)
+    self.jobs = jobs
     super.init(fileSystem: fileSystem)
   }
 
   override func start(_ engine: LLTaskBuildEngine) {
-    for (idx, job) in key.jobs.enumerated() {
-        let key = ExecuteJobRule.RuleKey(job: job)
-        engine.taskNeedsInput(key, inputID: idx)
+    for index in jobs.indices {
+      let key = ExecuteJobRule.RuleKey(index: index)
+      engine.taskNeedsInput(key, inputID: index)
     }
   }
 
@@ -340,7 +346,7 @@ class ExecuteJobRule: LLBuildRule {
     typealias BuildValue = DriverBuildValue
     typealias BuildRule = ExecuteJobRule
 
-    let job: Job
+    let index: Int
   }
 
   override class var ruleName: String { "\(ExecuteJobRule.self)" }
@@ -358,9 +364,9 @@ class ExecuteJobRule: LLBuildRule {
   }
 
   override func start(_ engine: LLTaskBuildEngine) {
-    for (idx, input) in key.job.inputs.enumerated() {
-      if let producingJob = context.producerMap[input.file] {
-        let key = ExecuteJobRule.RuleKey(job: producingJob)
+    for (idx, input) in context.jobs[key.index].inputs.enumerated() {
+      if let producingJobIndex = context.producerMap[input.file] {
+        let key = ExecuteJobRule.RuleKey(index: producingJobIndex)
         engine.taskNeedsInput(key, inputID: idx)
       }
     }
@@ -393,7 +399,7 @@ class ExecuteJobRule: LLBuildRule {
   private func executeJob(_ engine: LLTaskBuildEngine) {
     let context = self.context
     let resolver = context.argsResolver
-    let job = key.job
+    let job = context.jobs[key.index]
     let env = context.env.merging(job.extraEnvironment, uniquingKeysWith: { $1 })
 
     let value: DriverBuildValue