Merge pull request #1239 from artemcm/IncrementalSkipExplicitDependencies

[Explicit Module Builds] On an incremental build, skip re-building module dependencies when they are up-to-date

Author: artemcm

Sources/SwiftDriver/IncrementalCompilation/FirstWaveComputer.swift

@@ -27,6 +27,7 @@ extension IncrementalCompilationState {
     let fileSystem: FileSystem
     let showJobLifecycle: Bool
     let alwaysRebuildDependents: Bool
+    let rebuildExplicitModuleDependencies: Bool
     /// If non-null outputs information for `-driver-show-incremental` for input path
     private let reporter: Reporter?
 
@@ -49,6 +50,8 @@ extension IncrementalCompilationState {
       self.showJobLifecycle = driver.showJobLifecycle
       self.alwaysRebuildDependents = initialState.incrementalOptions.contains(
         .alwaysRebuildDependents)
+      self.rebuildExplicitModuleDependencies =
+        initialState.maybeUpToDatePriorInterModuleDependencyGraph != nil ? false : true
       self.reporter = reporter
     }
 
@@ -122,6 +125,11 @@ extension IncrementalCompilationState.FirstWaveComputer {
         : compileGroups[input]
     }
 
+    // If module dependencies are known to be up-to-date, do not rebuild them
+    let mandatoryBeforeCompilesJobs = self.rebuildExplicitModuleDependencies ?
+      jobsInPhases.beforeCompiles :
+      jobsInPhases.beforeCompiles.filter { $0.kind != .generatePCM && $0.kind != .compileModuleFromInterface }
+
     let batchedCompilationJobs = try batchJobFormer.formBatchedJobs(
       mandatoryCompileGroupsInOrder.flatMap {$0.allJobs()},
       showJobLifecycle: showJobLifecycle)
@@ -130,7 +138,7 @@ extension IncrementalCompilationState.FirstWaveComputer {
     // we can skip running `beforeCompiles` jobs if we also ensure that none of the `afterCompiles` jobs
     // have any dependencies on them.
     let skipAllJobs = batchedCompilationJobs.isEmpty ? !nonVerifyAfterCompileJobsDependOnBeforeCompileJobs() : false
-    let mandatoryJobsInOrder = skipAllJobs ? [] : jobsInPhases.beforeCompiles + batchedCompilationJobs
+    let mandatoryJobsInOrder = skipAllJobs ? [] : mandatoryBeforeCompilesJobs + batchedCompilationJobs
     return (initiallySkippedCompileGroups: initiallySkippedCompileGroups,
             mandatoryJobsInOrder: mandatoryJobsInOrder)
   }

Sources/SwiftDriver/IncrementalCompilation/IncrementalCompilationState+Extensions.swift

@@ -53,7 +53,7 @@ extension IncrementalCompilationState {
     /// Record about existence and time of the last compile.
     let maybeBuildRecord: BuildRecord?
     /// Record about the compiled module's module dependencies from the last compile.
-    let maybeInterModuleDependencyGraph: InterModuleDependencyGraph?
+    let maybeUpToDatePriorInterModuleDependencyGraph: InterModuleDependencyGraph?
     /// A set of inputs invalidated by external changes.
     let inputsInvalidatedByExternals: TransitivelyInvalidatedSwiftSourceFileSet
     /// Compiler options related to incremental builds.

Sources/SwiftDriver/IncrementalCompilation/IncrementalDependencyAndInputSetup.swift

@@ -330,7 +330,7 @@ extension IncrementalCompilationState {
       return InitialStateForPlanning(
         graph: graph, buildRecordInfo: buildRecordInfo,
         maybeBuildRecord: maybeBuildRecord,
-        maybeInterModuleDependencyGraph: maybeInterModuleDependencyGraph,
+        maybeUpToDatePriorInterModuleDependencyGraph: maybeInterModuleDependencyGraph,
         inputsInvalidatedByExternals: inputsInvalidatedByExternals,
         incrementalOptions: options, buildStartTime: buildStartTime,
         buildEndTime: buildEndTime)

Sources/SwiftDriver/Jobs/Planning.swift

@@ -142,7 +142,7 @@ extension Driver {
     let interModuleDependencyGraph: InterModuleDependencyGraph?
     if parsedOptions.contains(.driverExplicitModuleBuild) {
       interModuleDependencyGraph =
-        try initialIncrementalState?.maybeInterModuleDependencyGraph ??
+        try initialIncrementalState?.maybeUpToDatePriorInterModuleDependencyGraph ??
             gatherModuleDependencies()
     } else {
       interModuleDependencyGraph = nil

Tests/SwiftDriverTests/IncrementalCompilationTests.swift

@@ -887,11 +887,6 @@ extension IncrementalCompilationTests {
       implicitBuildRemarks
       readInterModuleGraph
       interModuleDependencyGraphUpToDate
-      // TODO: We can do better, but for now make sure the jobs are still run
-      // even if the graph is up-to-date
-      compilingExplicitClangDependency("SwiftShims")
-      compilingExplicitSwiftDependency("Swift")
-      compilingExplicitSwiftDependency("SwiftOnoneSupport")
     }
 
     touch("main")