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[Incremental] Try a cache for external dependency mod times #538

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merged 1 commit into from
Mar 13, 2021
Merged

[Incremental] Try a cache for external dependency mod times #538

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24 changes: 13 additions & 11 deletions Sources/SwiftDriver/IncrementalCompilation/ModuleDependencyGraph.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,9 @@ import SwiftOptions

@_spi(Testing) public var phase: Phase

/// Minimize the number of file system modification-time queries.
private var externalDependencyModTimeCache = [ExternalDependency: Bool]()

public init(_ info: IncrementalCompilationState.InitialStateComputer,
_ phase: Phase
) {
Expand Down Expand Up @@ -287,14 +290,10 @@ extension ModuleDependencyGraph {

let isNewToTheGraph = fingerprintedExternalDependencies.insert(fed).inserted

var lazyModTimer = LazyModTimer(
externalDependency: fed.externalDependency,
info: info)

// If the graph already includes prior externals, then any new externals are changes
// Short-circuit conjunction may avoid the modTime query
let shouldTryToProcess = info.isCrossModuleIncrementalBuildEnabled &&
(isNewToTheGraph || lazyModTimer.hasExternalFileChanged)
(isNewToTheGraph || hasFileChanged(of: fed.externalDependency))

// Do this no matter what in order to integrate any incremental external dependencies.
let invalidatedNodesFromIncrementalExternal = shouldTryToProcess
Expand All @@ -309,7 +308,7 @@ extension ModuleDependencyGraph {
/// When building a graph from scratch, an unchanged but new-to-the-graph external dependendcy should be ignored.
/// Otherwise, it represents an added Import
let callerWantsTheseChanges = (phase.isUpdating && isNewToTheGraph) ||
lazyModTimer.hasExternalFileChanged
hasFileChanged(of: fed.externalDependency)

guard callerWantsTheseChanges else {
return DirectlyInvalidatedNodeSet()
Expand All @@ -319,13 +318,16 @@ extension ModuleDependencyGraph {
// return anything that uses that dependency.
return invalidatedNodesFromIncrementalExternal ?? collectUntracedNodesUsing(fed)
}

private struct LazyModTimer {
let externalDependency: ExternalDependency
let info: IncrementalCompilationState.InitialStateComputer

lazy var hasExternalFileChanged = (externalDependency.modTime(info.fileSystem) ?? .distantFuture)
private func hasFileChanged(of externalDependency: ExternalDependency
) -> Bool {
if let hasChanged = externalDependencyModTimeCache[externalDependency] {
return hasChanged
}
let hasChanged = (externalDependency.modTime(info.fileSystem) ?? .distantFuture)
>= info.buildTime
externalDependencyModTimeCache[externalDependency] = hasChanged
return hasChanged
}

/// Try to read and integrate an external dependency.
Expand Down