Stage in Frontend/Driver Feature Flags for Cross-Module Incremental Builds

include/swift/Driver/Compilation.h

@@ -281,6 +281,9 @@ class Compilation {
   /// Experiment with source-range-based dependencies
   const bool EnableSourceRangeDependencies;
 
+  /// (experimental) Enable cross-module incremental build scheduling.
+  const bool EnableCrossModuleIncrementalBuild;
+
 public:
   /// Will contain a comparator if an argument demands it.
   Optional<IncrementalSchemeComparator> IncrementalComparator;
@@ -323,7 +326,8 @@ class Compilation {
               bool FineGrainedDependenciesIncludeIntrafileOnes = false,
               bool EnableSourceRangeDependencies = false,
               bool CompareIncrementalSchemes = false,
-              StringRef CompareIncrementalSchemesPath = "");
+              StringRef CompareIncrementalSchemesPath = "",
+              bool EnableCrossModuleIncrementalBuild = false);
   // clang-format on
   ~Compilation();
 
@@ -429,6 +433,10 @@ class Compilation {
     return ShowDriverTimeCompilation;
   }
 
+  bool getEnableCrossModuleIncrementalBuild() const {
+    return EnableCrossModuleIncrementalBuild;
+  }
+
   size_t getFilelistThreshold() const {
     return FilelistThreshold;
   }

include/swift/Frontend/FrontendOptions.h

@@ -276,6 +276,14 @@ class FrontendOptions {
   /// of the main Swift module's source files.
   bool ImportPrescan = false;
 
+  /// When performing an incremental build, ensure that cross-module incremental
+  /// build metadata is available in any swift modules emitted by this frontend
+  /// job.
+  ///
+  /// This flag is currently only propagated from the driver to
+  /// any merge-modules jobs.
+  bool EnableExperimentalCrossModuleIncrementalBuild = false;
+
   /// The different modes for validating TBD against the LLVM IR.
   enum class TBDValidationMode {
     Default,        ///< Do the default validation for the current platform.

include/swift/Option/Options.td

@@ -584,6 +584,11 @@ def experimental_cxx_stdlib :
   Separate<["-"], "experimental-cxx-stdlib">,
   HelpText<"C++ standard library to use; forwarded to Clang's -stdlib flag">;
 
+def enable_experimental_cross_module_incremental_build :
+  Flag<["-"], "enable-experimental-cross-module-incremental-build">,
+  HelpText<"(experimental) Enable cross-module incremental build metadata and "
+           "driver scheduling">;
+
 
 // Diagnostic control options
 def suppress_warnings : Flag<["-"], "suppress-warnings">,

include/swift/Serialization/SerializationOptions.h

@@ -131,6 +131,7 @@ namespace swift {
     bool SerializeAllSIL = false;
     bool SerializeOptionsForDebugging = false;
     bool IsSIB = false;
+    bool ExperimentalCrossModuleIncrementalInfo = false;
   };
 
 } // end namespace swift

lib/Driver/Compilation.cpp

@@ -127,7 +127,8 @@ Compilation::Compilation(DiagnosticEngine &Diags,
                          bool FineGrainedDependenciesIncludeIntrafileOnes,
                          bool EnableSourceRangeDependencies,
                          bool CompareIncrementalSchemes,
-                         StringRef CompareIncrementalSchemesPath)
+                         StringRef CompareIncrementalSchemesPath,
+                         bool EnableCrossModuleIncrementalBuild)
   : Diags(Diags), TheToolChain(TC),
     TheOutputInfo(OI),
     Level(Level),
@@ -155,7 +156,8 @@ Compilation::Compilation(DiagnosticEngine &Diags,
       EmitFineGrainedDependencyDotFileAfterEveryImport),
     FineGrainedDependenciesIncludeIntrafileOnes(
       FineGrainedDependenciesIncludeIntrafileOnes),
-    EnableSourceRangeDependencies(EnableSourceRangeDependencies)
+    EnableSourceRangeDependencies(EnableSourceRangeDependencies),
+    EnableCrossModuleIncrementalBuild(EnableCrossModuleIncrementalBuild)
     {
     if (CompareIncrementalSchemes)
       IncrementalComparator.emplace(

lib/Driver/Driver.cpp

@@ -1027,6 +1027,8 @@ Driver::buildCompilation(const ToolChain &TC,
             OPT_driver_emit_fine_grained_dependency_dot_file_after_every_import);
     const bool FineGrainedDependenciesIncludeIntrafileOnes =
         ArgList->hasArg(options::OPT_fine_grained_dependency_include_intrafile);
+    const bool EnableCrossModuleDependencies = ArgList->hasArg(
+        options::OPT_enable_experimental_cross_module_incremental_build);
 
     // clang-format off
     C = std::make_unique<Compilation>(
@@ -1054,7 +1056,8 @@ Driver::buildCompilation(const ToolChain &TC,
         FineGrainedDependenciesIncludeIntrafileOnes,
         EnableSourceRangeDependencies,
         CompareIncrementalSchemes,
-        CompareIncrementalSchemesPath);
+        CompareIncrementalSchemesPath,
+        EnableCrossModuleDependencies);
     // clang-format on
   }
 

lib/Driver/ToolChains.cpp

@@ -1047,6 +1047,10 @@ ToolChain::constructInvocation(const MergeModuleJobAction &job,
 
   context.Args.AddLastArg(Arguments, options::OPT_import_objc_header);
 
+  context.Args.AddLastArg(
+      Arguments,
+      options::OPT_enable_experimental_cross_module_incremental_build);
+
   Arguments.push_back("-module-name");
   Arguments.push_back(context.Args.MakeArgString(context.OI.ModuleName));
 

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -92,6 +92,9 @@ bool ArgsToFrontendOptionsConverter::convert(
 
   Opts.ImportPrescan |= Args.hasArg(OPT_import_prescan);
 
+  Opts.EnableExperimentalCrossModuleIncrementalBuild |=
+      Args.hasArg(OPT_enable_experimental_cross_module_incremental_build);
+
   // Always track system dependencies when scanning dependencies.
   if (const Arg *ModeArg = Args.getLastArg(OPT_modes_Group)) {
     if (ModeArg->getOption().matches(OPT_scan_dependencies)) {

lib/Frontend/Frontend.cpp

@@ -175,6 +175,9 @@ SerializationOptions CompilerInvocation::computeSerializationOptions(
       opts.SerializeOptionsForDebugging.getValueOr(
           !isModuleExternallyConsumed(module));
 
+  serializationOpts.ExperimentalCrossModuleIncrementalInfo =
+      opts.EnableExperimentalCrossModuleIncrementalBuild;
+
   return serializationOpts;
 }
 

test/Driver/cross_module.swift

@@ -0,0 +1,6 @@
+// RUN: %empty-directory(%t/sub)
+// RUN: echo "{\"\": {\"swift-dependencies\": \"cross_module.swiftdeps\"}}" > %t/ofm.json
+// RUN: %swiftc_driver -incremental -emit-module -module-name cross_module -output-file-map=%/t/ofm.json -driver-print-jobs -target x86_64-apple-macosx10.9 %s -enable-experimental-cross-module-incremental-build 2>^1 | %FileCheck -check-prefix ENABLE %s
+
+// ENABLE: {{bin(/|\\\\)swift(-frontend|c)?(\.exe)?"?}} -frontend -merge-modules
+// ENABLE-SAME: -enable-experimental-cross-module-incremental-build