Author: Naveen Seth Hanig
Date: 2026-04-08T23:09:02Z
New Revision: 6cb4f3955424c37261e90c9970e2a0fcaae4b23f

URL: 
https://github.com/llvm/llvm-project/commit/6cb4f3955424c37261e90c9970e2a0fcaae4b23f
DIFF: 
https://github.com/llvm/llvm-project/commit/6cb4f3955424c37261e90c9970e2a0fcaae4b23f.diff

LOG: [clang][ModulesDriver] Add support for Clang modules to -fmodules-driver 
(#187606)

This PR adds basic support for explicit module builds using Clang
modules only, managed natively by the Clang driver.
(Caching of built modules is not included in this PR.)

RFC for driver-managed module builds:

https://discourse.llvm.org/t/rfc-modules-support-simple-c-20-modules-use-from-the-clang-driver-without-a-build-system

Added: 
    clang/test/Driver/modules-driver-clang-modules-only.cpp

Modified: 
    clang/lib/Driver/ModulesDriver.cpp
    clang/test/Driver/modules-driver-manifest-input-args.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Driver/ModulesDriver.cpp 
b/clang/lib/Driver/ModulesDriver.cpp
index 2cd274a1f3099..2df40f761680f 100644
--- a/clang/lib/Driver/ModulesDriver.cpp
+++ b/clang/lib/Driver/ModulesDriver.cpp
@@ -25,10 +25,12 @@
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/DirectedGraph.h"
+#include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVectorExtras.h"
 #include "llvm/ADT/TypeSwitch.h"
 #include "llvm/ADT/iterator_range.h"
+#include "llvm/Option/ArgList.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/GraphWriter.h"
 #include "llvm/Support/JSON.h"
@@ -1248,20 +1250,20 @@ createClangModulePrecompileJob(Compilation &C, const 
Command &ImportingJob,
       /*Outputs=*/ArrayRef<InputInfo>{});
 }
 
-/// Creates a ClangModuleJobNode and its job for each unique Clang module
-/// in \p ModuleDepGraphsForScannedJobs.
+/// Creates a \c ClangModuleJobNode with associated job for each unique Clang
+/// module in \p ModuleDepGraphsForScannedJobs.
 ///
-/// Only the jobs at indices \p ScannedJobIndices in \p Jobs are expected to be
-/// non-null.
+/// \param ImportingJobs Jobs whose module dependencies were scanned.
+/// \param ModuleDepGraphsForScannedJobs Full Clang module dependency graphs
+/// corresponding to \p ImportingJobs, in order.
 static void createClangModuleJobsAndNodes(
     CompilationGraph &Graph, Compilation &C,
-    ArrayRef<std::unique_ptr<Command>> Jobs, ArrayRef<size_t> 
ScannedJobIndices,
+    ArrayRef<std::unique_ptr<Command>> ImportingJobs,
     SmallVectorImpl<deps::ModuleDepsGraph> &&ModuleDepGraphsForScannedJobs) {
   llvm::DenseSet<deps::ModuleID> AlreadySeen;
-  for (auto &&[ScanIndex, ModuleDepsGraph] :
-       llvm::enumerate(ModuleDepGraphsForScannedJobs)) {
-    const auto &ImportingJob = *Jobs[ScannedJobIndices[ScanIndex]];
-
+  for (auto &&[ImportingJob, ModuleDepsGraph] :
+       llvm::zip_equal(llvm::make_pointee_range(ImportingJobs),
+                       ModuleDepGraphsForScannedJobs)) {
     for (auto &MD : ModuleDepsGraph) {
       const auto Inserted = AlreadySeen.insert(MD.ID).second;
       if (!Inserted)
@@ -1274,6 +1276,31 @@ static void createClangModuleJobsAndNodes(
   }
 }
 
+/// Installs the command lines produced by the dependency scan into
+/// \p ScannedJobs.
+static void
+installScanCommandLines(Compilation &C,
+                        MutableArrayRef<std::unique_ptr<Command>> ScannedJobs,
+                        ArrayRef<InputDependencies> InputDepsForScannedJobs) {
+  for (auto &&[Job, InputDeps] : llvm::zip_equal(
+           llvm::make_pointee_range(ScannedJobs), InputDepsForScannedJobs)) {
+    const auto &BuildArgs = InputDeps.BuildArgs;
+    ArgStringList JobArgs;
+    JobArgs.reserve(BuildArgs.size());
+
+    const auto &SourceAction = Job.getSource();
+    const auto &TC = Job.getCreator().getToolChain();
+    auto &TCArgs =
+        C.getArgsForToolChain(&TC, SourceAction.getOffloadingArch(),
+                              SourceAction.getOffloadingDeviceKind());
+
+    for (const auto &Arg : BuildArgs)
+      JobArgs.push_back(TCArgs.MakeArgString(Arg));
+
+    Job.replaceArguments(std::move(JobArgs));
+  }
+}
+
 /// Creates nodes for all jobs which were scanned for dependencies.
 ///
 /// The updated command lines produced by the dependency scan are installed at 
a
@@ -1506,16 +1533,17 @@ void driver::modules::runModulesDriver(
       Graph, takeJobsAtIndices(Jobs, ScanResult.NonScannableJobIndices));
   auto UnusedStdlibModuleJobNodes = createNodesForUnusedStdlibModuleJobs(
       Graph, takeJobsAtIndices(Jobs, ScanResult.UnusedStdlibModuleJobIndices));
+
+  auto ScannedJobs = takeJobsAtIndices(Jobs, ScanResult.ScannedJobIndices);
   createClangModuleJobsAndNodes(
-      Graph, C, Jobs, ScanResult.ScannedJobIndices,
+      Graph, C, /*ImportingJobs*/ ScannedJobs,
       std::move(ScanResult.ModuleDepGraphsForScannedJobs));
-  createNodesForScannedJobs(
-      Graph, takeJobsAtIndices(Jobs, ScanResult.ScannedJobIndices),
-      std::move(ScanResult.InputDepsForScannedJobs));
-  createRegularEdges(Graph);
+  installScanCommandLines(C, ScannedJobs, ScanResult.InputDepsForScannedJobs);
+  createNodesForScannedJobs(Graph, std::move(ScannedJobs),
+                            std::move(ScanResult.InputDepsForScannedJobs));
 
+  createRegularEdges(Graph);
   pruneUnusedStdlibModuleJobs(Graph, UnusedStdlibModuleJobNodes);
-
   if (!createModuleDependencyEdges(Graph, Diags))
     return;
   createAndConnectRoot(Graph);
@@ -1524,12 +1552,14 @@ void driver::modules::runModulesDriver(
   if (!Diags.isLastDiagnosticIgnored())
     llvm::WriteGraph<const CompilationGraph *>(llvm::errs(), &Graph);
 
-  // TODO: Install all updated command-lines produced by the dependency scan.
   // TODO: Fix-up command-lines for named module imports.
 
-  // TODO: Sort the graph topologically before adding jobs back to the
-  // Compilation being built.
-  for (auto *N : Graph)
-    if (auto *JN = dyn_cast<JobNode>(N))
-      C.addCommand(std::move(JN->Job));
+  llvm::ReversePostOrderTraversal<CompilationGraph *> TopologicallySortedNodes(
+      &Graph);
+  assert(isa<RootNode>(*TopologicallySortedNodes.begin()) &&
+         "First node in topological order must be the root!");
+  auto TopologicallySortedJobNodes = llvm::map_range(
+      llvm::drop_begin(TopologicallySortedNodes), llvm::CastTo<JobNode>);
+  for (auto *JN : TopologicallySortedJobNodes)
+    C.addCommand(std::move(JN->Job));
 }

diff  --git a/clang/test/Driver/modules-driver-clang-modules-only.cpp 
b/clang/test/Driver/modules-driver-clang-modules-only.cpp
new file mode 100644
index 0000000000000..37a803f9b6fc0
--- /dev/null
+++ b/clang/test/Driver/modules-driver-clang-modules-only.cpp
@@ -0,0 +1,127 @@
+// Checks that -fmodules-driver correctly handles compilations using Clang 
modules.
+
+// RUN: split-file %s %t
+// RUN: rm -rf %t/modules-cache
+
+// RUN: %clang -std=c++23 \
+// RUN:   -fmodules-driver -Rmodules-driver \
+// RUN:   -fmodules -Rmodule-import \
+// RUN:   -fmodule-map-file=%t/module.modulemap \
+// RUN:   -fmodules-cache-path=%t/modules-cache \
+// RUN:   -fsyntax-only %t/main.cpp 2>&1 \
+// RUN:   | sed 's:\\\\\?:/:g' \
+// RUN:   | FileCheck -DPREFIX=%/t --check-prefix=CHECK-REMARKS %s
+
+// RUN: rm -rf %t/modules-cache
+// RUN: %clang -std=c++23 \
+// RUN:   -fmodules-driver \
+// RUN:   -fmodules \
+// RUN:   -fmodule-map-file=%t/module.modulemap \
+// RUN:   -fmodules-cache-path=%t/modules-cache \
+// RUN:   -fsyntax-only %t/main.cpp \
+// RUN:   -### 2>&1 \
+// RUN:   | sed 's:\\\\\?:/:g' \
+// RUN:   | FileCheck --check-prefix=CHECK-CC1 %s
+
+// The scan itself will also produce [-Rmodule-import] remarks.
+// Let's skip past them, we only care about the final -cc1 commands.
+// CHECK-REMARKS:       clang: remark: printing module dependency graph 
[-Rmodules-driver]
+// CHECK-REMARKS-NEXT:  digraph "Module Dependency Graph" {
+// CHECK-REMARKS:       }
+
+// CHECK-REMARKS: [[PREFIX]]/main.cpp:1:2: remark: importing module 'root' from
+// CHECK-REMARKS: [[PREFIX]]/main.cpp:1:2: remark: importing module 'direct1' 
into 'root'
+// CHECK-REMARKS: [[PREFIX]]/main.cpp:1:2: remark: importing module 
'transitive1' into 'direct1'
+// CHECK-REMARKS: [[PREFIX]]/main.cpp:1:2: remark: importing module 
'transitive2' into 'direct1'
+// CHECK-REMARKS: [[PREFIX]]/main.cpp:1:2: remark: importing module 'direct2' 
into 'root'
+// CHECK-REMARKS: [[PREFIX]]/main.cpp:1:2: remark: importing module 
'transitive2' into 'direct2'
+
+// CHECK-CC1: "-cc1"
+// CHECK-CC1-SAME: "-o" "[[TRANSITIVE2PCM:[^"]+]]"
+// CHECK-CC1-SAME: "-emit-module"
+// CHECK-CC1-SAME: "-fmodule-name=transitive2"
+// CHECK-CC1-SAME: "-fno-implicit-modules"
+
+// CHECK-CC1: "-cc1"
+// CHECK-CC1-SAME: "-o" "[[DIRECT2PCM:[^"]+]]"
+// CHECK-CC1-SAME: "-emit-module"
+// CHECK-CC1-SAME: "-fmodule-file=transitive2=[[TRANSITIVE2PCM]]"
+// CHECK-CC1-SAME: "-fmodule-name=direct2"
+// CHECK-CC1-SAME: "-fno-implicit-modules"
+
+// CHECK-CC1: "-cc1"
+// CHECK-CC1-SAME: "-o" "[[TRANSITIVE1PCM:[^"]+]]"
+// CHECK-CC1-SAME: "-emit-module"
+// CHECK-CC1-SAME: "-fmodule-name=transitive1"
+// CHECK-CC1-SAME: "-fno-implicit-modules"
+
+// CHECK-CC1: "-cc1"
+// CHECK-CC1-SAME: "-o" "[[DIRECT1PCM:[^"]+]]"
+// CHECK-CC1-SAME: "-emit-module"
+// CHECK-CC1-SAME: "-fmodule-file=transitive1=[[TRANSITIVE1PCM]]"
+// CHECK-CC1-SAME: "-fmodule-file=transitive2=[[TRANSITIVE2PCM]]"
+// CHECK-CC1-SAME: "-fmodule-name=direct1"
+// CHECK-CC1-SAME: "-fno-implicit-modules"
+
+// CHECK-CC1: "-cc1"
+// CHECK-CC1-SAME: "-o" "[[ROOTPCM:[^"]+]]"
+// CHECK-CC1-SAME: "-emit-module"
+// CHECK-CC1-SAME: "-fmodule-file=direct1=[[DIRECT1PCM]]"
+// CHECK-CC1-SAME: "-fmodule-file=direct2=[[DIRECT2PCM]]"
+// CHECK-CC1-SAME: "-fmodule-name=root"
+// CHECK-CC1-SAME: "-fno-implicit-modules"
+
+// CHECK-CC1: "-cc1"
+// CHECK-CC1-SAME: "-fsyntax-only"
+// CHECK-CC1-SAME: "{{.*}}/main.cpp"
+// CHECK-CC1-SAME: "-fmodule-file=root=[[ROOTPCM]]"
+// CHECK-CC1-SAME: "-fno-implicit-modules"
+
+// (Because of missing include guards, this example would also run into
+// redefinition errors when compiling without modules.)
+
+/--- module.modulemap
+module root { header "root.h"}
+module transitive1 { header "transitive1.h" }
+module transitive2 { header "transitive2.h" }
+module direct1 { header "direct1.h" }
+module direct2 { header "direct2.h" }
+
+//--- root.h
+#include "direct1.h"
+#include "direct2.h"
+int fromRoot() {
+  return fromDirect1() + fromDirect2();
+}
+
+//--- direct1.h
+#include "transitive1.h"
+#include "transitive2.h"
+
+int fromDirect1() {
+  return fromTransitive1() + fromTransitive2();
+}
+
+//--- direct2.h
+#include "transitive2.h"
+
+int fromDirect2() {
+  return fromTransitive2() + 2;
+}
+
+//--- transitive1.h
+int fromTransitive1() {
+    return 20;
+}
+
+//--- transitive2.h
+int fromTransitive2() {
+    return 10;
+}
+
+//--- main.cpp
+#include "root.h"
+
+int main() {
+ fromRoot();
+}

diff  --git a/clang/test/Driver/modules-driver-manifest-input-args.cpp 
b/clang/test/Driver/modules-driver-manifest-input-args.cpp
index 99765a1943faf..726fe03e27840 100644
--- a/clang/test/Driver/modules-driver-manifest-input-args.cpp
+++ b/clang/test/Driver/modules-driver-manifest-input-args.cpp
@@ -26,17 +26,15 @@
 // RUN:   %t/main.cpp \
 // RUN:   -### 2>&1 \
 // RUN:   | sed 's:\\\\\?:/:g' \
-// RUN:   | FileCheck %s -check-prefix=MAIN-CC1 -check-prefix=STDLIB-MOD-CC1 
-DPREFIX=%/t
+// RUN:   | FileCheck %s -DPREFIX=%/t
 
-// MAIN-CC1: "-cc1"
-// MAIN-CC1-SAME: "main.cpp"
-// MAIN-CC1-NOT: "-Wno-reserved-module-identifier"
-// MAIN-CC1-NOT: "-internal-isystem" 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/"
+// CHECK: "-cc1" {{.*}} "-Wno-reserved-module-identifier" {{.*}} 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/std.cppm" {{.*}} 
"-internal-isystem" 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/"
 
-// STDLIB-MOD-CC1: "-cc1"
-// STDLIB-MOD-CC1-SAME: 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/std.cppm"
-// STDLIB-MOD-CC1-SAME: "-Wno-reserved-module-identifier"
-// STDLIB-MOD-CC1-SAME: "-internal-isystem" 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/"
+// The adjustments should only be made for inputs from the Standard Library 
module manifest:
+// Check that the -cc1 command line does not contain those adjustments!
+// CHECK: "-cc1" {{.*}}main
+// CHECK-NOT: "-Wno-reserved-module-identifier"
+// CHECK-NOT: "-internal-isystem" 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/"
 
 //--- main.cpp
 import std;


        
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