https://github.com/naveen-seth updated 
https://github.com/llvm/llvm-project/pull/187606

>From c48ed203a98e7aa881d35306fac3b7715f570306 Mon Sep 17 00:00:00 2001
From: Naveen Seth Hanig <[email protected]>
Date: Thu, 19 Mar 2026 23:35:41 +0100
Subject: [PATCH 1/3] [clang][ModulesDriver] Add support for Clang modules to
 -fmodules-driver

This PR adds basic support for Clang modules to the -fmodules-driver
feature, enabling compilations with Clang modules managed natively by
the Clang driver.
Caching 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
---
 clang/lib/Driver/ModulesDriver.cpp            | 14 ++--
 .../modules-driver-clang-modules-only.cpp     | 75 +++++++++++++++++++
 .../modules-driver-manifest-input-args.cpp    | 14 +---
 3 files changed, 88 insertions(+), 15 deletions(-)
 create mode 100644 clang/test/Driver/modules-driver-clang-modules-only.cpp

diff --git a/clang/lib/Driver/ModulesDriver.cpp 
b/clang/lib/Driver/ModulesDriver.cpp
index 8740f9615d304..166c7749245c6 100644
--- a/clang/lib/Driver/ModulesDriver.cpp
+++ b/clang/lib/Driver/ModulesDriver.cpp
@@ -25,6 +25,7 @@
 #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"
@@ -1528,9 +1529,12 @@ void driver::modules::runModulesDriver(
   // 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..e99ce7883afba
--- /dev/null
+++ b/clang/test/Driver/modules-driver-clang-modules-only.cpp
@@ -0,0 +1,75 @@
+// 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 %s
+
+// The scan itself will also produce [-Rmodule-import] remarks.
+// Let's skip past them, we only care about the final -cc1 commands.
+// CHECK:       clang: remark: printing module dependency graph 
[-Rmodules-driver]
+// CHECK-NEXT:  digraph "Module Dependency Graph" {
+// CHECK:       }
+
+// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'root' from
+// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'direct1' 
into 'root'
+// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'transitive1' 
into 'direct1'
+// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'transitive2' 
into 'direct1'
+// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'direct2' 
into 'root'
+// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'transitive2' 
into 'direct2'
+
+// (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..d1c2938a73fb5 100644
--- a/clang/test/Driver/modules-driver-manifest-input-args.cpp
+++ b/clang/test/Driver/modules-driver-manifest-input-args.cpp
@@ -26,17 +26,11 @@
 // 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/"
-
-// 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/"
+// CHECK: "-cc1" {{.*}} 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/std.cppm"
+// CHECK-SAME: "-Wno-reserved-module-identifier"
+// CHECK-SAME: "-internal-isystem" 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/"
 
 //--- main.cpp
 import std;

>From 9f1ab126d79fc45b1bb4bbdfc12b1c5dfaa387b5 Mon Sep 17 00:00:00 2001
From: Naveen Seth Hanig <[email protected]>
Date: Thu, 2 Apr 2026 03:15:34 +0200
Subject: [PATCH 2/3] Install scan command-lines for all jobs

---
 clang/lib/Driver/ModulesDriver.cpp            | 49 ++++++++---
 .../modules-driver-clang-modules-only.cpp     | 86 +++++++++++++++----
 .../modules-driver-manifest-input-args.cpp    | 10 ++-
 3 files changed, 113 insertions(+), 32 deletions(-)

diff --git a/clang/lib/Driver/ModulesDriver.cpp 
b/clang/lib/Driver/ModulesDriver.cpp
index 7213bc9bde613..de42f4d1daa83 100644
--- a/clang/lib/Driver/ModulesDriver.cpp
+++ b/clang/lib/Driver/ModulesDriver.cpp
@@ -30,6 +30,7 @@
 #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"
@@ -1256,13 +1257,12 @@ createClangModulePrecompileJob(Compilation &C, const 
Command &ImportingJob,
 /// non-null.
 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)
@@ -1275,6 +1275,31 @@ 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)) {
+    auto BuildArgs = InputDeps.BuildArgs;
+    ArgStringList JobArgs;
+    JobArgs.reserve(BuildArgs.size());
+
+    const auto &SourceAction = Job.getSource();
+    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
@@ -1507,16 +1532,17 @@ 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);
@@ -1525,7 +1551,6 @@ 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.
 
   llvm::ReversePostOrderTraversal<CompilationGraph *> TopologicallySortedNodes(
diff --git a/clang/test/Driver/modules-driver-clang-modules-only.cpp 
b/clang/test/Driver/modules-driver-clang-modules-only.cpp
index e99ce7883afba..37a803f9b6fc0 100644
--- a/clang/test/Driver/modules-driver-clang-modules-only.cpp
+++ b/clang/test/Driver/modules-driver-clang-modules-only.cpp
@@ -1,28 +1,81 @@
 // 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 -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 %s
+// 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:       clang: remark: printing module dependency graph 
[-Rmodules-driver]
-// CHECK-NEXT:  digraph "Module Dependency Graph" {
-// CHECK:       }
+// 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:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'root' from
-// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'direct1' 
into 'root'
-// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'transitive1' 
into 'direct1'
-// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'transitive2' 
into 'direct1'
-// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'direct2' 
into 'root'
-// CHECK:      [[PREFIX]]/main.cpp:1:2: remark: importing module 'transitive2' 
into 'direct2'
+// 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.)
@@ -62,7 +115,6 @@ int fromTransitive1() {
 }
 
 //--- transitive2.h
-
 int fromTransitive2() {
     return 10;
 }
diff --git a/clang/test/Driver/modules-driver-manifest-input-args.cpp 
b/clang/test/Driver/modules-driver-manifest-input-args.cpp
index d1c2938a73fb5..726fe03e27840 100644
--- a/clang/test/Driver/modules-driver-manifest-input-args.cpp
+++ b/clang/test/Driver/modules-driver-manifest-input-args.cpp
@@ -28,9 +28,13 @@
 // RUN:   | sed 's:\\\\\?:/:g' \
 // RUN:   | FileCheck %s -DPREFIX=%/t
 
-// CHECK: "-cc1" {{.*}} 
"[[PREFIX]]/Inputs/usr/lib/x86_64-linux-gnu/../share/libc++/v1/std.cppm"
-// CHECK-SAME: "-Wno-reserved-module-identifier"
-// CHECK-SAME: "-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/"
+
+// 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;

>From cd66e7b90990f3831d4a50c0098b59186342a22e Mon Sep 17 00:00:00 2001
From: Naveen Seth Hanig <[email protected]>
Date: Thu, 2 Apr 2026 10:41:21 +0200
Subject: [PATCH 3/3] Avoid copy + const correctness

---
 clang/lib/Driver/ModulesDriver.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Driver/ModulesDriver.cpp 
b/clang/lib/Driver/ModulesDriver.cpp
index de42f4d1daa83..6dd5624fc2ae2 100644
--- a/clang/lib/Driver/ModulesDriver.cpp
+++ b/clang/lib/Driver/ModulesDriver.cpp
@@ -1283,12 +1283,12 @@ installScanCommandLines(Compilation &C,
                         ArrayRef<InputDependencies> InputDepsForScannedJobs) {
   for (auto &&[Job, InputDeps] : llvm::zip_equal(
            llvm::make_pointee_range(ScannedJobs), InputDepsForScannedJobs)) {
-    auto BuildArgs = InputDeps.BuildArgs;
+    const auto &BuildArgs = InputDeps.BuildArgs;
     ArgStringList JobArgs;
     JobArgs.reserve(BuildArgs.size());
 
     const auto &SourceAction = Job.getSource();
-    auto &TC = Job.getCreator().getToolChain();
+    const auto &TC = Job.getCreator().getToolChain();
     auto &TCArgs =
         C.getArgsForToolChain(&TC, SourceAction.getOffloadingArch(),
                               SourceAction.getOffloadingDeviceKind());

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