[clang][deps] Support object files

[jansvoboda11]

Summary

When a project uses PCH with explicit modules, the build will look like this:

1. scan PCH dependencies
2. explicitly build PCH
3. scan TU dependencies
4. explicitly build TU

Step 2 produces an object file for the PCH, which the dependency scanner needs to read in step 3. This patch adds support for this.

The clang-scan-deps invocation in the attached test would fail without this change.

Depends on D103516.

[Bigcheese]

lgtm

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

161–162

This should have a comment that we don't actually write out any PCHs, but this is still needed due to how things are currently implemented.

clang/lib/Tooling/DependencyScanning/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
+  ${LLVM_TARGETS_TO_BUILD}
   Core
   Support
   )
 
 add_clang_library(clangDependencyScanning
   DependencyScanningFilesystem.cpp
   DependencyScanningService.cpp
   DependencyScanningWorker.cpp
   DependencyScanningTool.cpp
   ModuleDepCollector.cpp
 
   DEPENDS
   ClangDriverOptions
 
   LINK_LIBS
   clangAST
   clangBasic
+  clangCodeGen
   clangDriver
   clangFrontend
   clangFrontendTool
   clangLex
   clangParse
   clangSerialization
   clangTooling
 )

clang/lib/Tooling/DependencyScanning/DependencyScanningService.cpp

 //===- DependencyScanningService.cpp - clang-scan-deps service ------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Tooling/DependencyScanning/DependencyScanningService.h"
+#include "llvm/Support/TargetSelect.h"
 
 using namespace clang;
 using namespace tooling;
 using namespace dependencies;
 
 DependencyScanningService::DependencyScanningService(
     ScanningMode Mode, ScanningOutputFormat Format, bool ReuseFileManager,
     bool SkipExcludedPPRanges)
     : Mode(Mode), Format(Format), ReuseFileManager(ReuseFileManager),
-      SkipExcludedPPRanges(SkipExcludedPPRanges) {}
+      SkipExcludedPPRanges(SkipExcludedPPRanges) {
+  // Initialize targets for object file support.
+  llvm::InitializeAllTargets();
+  llvm::InitializeAllTargetMCs();
+  llvm::InitializeAllAsmPrinters();
+  llvm::InitializeAllAsmParsers();
+}

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

 //===- DependencyScanningWorker.cpp - clang-scan-deps worker --------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Tooling/DependencyScanning/DependencyScanningWorker.h"
+#include "clang/CodeGen/ObjectFilePCHContainerOperations.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Frontend/FrontendActions.h"
 #include "clang/Frontend/TextDiagnosticPrinter.h"
 #include "clang/Frontend/Utils.h"
 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Tooling/DependencyScanning/DependencyScanningService.h"
 #include "clang/Tooling/DependencyScanning/ModuleDepCollector.h"

 };
 
 } // end anonymous namespace
 
 DependencyScanningWorker::DependencyScanningWorker(
     DependencyScanningService &Service)
     : Format(Service.getFormat()) {
   DiagOpts = new DiagnosticOptions();
+
   PCHContainerOps = std::make_shared<PCHContainerOperations>();
+  PCHContainerOps->registerReader(
+      std::make_unique<ObjectFilePCHContainerReader>());
+  PCHContainerOps->registerWriter(
+      std::make_unique<ObjectFilePCHContainerWriter>());
+
   RealFS = llvm::vfs::createPhysicalFileSystem();
   if (Service.canSkipExcludedPPRanges())
     PPSkipMappings =
         std::make_unique<ExcludedPreprocessorDirectiveSkipMapping>();
   if (Service.getMode() == ScanningMode::MinimizedSourcePreprocessing)
     DepFS = new DependencyScanningWorkerFilesystem(
         Service.getSharedCache(), RealFS, PPSkipMappings.get());
   if (Service.canReuseFileManager())

clang/test/ClangScanDeps/Inputs/modules-pch/cdb_tu.json

+[
+  {
+    "directory": "DIR",
+    "command": "clang -fsyntax-only DIR/tu.c -fmodules -gmodules -fimplicit-module-maps -fmodules-cache-path=DIR/cache -include DIR/pch.h -o DIR/tu.o",
+    "file": "DIR/tu.c"
+  }
+]

clang/test/ClangScanDeps/Inputs/modules-pch/mod_tu.h

+// mod_tu.h

clang/test/ClangScanDeps/Inputs/modules-pch/module.modulemap

+module ModTU {
+    header "mod_tu.h"
+}

clang/test/ClangScanDeps/Inputs/modules-pch/pch.h

+// pch.h

clang/test/ClangScanDeps/Inputs/modules-pch/tu.c

+// tu.c
+
+#include "mod_tu.h"

clang/test/ClangScanDeps/modules-pch.c

+// RUN: rm -rf %t && mkdir %t
+// RUN: cp %S/Inputs/modules-pch/* %t
+
+// Explicitly build the PCH:
+//
+// RUN: %clang -x c-header %t/pch.h -fmodules -gmodules -fimplicit-module-maps \
+// RUN:   -fmodules-cache-path=%t/cache -o %t/pch.h.gch
+
+// Scan dependencies of the TU:
+//
+// RUN: sed "s|DIR|%/t|g" %S/Inputs/modules-pch/cdb_tu.json > %t/cdb_tu.json
+// RUN: clang-scan-deps -compilation-database %t/cdb_tu.json -format experimental-full \
+// RUN:   -generate-modules-path-args -build-dir %t/build