llvm · ilya-biryukov · Apr 16, 2024
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
@@ -3179,6 +3179,12 @@ def fmodule_map_file : Joined<["-"], "fmodule-map-file=">,
   MetaVarName<"<file>">,
   HelpText<"Load this module map file">,
   MarshallingInfoStringVector<FrontendOpts<"ModuleMapFiles">>;
+def flate_module_map_file : Joined<["-"], "flate-module-map-file=">,
+  Group<f_Group>,
+  Visibility<[CC1Option]>,
+  MetaVarName<"<file>">,
+  HelpText<"Load this module map file after all modules">,
+  MarshallingInfoStringVector<FrontendOpts<"LateModuleMapFiles">>;
 def fmodule_file : Joined<["-"], "fmodule-file=">,
   Group<i_Group>,
   Visibility<[ClangOption, CC1Option, CLOption]>,

diff --git a/clang/include/clang/Frontend/FrontendOptions.h b/clang/include/clang/Frontend/FrontendOptions.h
@@ -536,6 +536,9 @@ class FrontendOptions {
   /// The list of module map files to load before processing the input.
   std::vector<std::string> ModuleMapFiles;
 
+  /// \brief The list of module map files to load after ModuleFile.
+  std::vector<std::string> LateModuleMapFiles;
+
   /// The list of additional prebuilt module files to load before
   /// processing the input.
   std::vector<std::string> ModuleFiles;

diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
@@ -919,14 +919,17 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
   if (!BeginSourceFileAction(CI))
     return false;
 
-  // If we were asked to load any module map files, do so now.
-  for (const auto &Filename : CI.getFrontendOpts().ModuleMapFiles) {
+  auto LoadModuleMap = [&](StringRef Filename) {
     if (auto File = CI.getFileManager().getOptionalFileRef(Filename))
       CI.getPreprocessor().getHeaderSearchInfo().loadModuleMapFile(
           *File, /*IsSystem*/false);
     else
       CI.getDiagnostics().Report(diag::err_module_map_not_found) << Filename;
-  }
+  };
+  // If we were asked to load any module map files, do so now.
+  for (StringRef Filename : CI.getFrontendOpts().ModuleMapFiles)
+    LoadModuleMap(Filename);
+  // Note that late module maps will be loaded after modules.
 
   // If compiling implementation of a module, load its module map file now.
   (void)CI.getPreprocessor().getCurrentModuleImplementation();
@@ -1038,6 +1041,11 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
           diag::warn_eagerly_load_for_standard_cplusplus_modules);
   }
 
+  // Some module maps are loaded after modules to allow avoiding redundant
+  // processing if they were processed by modules.
+  for (StringRef Filename : CI.getFrontendOpts().LateModuleMapFiles)
+    LoadModuleMap(Filename);
+
   // If there is a layout overrides file, attach an external AST source that
   // provides the layouts from that file.
   if (!CI.getFrontendOpts().OverrideRecordLayoutsFile.empty() &&

diff --git a/clang/lib/Frontend/Rewrite/FrontendActions.cpp b/clang/lib/Frontend/Rewrite/FrontendActions.cpp
@@ -255,6 +255,7 @@ class RewriteIncludesAction::RewriteImportsListener : public ASTReaderListener {
         Filename, InputKind(Language::Unknown, InputKind::Precompiled));
     Instance.getFrontendOpts().ModuleFiles.clear();
     Instance.getFrontendOpts().ModuleMapFiles.clear();
+    Instance.getFrontendOpts().LateModuleMapFiles.clear();
     // Don't recursively rewrite imports. We handle them all at the top level.
     Instance.getPreprocessorOutputOpts().RewriteImports = false;
 

diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
@@ -3130,7 +3130,10 @@ bool ModuleMap::parseModuleMapFile(FileEntryRef File, bool IsSystem,
   if (ID.isInvalid()) {
     auto FileCharacter =
         IsSystem ? SrcMgr::C_System_ModuleMap : SrcMgr::C_User_ModuleMap;
-    ID = SourceMgr.createFileID(File, ExternModuleLoc, FileCharacter);
+    if (ExternModuleLoc.isValid())
+      ID = SourceMgr.createFileID(File, ExternModuleLoc, FileCharacter);
+    else // avoid creating redundant FileIDs, they take sloc space in PCMs.
+      ID = SourceMgr.getOrCreateFileID(File, FileCharacter);
   }
 
   assert(Target && "Missing target information");

diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -242,6 +242,8 @@ ModuleDepCollector::getInvocationAdjustedForModuleBuildWithoutOutputs(
   // Remove directly passed modulemap files. They will get added back if they
   // were actually used.
   CI.getMutFrontendOpts().ModuleMapFiles.clear();
+  // Late module maps can only be readded into ModuleMapFiles.
+  CI.getMutFrontendOpts().LateModuleMapFiles.clear();
 
   auto DepModuleMapFiles = collectModuleMapFiles(Deps.ClangModuleDeps);
   for (StringRef ModuleMapFile : Deps.ModuleMapFileDeps) {

diff --git a/clang/test/Modules/late-module-maps.cpp b/clang/test/Modules/late-module-maps.cpp
@@ -0,0 +1,93 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// We need to check we don't waste source location space for the same file
+// (i.e. base.modulemap) when it's passed to multiple PCM file.
+//
+// *** First, try to use normal module map files.
+// RUN: %clang_cc1 -fmodules -fno-implicit-modules \
+// RUN:   -fmodule-map-file=%t/base.modulemap -fmodule-map-file=%t/a.modulemap \
+// RUN:   -fmodule-name=a -xc++ -emit-module -o %t/a.pcm %t/a.modulemap
+
+// RUN: %clang_cc1 -fmodules -fno-implicit-modules \
+// RUN:   -fmodule-map-file=%t/base.modulemap -fmodule-map-file=%t/a.modulemap -fmodule-map-file=%t/b.modulemap \
+// RUN:   -fmodule-file=%t/a.pcm \
+// RUN:   -fmodule-name=b -xc++ -emit-module -o %t/b.pcm %t/b.modulemap
+
+// RUN: %clang_cc1 -fmodules -fno-implicit-modules \
+// RUN:   -fmodule-map-file=%t/base.modulemap -fmodule-map-file=%t/a.modulemap -fmodule-map-file=%t/b.modulemap \
+// RUN:   -fmodule-file=%t/a.pcm -fmodule-file=%t/b.pcm \
+// RUN:   -fsyntax-only -print-stats %t/use.cpp 2>&1 \
+// RUN:      | FileCheck %t/use.cpp
+
+// *** Switch to -flate-module-map-file and check it produces less loaded SLO entries.
+// RUN: rm %t/*.pcm
+
+// RUN: %clang_cc1 -fmodules -fno-implicit-modules \
+// RUN:   -flate-module-map-file=%t/base.modulemap -flate-module-map-file=%t/a.modulemap \
+// RUN:   -fmodule-name=a -xc++ -emit-module -o %t/a.pcm %t/a.modulemap
+
+// RUN: %clang_cc1 -fmodules -fno-implicit-modules \
+// RUN:   -flate-module-map-file=%t/base.modulemap -flate-module-map-file=%t/a.modulemap -flate-module-map-file=%t/b.modulemap \
+// RUN:   -fmodule-file=%t/a.pcm \
+// RUN:   -fmodule-name=b -xc++ -emit-module -o %t/b.pcm %t/b.modulemap
+
+// RUN: %clang_cc1 -fmodules -fno-implicit-modules \
+// RUN:   -flate-module-map-file=%t/base.modulemap -flate-module-map-file=%t/a.modulemap -flate-module-map-file=%t/b.modulemap \
+// RUN:   -fmodule-file=%t/a.pcm -fmodule-file=%t/b.pcm \
+// RUN:   -fsyntax-only -print-stats %t/use.cpp 2>&1 \
+// RUN:      | FileCheck --check-prefix=CHECK-LATE %t/use.cpp
+
+//--- use.cpp
+// This is a very shaky check, it would be nice if it was more directly looking at which files were loaded.
+// We load 2 SLocEntries less with flate-module-map-file, they correspond to savings from base.modulemap and a.modulemap
+// reusing the FileID in a.pcm and b.pcm.
+// We also have 3 less local SLocEntries, because we get to reuse FileIDs all module maps from PCMs.
+//
+// CHECK: Source Manager Stats:
+// CHECK: 7 local SLocEntries
+// CHECK: 13 loaded SLocEntries
+
+// CHECK-LATE: Source Manager Stats:
+// CHECK-LATE: 4 local SLocEntries
+// CHECK-LATE: 11 loaded SLocEntries
+#include "a.h"
+#include "b.h"
+#include "assert.h"
+
+int main() {
+    return a() + b();
+}
+
+//--- base.modulemap
+module "base" {
+    textual header "assert.h"
+}
+
+//--- a.modulemap
+module "a" {
+    header "a.h"
+    use "base"
+}
+
+//--- b.modulemap
+module "b" {
+    header "b.h"
+    use "a"
+    use "base"
+}
+
+
+//--- assert.h
+#define ASSERT
+
+//--- a.h
+#include "assert.h"
+inline int a() { return 1; }
+
+//--- b.h
+#include "a.h"
+#include "assert.h"
+
+inline int b() { return a() + 1; }
+