[RFC][Clang] Allow plugins to hook into back-end

clang/include/clang/CodeGen/BackendUtil.h

@@ -10,7 +10,9 @@
 #define LLVM_CLANG_CODEGEN_BACKENDUTIL_H
 
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/IR/ModuleSummaryIndex.h"
+#include "llvm/Support/Registry.h"
 #include <memory>
 
 namespace llvm {
@@ -50,6 +52,27 @@ void EmbedBitcode(llvm::Module *M, const CodeGenOptions &CGOpts,
 
 void EmbedObject(llvm::Module *M, const CodeGenOptions &CGOpts,
                  llvm::vfs::FileSystem &VFS, DiagnosticsEngine &Diags);
+
+class BackendPlugin {
+public:
+  BackendPlugin() = default;
+  virtual ~BackendPlugin();
+
+  // Hook to run before codegen passes are executed. Return true if codegen
+  // passes should get executed as usual; return false if output was written or
+  // an error was emitted.
+  virtual bool preCodeGenModuleHook(CompilerInstance &CI, raw_pwrite_stream &OS,
+                                    llvm::Module &M) {
+    return true;
+  }
+};
+
+/// The backend plugin registry.
+using BackendPluginRegistry = llvm::Registry<BackendPlugin>;
 } // namespace clang
 
+namespace llvm {
+extern template class CLANG_TEMPLATE_ABI Registry<clang::BackendPlugin>;
+} // namespace llvm
+
 #endif

clang/lib/CodeGen/BackendUtil.cpp

@@ -49,6 +49,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/Program.h"
+#include "llvm/Support/Registry.h"
 #include "llvm/Support/TimeProfiler.h"
 #include "llvm/Support/Timer.h"
 #include "llvm/Support/ToolOutputFile.h"
@@ -96,6 +97,8 @@
 using namespace clang;
 using namespace llvm;
 
+LLVM_INSTANTIATE_REGISTRY(BackendPluginRegistry)
+
 #define HANDLE_EXTENSION(Ext)                                                  \
   llvm::PassPluginLibraryInfo get##Ext##PluginInfo();
 #include "llvm/Support/Extension.def"
@@ -1234,6 +1237,12 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
 void EmitAssemblyHelper::RunCodegenPipeline(
     BackendAction Action, std::unique_ptr<raw_pwrite_stream> &OS,
     std::unique_ptr<llvm::ToolOutputFile> &DwoOS) {
+  for (auto &Plugin : BackendPluginRegistry::entries()) {
+    std::unique_ptr<BackendPlugin> P = Plugin.instantiate();
+    if (!P->preCodeGenModuleHook(CI, *OS, *TheModule))
+      return;
+  }
+
   // We still use the legacy PM to run the codegen pipeline since the new PM
   // does not work with the codegen pipeline.
   // FIXME: make the new PM work with the codegen pipeline.
@@ -1515,3 +1524,6 @@ void clang::EmbedObject(llvm::Module *M, const CodeGenOptions &CGOpts,
                               Align(object::OffloadBinary::getAlignment()));
   }
 }
+
+// Out-of-line destructor to provide a home for the class.
+clang::BackendPlugin::~BackendPlugin() = default;