[flang] Add -mlink-builtin-bitcode option to fc1 (#94763)

This patch enables the -mlink-builtin-bitcode flag in fc1 so that
bitcode libraries can be linked in. This is needed for OpenMP offloading
libraries.

clang/include/clang/Driver/Options.td

@@ -7036,6 +7036,12 @@ def as_secure_log_file : Separate<["-"], "as-secure-log-file">,
 
 } // let Visibility = [CC1Option, CC1AsOption]
 
+let Visibility = [CC1Option, FC1Option] in {
+def mlink_builtin_bitcode : Separate<["-"], "mlink-builtin-bitcode">,
+  HelpText<"Link and internalize needed symbols from the given bitcode file "
+           "before performing optimizations.">;
+} // let Visibility = [CC1Option, FC1Option]
+
 let Visibility = [CC1Option] in {
 
 def llvm_verify_each : Flag<["-"], "llvm-verify-each">,
@@ -7138,9 +7144,6 @@ defm constructor_aliases : BoolMOption<"constructor-aliases",
           " emitting complete constructors and destructors as aliases when possible">>;
 def mlink_bitcode_file : Separate<["-"], "mlink-bitcode-file">,
   HelpText<"Link the given bitcode file before performing optimizations.">;
-def mlink_builtin_bitcode : Separate<["-"], "mlink-builtin-bitcode">,
-  HelpText<"Link and internalize needed symbols from the given bitcode file "
-           "before performing optimizations.">;
 defm link_builtin_bitcode_postopt: BoolMOption<"link-builtin-bitcode-postopt",
   CodeGenOpts<"LinkBitcodePostopt">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption], "Link builtin bitcodes after the "

flang/include/flang/Frontend/CodeGenOptions.h

@@ -56,6 +56,10 @@ public:
   /// are offloading binaries containing device images and metadata.
   std::vector<std::string> OffloadObjects;
 
+  /// List of filenames passed in using the -mlink-builtin-bitcode. These
+  /// are bc libraries that should be linked in and internalized;
+  std::vector<std::string> BuiltinBCLibs;
+
   /// The directory where temp files are stored if specified by -save-temps
   std::optional<std::string> SaveTempsDir;
 

flang/include/flang/Frontend/FrontendActions.h

@@ -223,9 +223,12 @@ protected:
   std::unique_ptr<llvm::LLVMContext> llvmCtx;
   std::unique_ptr<llvm::Module> llvmModule;
 
-  /// Embeds offload objects given with specified with -fembed-offload-object
+  /// Embeds offload objects specified with -fembed-offload-object
   void embedOffloadObjects();
 
+  /// Links in BC libraries spefified with -mlink-builtin-bitcode
+  void linkBuiltinBCLibs();
+
   /// Runs pass pipeline to lower HLFIR into FIR
   void lowerHLFIRToFIR();
 

flang/lib/Frontend/CompilerInvocation.cpp

@@ -347,6 +347,11 @@ static void parseCodeGenArgs(Fortran::frontend::CodeGenOptions &opts,
   if (auto *a = args.getLastArg(clang::driver::options::OPT_save_temps_EQ))
     opts.SaveTempsDir = a->getValue();
 
+  // -mlink-builtin-bitcode
+  for (auto *a :
+       args.filtered(clang::driver::options::OPT_mlink_builtin_bitcode))
+    opts.BuiltinBCLibs.push_back(a->getValue());
+
   // -mrelocation-model option.
   if (const llvm::opt::Arg *a =
           args.getLastArg(clang::driver::options::OPT_mrelocation_model)) {

flang/lib/Frontend/FrontendActions.cpp

@@ -43,6 +43,8 @@
 #include "mlir/Target/LLVMIR/ModuleTranslation.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/DiagnosticFrontend.h"
+#include "clang/Basic/FileManager.h"
+#include "clang/Basic/FileSystemOptions.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringRef.h"
@@ -55,6 +57,7 @@
 #include "llvm/IR/Verifier.h"
 #include "llvm/IRPrinter/IRPrintingPasses.h"
 #include "llvm/IRReader/IRReader.h"
+#include "llvm/Linker/Linker.h"
 #include "llvm/Object/OffloadBinary.h"
 #include "llvm/Passes/PassBuilder.h"
 #include "llvm/Passes/PassPlugin.h"
@@ -69,6 +72,7 @@
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/TargetParser/RISCVISAInfo.h"
 #include "llvm/TargetParser/RISCVTargetParser.h"
+#include "llvm/Transforms/IPO/Internalize.h"
 #include "llvm/Transforms/Utils/ModuleUtils.h"
 #include <memory>
 #include <system_error>
@@ -1149,6 +1153,54 @@ void CodeGenAction::embedOffloadObjects() {
   }
 }
 
+void CodeGenAction::linkBuiltinBCLibs() {
+  auto options = clang::FileSystemOptions();
+  clang::FileManager fileManager(options);
+  CompilerInstance &ci = this->getInstance();
+  const auto &cgOpts = ci.getInvocation().getCodeGenOpts();
+
+  std::vector<std::unique_ptr<llvm::Module>> modules;
+
+  // Load LLVM modules
+  for (llvm::StringRef bcLib : cgOpts.BuiltinBCLibs) {
+    auto BCBuf = fileManager.getBufferForFile(bcLib);
+    if (!BCBuf) {
+      auto diagID = ci.getDiagnostics().getCustomDiagID(
+          clang::DiagnosticsEngine::Error, "could not open '%0' for linking");
+      ci.getDiagnostics().Report(diagID) << bcLib;
+      return;
+    }
+
+    llvm::Expected<std::unique_ptr<llvm::Module>> ModuleOrErr =
+        getOwningLazyBitcodeModule(std::move(*BCBuf), *llvmCtx);
+    if (!ModuleOrErr) {
+      auto diagID = ci.getDiagnostics().getCustomDiagID(
+          clang::DiagnosticsEngine::Error, "error loading '%0' for linking");
+      ci.getDiagnostics().Report(diagID) << bcLib;
+      return;
+    }
+    modules.push_back(std::move(ModuleOrErr.get()));
+  }
+
+  // Link modules and internalize functions
+  for (auto &module : modules) {
+    bool Err;
+    Err = llvm::Linker::linkModules(
+        *llvmModule, std::move(module), llvm::Linker::Flags::LinkOnlyNeeded,
+        [](llvm::Module &M, const llvm::StringSet<> &GVS) {
+          llvm::internalizeModule(M, [&GVS](const llvm::GlobalValue &GV) {
+            return !GV.hasName() || (GVS.count(GV.getName()) == 0);
+          });
+        });
+    if (Err) {
+      auto diagID = ci.getDiagnostics().getCustomDiagID(
+          clang::DiagnosticsEngine::Error, "link error when linking '%0'");
+      ci.getDiagnostics().Report(diagID) << module->getSourceFileName();
+      return;
+    }
+  }
+}
+
 static void reportOptRecordError(llvm::Error e, clang::DiagnosticsEngine &diags,
                                  const CodeGenOptions &codeGenOpts) {
   handleAllErrors(
@@ -1240,6 +1292,10 @@ void CodeGenAction::executeAction() {
   llvmModule->setTargetTriple(theTriple);
   llvmModule->setDataLayout(targetMachine.createDataLayout());
 
+  // Link in builtin bitcode libraries
+  if (!codeGenOpts.BuiltinBCLibs.empty())
+    linkBuiltinBCLibs();
+
   // Embed offload objects specified with -fembed-offload-object
   if (!codeGenOpts.OffloadObjects.empty())
     embedOffloadObjects();

flang/test/Driver/Inputs/libfun.f90

@@ -0,0 +1,4 @@
+subroutine libfun(x)
+  integer :: x
+end subroutine
+

flang/test/Driver/mlink-builtin-bc.f90

@@ -0,0 +1,15 @@
+! Test -mlink-builtin-bitcode flag
+! RUN: %flang -emit-llvm -c -o %t.bc %S/Inputs/libfun.f90
+! RUN: %flang_fc1 -emit-llvm -o - -mlink-builtin-bitcode %t.bc %s 2>&1 | FileCheck %s
+
+! CHECK: define internal void @libfun_
+
+! RUN: not %flang_fc1 -emit-llvm -o - -mlink-builtin-bitcode %no-%t.bc %s 2>&1 | FileCheck %s --check-prefix=ERROR
+
+! ERROR: error: could not open {{.*}}.bc
+
+external libfun
+parameter(i=1)
+integer :: j
+call libfun(j)
+end program