[CIR][link-builtin-code] This PR adds support to link in bytecodes on CC1. (#2010)

@bcardosolopes I need some advice here. Is this a valid direction, do I
respect sufficiently the original driver? If not, any pointers?

Author: koparasy

clang/lib/CIR/FrontendAction/CIRGenAction.cpp

@@ -40,6 +40,7 @@
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/DiagnosticPrinter.h"
+#include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/LLVMRemarkStreamer.h"
@@ -48,6 +49,7 @@
 #include "llvm/LTO/LTOBackend.h"
 #include "llvm/Linker/Linker.h"
 #include "llvm/Pass.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Signals.h"
@@ -127,6 +129,27 @@ class CIRGenConsumer : public clang::ASTConsumer {
   IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS;
   std::unique_ptr<CIRGenerator> Gen;
 
+  /// NOTE: LinkModule is taken from clang/include/clang/CodeGen/CodeGenAction.h
+  /// This is clearly suboptimal and we should reuse their functionality.
+  /// Info about module to link into a module we're generating.
+  struct LinkModule {
+    /// The module to link in.
+    std::unique_ptr<llvm::Module> Module;
+
+    /// If true, we set attributes on Module's functions according to our
+    /// CodeGenOptions and LangOptions, as though we were generating the
+    /// function ourselves.
+    bool PropagateAttrs;
+
+    /// If true, we use LLVM module internalizer.
+    bool Internalize;
+
+    /// Bitwise combination of llvm::LinkerFlags used when we link the module.
+    unsigned LinkFlags;
+  };
+  /// Bitcode modules to link in to our module.
+  SmallVector<LinkModule, 4> LinkModules;
+
 public:
   CIRGenConsumer(CIRGenAction::OutputType Action, class CompilerInstance &CI,
                  class DiagnosticsEngine &Diags,
@@ -344,14 +367,27 @@ class CIRGenConsumer : public clang::ASTConsumer {
     case CIRGenAction::OutputType::EmitBC:
     case CIRGenAction::OutputType::EmitObj:
     case CIRGenAction::OutputType::EmitAssembly: {
+      auto &CGOpts = CI.getCodeGenOpts();
+
       llvm::LLVMContext LlvmCtx;
+      LlvmCtx.setDefaultTargetCPU(TargetOpts.CPU);
+      LlvmCtx.setDefaultTargetFeatures(llvm::join(TargetOpts.Features, ","));
+
       bool DisableDebugInfo =
           CodeGenOpts.getDebugInfo() == llvm::codegenoptions::NoDebugInfo;
+
+      LoadLinkModules(LlvmCtx);
+
       auto LlvmModule = lowerFromCIRToLLVMIR(
           FeOptions, MlirMod, std::move(MlirCtx), LlvmCtx,
           FeOptions.ClangIRDisableCIRVerifier,
           !FeOptions.ClangIRCallConvLowering, DisableDebugInfo);
 
+      LlvmModule->setTargetTriple(llvm::Triple(CI.getTargetOpts().Triple));
+      LlvmModule->setDataLayout(C.getTargetInfo().getDataLayoutString());
+
+      LinkInModules(*LlvmModule);
+
       BackendAction BackendAction = getBackendActionFromOutputType(Action);
 
       emitBackendOutput(
@@ -364,6 +400,47 @@ class CIRGenConsumer : public clang::ASTConsumer {
     }
   }
 
+  void LoadLinkModules(llvm::LLVMContext &LlvmCtx) {
+    for (const CodeGenOptions::BitcodeFileToLink &F :
+         CI.getCodeGenOpts().LinkBitcodeFiles) {
+      auto BCBuf = CI.getFileManager().getBufferForFile(F.Filename);
+      if (!BCBuf) {
+        CI.getDiagnostics().Report(diag::err_cannot_open_file)
+            << F.Filename << BCBuf.getError().message();
+        LinkModules.clear();
+        return;
+      }
+
+      Expected<std::unique_ptr<llvm::Module>> ModuleOrErr =
+          getOwningLazyBitcodeModule(std::move(*BCBuf), LlvmCtx);
+      if (!ModuleOrErr) {
+        handleAllErrors(ModuleOrErr.takeError(), [&](llvm::ErrorInfoBase &EIB) {
+          CI.getDiagnostics().Report(diag::err_cannot_open_file)
+              << F.Filename << EIB.message();
+        });
+        LinkModules.clear();
+        return;
+      }
+      LinkModules.push_back({std::move(ModuleOrErr.get()), F.PropagateAttrs,
+                             F.Internalize, F.LinkFlags});
+    }
+    return;
+  }
+
+  // Links each entry in LinkModules into our module. Returns true on error.
+  void LinkInModules(llvm::Module &M) {
+    llvm::Linker L(M);
+
+    for (auto &LM : LinkModules) {
+      // Link the module using LLVM's linker
+      if (llvm::Linker::linkModules(M, std::move(LM.Module), LM.LinkFlags)) {
+        CI.getDiagnostics().Report(diag::err_fe_linking_module)
+            << M.getModuleIdentifier() << LM.Module->getModuleIdentifier();
+        return;
+      }
+    }
+  }
+
   void HandleTagDeclDefinition(TagDecl *D) override {
     PrettyStackTraceDecl CrashInfo(D, SourceLocation(),
                                    AstContext->getSourceManager(),

clang/test/CIR/CodeGen/link-bitcode-file.c

@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -O1 -triple x86_64-unknown-linux-gpu -fclangir -DBITCODE -emit-llvm-bc -o %t.bc %s
+// RUN: %clang_cc1 -O1 -triple x86_64-unknown-linux-gpu -fclangir -DBITCODE2 -emit-llvm-bc -o %t-2.bc %s
+// RUN: %clang_cc1 -O1 -triple x86_64-unknown-linux-gpu -fclangir -mlink-bitcode-file %t.bc \
+// RUN:     -O3 -emit-llvm -o - %s | FileCheck -check-prefix=CHECK-NO-BC %s
+// RUN: %clang_cc1 -O1 -triple x86_64-unknown-linux-gpu -fclangir -emit-llvm -o - \
+// RUN:     -mlink-bitcode-file %t.bc -mlink-bitcode-file %t-2.bc %s \
+// RUN:     | FileCheck -check-prefix=CHECK-NO-BC -check-prefix=CHECK-NO-BC2 %s
+// RUN: not %clang_cc1 -O1 -triple x86_64-unknown-linux-gpu -fclangir -DBITCODE -O3 -emit-llvm -o - \
+// RUN:     -mlink-bitcode-file %t.bc %s 2>&1 | FileCheck -check-prefix=CHECK-BC %s
+// Make sure we deal with failure to load the file.
+// RUN: not %clang_cc1 -O1 -triple x86_64-unknown-linux-gpu -fclangir -mlink-bitcode-file no-such-file.bc \
+// RUN:    -emit-llvm -o - %s 2>&1 | FileCheck -check-prefix=CHECK-NO-FILE %s
+
+
+int f(void);
+
+#ifdef BITCODE
+
+extern int f2(void);
+// CHECK-BC: error: Linking globals named {{.*}}'f': symbol multiply defined
+int f(void) {
+  f2();
+  return 42;
+}
+
+#elif BITCODE2
+int f2(void) { return 43; }
+#else
+
+// CHECK-NO-BC-LABEL: define{{.*}} i32 @g
+// CHECK-NO-BC: ret i32 42
+int g(void) {
+  return f();
+}
+
+// CHECK-NO-BC-LABEL: define{{.*}} i32 @f
+// CHECK-NO-BC2-LABEL: define{{.*}} i32 @f2
+
+#endif
+
+// CHECK-NO-FILE: fatal error: cannot open file 'no-such-file.bc'