[Driver] Support linking to compiler-rt for target AVR

[benshi001]

clang/lib/Driver/ToolChains/AVR.cpp

429

1. Though I expect each device family has its own optimized build of compiler-rt binary, I found most targets such as arm/x86 use unique libclang-rt.builtins.a. So I will follow this tradition for avr, a compitable avr binary built with the minimal instruction set is used.

2. I have to explicitly inherit getCompilerRTPath, since AVR can never be a host environment, the default path $resource_dir/lib is not suitable for AVR.

[MaskRay]

clang/test/Driver/avr-toolchain.c

83

libclang_rt.builtins-avr.a is the non-longer-recommended LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=off path. Use the LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=on path.

-fuse-ld=abs/path is deprecated. Use --ld-path or carefully use -fuse-ld=lld to select lld.

[benshi001]

clang/test/Driver/avr-toolchain.c

83

Thanks. I will fix that in another review request https://reviews.llvm.org/D128133.

clang/lib/Driver/ToolChains/AVR.h

public:
 
   void
   addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                         llvm::opt::ArgStringList &CC1Args,
                         Action::OffloadKind DeviceOffloadKind) const override;
 
   llvm::Optional<std::string> findAVRLibcInstallation() const;
   StringRef getGCCInstallPath() const { return GCCInstallPath; }
+  std::string getCompilerRTPath() const override;
 
 protected:
   Tool *buildLinker() const override;
 
 private:
   StringRef GCCInstallPath;
+  std::string MCU;
 };
 
 } // end namespace toolchains
 
 namespace tools {
 namespace AVR {
 class LLVM_LIBRARY_VISIBILITY Linker : public Tool {
 public:

clang/lib/Driver/ToolChains/AVR.cpp

 #include "clang/Driver/Options.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
 
 using namespace clang::driver;
 using namespace clang::driver::toolchains;
 using namespace clang::driver::tools;
 using namespace clang;
 using namespace llvm::opt;
 
 namespace {

 } // end anonymous namespace
 
 /// AVR Toolchain
 AVRToolChain::AVRToolChain(const Driver &D, const llvm::Triple &Triple,
                            const ArgList &Args)
     : Generic_ELF(D, Triple, Args) {
   GCCInstallation.init(Triple, Args);
 
-  std::string CPU = getCPUName(D, Args, Triple);
-  if (CPU.empty())
+  MCU = getCPUName(D, Args, Triple);
+  if (MCU.empty())
     D.Diag(diag::warn_drv_avr_mcu_not_specified);
 
   // Only add default libraries if the user hasn't explicitly opted out.
   if (!Args.hasArg(options::OPT_nostdlib) &&
       !Args.hasArg(options::OPT_nodefaultlibs) && GCCInstallation.isValid()) {
     GCCInstallPath = GCCInstallation.getInstallPath();
     std::string GCCParentPath(GCCInstallation.getParentLibPath());
     getProgramPaths().push_back(GCCParentPath + "/../bin");
if (!DriverArgs.hasFlag(options::OPT_fuse_cxa_atexit,
                           options::OPT_fno_use_cxa_atexit, false))
     CC1Args.push_back("-fno-use-cxa-atexit");
 }
 
 Tool *AVRToolChain::buildLinker() const {
   return new tools::AVR::Linker(getTriple(), *this);
 }
 
+std::string AVRToolChain::getCompilerRTPath() const {
+  // Return the default path appended with device family name, such as
+  // `$RESOURCE_DIR/lib/avr5`, since we expect each device family has its
+  // own optimized compiler-rt library files.
+  // If no `-mmcu=` is specified, it falls back to the default path. However
+  // this is unexpected, since avr can not be a host environment.
+  SmallString<128> Path(ToolChain::getCompilerRTPath());
+  Optional<StringRef> FamilyName = GetMCUFamilyName(MCU);
+  if (FamilyName)
+    llvm::sys::path::append(Path, *FamilyName);
+  return std::string(Path.str());
+}
+
 void AVR::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                const InputInfo &Output,
                                const InputInfoList &Inputs, const ArgList &Args,
                                const char *LinkingOutput) const {
   const auto &TC = static_cast<const AVRToolChain &>(getToolChain());
   const Driver &D = getToolChain().getDriver();
 
   // Compute information about the target AVR.
void AVR::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   // Enable garbage collection of unused sections.
   CmdArgs.push_back("--gc-sections");
 
   // Add library search paths before we specify libraries.
   Args.AddAllArgs(CmdArgs, options::OPT_L);
   getToolChain().AddFilePathLibArgs(Args, CmdArgs);
 
+  // Currently we only support libgcc and compiler-rt.
+  auto RtLib = TC.GetRuntimeLibType(Args);
+  assert(
+      (RtLib == ToolChain::RLT_Libgcc || RtLib == ToolChain::RLT_CompilerRT) &&
+      "unknown runtime library");
+
   // Only add default libraries if the user hasn't explicitly opted out.
   bool LinkStdlib = false;
   if (!Args.hasArg(options::OPT_nostdlib) &&
       !Args.hasArg(options::OPT_nodefaultlibs)) {
     if (!CPU.empty()) {
       if (!FamilyName) {
         // We do not have an entry for this CPU in the family
         // mapping table yet.
         D.Diag(diag::warn_drv_avr_family_linking_stdlibs_not_implemented)
             << CPU;
       } else if (!AVRLibcRoot) {
         // No avr-libc found and so no runtime linked.
         D.Diag(diag::warn_drv_avr_libc_not_found);
       } else {
         std::string SubPath = GetMCUSubPath(CPU);
+        // Add path of avr-libc.
         CmdArgs.push_back(
             Args.MakeArgString(Twine("-L") + *AVRLibcRoot + "/lib/" + SubPath));
-        CmdArgs.push_back(
-            Args.MakeArgString("-L" + TC.getGCCInstallPath() + "/" + SubPath));
+        // Add path of libgcc.
+        if (RtLib == ToolChain::RLT_Libgcc)
+          CmdArgs.push_back(Args.MakeArgString("-L" + TC.getGCCInstallPath() +
+                                               "/" + SubPath));
         LinkStdlib = true;
       }
     }
     if (!LinkStdlib)
       D.Diag(diag::warn_drv_avr_stdlib_not_linked);
   }
 
   if (SectionAddressData.hasValue()) {
if (LinkStdlib) {
     assert(!CPU.empty() && "CPU name must be known in order to link stdlibs");
 
     CmdArgs.push_back("--start-group");
 
     // Add the object file for the CRT.
     std::string CrtFileName = std::string("-l:crt") + CPU + std::string(".o");
     CmdArgs.push_back(Args.MakeArgString(CrtFileName));
 
+    // Link to libgcc.
+    if (RtLib == ToolChain::RLT_Libgcc)
       CmdArgs.push_back("-lgcc");
+
+    // Link to generic libraries of avr-libc.
     CmdArgs.push_back("-lm");
     CmdArgs.push_back("-lc");
 
     // Add the link library specific to the MCU.
     CmdArgs.push_back(Args.MakeArgString(std::string("-l") + CPU));
 
     CmdArgs.push_back("--end-group");
 
+    // Link to compiler-rt.
+    if (RtLib == ToolChain::RLT_CompilerRT) {
+      std::string RtLib =
+          getToolChain().getCompilerRT(Args, "builtins", ToolChain::FT_Static);
+      if (llvm::sys::fs::exists(RtLib))
+        CmdArgs.push_back(Args.MakeArgString(RtLib));
+    }
+
     // Add user specified linker script.
     Args.AddAllArgs(CmdArgs, options::OPT_T);
 
     // Specify the family name as the emulation mode to use.
     // This is almost always required because otherwise avr-ld
     // will assume 'avr2' and warn about the program being larger
     // than the bare minimum supports.
     if (Linker.find("avr-ld") != std::string::npos)

clang/test/Driver/avr-toolchain.c

 // LLD-NOT: "-mavr5"
 
 // RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree -mmcu=atmega328 %s -T avr.lds 2>&1 | FileCheck --check-prefix=LDS0 %s
 // LDS0: "-T" "avr.lds" "-mavr5"
 
 // RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree -mmcu=atmega328 %s -fuse-ld=lld -T avr.lds 2>&1 | FileCheck --check-prefix=LDS1 %s
 // LDS1: "-T" "avr.lds"
 // LDS1-NOT: "-mavr5"
+
+// RUN: %clang %s -### --target=avr -mmcu=atmega328 --sysroot=%S/Inputs/basic_avr_tree/ -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir 2>&1 | FileCheck --check-prefix=LIBGCC %s
+// RUN: %clang %s -### --target=avr -mmcu=atmega328 --sysroot=%S/Inputs/basic_avr_tree/ -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir --rtlib=libgcc 2>&1 | FileCheck --check-prefix=LIBGCC %s
+// LIBGCC: "-lgcc"
+// LIBGCC-NOT: libclang_rt
+
+// RUN: %clang %s -### --target=avr -mmcu=atmega328 --sysroot=%S/Inputs/basic_avr_tree/ -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir --rtlib=compiler-rt 2>&1 | FileCheck --check-prefix=COMRT %s
+// COMRT: avr5/libclang_rt.builtins-avr.a
+// COMRT-NOT: "-lgcc"
+
+// RUN: %clang %s -### --target=avr --sysroot=%S/Inputs/basic_avr_tree/ -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir --rtlib=compiler-rt 2>&1 | FileCheck --check-prefix=NOMCU %s
+// RUN: %clang %s -### --target=avr --sysroot=%S/Inputs/basic_avr_tree/ -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir --rtlib=libgcc 2>&1 | FileCheck --check-prefix=NOMCU %s
+// NOMCU-NOT: libclang_rt
+// NOMCU-NOT: "-lgcc"