[MinGW] Allow using LTO when lld is used as linker

[mstorsjo]

Added a minimal testcase.

[rnk]

lgtm

lib/Driver/ToolChains/MinGW.cpp

383

I thought we supported putting paths in this option, but I see we already use this pattern almost everywhere throughout the driver, so I guess checking for the symbolic name is fine.

[mstorsjo]

lib/Driver/ToolChains/MinGW.cpp

383

Well, in ToolChain::GetLinkerPath(), we do support both an absolute path and a symbolic name, but yes, there are other checks for symbolic names as well. Not sure if we should try to guess the kind of linker from an absolute pathname though...

lib/Driver/ToolChains/MinGW.h

 
 namespace toolchains {
 
 class LLVM_LIBRARY_VISIBILITY MinGW : public ToolChain {
 public:
   MinGW(const Driver &D, const llvm::Triple &Triple,
         const llvm::opt::ArgList &Args);
 
+  bool HasNativeLLVMSupport() const override;
+
   bool IsIntegratedAssemblerDefault() const override;
   bool IsUnwindTablesDefault(const llvm::opt::ArgList &Args) const override;
   bool isPICDefault() const override;
   bool isPIEDefault() const override;
   bool isPICDefaultForced() const override;
 
   SanitizerMask getSupportedSanitizers() const override;
 
private:
   std::string GccLibDir;
   std::string Ver;
   std::string Arch;
   mutable std::unique_ptr<tools::gcc::Preprocessor> Preprocessor;
   mutable std::unique_ptr<tools::gcc::Compiler> Compiler;
   void findGccLibDir();
   llvm::ErrorOr<std::string> findGcc();
   llvm::ErrorOr<std::string> findClangRelativeSysroot();
+
+  bool NativeLLVMSupport;
 };
 
 } // end namespace toolchains
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_MINGW_H

lib/Driver/ToolChains/MinGW.cpp

 //===--- MinGW.cpp - MinGWToolChain Implementation ------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "MinGW.h"
 #include "InputInfo.h"
 #include "CommonArgs.h"
+#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
toolchains::MinGW::MinGW(const Driver &D, const llvm::Triple &Triple,
   // GccLibDir must precede Base/lib so that the
   // correct crtbegin.o ,cetend.o would be found.
   getFilePaths().push_back(GccLibDir);
   getFilePaths().push_back(
       (Base + Arch + llvm::sys::path::get_separator() + "lib").str());
   getFilePaths().push_back(Base + "lib");
   // openSUSE
   getFilePaths().push_back(Base + Arch + "/sys-root/mingw/lib");
+
+  NativeLLVMSupport =
+      Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER)
+          .equals_lower("lld");
 }
 
 bool toolchains::MinGW::IsIntegratedAssemblerDefault() const { return true; }
 
 Tool *toolchains::MinGW::getTool(Action::ActionClass AC) const {
   switch (AC) {
   case Action::PreprocessJobClass:
     if (!Preprocessor)

 Tool *toolchains::MinGW::buildAssembler() const {
   return new tools::MinGW::Assembler(*this);
 }
 
 Tool *toolchains::MinGW::buildLinker() const {
   return new tools::MinGW::Linker(*this);
 }
 
+bool toolchains::MinGW::HasNativeLLVMSupport() const {
+  return NativeLLVMSupport;
+}
+
 bool toolchains::MinGW::IsUnwindTablesDefault(const ArgList &Args) const {
   return getArch() == llvm::Triple::x86_64;
 }
 
 bool toolchains::MinGW::isPICDefault() const {
   return getArch() == llvm::Triple::x86_64;
 }
 

test/Driver/mingw-lto.c

+// The default linker doesn't support LLVM bitcode
+// RUN: not %clang -target i686-pc-windows-gnu %s -flto -fuse-ld=bfd
+// When using lld, this is allowed though.
+// RUN: %clang -target i686-pc-windows-gnu -### %s -flto -fuse-ld=lld