[MinGW] Look for a cross sysroot relative to the clang binary

[mstorsjo]

Summary

If found, prefer this over looking for a similar gcc later in the system path.

This implements what @martell suggested in D45152 in a much neater way.

Tests still are TBD, but posting this early to see if there's comments. (How do I easily do a test that checks something relative to the clang binary, since I don't control the location of the tested binary when running tests?)

[mstorsjo]

Fixed the hardcoded triplet suffix, previously I erroneously had a "-gcc" suffix there.

[mstorsjo]

Ping, any comments on the change itself, or tips on how to create a test for it?

[mstorsjo]

Ping

[rnk]

lgtm

[rnk]

Sorry, I skipped over the message and looked at the code, which seems pretty straightforward.

Tests still are TBD, but posting this early to see if there's comments. (How do I easily do a test that checks something relative to the clang binary, since I don't control the location of the tested binary when running tests?)

As much fun as it is to create sysroot subtrees in the clang test input directories and test them with -#, I don't feel like they have that much value. I've seen people write tests that do things like `mkdir -p %t/bin ... cp %clang %t/bin/clang && %t/bin/clang -#`, but it's pretty expensive, and the tests are hard to debug and modify.

[mstorsjo]

In D45504#1070198, @rnk wrote:

Sorry, I skipped over the message and looked at the code, which seems pretty straightforward.

Tests still are TBD, but posting this early to see if there's comments. (How do I easily do a test that checks something relative to the clang binary, since I don't control the location of the tested binary when running tests?)

As much fun as it is to create sysroot subtrees in the clang test input directories and test them with -#, I don't feel like they have that much value. I've seen people write tests that do things like `mkdir -p %t/bin ... cp %clang %t/bin/clang && %t/bin/clang -#`, but it's pretty expensive, and the tests are hard to debug and modify.

Yeah, I also agree that's kinda overkill. Proceeding without tests for this then.

cfe/trunk/lib/Driver/ToolChains/MinGW.h

private:
   std::string Base;
   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();
 };
 
 } // end namespace toolchains
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_MINGW_H

cfe/trunk/lib/Driver/ToolChains/MinGW.cpp

static bool findGccVersion(StringRef LibDir, std::string &GccLibDir,
   return Ver.size();
 }
 
 void toolchains::MinGW::findGccLibDir() {
   llvm::SmallVector<llvm::SmallString<32>, 2> Archs;
   Archs.emplace_back(getTriple().getArchName());
   Archs[0] += "-w64-mingw32";
   Archs.emplace_back("mingw32");
+  if (Arch.empty())
     Arch = Archs[0].str();
   // lib: Arch Linux, Ubuntu, Windows
   // lib64: openSUSE Linux
   for (StringRef CandidateLib : {"lib", "lib64"}) {
     for (StringRef CandidateArch : Archs) {
       llvm::SmallString<1024> LibDir(Base);
       llvm::sys::path::append(LibDir, CandidateLib, "gcc", CandidateArch);
       if (findGccVersion(LibDir, GccLibDir, Ver)) {
         Arch = CandidateArch;
llvm::ErrorOr<std::string> toolchains::MinGW::findGcc() {
   Gccs.emplace_back("mingw32-gcc");
   // Please do not add "gcc" here
   for (StringRef CandidateGcc : Gccs)
     if (llvm::ErrorOr<std::string> GPPName = llvm::sys::findProgramByName(CandidateGcc))
       return GPPName;
   return make_error_code(std::errc::no_such_file_or_directory);
 }
 
+llvm::ErrorOr<std::string> toolchains::MinGW::findClangRelativeSysroot() {
+  llvm::SmallVector<llvm::SmallString<32>, 2> Subdirs;
+  Subdirs.emplace_back(getTriple().str());
+  Subdirs.emplace_back(getTriple().getArchName());
+  Subdirs[1] += "-w64-mingw32";
+  Twine ClangRoot =
+      llvm::sys::path::parent_path(getDriver().getInstalledDir()) +
+      llvm::sys::path::get_separator();
+  for (StringRef CandidateSubdir : Subdirs) {
+    Twine Subdir = ClangRoot + CandidateSubdir;
+    if (llvm::sys::fs::is_directory(Subdir)) {
+      Arch = CandidateSubdir;
+      return Subdir.str();
+    }
+  }
+  return make_error_code(std::errc::no_such_file_or_directory);
+}
+
 toolchains::MinGW::MinGW(const Driver &D, const llvm::Triple &Triple,
                          const ArgList &Args)
     : ToolChain(D, Triple, Args), CudaInstallation(D, Triple, Args) {
   getProgramPaths().push_back(getDriver().getInstalledDir());
 
   if (getDriver().SysRoot.size())
     Base = getDriver().SysRoot;
+  // Look for <clang-bin>/../<triplet>; if found, use <clang-bin>/.. as the
+  // base as it could still be a base for a gcc setup with libgcc.
+  else if (llvm::ErrorOr<std::string> TargetSubdir = findClangRelativeSysroot())
+    Base = llvm::sys::path::parent_path(TargetSubdir.get());
   else if (llvm::ErrorOr<std::string> GPPName = findGcc())
     Base = llvm::sys::path::parent_path(
         llvm::sys::path::parent_path(GPPName.get()));
   else
     Base = llvm::sys::path::parent_path(getDriver().getInstalledDir());
 
   Base += llvm::sys::path::get_separator();
   findGccLibDir();