[clang] [MinGW] Improve detection of libstdc++ headers on Fedora

[mstorsjo]

Summary

There's some variation in where different toolchain distributions
(and linux distributions) package the mingw sysroots - this is
so far handled by adding specific known subdirectory paths
to the include and lib directory lists.

There are multiple degrees of combinatorics involved here though;
the distros may use different locations such as
/usr/x86_64-w64-mingw32/include or
/usr/x86_64-w64-mingw32/sys-root/mingw/include.

So far, this setup has been treated as base=/usr, subdir=x86_64-w64-mingw32,
and the driver tries to add further subdirectories such as
<base>/<subdir>/include, <base>/<subdir>/sys-root/mingw/include.

When it comes to libstdc++ (and libc++), each of these come with
a large number of potential subdirectories. Instead of further
exploding the combinatorics another step by adding all combinations
of all paths, check whether <base>/<subdir>/sys-root/mingw/include
exists, and if it does, append that subpath into the subdir variable.

This allows finding libstdc++ headers in e.g.
/usr/x86_64-w64-mingw32/sys-root/mingw/include/c++/x86_64-w64-mingw32
on Fedora.

The same logic (where everything belonging to this target fits
under one expanded <subdir> path, with just /include and /lib
under it) doesn't seem to apply on Gentoo, where the includes
are found in <base>/<subdir>/usr/include while the libraries
are in <base>/<subdir>/mingw/lib (see
8e218026f8d5eabfdef9141ae5e26aa91d1933e6). But apparently
the libstdc++ headers aren't installed under
<base>/<subdir>/usr/include, so that path hierarchy quirk doesn't
need to be taken into account in AddClangCXXStdlibIncludeArgs.

[mati865]

LGTM

clang/lib/Driver/ToolChains/MinGW.h

private:
   CudaInstallationDetector CudaInstallation;
   RocmInstallationDetector RocmInstallation;
 
   std::string Base;
   std::string GccLibDir;
   clang::driver::toolchains::Generic_GCC::GCCVersion GccVer;
   std::string Ver;
   std::string SubdirName;
+  std::string TripleDirName;
   mutable std::unique_ptr<tools::gcc::Preprocessor> Preprocessor;
   mutable std::unique_ptr<tools::gcc::Compiler> Compiler;
   void findGccLibDir(const llvm::Triple &LiteralTriple);
 
   bool NativeLLVMSupport;
 };
 
 } // end namespace toolchains
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_MINGW_H

clang/lib/Driver/ToolChains/MinGW.cpp

else if (llvm::ErrorOr<std::string> GPPName =
     Base = std::string(llvm::sys::path::parent_path(
         llvm::sys::path::parent_path(GPPName.get())));
   else
     Base = std::string(
         llvm::sys::path::parent_path(getDriver().getInstalledDir()));
 
   Base += llvm::sys::path::get_separator();
   findGccLibDir(LiteralTriple);
+  TripleDirName = SubdirName;
   // GccLibDir must precede Base/lib so that the
   // correct crtbegin.o ,cetend.o would be found.
   getFilePaths().push_back(GccLibDir);
+
+  // openSUSE/Fedora
+  std::string CandidateSubdir = SubdirName + "/sys-root/mingw";
+  if (getDriver().getVFS().exists(Base + CandidateSubdir))
+    SubdirName = CandidateSubdir;
+
   getFilePaths().push_back(
       (Base + SubdirName + llvm::sys::path::get_separator() + "lib").str());
 
   // Gentoo
   getFilePaths().push_back(
       (Base + SubdirName + llvm::sys::path::get_separator() + "mingw/lib").str());
 
   getFilePaths().push_back(Base + "lib");
-  // openSUSE
-  getFilePaths().push_back(Base + SubdirName + "/sys-root/mingw/lib");
 
   NativeLLVMSupport =
       Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER)
           .equals_insensitive("lld");
 }
 
 bool toolchains::MinGW::IsIntegratedAssemblerDefault() const { return true; }
 
if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<1024> P(getDriver().ResourceDir);
     llvm::sys::path::append(P, "include");
     addSystemInclude(DriverArgs, CC1Args, P.str());
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  if (GetRuntimeLibType(DriverArgs) == ToolChain::RLT_Libgcc) {
-    // openSUSE
-    addSystemInclude(DriverArgs, CC1Args,
-                     Base + SubdirName + "/sys-root/mingw/include");
-  }
-
   addSystemInclude(DriverArgs, CC1Args,
                    Base + SubdirName + llvm::sys::path::get_separator() +
                        "include");
 
   // Gentoo
   addSystemInclude(DriverArgs, CC1Args,
                    Base + SubdirName + llvm::sys::path::get_separator() + "usr/include");
 
case ToolChain::CST_Libstdcxx:
     llvm::sys::path::append(CppIncludeBases[5], "include",
                             "g++-v" + GccVer.MajorStr + "." + GccVer.MinorStr);
     CppIncludeBases.emplace_back(GccLibDir);
     llvm::sys::path::append(CppIncludeBases[6], "include",
                             "g++-v" + GccVer.MajorStr);
     for (auto &CppIncludeBase : CppIncludeBases) {
       addSystemInclude(DriverArgs, CC1Args, CppIncludeBase);
       CppIncludeBase += Slash;
-      addSystemInclude(DriverArgs, CC1Args, CppIncludeBase + SubdirName);
+      addSystemInclude(DriverArgs, CC1Args, CppIncludeBase + TripleDirName);
       addSystemInclude(DriverArgs, CC1Args, CppIncludeBase + "backward");
     }
     break;
   }
 }
 
 static bool testTriple(const Driver &D, const llvm::Triple &Triple,
                        const ArgList &Args) {

clang/test/Driver/mingw.cpp

 // RUN: %clang -target x86_64-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_opensuse_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_OPENSUSE_TREE %s
 // CHECK_MINGW_OPENSUSE_TREE: "[[BASE:[^"]+]]/Inputs/mingw_opensuse_tree/usr{{/|\\\\}}lib64{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}5.1.0{{/|\\\\}}include{{/|\\\\}}c++"
 // CHECK_MINGW_OPENSUSE_TREE: "[[BASE]]/Inputs/mingw_opensuse_tree/usr{{/|\\\\}}lib64{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}5.1.0{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}x86_64-w64-mingw32"
 // CHECK_MINGW_OPENSUSE_TREE: "[[BASE]]/Inputs/mingw_opensuse_tree/usr{{/|\\\\}}lib64{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}5.1.0{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}backward"
 // CHECK_MINGW_OPENSUSE_TREE: "[[BASE]]/Inputs/mingw_opensuse_tree/usr{{/|\\\\}}x86_64-w64-mingw32/sys-root/mingw/include"
 
 
 // RUN: %clang -target x86_64-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_fedora_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_FEDORA_TREE %s
-// CHECK_MINGW_FEDORA_TREE: "[[BASE:[^"]+]]/Inputs/mingw_fedora_tree/usr{{/|\\\\}}x86_64-w64-mingw32ucrt/sys-root/mingw/include"
+// CHECK_MINGW_FEDORA_TREE: "[[BASE:[^"]+]]/Inputs/mingw_fedora_tree/usr{{/|\\\\}}x86_64-w64-mingw32ucrt/sys-root/mingw/include/c++"
+// CHECK_MINGW_FEDORA_TREE: "[[BASE]]/Inputs/mingw_fedora_tree/usr{{/|\\\\}}x86_64-w64-mingw32ucrt/sys-root/mingw/include/c++/x86_64-w64-mingw32ucrt"
+// CHECK_MINGW_FEDORA_TREE: "[[BASE]]/Inputs/mingw_fedora_tree/usr{{/|\\\\}}x86_64-w64-mingw32ucrt/sys-root/mingw/include/c++/backward"
+// CHECK_MINGW_FEDORA_TREE: "[[BASE]]/Inputs/mingw_fedora_tree/usr{{/|\\\\}}x86_64-w64-mingw32ucrt/sys-root/mingw/include"
 
 
 // RUN: %clang -target i686-pc-windows-gnu -rtlib=platform -stdlib=libstdc++ -c -### --sysroot=%S/Inputs/mingw_arch_tree/usr %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_ARCH_TREE %s
 // CHECK_MINGW_ARCH_TREE: "[[BASE:[^"]+]]/Inputs/mingw_arch_tree/usr{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}5.1.0"
 // CHECK_MINGW_ARCH_TREE: "[[BASE]]/Inputs/mingw_arch_tree/usr{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}5.1.0{{/|\\\\}}i686-w64-mingw32"
 // CHECK_MINGW_ARCH_TREE: "[[BASE]]/Inputs/mingw_arch_tree/usr{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}5.1.0{{/|\\\\}}backward"
 // CHECK_MINGW_ARCH_TREE: "[[BASE]]/Inputs/mingw_arch_tree/usr{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include"