[Clang] [Driver] add a Cygwin ToolChain (llvm#135691)

Add a new Cygwin toolchain that just goes through the motions to
initialize the Generic_GCC base properly. This allows removing some old,
almost certainly wrong hard-coded paths from Lex/InitHeaderSearch.cpp.

MSYS2 (GCC triple (arch)-pc-msys) is a fork of Cygwin (GCC triple
(arch)-pc-cygwin), and this driver can be used for either.

Add a simple test for this driver.

Author: jeremyd2019

clang/lib/Driver/CMakeLists.txt

@@ -51,6 +51,7 @@ add_clang_library(clangDriver
   ToolChains/CrossWindows.cpp
   ToolChains/CSKYToolChain.cpp
   ToolChains/Cuda.cpp
+  ToolChains/Cygwin.cpp
   ToolChains/Darwin.cpp
   ToolChains/DragonFly.cpp
   ToolChains/Flang.cpp

clang/lib/Driver/Driver.cpp

@@ -17,6 +17,7 @@
 #include "ToolChains/Clang.h"
 #include "ToolChains/CrossWindows.h"
 #include "ToolChains/Cuda.h"
+#include "ToolChains/Cygwin.h"
 #include "ToolChains/Darwin.h"
 #include "ToolChains/DragonFly.h"
 #include "ToolChains/FreeBSD.h"
@@ -6692,6 +6693,9 @@ const ToolChain &Driver::getToolChain(const ArgList &Args,
       case llvm::Triple::GNU:
         TC = std::make_unique<toolchains::MinGW>(*this, Target, Args);
         break;
+      case llvm::Triple::Cygnus:
+        TC = std::make_unique<toolchains::Cygwin>(*this, Target, Args);
+        break;
       case llvm::Triple::Itanium:
         TC = std::make_unique<toolchains::CrossWindowsToolChain>(*this, Target,
                                                                   Args);

clang/lib/Driver/ToolChains/Cygwin.cpp

@@ -0,0 +1,109 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "Cygwin.h"
+#include "CommonArgs.h"
+#include "clang/Config/config.h"
+#include "clang/Driver/Driver.h"
+#include "clang/Driver/Options.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/VirtualFileSystem.h"
+
+using namespace clang::driver;
+using namespace clang::driver::toolchains;
+using namespace clang;
+using namespace llvm::opt;
+
+using tools::addPathIfExists;
+
+Cygwin::Cygwin(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+    : Generic_GCC(D, Triple, Args) {
+  GCCInstallation.init(Triple, Args);
+  std::string SysRoot = computeSysRoot();
+  ToolChain::path_list &PPaths = getProgramPaths();
+
+  Generic_GCC::PushPPaths(PPaths);
+
+  path_list &Paths = getFilePaths();
+
+  Generic_GCC::AddMultiarchPaths(D, SysRoot, "lib", Paths);
+
+  // Similar to the logic for GCC above, if we are currently running Clang
+  // inside of the requested system root, add its parent library path to those
+  // searched.
+  // FIXME: It's not clear whether we should use the driver's installed
+  // directory ('Dir' below) or the ResourceDir.
+  if (StringRef(D.Dir).starts_with(SysRoot))
+    addPathIfExists(D, D.Dir + "/../lib", Paths);
+
+  addPathIfExists(D, SysRoot + "/lib", Paths);
+  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
+  addPathIfExists(D, SysRoot + "/usr/lib/w32api", Paths);
+}
+
+llvm::ExceptionHandling Cygwin::GetExceptionModel(const ArgList &Args) const {
+  if (getArch() == llvm::Triple::x86_64 || getArch() == llvm::Triple::aarch64 ||
+      getArch() == llvm::Triple::arm || getArch() == llvm::Triple::thumb)
+    return llvm::ExceptionHandling::WinEH;
+  return llvm::ExceptionHandling::DwarfCFI;
+}
+
+void Cygwin::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                       ArgStringList &CC1Args) const {
+  const Driver &D = getDriver();
+  std::string SysRoot = computeSysRoot();
+
+  if (DriverArgs.hasArg(clang::driver::options::OPT_nostdinc))
+    return;
+
+  if (!DriverArgs.hasArg(options::OPT_nostdlibinc))
+    addSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/local/include");
+
+  if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
+    SmallString<128> P(D.ResourceDir);
+    llvm::sys::path::append(P, "include");
+    addSystemInclude(DriverArgs, CC1Args, P);
+  }
+
+  if (DriverArgs.hasArg(options::OPT_nostdlibinc))
+    return;
+
+  // Check for configure-time C include directories.
+  StringRef CIncludeDirs(C_INCLUDE_DIRS);
+  if (CIncludeDirs != "") {
+    SmallVector<StringRef, 5> Dirs;
+    CIncludeDirs.split(Dirs, ":");
+    for (StringRef Dir : Dirs) {
+      StringRef Prefix =
+          llvm::sys::path::is_absolute(Dir) ? "" : StringRef(SysRoot);
+      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + Dir);
+    }
+    return;
+  }
+
+  // Lacking those, try to detect the correct set of system includes for the
+  // target triple.
+
+  AddMultilibIncludeArgs(DriverArgs, CC1Args);
+
+  // On systems using multiarch, add /usr/include/$triple before
+  // /usr/include.
+  std::string MultiarchIncludeDir = getTriple().str();
+  if (!MultiarchIncludeDir.empty() &&
+      D.getVFS().exists(SysRoot + "/usr/include/" + MultiarchIncludeDir))
+    addExternCSystemInclude(DriverArgs, CC1Args,
+                            SysRoot + "/usr/include/" + MultiarchIncludeDir);
+
+  // Add an include of '/include' directly. This isn't provided by default by
+  // system GCCs, but is often used with cross-compiling GCCs, and harmless to
+  // add even when Clang is acting as-if it were a system compiler.
+  addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/include");
+
+  addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/include");
+  addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/include/w32api");
+}

clang/lib/Driver/ToolChains/Cygwin.h

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_CYGWIN_H
+#define LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_CYGWIN_H
+
+#include "Gnu.h"
+#include "clang/Driver/ToolChain.h"
+
+namespace clang {
+namespace driver {
+namespace toolchains {
+
+class LLVM_LIBRARY_VISIBILITY Cygwin : public Generic_GCC {
+public:
+  Cygwin(const Driver &D, const llvm::Triple &Triple,
+         const llvm::opt::ArgList &Args);
+
+  llvm::ExceptionHandling
+  GetExceptionModel(const llvm::opt::ArgList &Args) const override;
+
+  void
+  AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                            llvm::opt::ArgStringList &CC1Args) const override;
+};
+
+} // end namespace toolchains
+} // end namespace driver
+} // end namespace clang
+
+#endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_CYGWIN_H

clang/lib/Driver/ToolChains/Gnu.cpp

@@ -2630,6 +2630,22 @@ void Generic_GCC::GCCInstallationDetector::AddDefaultGCCPrefixes(
     return;
   }
 
+  if (TargetTriple.isWindowsCygwinEnvironment()) {
+    LibDirs.push_back("/lib");
+    switch (TargetTriple.getArch()) {
+    case llvm::Triple::x86_64:
+      TripleAliases.append({"x86_64-pc-cygwin", "x86_64-pc-msys"});
+      break;
+    case llvm::Triple::x86:
+      TripleAliases.append({"i686-pc-cygwin", "i686-pc-msys"});
+      break;
+    default:
+      break;
+    }
+
+    return;
+  }
+
   switch (TargetTriple.getArch()) {
   case llvm::Triple::aarch64:
     LibDirs.append(begin(AArch64LibDirs), end(AArch64LibDirs));

clang/lib/Lex/InitHeaderSearch.cpp

@@ -74,20 +74,10 @@ class InitHeaderSearch {
     SystemHeaderPrefixes.emplace_back(std::string(Prefix), IsSystemHeader);
   }
 
-  /// Add the necessary paths to support a MinGW libstdc++.
-  void AddMinGWCPlusPlusIncludePaths(StringRef Base,
-                                     StringRef Arch,
-                                     StringRef Version);
-
   /// Add paths that should always be searched.
   void AddDefaultCIncludePaths(const llvm::Triple &triple,
                                const HeaderSearchOptions &HSOpts);
 
-  /// Add paths that should be searched when compiling c++.
-  void AddDefaultCPlusPlusIncludePaths(const LangOptions &LangOpts,
-                                       const llvm::Triple &triple,
-                                       const HeaderSearchOptions &HSOpts);
-
   /// Returns true iff AddDefaultIncludePaths should do anything.  If this
   /// returns false, include paths should instead be handled in the driver.
   bool ShouldAddDefaultIncludePaths(const llvm::Triple &triple);
@@ -180,35 +170,14 @@ bool InitHeaderSearch::AddUnmappedPath(const Twine &Path, IncludeDirGroup Group,
   return false;
 }
 
-void InitHeaderSearch::AddMinGWCPlusPlusIncludePaths(StringRef Base,
-                                                     StringRef Arch,
-                                                     StringRef Version) {
-  AddPath(Base + "/" + Arch + "/" + Version + "/include/c++",
-          CXXSystem, false);
-  AddPath(Base + "/" + Arch + "/" + Version + "/include/c++/" + Arch,
-          CXXSystem, false);
-  AddPath(Base + "/" + Arch + "/" + Version + "/include/c++/backward",
-          CXXSystem, false);
-}
-
 void InitHeaderSearch::AddDefaultCIncludePaths(const llvm::Triple &triple,
                                             const HeaderSearchOptions &HSOpts) {
   if (!ShouldAddDefaultIncludePaths(triple))
     llvm_unreachable("Include management is handled in the driver.");
 
-  llvm::Triple::OSType os = triple.getOS();
-
   if (HSOpts.UseStandardSystemIncludes) {
-    switch (os) {
-    case llvm::Triple::Win32:
-      if (triple.getEnvironment() != llvm::Triple::Cygnus)
-        break;
-      [[fallthrough]];
-    default:
-      // FIXME: temporary hack: hard-coded paths.
-      AddPath("/usr/local/include", System, false);
-      break;
-    }
+    // FIXME: temporary hack: hard-coded paths.
+    AddPath("/usr/local/include", System, false);
   }
 
   // Builtin includes use #include_next directives and should be positioned
@@ -236,51 +205,9 @@ void InitHeaderSearch::AddDefaultCIncludePaths(const llvm::Triple &triple,
     return;
   }
 
-  switch (os) {
-  case llvm::Triple::Win32:
-    switch (triple.getEnvironment()) {
-    default: llvm_unreachable("Include management is handled in the driver.");
-    case llvm::Triple::Cygnus:
-      AddPath("/usr/include/w32api", System, false);
-      break;
-    case llvm::Triple::GNU:
-      break;
-    }
-    break;
-  default:
-    break;
-  }
-
   AddPath("/usr/include", ExternCSystem, false);
 }
 
-void InitHeaderSearch::AddDefaultCPlusPlusIncludePaths(
-    const LangOptions &LangOpts, const llvm::Triple &triple,
-    const HeaderSearchOptions &HSOpts) {
-  if (!ShouldAddDefaultIncludePaths(triple))
-    llvm_unreachable("Include management is handled in the driver.");
-
-  // FIXME: temporary hack: hard-coded paths.
-  llvm::Triple::OSType os = triple.getOS();
-  switch (os) {
-  case llvm::Triple::Win32:
-    switch (triple.getEnvironment()) {
-    default: llvm_unreachable("Include management is handled in the driver.");
-    case llvm::Triple::Cygnus:
-      // Cygwin-1.7
-      AddMinGWCPlusPlusIncludePaths("/usr/lib/gcc", "i686-pc-cygwin", "4.7.3");
-      AddMinGWCPlusPlusIncludePaths("/usr/lib/gcc", "i686-pc-cygwin", "4.5.3");
-      AddMinGWCPlusPlusIncludePaths("/usr/lib/gcc", "i686-pc-cygwin", "4.3.4");
-      // g++-4 / Cygwin-1.5
-      AddMinGWCPlusPlusIncludePaths("/usr/lib/gcc", "i686-pc-cygwin", "4.3.2");
-      break;
-    }
-    break;
-  default:
-    break;
-  }
-}
-
 bool InitHeaderSearch::ShouldAddDefaultIncludePaths(
     const llvm::Triple &triple) {
   switch (triple.getOS()) {
@@ -303,15 +230,10 @@ bool InitHeaderSearch::ShouldAddDefaultIncludePaths(
   case llvm::Triple::Solaris:
   case llvm::Triple::UEFI:
   case llvm::Triple::WASI:
+  case llvm::Triple::Win32:
   case llvm::Triple::ZOS:
     return false;
 
-  case llvm::Triple::Win32:
-    if (triple.getEnvironment() != llvm::Triple::Cygnus ||
-        triple.isOSBinFormatMachO())
-      return false;
-    break;
-
   case llvm::Triple::UnknownOS:
     if (triple.isWasm() || triple.isAppleMachO())
       return false;
@@ -355,8 +277,6 @@ void InitHeaderSearch::AddDefaultIncludePaths(
       HSOpts.UseStandardCXXIncludes && HSOpts.UseStandardSystemIncludes) {
     if (HSOpts.UseLibcxx) {
       AddPath("/usr/include/c++/v1", CXXSystem, false);
-    } else {
-      AddDefaultCPlusPlusIncludePaths(Lang, triple, HSOpts);
     }
   }