[PATCH] D141206: [clang] [MinGW] Avoid adding <base>/include and <base>/lib when cross compiling

[Martin Storsjö via Phabricator via cfe-commits]

mstorsjo created this revision.
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The MinGW compiler driver first tries to deduce the root of
the toolchain installation (either clang itself or a separate
cross mingw gcc installation). On top of this root, a number
of include and lib paths are added (some added unconditionally,
some only if they exist):

- <base>/x86_64-w64-mingw32/include
- <base>/include
- <base>/include/x86_64-w64-windows-gnu

(Some more are also added for libstdc++ and/or libc++.)

The first one is the one commonly used for MinGW targets so
far. For LLVM runtimes installed with the
LLVM_ENABLE_PER_TARGET_RUNTIME_DIR option, the latter two are
used though (this is currently not the default, not yet at least).

For cross compiling, if base is a separate dedicated directory,
this is fine, but when using the sysroots of a distro-installed
cross mingw toolchain, base is /usr - and having /usr/include
in the include path for cross compilation is a potential
source for problems; see
https://github.com/llvm/llvm-project/issues/59871.

If not cross compiling though, <base>/include needs to be included
too. E.g. in the case of msys2, most headers are in e.g.
/mingw64/include while the compiler is /mingw64/bin/clang.

When cross compiling, if the sysroot has been explicitly set
by the user, keep <base>/include too. (In the case of a distro
provided cross gcc toolchain in /usr, the sysroot needs to be set
to /usr and not /usr/x86_64-w64-mingw32 though, to be able to find
libgcc files under /usr/lib/gcc/x86_64-w64-mingw32. So with such a
toolchain, setting the sysroot explicitly does retain the problem.)

All in all - this avoids adding /usr/include and /usr/lib to the
include/lib paths when doing mingw cross compilation with a
distro-provided sysroot in /usr/x86_64-w64-mingw32.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D141206

Files:
  clang/lib/Driver/ToolChains/MinGW.cpp


Index: clang/lib/Driver/ToolChains/MinGW.cpp
===================================================================
--- clang/lib/Driver/ToolChains/MinGW.cpp
+++ clang/lib/Driver/ToolChains/MinGW.cpp
@@ -348,6 +348,15 @@
                                          Exec, CmdArgs, Inputs, Output));
 }
 
+static bool isCrossCompiling(const llvm::Triple &T, bool RequireArchMatch) {
+  llvm::Triple HostTriple(llvm::Triple::normalize(LLVM_HOST_TRIPLE));
+  if (HostTriple.getOS() != llvm::Triple::Win32)
+    return true;
+  if (RequireArchMatch && HostTriple.getArch() != T.getArch())
+    return true;
+  return false;
+}
+
 // Simplified from Generic_GCC::GCCInstallationDetector::ScanLibDirForGCCTriple.
 static bool findGccVersion(StringRef LibDir, std::string &GccLibDir,
                            std::string &Ver,
@@ -487,7 +496,13 @@
   getFilePaths().push_back(
       (Base + SubdirName + llvm::sys::path::get_separator() + "mingw/lib").str());
 
-  getFilePaths().push_back(Base + "lib");
+  // Only include <base>/lib if we're not cross compiling (not even for
+  // windows->windows to a different arch), or if the sysroot has been set
+  // (where we presume the user has pointed it at an arch specific
+  // subdirectory).
+  if (!::isCrossCompiling(getTriple(), /*RequireArchMatch=*/true) ||
+      getDriver().SysRoot.size())
+    getFilePaths().push_back(Base + "lib");
 
   NativeLLVMSupport =
       Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER)
@@ -649,7 +664,13 @@
   addSystemInclude(DriverArgs, CC1Args,
                    Base + SubdirName + llvm::sys::path::get_separator() + "usr/include");
 
-  addSystemInclude(DriverArgs, CC1Args, Base + "include");
+  // Only include <base>/include if we're not cross compiling (but do allow it
+  // if we're on Windows and building for Windows on another architecture),
+  // or if the sysroot has been set (where we presume the user has pointed it
+  // at an arch specific subdirectory).
+  if (!::isCrossCompiling(getTriple(), /*RequireArchMatch=*/false) ||
+      getDriver().SysRoot.size())
+    addSystemInclude(DriverArgs, CC1Args, Base + "include");
 }
 
 void toolchains::MinGW::addClangTargetOptions(


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