[MinGW] Add option for disabling looking for a mingw gcc in PATH

[mstorsjo]

Summary

This avoids looking for a mingw gcc to use as sysroot, preferring the clang installation itself over a similar gcc found in the path.

The option name, --ignore-gcc, might not be ideal - any suggestions for a better name?

Currently, I'm injecting a --sysroot parameter via a wrapper script, forcing the clang invocation to use clang_bin/../triple as sysroot, even if there's a similar named cross gcc elsewhere in PATH. With this option, I wouldn't need to use a wrapper script to manually set the sysroot.

[mstorsjo]

include/clang/Driver/Options.td

1735

Perhaps --ignore-gcc-toolchain would be better?

[rnk]

Seems reasonable, looks good.

[mstorsjo]

In D45152#1055871, @rnk wrote:

Seems reasonable, looks good.

Any opinion on the wording of the option name?

[rnk]

In D45152#1056122, @mstorsjo wrote:

In D45152#1055871, @rnk wrote:

Seems reasonable, looks good.

Any opinion on the wording of the option name?

Maybe what we're trying to do is find the sysroot relative to clang, so an option name phrased along those lines makes more sense? --clang-in-sysroot-bin? --from-sysroot-bin? --assume-sysroot-bin? --in-sysroot-bin?

[mstorsjo]

In D45152#1056134, @rnk wrote:

In D45152#1056122, @mstorsjo wrote:

In D45152#1055871, @rnk wrote:

Seems reasonable, looks good.

Any opinion on the wording of the option name?

Maybe what we're trying to do is find the sysroot relative to clang, so an option name phrased along those lines makes more sense? --clang-in-sysroot-bin? --from-sysroot-bin? --assume-sysroot-bin? --in-sysroot-bin?

That sounds sensible - and positive options is often better than negated/ignore etc. I think I prefer --assume-sysroot-bin out of those.

[martell]

@mstorsjo I would much prefer to detect the clang sysroot first and if that exists just ignore the gcc one.
Most of the time clang and gcc will be in the same bin folder and in the case where the clang sysroot with mingw prefix folders is not found we can just default back to the default gcc behavior.
This should cover the use case for existing gcc users while not blocking us to move forward with clang only toolchains.
If someone really wants to ignore the clang sysroot with mingw folders we could add a flag for that and not the other way around.
What are your thoughts here?

Though I do like the idea of having an --assume-sysroot-bin as an option for all toolchains

[mstorsjo]

In D45152#1057787, @martell wrote:

@mstorsjo I would much prefer to detect the clang sysroot first and if that exists just ignore the gcc one.
Most of the time clang and gcc will be in the same bin folder and in the case where the clang sysroot with mingw prefix folders is not found we can just default back to the default gcc behavior.
This should cover the use case for existing gcc users while not blocking us to move forward with clang only toolchains.

That's probably an even better idea - I'll give that a try.

If someone really wants to ignore the clang sysroot with mingw folders we could add a flag for that and not the other way around.
What are your thoughts here?

I guess that could be useful in theory, but I'd hold off adding that until there's a concrete need for that case (it sounds quite contrieved to me, and there's always the --sysroot= option).

Though I do like the idea of having an --assume-sysroot-bin as an option for all toolchains

Well ideally all toolchains should use similar logic for finding sysroots, except for cases where they by design are different. I haven't looked for how many other cases of similar logic there is.

[mstorsjo]

D45504 fixed the same issue in a better way.

include/clang/Driver/Options.td

   HelpText<"Add directory to AFTER include search path">;
 def iframework : JoinedOrSeparate<["-"], "iframework">, Group<clang_i_Group>, Flags<[CC1Option]>,
   HelpText<"Add directory to SYSTEM framework search path">;
 def iframeworkwithsysroot : JoinedOrSeparate<["-"], "iframeworkwithsysroot">,
   Group<clang_i_Group>,
   HelpText<"Add directory to SYSTEM framework search path, "
            "absolute paths are relative to -isysroot">,
   MetaVarName<"<directory>">, Flags<[CC1Option]>;
+def ignore_gcc : Joined<["--"], "ignore-gcc">, Flags<[DriverOption]>,
+  HelpText<"Don't look for gcc for finding a suitable sysroot">;
 def imacros : JoinedOrSeparate<["-", "--"], "imacros">, Group<clang_i_Group>, Flags<[CC1Option]>,
   HelpText<"Include macros from file before parsing">, MetaVarName<"<file>">;
 def image__base : Separate<["-"], "image_base">;
 def include_ : JoinedOrSeparate<["-", "--"], "include">, Group<clang_i_Group>, EnumName<"include">,
     MetaVarName<"<file>">, HelpText<"Include file before parsing">, Flags<[CC1Option]>;
 def include_pch : Separate<["-"], "include-pch">, Group<clang_i_Group>, Flags<[CC1Option]>,
   HelpText<"Include precompiled header file">, MetaVarName<"<file>">;
 def relocatable_pch : Flag<["-", "--"], "relocatable-pch">, Flags<[CC1Option]>,

lib/Driver/ToolChains/MinGW.cpp

 
 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;
-  else if (llvm::ErrorOr<std::string> GPPName = findGcc())
+  else {
+    llvm::ErrorOr<std::string> GPPName("");
+    if (!Args.hasArg(options::OPT_ignore_gcc) && (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();
   // 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());

test/Driver/mingw-gcc.c

+// RUN: env PATH=%S/Inputs/mingw_gcc/bin \
+// RUN:    %clang -target x86_64-w64-mingw32 -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_GCC %s
+// CHECK_MINGW_GCC: "{{.*}}{{/|\\\\}}Inputs{{/|\\\\}}mingw_gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}include"
+
+// RUN: env PATH=%S/Inputs/mingw_gcc/bin \
+// RUN:    %clang -target x86_64-w64-mingw32 -c -### %s --ignore-gcc 2>&1 | FileCheck -check-prefix=CHECK_NOT_MINGW_GCC %s
+// CHECK_NOT_MINGW_GCC-NOT: "{{.*}}{{/|\\\\}}Inputs{{/|\\\\}}mingw_gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}include"