[clang] [MinGW] Add an implicit .exe suffix even when crosscompiling

[mstorsjo]

Summary

GCC 8 changed behaviour wrt this, and made it consistent for cross compilation cases. While it's a change, it's a more sensible behaviour going forward.

[mati865]

LGTM
Confirmed that GCC 9 still adds .exe.

[rnk]

lgtm

[dmajor]

This change broke the configure step of Firefox mingw builds.

The build bot won't give me the full details, so I'll need to set up a local repro next week if needed, but my hunch is that we have some test like $CC $CFLAGS conftest.c -o conftest and then check for the existence of conftest.

Is that type of pattern an acceptable casualty of this change?

[mstorsjo]

In D88005#2296254, @dmajor wrote:

This change broke the configure step of Firefox mingw builds.

The build bot won't give me the full details, so I'll need to set up a local repro next week if needed, but my hunch is that we have some test like $CC $CFLAGS conftest.c -o conftest and then check for the existence of conftest.

Is that type of pattern an acceptable casualty of this change?

I presume that's to be expected - it's certainly a pain, but anybody crosscompiling with GCC and updating to 8 or newer is going to be running into the same there as well.

FWIW, the change in GCC that changes this was this one: https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=5bc86b599054f494ec0a45e49b82749320eaa9c4;hp=77efd154f33154e819186de79687ea55552139f4

This at least clarifies the situation, because the inconsistency (which show up e.g. in handwritten makefiles) between compiling natively vs crosscompiling has been pretty weird.

clang/lib/Driver/ToolChains/MinGW.cpp

if (Args.hasArg(options::OPT_mdll) || Args.hasArg(options::OPT_shared)) {
     else
       CmdArgs.push_back("DllMainCRTStartup");
     CmdArgs.push_back("--enable-auto-image-base");
   }
 
   CmdArgs.push_back("-o");
   const char *OutputFile = Output.getFilename();
   // GCC implicitly adds an .exe extension if it is given an output file name
-  // that lacks an extension. However, GCC only does this when actually
-  // running on windows, not when operating as a cross compiler. As some users
-  // have come to rely on this behaviour, try to replicate it.
-#ifdef _WIN32
+  // that lacks an extension.
+  // GCC used to do this only when the compiler itself runs on windows, but
+  // since GCC 8 it does the same when cross compiling as well.
   if (!llvm::sys::path::has_extension(OutputFile))
     CmdArgs.push_back(Args.MakeArgString(Twine(OutputFile) + ".exe"));
   else
     CmdArgs.push_back(OutputFile);
-#else
-  CmdArgs.push_back(OutputFile);
-#endif
 
   Args.AddAllArgs(CmdArgs, options::OPT_e);
   // FIXME: add -N, -n flags
   Args.AddLastArg(CmdArgs, options::OPT_r);
   Args.AddLastArg(CmdArgs, options::OPT_s);
   Args.AddLastArg(CmdArgs, options::OPT_t);
   Args.AddAllArgs(CmdArgs, options::OPT_u_Group);
   Args.AddLastArg(CmdArgs, options::OPT_Z_Flag);

clang/test/Driver/mingw-implicit-extension-cross.c

-// Test how an implicit .exe extension is added. If not running the compiler
-// on windows, no implicit extension is added. (Therefore, this test is skipped
-// when running on windows.)
-
-// UNSUPPORTED: system-windows
-
-// RUN: %clang -target i686-windows-gnu -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s -o outputname 2>&1 | FileCheck %s
-
-// CHECK: "-o" "outputname"

clang/test/Driver/mingw-implicit-extension-windows.c

-// Test how an implicit .exe extension is added. If running the compiler
-// on windows, an implicit extension is added if none is provided in the
-// given name. (Therefore, this test is skipped when not running on windows.)
-
-// REQUIRES: system-windows
+// Test how an implicit .exe extension is added.
 
 // RUN: %clang -target i686-windows-gnu -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s -o outputname 2>&1 | FileCheck %s --check-prefix=CHECK-OUTPUTNAME-EXE
 
 // RUN: %clang -target i686-windows-gnu -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s -o outputname.exe 2>&1 | FileCheck %s --check-prefix=CHECK-OUTPUTNAME-EXE
 
 // RUN: %clang -target i686-windows-gnu -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s -o outputname.q 2>&1 | FileCheck %s --check-prefix=CHECK-OUTPUTNAME-Q
 
 // CHECK-OUTPUTNAME-EXE: "-o" "outputname.exe"
 // CHECK-OUTPUTNAME-Q: "-o" "outputname.q"