[LLD] [MinGW] Print the lld-link command to stderr if running with -verbose

[mstorsjo]

Summary

When testing with -###, we print the output to stdout, as that's the
main purpose of the link command (as it exits after printing).

When linking with -verbose, we continue and then get log messages
from the actual link. Those log messages are printed to stderr. By
printing the command to the same stream, we make sure they appear
in a sensible chronological order.

[rnk]

lgtm

[rnk]

Actually, maybe we should aim for consistency with clang and GCC, and they both print this stuff to stderr:

$ clang -c t.cpp -### > /dev/null
clang version 13.0.0 ([e-mail]:llvm/llvm-project.git 621d93d263f82059c2826fe919a1a138b65627a3)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/google/home/rnk/llvm-project/build/bin
 (in-process)
 "/usr/local/google/home/rnk/llvm-project/build/bin/clang-13" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-emit-obj" "-mrelax-all" "--mrelax-relocations" "-disable-free" "-main-file-name" "t.cpp" "-mrelocation-model" "static" "-mframe-pointer=all" "-fmath-errno" "-fno-rounding-math" "-mconstructor-aliases" "-munwind-tables" "-target-cpu" "x86-64" "-tune-cpu" "generic" "-debugger-tuning=gdb" "-fcoverage-compilation-dir=/usr/local/google/home/rnk/llvm-project/build" "-resource-dir" "/usr/local/google/home/rnk/llvm-project/build/lib/clang/13.0.0" "-internal-isystem" "/usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10" "-internal-isystem" "/usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/x86_64-linux-gnu/c++/10" "-internal-isystem" "/usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/backward" "-internal-isystem" "/usr/local/google/home/rnk/llvm-project/build/lib/clang/13.0.0/include" "-internal-isystem" "/usr/local/include" "-internal-isystem" "/usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include" "-internal-externc-isystem" "/usr/include/x86_64-linux-gnu" "-internal-externc-isystem" "/include" "-internal-externc-isystem" "/usr/include" "-fdeprecated-macro" "-fdebug-compilation-dir=/usr/local/google/home/rnk/llvm-project/build" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fcxx-exceptions" "-fexceptions" "-fcolor-diagnostics" "-faddrsig" "-D__GCC_HAVE_DWARF2_CFI_ASM=1" "-o" "t.o" "-x" "c++" "t.cpp"

$ gcc -c t.cpp -### > /dev/null
Using built-in specs.
COLLECT_GCC=gcc
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 10.2.1-6+build2' --with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-10 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none=/build/gcc-10-i0uLfW/gcc-10-10.2.1/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-10-i0uLfW/gcc-10-10.2.1/debian/tmp-gcn/usr,hsa --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu --with-build-config=bootstrap-lto-lean --enable-link-mutex
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.1 20210110 (Debian 10.2.1-6+build2) 
COLLECT_GCC_OPTIONS='-c' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/10/cc1plus -quiet -imultiarch x86_64-linux-gnu -D_GNU_SOURCE t.cpp -quiet -dumpbase t.cpp "-mtune=generic" "-march=x86-64" -auxbase t -fasynchronous-unwind-tables -o /tmp/cciMprQs.s
COLLECT_GCC_OPTIONS='-c' '-mtune=generic' '-march=x86-64'
 as --64 -o t.o /tmp/cciMprQs.s
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-c' '-mtune=generic' '-march=x86-64'

[mstorsjo]

Unconditionally printing the command to stderr.

[rnk]

lgtm

lld/MinGW/Driver.cpp

case OPT_Bdynamic:
       break;
     }
   }
 
   if (errorCount())
     return false;
 
   if (args.hasArg(OPT_verbose) || args.hasArg(OPT__HASH_HASH_HASH))
-    lld::outs() << llvm::join(linkArgs, " ") << "\n";
+    // Print to stdout if testing with -###, otherwise to stderr like other
+    // regular logging.
+    (args.hasArg(OPT__HASH_HASH_HASH) ? lld::outs() : lld::errs())
+        << llvm::join(linkArgs, " ") << "\n";
 
   if (args.hasArg(OPT__HASH_HASH_HASH))
     return true;
 
   // Repack vector of strings to vector of const char pointers for coff::link.
   std::vector<const char *> vec;
   for (const std::string &s : linkArgs)
     vec.push_back(s.c_str());
   // Pass the actual binary name, to make error messages be printed with
   // the right prefix.
   vec[0] = argsArr[0];
   return coff::link(vec, canExitEarly, stdoutOS, stderrOS);
 }