clang-cl: Add /showFilenames option (PR31957)

[hans]

Summary

Add a /showFilenames option for users who want clang to echo the currently compiled filename. MSVC does this echoing by default, and it's useful for showing progress in build systems that doesn't otherwise provide any progress report, such as MSBuild.

[steveire]

lib/Frontend/CompilerInvocation.cpp

792

I'll have to keep a patch around anyway for myself locally to remove this condition. But maybe someone else will benefit from this.

What do you think about changing CMake to so that this is passed by default when using Clang-CL?

[zturner]

lib/Frontend/CompilerInvocation.cpp

792

Do you mean llvms cmake? Or cmake itself? Which generator are you using?

[hans]

lib/Frontend/CompilerInvocation.cpp

792

Can't you just configure your build to pass the flag to clang-cl?

I suppose CMake could be made to do that by default when using clang-cl versions that support the flag and using the MSBuild generator, but that's for the CMake community to decide I think. Or perhaps our VS integration could do that, but it gets tricky because it needs to know whether the flag is supported or not.

[steveire]

lib/Frontend/CompilerInvocation.cpp

792

I mean upstream cmake. My suggestion is independent of the generator, but it would depend on what Brad decides anyway. I don't intend to implement it, just report it.

I only have one clang but I have multiple buildsystems, and I don't want to have to add a new flag too all of them. In each toplevel CMakeLists everyone will need this to make use of the flag:

# Have to remember to use "${CMAKE_CXX_SIMULATE_ID}" instead of 
# Undecorated "CMAKE_CXX_SIMULATE_ID" because there is a 
# variable named "MSVC" and
# the way CMake variables and the "if()" command work requires this. 
if (CMAKE_CXX_COMPILER_ID STREQUAL Clang 
        AND ${CMAKE_CXX_SIMULATE_ID} STREQUAL MSVC)
    # CMake does not have explicit Clang-CL support yet.
    # It should have a COMPILER_ID for it.
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /showFilename")
    # etc
endif()

Upstream CMake can have the logic to add the flag instead.

[thakis]

Looks good. If this is passed and we invoke lld-link, should we give that a similar flag and pass that to lld-link as well? I think link.exe also prints its outputs.

include/clang/Driver/CLCompatOptions.td

163

Can you add /showFilenames- (a no-op) too, for symmetry?

[zturner]

Canyou add a test that demonstrates that multiple input files on the command line will print all of them? Also does this really need to be a cc1 arg? Why not just print it in the driver?

[zturner]

lib/Frontend/CompilerInvocation.cpp

792

But then what if you don’t want it? There would be no way to turn it off. I don’t think it’s a good fit for cmake

792

Yes, and actually for this reason i was wondering if we can do it without a flag at all. What if we just set an magic environment variable? It handles Stephen’s use case (he can just set it globally), and MSBuild (we can set it in the extension).

[rnk]

I support continuing our practice of being silent by default, and not implementing anything like the noisy default version banner printing that MSVC does, or this filename printing. I think setting this flag is something for cmake or the VS integration to do. Only someone who knows something about the progress printing model can set it correctly.

lib/Driver/ToolChains/Clang.cpp

3533–3534

Is a -cc1 flag actually necessary? I was imagining we'd print it in the driver before we launch the compile job.

[steveire]

lib/Frontend/CompilerInvocation.cpp

792

But then what if you don’t want it? There would be no way to turn it off.

Oh, I thought that the last flag would dominate. ie, if cmake generated /showFilename and the user adds /showFilename-, then you would end up with

clang-cl.exe /showFilename /showFilename-

and it would not be shown. I guess that's not how it works.

Maybe users want to not show it, but not seeing the filename is a surprising first-time experience when porting from MSVC to clang-cl using Visual Studio.

However, I'll just drop out of the discussion and not make any bug to CMake. If anyone else feels strongly, they can do so.

Thanks!

[zturner]

lib/Frontend/CompilerInvocation.cpp

792

Right, but if we update the VS Integration Extension so that MSBuild specifies the flag (or sets the environment variable, etc), then any time you use MSBuild (even if not through the IDE) you would get the output, so to the user it would look no different.

[hans]

In D52773#1252584, @zturner wrote:

Canyou add a test that demonstrates that multiple input files on the command line will print all of them?

Will do.

Also does this really need to be a cc1 arg? Why not just print it in the driver?

Yeah, I'll give printing from the driver a try.

include/clang/Driver/CLCompatOptions.td

163

Will do. Actually not just a no-op, but the last option should win.

lib/Driver/ToolChains/Clang.cpp

3533–3534

Yeah, that's probably better, but will take a bit more work to keep track of if and what to print in the compile job. I'll give it a try.

lib/Frontend/CompilerInvocation.cpp

792

I think we should avoid magic environment variables as much as possible.

[zturner]

I agree magic environment variables are bad, but without it we don’t
address the only current actual use we have for this, which is making the
vs integration print filenames. Detecting compiler version from inside the
integration is hard, but with an environment variable it’s very easy to
solve.

I’m not against a flag as the supported way, but I think we should also
have some backdoor into this functionality, because if we’re not going to
satisfy the only known use case, then maybe it’s better to not even do it
at all.

[thakis]

In D52773#1255093, @zturner wrote:

I agree magic environment variables are bad, but without it we don’t
address the only current actual use we have for this, which is making the
vs integration print filenames. Detecting compiler version from inside the
integration is hard

We need some solution to this anyhow; e.g. say "this now requires clang 8.0", or have a clang version dropdown in the UI (which defaults to the latest release), or something. We can't add an env var for every future flag that the vs integration might want to use.

[zturner]

In D52773#1255491, @thakis wrote:

In D52773#1255093, @zturner wrote:

I agree magic environment variables are bad, but without it we don’t
address the only current actual use we have for this, which is making the
vs integration print filenames. Detecting compiler version from inside the
integration is hard

We need some solution to this anyhow; e.g. say "this now requires clang 8.0", or have a clang version dropdown in the UI (which defaults to the latest release), or something. We can't add an env var for every future flag that the vs integration might want to use.

But it is very hard to automatically detect the version from the integration. I tried this and gave up because it was flaky. So sure, we can present a drop-down in the UI, but it could be mismatched, and that would end up creating more problems than it solves.

Right now we have exactly 1 use case for showing filenames from clang-cl, and there's no good way to satisfy that use case with a command line option.

I agree that we can't add an environment variable for every future flag that the VS integration might want to use, but until that happens, YAGNI. And if and when we do need it, if we manage to come up with a solution to the problem, we can delete support for the environment variable and make it use the new method.

[rnk]

It doesn't address the version skew issue, but my blanket argument against any new environment variable is the existance of things like _CL_ and CCC_OVERRIDE_OPTIONS. You can set any compiler flag you want from the environment, so we should standardize on one way of setting options: flags.

[hans]

Here's a version now using cc1 flags, but printing directly from the driver. Please take a look.

[rnk]

lgtm

lib/Driver/Job.cpp

319 ↗

(On Diff #168999)

Huh, a -cc1 action can have multiple inputs? Go figure.

test/Driver/cl-showfilenames.c

7–8 ↗

(On Diff #168999)

I think it'd be nice to have the test show that diagnostics come out interleaved between the filenames. You can use #pragma message in the input files or something else to create warnings.

[hans]

test/Driver/cl-showfilenames.c

7–8 ↗

(On Diff #168999)

Good idea, thanks.

[asukainori]

I'm sorry to disturb.

But I found this option is conflict with -flto. e.g.

clang-cl -fuse-ld=lld -flto=thin /showFilenames .\test.cpp

will output:

clang-cl: warning: argument unused during compilation: '/showFilenames' [-Wunused-command-line-argument]

include/clang/Driver/CC1Options.td

def version : Flag<["-"], "version">,
   HelpText<"Print the compiler version">;
 def main_file_name : Separate<["-"], "main-file-name">,
   HelpText<"Main file name to use for debug info">;
 def split_dwarf_file : Separate<["-"], "split-dwarf-file">,
   HelpText<"File name to use for split dwarf debug info output">;
 
 }
 
+def echo_main_file_name : Flag<["-"], "echo-main-file-name">,
+  HelpText<"Echo the main file name">;
 def fblocks_runtime_optional : Flag<["-"], "fblocks-runtime-optional">,
   HelpText<"Weakly link in the blocks runtime">;
 def fexternc_nounwind : Flag<["-"], "fexternc-nounwind">,
   HelpText<"Assume all functions with C linkage do not unwind">;
 def enable_split_dwarf : Flag<["-"], "enable-split-dwarf">,
   HelpText<"Use split dwarf/Fission">;
 def fno_wchar : Flag<["-"], "fno-wchar">,
   HelpText<"Disable C++ builtin type wchar_t">;

include/clang/Driver/CLCompatOptions.td

def _SLASH_QUESTION : CLFlag<"?">, Alias<help>,
   HelpText<"Display available options">;
 def _SLASH_Qvec : CLFlag<"Qvec">,
   HelpText<"Enable the loop vectorization passes">, Alias<fvectorize>;
 def _SLASH_Qvec_ : CLFlag<"Qvec-">,
   HelpText<"Disable the loop vectorization passes">, Alias<fno_vectorize>;
 def _SLASH_showIncludes : CLFlag<"showIncludes">,
   HelpText<"Print info about included files to stderr">,
   Alias<show_includes>;
+def _SLASH_showFilenames : CLFlag<"showFilenames">,
+  HelpText<"Print the name of each compiled file">,
+  Alias<echo_main_file_name>;
 def _SLASH_source_charset : CLCompileJoined<"source-charset:">,
   HelpText<"Source encoding, supports only UTF-8">, Alias<finput_charset_EQ>;
 def _SLASH_execution_charset : CLCompileJoined<"execution-charset:">,
   HelpText<"Runtime encoding, supports only UTF-8">, Alias<fexec_charset_EQ>;
 def _SLASH_std : CLCompileJoined<"std:">,
   HelpText<"Language standard to compile for">;
 def _SLASH_U : CLJoinedOrSeparate<"U">, HelpText<"Undefine macro">,
   MetaVarName<"<macro>">, Alias<U>;

lib/Driver/ToolChains/Clang.cpp

#endif
   if (Args.hasFlag(options::OPT_fdiscard_value_names,
                    options::OPT_fno_discard_value_names, !IsAssertBuild))
     CmdArgs.push_back("-discard-value-names");
 
   // Set the main file name, so that debug info works even with
   // -save-temps.
   CmdArgs.push_back("-main-file-name");
   CmdArgs.push_back(getBaseInputName(Args, Input));
+  if (Arg *A = Args.getLastArg(options::OPT_echo_main_file_name))
+    A->render(Args, CmdArgs);
 
   // Some flags which affect the language (via preprocessor
   // defines).
   if (Args.hasArg(options::OPT_static))
     CmdArgs.push_back("-static-define");
 
   if (Args.hasArg(options::OPT_municode))
     CmdArgs.push_back("-DUNICODE");

lib/Frontend/CompilerInvocation.cpp

static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.MSVolatile = Args.hasArg(OPT_fms_volatile);
 
   Opts.VectorizeLoop = Args.hasArg(OPT_vectorize_loops);
   Opts.VectorizeSLP = Args.hasArg(OPT_vectorize_slp);
 
   Opts.PreferVectorWidth = Args.getLastArgValue(OPT_mprefer_vector_width_EQ);
 
   Opts.MainFileName = Args.getLastArgValue(OPT_main_file_name);
+  if (Args.hasArg(OPT_echo_main_file_name))
+    llvm::outs() << Opts.MainFileName << "\n";
+
   Opts.VerifyModule = !Args.hasArg(OPT_disable_llvm_verifier);
 
   Opts.ControlFlowGuard = Args.hasArg(OPT_cfguard);
 
   Opts.DisableGCov = Args.hasArg(OPT_test_coverage);
   Opts.EmitGcovArcs = Args.hasArg(OPT_femit_coverage_data);
   Opts.EmitGcovNotes = Args.hasArg(OPT_femit_coverage_notes);
   if (Opts.EmitGcovArcs || Opts.EmitGcovNotes) {

test/CodeGen/echo-main-filename.c

+// RUN: %clang_cc1 -main-file-name foobar -echo-main-file-name %s -emit-llvm -o - | FileCheck %s
+
+// CHECK: foobar

test/Driver/cl-options.c

 // GX: "-fcxx-exceptions" "-fexceptions"
 
 // RUN: %clang_cl /TP /c /GX /GX- -### -- %s 2>&1 | FileCheck -check-prefix=GX_ %s
 // GX_-NOT: "-fcxx-exceptions" "-fexceptions"
 
 // RUN: %clang_cl /d1PP -### -- %s 2>&1 | FileCheck -check-prefix=d1PP %s
 // d1PP: -dD
 
+// RUN: %clang_cl /showFilenames -### -- %s 2>&1 | FileCheck -check-prefix=showFilenames %s
+// showFilenames: -echo-main-file-name
+
 // We forward any unrecognized -W diagnostic options to cc1.
 // RUN: %clang_cl -Wunused-pragmas -### -- %s 2>&1 | FileCheck -check-prefix=WJoined %s
 // WJoined: "-cc1"
 // WJoined: "-Wunused-pragmas"
 
 // We recognize -f[no-]strict-aliasing.
 // RUN: %clang_cl -c -### -- %s 2>&1 | FileCheck -check-prefix=DEFAULTSTRICT %s
 // DEFAULTSTRICT: "-relaxed-aliasing"