r274991 - [clang-cl] Add support for /Zd

Nico Weber via cfe-commits cfe-commits at lists.llvm.org
Mon Jul 11 12:18:01 PDT 2016 

On Mon, Jul 11, 2016 at 12:19 PM, David Majnemer <david.majnemer at gmail.com>
wrote:

>
>
> On Mon, Jul 11, 2016 at 9:03 AM, Nico Weber <thakis at chromium.org> wrote:
>
>> On Mon, Jul 11, 2016 at 11:51 AM, David Majnemer <
>> david.majnemer at gmail.com> wrote:
>>
>>>
>>>
>>> On Mon, Jul 11, 2016 at 8:42 AM, Nico Weber <thakis at chromium.org> wrote:
>>>
>>>> On Mon, Jul 11, 2016 at 11:36 AM, David Majnemer <
>>>> david.majnemer at gmail.com> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Mon, Jul 11, 2016 at 7:18 AM, Nico Weber <thakis at chromium.org>
>>>>> wrote:
>>>>>
>>>>>> VS2013's cl.exe doesn't understand /Zd, 2015's doesn't either. This
>>>>>> means people who want to ask clang-cl for line tables only will have to add
>>>>>> this flag in some if(is_clang) block in their build file anyways. What's
>>>>>> the advantage of giving this flag a spelling that's different from both cl
>>>>>> and clang? With -gline-tables-only, an if(is_clang) works on Linux, Mac,
>>>>>> Windows.
>>>>>>
>>>>>> (Even if there's a good case for /Zd, I don't think we should remove
>>>>>> user-exposed flags without a strong reason, so even if we keep /Zd I think
>>>>>> we should also keep exposing -gline-tables-only.)
>>>>>>
>>>>>
>>>>> Existing users of -gline-tables-only?  I'd imagine any responsible
>>>>> users of -gline-tables-only would probably use their build system to verify
>>>>> that the flag exists.  We have never released an official LLVM which
>>>>> supported it (LLVM 3.8 came out in early March and -gline-tables-only was
>>>>> exposed via clang-cl in mid March).
>>>>>
>>>>
>>>> Ok, but why is /Zd better than -gline-tables-only?
>>>>
>>>
>>> I see a few reasons:
>>> - It is less surprising for a debug flag in the cl world to be called
>>> /Zsomething instead of -gsomething.
>>>
>>
>> Eh, you'll have to look it up either way to find the flag.
>>
>
> I agree.
>
>
>> And when seeing the flag, the -g flag is more self-explanatory.
>>
>
> I disagree, I had no idea what that flag did until I started working on
> debug info.
>
>
>> Also, it is surprising that a clang-cl /-style flag doesn't work with cl,
>> so it just moves the surprise around a bit.
>>
>
> It is surprising when that happens in either direction.  If this is
> considered a bug, we will never "fix" it.
>
>
>>
>>
>>> - I think that avoiding invasion of their namespace, when possible, is a
>>> good thing.  It makes it less likely that we will conflict with a flag they
>>> want to add in the future.
>>>
>>
>> I don't understand this point. Doesn't invading their namespace make
>> collisions _more_ likely?
>>
>>
>>> - I imagine that if they wanted to add support back for
>>> -gline-tables-only, they'd name it /Zd.
>>>
>>
>> Given they had this flag and removed it, they probably didn't like it
>> very much :-)
>>
>>
>>> I'm sympathetic to the argument that "-gline-tables-only" is more
>>> familiar to Linux/Mac OS X folks and that /Zd won't work across all
>>> platforms.
>>>
>>> Here why I think that's ok:
>>> - This is not really a new problem.  If you want to select c++1z you get
>>> to spell it /std:c++latest for clang-cl and -std=c++14.
>>>
>>
>> Sure, but these are flags that clang/gcc and cl interpret. So if you have
>> a gcc build and a visual studio build, it's fairly easy to get each going
>> with clang / clang-cl.
>>
>> With /Zd, we're needlessly inventing a new spelling for an existing clang
>> flag.
>>
>
> icl also supports /Zd.
>

That's a big point in favor of this change, I think. Thanks for pointing it
out.


> As far as I can see, the new name creates a (small) problem without
>> solving one.
>>
>
> This is an attempt to reduce unneeded diversity.
>

>From my point of view, it increased diversity: Before, this feature had one
name, now it has two, and the second name is our own invention. (But if icl
also uses that flag, then it's less bad.)


> So far, when we wanted to add a flag that cl doesn't have and that clang
>> has, we've always gone for the clang spelling of that flag. That seems like
>> a good guideline to me.
>>
>
> Often but not always.  For example, we have /Qvec instead of -fvectorize
> because icl has the flag.
>

Hm, I'd (weakly) argue that that's not ideal either :-)

Anyhow, I think this isn't a good change, and it sounds like you disagree
with that. So I guess the next step here is that Hans gets to make a
decision once he's back?


>
>
>>
>>
>>> - People who want harmony between Mac OS X, Linux and Windows on the
>>> driver side can just use clang++.
>>>
>>>
>>>>
>>>>
>>>>>
>>>>> I'd consider it in poor form for users to take a hard dependency on a
>>>>> flag which only exists in a compiler which has never been released.
>>>>>
>>>>> I'd agree with you if -gline-tables-only had made its way to an actual
>>>>> release.
>>>>>
>>>>>
>>>>>>
>>>>>> On Mon, Jul 11, 2016 at 10:08 AM, Nico Weber <thakis at chromium.org>
>>>>>> wrote:
>>>>>>
>>>>>>> This breaks existing users of -gline-tables-only. What's the
>>>>>>> motivation for this change?
>>>>>>>
>>>>>>
>>>>>>> On Sat, Jul 9, 2016 at 5:49 PM, David Majnemer via cfe-commits <
>>>>>>> cfe-commits at lists.llvm.org> wrote:
>>>>>>>
>>>>>>>> Author: majnemer
>>>>>>>> Date: Sat Jul  9 16:49:16 2016
>>>>>>>> New Revision: 274991
>>>>>>>>
>>>>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=274991&view=rev
>>>>>>>> Log:
>>>>>>>> [clang-cl] Add support for /Zd
>>>>>>>>
>>>>>>>> MASM (ML.exe and ML64.exe) and older versions of MSVC (CL.exe)
>>>>>>>> support a
>>>>>>>> flag called /Zd which is more-or-less -gline-tables-only.
>>>>>>>>
>>>>>>>> It seems nicer to support this flag instead of exposing
>>>>>>>> -gline-tables-only.
>>>>>>>>
>>>>>>>> Modified:
>>>>>>>>     cfe/trunk/include/clang/Driver/CLCompatOptions.td
>>>>>>>>     cfe/trunk/include/clang/Driver/Options.td
>>>>>>>>     cfe/trunk/lib/Driver/Tools.cpp
>>>>>>>>     cfe/trunk/test/Driver/cl-options.c
>>>>>>>>
>>>>>>>> Modified: cfe/trunk/include/clang/Driver/CLCompatOptions.td
>>>>>>>> URL:
>>>>>>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Driver/CLCompatOptions.td?rev=274991&r1=274990&r2=274991&view=diff
>>>>>>>>
>>>>>>>> ==============================================================================
>>>>>>>> --- cfe/trunk/include/clang/Driver/CLCompatOptions.td (original)
>>>>>>>> +++ cfe/trunk/include/clang/Driver/CLCompatOptions.td Sat Jul  9
>>>>>>>> 16:49:16 2016
>>>>>>>> @@ -166,6 +166,8 @@ def _SLASH_Zc_trigraphs_off : CLFlag<"Zc
>>>>>>>>    HelpText<"Disable trigraphs (default)">, Alias<fno_trigraphs>;
>>>>>>>>  def _SLASH_Z7 : CLFlag<"Z7">,
>>>>>>>>    HelpText<"Enable CodeView debug information in object files">;
>>>>>>>> +def _SLASH_Zd : CLFlag<"Zd">,
>>>>>>>> +  HelpText<"Emit debug line number tables only">;
>>>>>>>>  def _SLASH_Zi : CLFlag<"Zi">, Alias<_SLASH_Z7>,
>>>>>>>>    HelpText<"Alias for /Z7. Does not produce PDBs.">;
>>>>>>>>  def _SLASH_Zp : CLJoined<"Zp">,
>>>>>>>>
>>>>>>>> Modified: cfe/trunk/include/clang/Driver/Options.td
>>>>>>>> URL:
>>>>>>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Driver/Options.td?rev=274991&r1=274990&r2=274991&view=diff
>>>>>>>>
>>>>>>>> ==============================================================================
>>>>>>>> --- cfe/trunk/include/clang/Driver/Options.td (original)
>>>>>>>> +++ cfe/trunk/include/clang/Driver/Options.td Sat Jul  9 16:49:16
>>>>>>>> 2016
>>>>>>>> @@ -1229,7 +1229,7 @@ def fdebug_prefix_map_EQ
>>>>>>>>  def g_Flag : Flag<["-"], "g">, Group<g_Group>,
>>>>>>>>    HelpText<"Generate source-level debug information">;
>>>>>>>>  def gline_tables_only : Flag<["-"], "gline-tables-only">,
>>>>>>>> Group<gN_Group>,
>>>>>>>> -  Flags<[CoreOption]>, HelpText<"Emit debug line number tables
>>>>>>>> only">;
>>>>>>>> +  HelpText<"Emit debug line number tables only">;
>>>>>>>>  def gmlt : Flag<["-"], "gmlt">, Alias<gline_tables_only>;
>>>>>>>>  def g0 : Flag<["-"], "g0">, Group<gN_Group>;
>>>>>>>>  def g1 : Flag<["-"], "g1">, Group<gN_Group>,
>>>>>>>> Alias<gline_tables_only>;
>>>>>>>>
>>>>>>>> Modified: cfe/trunk/lib/Driver/Tools.cpp
>>>>>>>> URL:
>>>>>>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/Tools.cpp?rev=274991&r1=274990&r2=274991&view=diff
>>>>>>>>
>>>>>>>> ==============================================================================
>>>>>>>> --- cfe/trunk/lib/Driver/Tools.cpp (original)
>>>>>>>> +++ cfe/trunk/lib/Driver/Tools.cpp Sat Jul  9 16:49:16 2016
>>>>>>>> @@ -6269,12 +6269,18 @@ void Clang::AddClangCLArgs(const ArgList
>>>>>>>>
>>>>>>>>  CmdArgs.push_back(Args.MakeArgString(Twine(LangOptions::SSPStrong)));
>>>>>>>>    }
>>>>>>>>
>>>>>>>> -  // Emit CodeView if -Z7 is present.
>>>>>>>> -  *EmitCodeView = Args.hasArg(options::OPT__SLASH_Z7);
>>>>>>>> -  if (*EmitCodeView)
>>>>>>>> -    *DebugInfoKind = codegenoptions::LimitedDebugInfo;
>>>>>>>> -  if (*EmitCodeView)
>>>>>>>> +  // Emit CodeView if -Z7 or -Zd are present.
>>>>>>>> +  if (Arg *DebugInfoArg =
>>>>>>>> +          Args.getLastArg(options::OPT__SLASH_Z7,
>>>>>>>> options::OPT__SLASH_Zd)) {
>>>>>>>> +    *EmitCodeView = true;
>>>>>>>> +    if (DebugInfoArg->getOption().matches(options::OPT__SLASH_Z7))
>>>>>>>> +      *DebugInfoKind = codegenoptions::LimitedDebugInfo;
>>>>>>>> +    else
>>>>>>>> +      *DebugInfoKind = codegenoptions::DebugLineTablesOnly;
>>>>>>>>      CmdArgs.push_back("-gcodeview");
>>>>>>>> +  } else {
>>>>>>>> +    *EmitCodeView = false;
>>>>>>>> +  }
>>>>>>>>
>>>>>>>>    const Driver &D = getToolChain().getDriver();
>>>>>>>>    EHFlags EH = parseClangCLEHFlags(D, Args);
>>>>>>>> @@ -9964,7 +9970,8 @@ void visualstudio::Linker::ConstructJob(
>>>>>>>>
>>>>>>>>    CmdArgs.push_back("-nologo");
>>>>>>>>
>>>>>>>> -  if (Args.hasArg(options::OPT_g_Group, options::OPT__SLASH_Z7))
>>>>>>>> +  if (Args.hasArg(options::OPT_g_Group, options::OPT__SLASH_Z7,
>>>>>>>> +                  options::OPT__SLASH_Zd))
>>>>>>>>      CmdArgs.push_back("-debug");
>>>>>>>>
>>>>>>>>    bool DLL = Args.hasArg(options::OPT__SLASH_LD,
>>>>>>>> options::OPT__SLASH_LDd,
>>>>>>>>
>>>>>>>> Modified: cfe/trunk/test/Driver/cl-options.c
>>>>>>>> URL:
>>>>>>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Driver/cl-options.c?rev=274991&r1=274990&r2=274991&view=diff
>>>>>>>>
>>>>>>>> ==============================================================================
>>>>>>>> --- cfe/trunk/test/Driver/cl-options.c (original)
>>>>>>>> +++ cfe/trunk/test/Driver/cl-options.c Sat Jul  9 16:49:16 2016
>>>>>>>> @@ -420,7 +420,7 @@
>>>>>>>>  // Z7: "-gcodeview"
>>>>>>>>  // Z7: "-debug-info-kind=limited"
>>>>>>>>
>>>>>>>> -// RUN: %clang_cl -gline-tables-only /Z7 /c -### -- %s 2>&1 |
>>>>>>>> FileCheck -check-prefix=Z7GMLT %s
>>>>>>>> +// RUN: %clang_cl /Zd /c -### -- %s 2>&1 | FileCheck
>>>>>>>> -check-prefix=Z7GMLT %s
>>>>>>>>  // Z7GMLT: "-gcodeview"
>>>>>>>>  // Z7GMLT: "-debug-info-kind=line-tables-only"
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> cfe-commits mailing list
>>>>>>>> cfe-commits at lists.llvm.org
>>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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