[patch, clang-cl] Implement /Zc:trigraphs support, disable trigraphs by default

[Richard Smith]

On Fri, Dec 19, 2014 at 6:08 PM, Nico Weber <thakis at chromium.org> wrote:
>
> Forgot to say: Fixes PR21974.
>
> On Fri, Dec 19, 2014 at 6:07 PM, Nico Weber <thakis at chromium.org> wrote:
>
>> Hi,
>>
>> the attached patch disables trigraphs by default in clang-cl mode. To do
>> so, I'm renaming the cc1 trigraph flag to -ftrigraphs, and I'm adding a
>> -fno-trigraphs flag. (This requires updating a handful of cc1 tests, and
>> translating -trigraphs to -ftrigraphs in the driver.)
>>
>> The driver grows parsing logic for /Zc:, everything other than trigraphs
>> is ignored for now. (We probably want to implement at least /Zc:inline at
>> some point, which is why I added parsing code for this instead of always
>> sending -fno-trigraphs to cc1 in clang-cl mode.)
>>
>
-def trigraphs : Flag<["-", "--"], "trigraphs">, Flags<[CC1Option]>,
+def trigraphs : Flag<["-", "--"], "trigraphs">, Flags<[DriverOption]>,

I don't think DriverOption is right here; that means we don't forward the
flag to a gcc invocation. Now, we never invoke GCC for C-like languages any
more, but if we did, this would be wrong (and for all I know, it's wrong
for Fortran...). You should be able to just drop the Flags.


     if (Arg *A = Args.getLastArg(options::OPT_std_EQ, options::OPT_ansi,
-                                 options::OPT_trigraphs))
-      if (A != Std)
+                                 options::OPT_trigraphs)) {
+      if (A->getOption().matches(options::OPT_trigraphs))
+        CmdArgs.push_back("-ftrigraphs");
+      else if (A != Std)
         A->render(Args, CmdArgs);

Std here is Args.getLastArg(options::OPT_std_EQ, options::OPT_ansi), so
your 'else if' clause is unreachable. Something like this would be simpler
and more obvious:

// If -trigraphs appears after the language standard flag, honor it.
if (Args.getLastArg(options::OPT_std_EQ, options::OPT_ansi,
options::OPT_trigraphs) != Std)
  CmdArgs.push_back("-ftrigraphs");

You could even sink this below the 'if (Std)' block to avoid duplicating it
between the cases where we do and don't have a Std flag.

Ok?
>>
>> Nico
>>
>
>
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