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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Hi all,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">> It may be feasible for us to use a "-std=gnu++latest" behavior and not have<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">> to have a PS4-specific default; CC'ing Warren and Paul.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">As Sean pointed out, he did some tests and found we'd need to enable the GNU<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">keywords on PS4. Having a PS4-specific patch for this wouldn't be a problem<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">for us, though. So if the related issues mentioned in this thread for other<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">platforms (e.g., standard system headers needing GNU extensions enabled just<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">to parse them without error) are easily resolved, and so the default behavior<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">becomes to disable GNU keywords, it's easy enough for us to enable what we<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">need in this area for PS4.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">>> Note that at this point I'd like to mainly focus on what our policy should<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">>> be; there are certainly technical challenges involved in actually applying<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">>> the policy (another one is that clang's test suite still has some failures<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">>> when the default is changed, but Charles Li has made tremendous headway on<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">>> this), and if we can't actually prepare for the transition in the C++<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">>> default in time for 3.9, then so be it.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Internally on PS4, we default to C++11. FTR, the biggest issues we've had<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">on that point (by far) were clang's tests. That's much less of a headache<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">today, due to Charles' work on this, but as you said, some failures remain.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">I'd expect those could be dealt with in time for 3.9 without too much<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">difficulty if there was a strong desire to change the default that quickly.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">That said, independent of what default is selected at 3.9, for PS4 we will<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">most likely prefer to stay with our current default (gnu++11) at 3.9. We'll<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">revisit switching to 14 later, and consider future language dialect changes on<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">a case by case basis.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">-Warren Ristow</span><span style="font-size:11.0pt;font-family:
"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Sean Silva [mailto:chisophugis@gmail.com]
<br>
<b>Sent:</b> Wednesday, June 29, 2016 1:35 PM<br>
<b>To:</b> Richard Smith<br>
<b>Cc:</b> cfe-commits; Clang Dev; Ristow, Warren; Robinson, Paul<br>
<b>Subject:</b> Re: RFC: Default language standard mode policy<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Jun 29, 2016 at 1:34 PM, Sean Silva <<a href="mailto:chisophugis@gmail.com" target="_blank">chisophugis@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Jun 29, 2016 at 12:51 PM, Richard Smith <<a href="mailto:richard@metafoo.co.uk" target="_blank">richard@metafoo.co.uk</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">On Wed, Jun 29, 2016 at 12:30 PM, Sean Silva <<a href="mailto:chisophugis@gmail.com" target="_blank">chisophugis@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Jun 29, 2016 at 12:09 PM, Richard Smith via cfe-commits <<a href="mailto:cfe-commits@lists.llvm.org" target="_blank">cfe-commits@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hi all!<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I'd like to establish a policy for Clang's default language standard (if none is specified with -std), as follows:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> Clang defaults to the most recent published standard for the selected language that it fully implements.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The practical impact of this is that clang++ will default to C++14 for C++ compilations (for version 3.9 onwards) and will default to C++17 once our implementation support is complete and the standard is published (whichever happens later).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I'd suggest that we apply the same policy for clang-cl, but if it's important that we enable a not-yet-fully-implemented standard for cl compatibility, that seems reasonable.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The question of whether the default mode for the GCC-compatible driver should be -std=gnuXXX or -std=cXXX is separate, but also likely worth discussing. Enabling GNU keywords by default is a very odd choice, and if we believe we can change
our defaults without breaking the world then this seems like a good time to do so.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Using cXXX instead of gnuXXX would break the world on PS4. So for sure with `-std=c++latest` we would end up proposing a patch to change this for the PS4 target to gnu++latest (or gnu++11 if gnu++latest is not feasible). <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">OK. Out of interest, is it the GNU keywords that you need, or some other effect of the difference between modes?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">A quick check of two titles I have at hand shows that at least `typeof` is in use.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">(this check consisted of using -std=c++11 instead of -std=gnu++11 and seeing what breaks)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- Sean Silva<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#888888"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888">-- Sean Silva<o:p></o:p></span></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">(As I'm sure you're aware, we have pending to upstream a patch that makes -std=gnu++11 the default C++ language mode on PS4 (just blocked on fixing tests to not assume the existing std)).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">It may be feasible for us to use a "-std=gnu++latest" behavior and not have to have a PS4-specific default; CC'ing Warren and Paul.<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#888888"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888">-- Sean Silva<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888"> <o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I also intend to make explicit in our documentation that our -std=XXX flag enables the selected standard, *plus all relevant issues in Defect Report status from the relevant language committee* (it doesn't make sense to support a language
without its bugfixes).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thoughts?<o:p></o:p></p>
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_______________________________________________<br>
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<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits</a><o:p></o:p></p>
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