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<p class="MsoNormal">Hi Chandler,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Yes, this is a known issue with libstdc++ ABI.<o:p></o:p></p>
<p class="MsoNormal">What if we use _GLIBCXX_USE_CXX11_ABI=0 as recommended by <a href="https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html">
https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html</a> ?<o:p></o:p></p>
<p class="MsoNormal">Gcc also provides the -Wabi-tag option to detect library ABI issues.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Evgeny<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">Chandler Carruth <chandlerc@google.com><br>
<b>Date: </b>Thursday, 10 May 2018 at 21:50<br>
<b>To: </b>JF Bastien <jfbastien@apple.com><br>
<b>Cc: </b>Evgeny Astigeevich <Evgeny.Astigeevich@arm.com>, llvm-dev <llvm-dev@lists.llvm.org>, nd <nd@arm.com><br>
<b>Subject: </b>Re: [llvm-dev] Using C++14 code in LLVM<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:36.0pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Last time this came up, there were a lot of people that were stuck on GCC 4.9 due to ABI reasons. I think forcing that upgrade is going to be the most disruptive part of this, and I think that will really need
a decent amount of time. =[<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">On Thu, May 10, 2018 at 2:26 PM JF Bastien via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">On May 10, 2018, at 12:25 PM, Evgeny Astigeevich via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Hi,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">IMHO, it’s a good idea to move to C++14 first.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">What do you think about doing this by two phases:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Phase1: require GCC >= 5 but build in C++11 mode (this will give time to adapt build infrastructure to a new gcc)<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Phase2: switch to C++14<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Sounds reasonable, here’s a patch:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt;background:white"><u><span style="font-size:8.5pt;font-family:Menlo"><a href="https://reviews.llvm.org/D46723" target="_blank">https://reviews.llvm.org/D46723</a></span></u><span style="font-size:8.5pt;font-family:Menlo"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Thanks,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Evgeny<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"><b><span style="font-size:12.0pt">From:<span class="m1966951477189470441apple-converted-space"> </span></span></b><span style="font-size:12.0pt">llvm-dev <<a href="mailto:llvm-dev-bounces@lists.llvm.org" target="_blank"><span style="color:purple">llvm-dev-bounces@lists.llvm.org</span></a>>
on behalf of Reid Kleckner via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><span style="color:purple">llvm-dev@lists.llvm.org</span></a>><br>
<b>Reply-To:<span class="m1966951477189470441apple-converted-space"> </span></b>Reid Kleckner <<a href="mailto:rnk@google.com" target="_blank"><span style="color:purple">rnk@google.com</span></a>><br>
<b>Date:<span class="m1966951477189470441apple-converted-space"> </span></b>Thursday, 10 May 2018 at 19:50<br>
<b>To:<span class="m1966951477189470441apple-converted-space"> </span></b>Zachary Turner <<a href="mailto:zturner@google.com" target="_blank"><span style="color:purple">zturner@google.com</span></a>><br>
<b>Cc:<span class="m1966951477189470441apple-converted-space"> </span></b>llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><span style="color:purple">llvm-dev@lists.llvm.org</span></a>><br>
<b>Subject:<span class="m1966951477189470441apple-converted-space"> </span></b>Re: [llvm-dev] Using C++14 code in LLVM</span><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">The easy way not to have a three year discussion is to not worry about it for another three years. :)<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">So, I think we should take the easy things on the table and just move to C++14 in the near future. It's just a matter of dropping support for building on distros that only have GCC <5 (aka Trusty, which is from
2014 itself). Let's do that and call it a day.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">---<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Aside: I'm always kind of amused by talk of moving to the next "standard version" when the reality is that every C++ project is always held back by the compilers and standard libraries that they actually use in
practice. We say LLVM requires C++11 which mandates a working set of threading primitives, but in practice those don't exist on some platforms that people would like us to support, so we end up maintaining the LLVM_ENABLE_THREADING=0 build for them.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">It seems more practical to simply list the minimum versions of supported toolchains that are commonly used to build, i.e. GCC 5, MSVC 2015, Clang 3.N, libc++ 3.N, libstdc++ 3.N, etc.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">On Thu, May 10, 2018 at 11:36 AM Zachary Turner via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><span style="color:purple">llvm-dev@lists.llvm.org</span></a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">If it's the only thing we can agree then I'll take it, but I just worry that 3 years from now we're going to start another 3 year discussion, so that any actual move to C++17 would end up taking double the time.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Are the issues specific to C++17 additions to the standard library? What if you allow C++17 language features but not C++17 library features? I'm guessing this is too simple though and isn't sufficient to avoid
the problems (which I don't know anything about, so you'll have to enlighten me)?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">On Thu, May 10, 2018 at 11:28 AM JF Bastien <<a href="mailto:jfbastien@apple.com" target="_blank"><span style="color:purple">jfbastien@apple.com</span></a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">On May 10, 2018, at 11:22 AM, Zachary Turner <<a href="mailto:zturner@google.com" target="_blank"><span style="color:purple">zturner@google.com</span></a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Windows has never been the issue. Honestly, MSVC on Windows is "fully C++17 conformant" [1].<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">The issue has and always will be GCC. Given that a bump in any version of GCC has been (and will remain) difficult for some time, I propose that we skip C++14 and move to 17. We don't want to have a multi-year
disccusion about this again any time soon, and from what I gather, nobody has any more reservations about moving to C++17 than they do about moving to C++14. They only have reservations about moving to anything at all. So if we're gonna move, we should go
all the way.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">WebKit’s move to C++17 hasn’t been super smooth because of GCC / libstdc++ issues in both GCC 6 and GCC 7. It’s all fixable, but given LLVM's slow move out of C++11 I’d rather get C++14 now rather than a painful
transition to C++17 that drags on as we discover issues.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Just my 2c.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">[1]<span class="m1966951477189470441apple-converted-space"> </span><a href="https://blogs.msdn.microsoft.com/vcblog/2018/05/07/announcing-msvc-conforms-to-the-c-standard/" target="_blank"><span style="color:purple">https://blogs.msdn.microsoft.com/vcblog/2018/05/07/announcing-msvc-conforms-to-the-c-standard/</span></a><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">On Thu, May 10, 2018 at 11:18 AM Eric Christopher <<a href="mailto:echristo@gmail.com" target="_blank"><span style="color:purple">echristo@gmail.com</span></a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Once again, I'm totally down for this and think we should do it. I worry about windows, but ...<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Zach: How's windows c++14 support looking?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">-eric<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">On Thu, May 10, 2018 at 10:01 AM JF Bastien via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><span style="color:purple">llvm-dev@lists.llvm.org</span></a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Hi folks!<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Six more months have come and gone, and maybe we could move LLVM to C++14 now?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">The issues I picked out from the last discussion:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">1.<span style="font-size:7.0pt;font-family:"Times New Roman",serif"> <span class="m1966951477189470441apple-converted-space"> </span></span>Some folks want an official policy about compiler support before
updating the standard version we use.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">2.<span style="font-size:7.0pt;font-family:"Times New Roman",serif"> <span class="m1966951477189470441apple-converted-space"> </span></span>Worries about which GCC version is available in which distro.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">3.<span style="font-size:7.0pt;font-family:"Times New Roman",serif"> <span class="m1966951477189470441apple-converted-space"> </span></span>Worries about MSVC.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Instead of rehashing the compiler per distro surveys from previous discussion, and instead of talking bootstrap, let me offer three data points:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:10.0pt;font-family:Symbol">·</span><span style="font-size:7.0pt;font-family:"Times New Roman",serif"> <span class="m1966951477189470441apple-converted-space"> </span></span>WebKit
is <a href="https://lists.webkit.org/pipermail/webkit-dev/2018-March/029922.html" target="_blank"><span style="color:purple">moving to C++17</span></a> (from C++14) right now †<o:p></o:p></p>
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<div style="margin-left:72.0pt">
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:10.0pt;font-family:Symbol">·</span><span style="font-size:7.0pt;font-family:"Times New Roman",serif"> <span class="m1966951477189470441apple-converted-space"> </span></span>Chromium <a href="https://groups.google.com/a/chromium.org/d/msg/cxx/ow7hmdDm4yw/eV6KWL2yAQAJ" target="_blank"><span style="color:purple">started
moving to C++14</span></a> in August of last year<o:p></o:p></p>
</div>
<div style="margin-left:72.0pt">
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:10.0pt;font-family:Symbol">·</span><span style="font-size:7.0pt;font-family:"Times New Roman",serif"> <span class="m1966951477189470441apple-converted-space"> </span></span>Firefox
uses <a href="https://developer.mozilla.org/en-US/docs/Mozilla/Using_CXX_in_Mozilla_code" target="_blank"><span style="color:purple">some C++14</span></a><o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">What I get from this data: if your distro bundles a modern web browser, it already builds some C++14,<span class="m1966951477189470441apple-converted-space"> </span><i>somehow</i>.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">The LLVM community has been talking about this for a while now, and I’m not aware of a policy coming to light. I don’t think we need a policy given the above data. So how about we… just kinda... move LLVM to C++14?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">Thanks!<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">JF<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">† the move to C++17 is very painful, but 14 has been working great in WebKit for quite a long time.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt"> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Last time we discussed this, the consensus was "I think we can survive<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> another year without generalized constexpr and variable templates".<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Well, we did indeed survive. And it's been exactly a year! So naturally,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> it only makes sense to revive this :)<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> There's an active conversation going on in IRC right now, and it seems like<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> there is more desire than there was last year.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> What are the main gains from allowing C++14?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> * Variable templates<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> * Generalized constexpr<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> * Return-type Deduction<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> * Generic Lambdas<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * std::make_unique<> (the source of many build bot breakages)<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> What are the main gains from allowing C++17? [1]<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> * [[nodiscard]] attribute<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> * structured bindings<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> * constexpr-if<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * guaranteed copy elision<o:p></o:p></p>
</div>
</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * numerous new library types: optional, string_view, variant, byte,<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * numerous new algorithms: parallel algorithms, too many to list<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * Probably some more, but I just tried to hit the biggest ones.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> First, it seems like if we want to enable C++14 we need GCC >= 5.<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> And if we want to enable C++17 we need GCC >= 7.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> With that out of the way, here were some of the issues that were raised<o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> last time:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Issue: Ubuntu 14.04 LTS is on GCC 4.8.x, and we have to support it until<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> end of life.<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Resolution: LTS is right around the corner, in 6 more months.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Issue: Various other platforms have older GCCs as their system compiler,<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> and it's annoying to upgrade.<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Question: Do any of these not have a port you can install? For example,<o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> NetBSD 7 appears to have GCC 5.3 as a port, if DistroWatch is any<o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> indication. It could be wrong though and I could also be misinterpreting<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> it.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Issue: If we're going to make people bootstrap a compiler, we might as well<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> go all the way to C++17.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> Comment: I'm not opposed.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Some questions / comments of my own:<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * Where is this policy about Ubuntu and LTS documented? Does this mean,<o:p></o:p></p>
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</div>
<div>
<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> for example, that we will not be able to use C++17 until 2023 (16.04 LTS<o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> has only GCC 5.3.1)? That seems a bit unreasonable. And there's no<o:p></o:p></p>
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</div>
<div>
<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> guarantee that 18.04 LTS will even have GCC 7 or higher either, so it could<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> be 2025 or 2027.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * We've asked people in the past to build a modern toolchain. For example,<o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> we did it with C++11 and Ubuntu 12.04 LTS. Is C++17 compelling enough to<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> justify this again?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * GCC 4.9 probably isn't sufficient to justify an increase for anyone, as<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> it lacks two of the more sought-after features of C++14 (variable templates<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> and generalized constexpr). So IMO we should require a bump to GCC 5 or<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> higher, or not at all.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> * Clang 6 supports all of C++20, and it builds with only C++11, so we<o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> shouldn't have to worry too much about the problem of needing to "daisy<o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> chain" compilers to finally get the latest version of LLVM building. "GCC<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> 4.8 -> Clang 6 - > Clang ToT" should hold up through C++1z.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> * While we obviously can't be tied to the versioning of every single distro<o:p></o:p></p>
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</div>
<div>
<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> out there, some are "bigger" than others. Which are big enough that<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> warrant serious consideration? The ones I found are (and I did my best to<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> aggregate all this, but please correct me if anything is incorrect or<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> misrepresented):<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> OpenBSD - Ships with GCC 4.2.1 anyway. They are already having to<o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> bootstrap something, so the proposal here does not change anything, because<o:p></o:p></p>
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</div>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> even current LLVM doesn't compile with GCC 4.2.1<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> CentOS & RHEL - No version of Distro, including trunk, has GCC >= 4.8.5<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> (are there ports?)<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Debian - Minimum version 9 for GCC >= 5 (are there ports for earlier<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> releases?)<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">> Fedora - Minimum version 24 for GCC >= 5, minimum version 26 for GCC >= 7<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> Ubuntu - Minimum LTS 16.04 for GCC >= 5<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> NetBSD - Version 7 has GCC 4.8.4 by default, but contains port for 5.3.0<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> FreeBSD - Minimum Version 11 for GCC >= 5<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> So, thoughts?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> [1] - Note that we'd need to wait a few more revs for MSVC before allowing<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> C++17, but given that it's becoming easier and easier to bump the minimum<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> MSVC version, I'm discounting this as a factor, as MSVC will not really be<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> the bottleneck in any real sense.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> On Tue, Oct 4, 2016 at 2:15 PM Mehdi Amini <mehdi.amini at<span class="m1966951477189470441apple-converted-space"> </span><a href="http://apple.com/" target="_blank"><span style="color:purple">apple.com</span></a>>
wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> On Oct 4, 2016, at 2:10 PM, Reid Kleckner <rnk at<span class="m1966951477189470441apple-converted-space"> </span><a href="http://google.com/" target="_blank"><span style="color:purple">google.com</span></a>>
wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> On Tue, Oct 4, 2016 at 11:58 AM, Mehdi Amini <mehdi.amini at<span class="m1966951477189470441apple-converted-space"> </span><a href="http://apple.com/" target="_blank"><span style="color:purple">apple.com</span></a>><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> On Oct 4, 2016, at 8:40 AM, Reid Kleckner via llvm-dev <<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> llvm-dev at<span class="m1966951477189470441apple-converted-space"> </span><a href="http://lists.llvm.org/" target="_blank"><span style="color:purple">lists.llvm.org</span></a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> On Tue, Oct 4, 2016 at 8:29 AM, Zachary Turner <zturner at<span class="m1966951477189470441apple-converted-space"> </span><a href="http://google.com/" target="_blank"><span style="color:purple">google.com</span></a>><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>>> I ask because many of these LTS distros are notoriously slow at updating<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>>> their packages. While some people may think C++14 doesn't provide enough<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>>> bang for the buck to justify bumping to GCC 4.9, C++17 definitely does. But<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>>> at that point we're going to be talking about GCC 6.1 or 6.2, which is<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>>> going to be significantly harder unless we want to wait 5-7 years, and I<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>>> suspect people won't.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> If by "notoriously slow" you mean they don't bump their toolchain<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> versions at all, then yeah. We just wait until the LTS release is at<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> end-of-life before dropping it.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> That’s the first time I read about this policy: we support every linux<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> LTS distribution till their end-of-life? Only Ubuntu? Do you have a pointer<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> where it is documented / discussed?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> (Note that Ubuntu LTS is 5 years AFAIK.)<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> Sorry, I didn't mean to refer to the LTS support lifetime. I just meant we<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> support the last LTS until we can reasonably expect users to have upgraded<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> to the new one. If there's an LTS release every two years, then we want to<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> keep supporting them for at least three years to give people a year to<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> upgrade.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> OK, got it.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> Thanks for clarifying!<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> Mehdi<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:36.0pt">>> <o:p></o:p></p>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">_______________________________________________<br>
LLVM Developers mailing list<br>
<a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><span style="color:purple">llvm-dev@lists.llvm.org</span></a><br>
<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank"><span style="color:purple">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</span></a><o:p></o:p></p>
</div>
</blockquote>
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</div>
</blockquote>
</div>
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</blockquote>
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</blockquote>
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<div style="margin-left:36.0pt">
<p class="MsoNormal" style="margin-left:36.0pt">_______________________________________________<br>
LLVM Developers mailing list<br>
<a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><span style="color:purple">llvm-dev@lists.llvm.org</span></a><br>
<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank"><span style="color:purple">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</span></a><o:p></o:p></p>
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</blockquote>
</div>
</div>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:9.0pt;font-family:Helvetica">_______________________________________________<br>
LLVM Developers mailing list<br>
</span><a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><span style="font-size:9.0pt;font-family:Helvetica;color:purple">llvm-dev@lists.llvm.org</span></a><span style="font-size:9.0pt;font-family:Helvetica"><br>
</span><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank"><span style="font-size:9.0pt;font-family:Helvetica;color:purple">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</span></a><o:p></o:p></p>
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</blockquote>
</div>
</div>
<p class="MsoNormal" style="margin-left:36.0pt">_______________________________________________<br>
LLVM Developers mailing list<br>
<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br>
<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></p>
</blockquote>
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