<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:x="urn:schemas-microsoft-com:office:excel" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 14 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;}
@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman","serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
span.m-678642296597797418apple-tab-span
{mso-style-name:m_-678642296597797418apple-tab-span;}
span.EmailStyle18
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri","sans-serif";}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
/* List Definitions */
@list l0
{mso-list-id:283780148;
mso-list-template-ids:243852270;}
@list l1
{mso-list-id:824784998;
mso-list-template-ids:-637007486;}
@list l1:level1
{mso-level-number-format:bullet;
mso-level-text:;
mso-level-tab-stop:.5in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:Symbol;}
@list l1:level2
{mso-level-number-format:bullet;
mso-level-text:o;
mso-level-tab-stop:1.0in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:"Courier New";
mso-bidi-font-family:"Times New Roman";}
@list l1:level3
{mso-level-number-format:bullet;
mso-level-text:;
mso-level-tab-stop:1.5in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:Wingdings;}
@list l1:level4
{mso-level-number-format:bullet;
mso-level-text:;
mso-level-tab-stop:2.0in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:Wingdings;}
@list l1:level5
{mso-level-number-format:bullet;
mso-level-text:;
mso-level-tab-stop:2.5in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:Wingdings;}
@list l1:level6
{mso-level-number-format:bullet;
mso-level-text:;
mso-level-tab-stop:3.0in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:Wingdings;}
@list l1:level7
{mso-level-number-format:bullet;
mso-level-text:;
mso-level-tab-stop:3.5in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:Wingdings;}
@list l1:level8
{mso-level-number-format:bullet;
mso-level-text:;
mso-level-tab-stop:4.0in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:Wingdings;}
@list l1:level9
{mso-level-number-format:bullet;
mso-level-text:;
mso-level-tab-stop:4.5in;
mso-level-number-position:left;
text-indent:-.25in;
mso-ansi-font-size:10.0pt;
font-family:Wingdings;}
ol
{margin-bottom:0in;}
ul
{margin-bottom:0in;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Well… Ubuntu 16.04 came with gcc 5, and deploying Visual Studio 2015 should be a done deal in Windows shops, which suggests moving to C++14 should be no problem.<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's nice to see this week's version of MSVC supports C++17 but deploying through corporate IT can take a while. ("This week's version" because the blog post
is dated Monday.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt">
<div>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<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""> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>Zachary Turner via llvm-dev<br>
<b>Sent:</b> Thursday, May 10, 2018 3:00 PM<br>
<b>To:</b> JF Bastien<br>
<b>Cc:</b> via llvm-dev<br>
<b>Subject:</b> Re: [llvm-dev] Using C++14 code in LLVM<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal">Consider me on board with the highest version we can come to an agreement on :)<o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal">On Thu, May 10, 2018 at 11:50 AM JF Bastien <<a href="mailto:jfbastien@apple.com">jfbastien@apple.com</a>> wrote:<o:p></o:p></p>
</div>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<div>
<div>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<div>
<p class="MsoNormal">On May 10, 2018, at 11:35 AM, Zachary Turner <<a href="mailto:zturner@google.com" target="_blank">zturner@google.com</a>> wrote:<o:p></o:p></p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal">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>
</div>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
<div>
<div>
<div>
<p class="MsoNormal">Such a fatalistic view, let’s trust ourselves to be better next time ;-)<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">But seriously: we can learn from moving to C++14, and use what we’ve learned to move to C++17 faster next time. Also consider the code churn we’ll encounter as we fix incompatibilities with C++11 / C++14, drop unnecessary code, upgrade
various uses, that will happen regardless of moving to C++17 and will take a little while to occur. There would be more of that type of churn if we went straight to C++17.<o:p></o:p></p>
</div>
</div>
</div>
<div>
<div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<div>
<div>
<div>
<p class="MsoNormal">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>
</div>
</div>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
<div>
<div>
<div>
<p class="MsoNormal">Mostly library so far, yes, but the GCC 6 support for C++17 language isn’t great either:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<div>
<p class="MsoNormal"> - New auto rules for direct-list-initialization<span class="m-678642296597797418apple-tab-span">
</span><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - static_assert with no message<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - typename in a template template parameter<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - Nested namespace definition<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - Attributes for namespaces and enumerators<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - u8 character literals<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - Allow constant evaluation for all non-type template arguments<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - Fold Expressions<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - Unary fold expressions and empty parameter packs<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - __has_include in preprocessor conditional<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> - Differing begin and end types in range-based for\<o:p></o:p></p>
</div>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">From: <a href="https://en.cppreference.com/w/cpp/compiler_support" target="_blank">https://en.cppreference.com/w/cpp/compiler_support</a><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">The only thing that’s really nice are fold expressions, and I hope they’re not buggy in GCC 6.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Otherwise the list is missing a good amount for C++17 language features, and brings up the discussion of which GCC version is the minimum we mandate. I’d rather avoid that discussion. Let’s assume GCC 6, if we get 7 then great, but it doesn’t
matter if we stick to C++14.<o:p></o:p></p>
</div>
</div>
</div>
<div>
<div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<div>
<div>
<div>
<p class="MsoNormal">On Thu, May 10, 2018 at 11:28 AM JF Bastien <<a href="mailto:jfbastien@apple.com" target="_blank">jfbastien@apple.com</a>> wrote:<o:p></o:p></p>
</div>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<div>
<div>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<div>
<p class="MsoNormal">On May 10, 2018, at 11:22 AM, Zachary Turner <<a href="mailto:zturner@google.com" target="_blank">zturner@google.com</a>> wrote:<o:p></o:p></p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal">Windows has never been the issue. Honestly, MSVC on Windows is "fully C++17 conformant" [1].<o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">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>
</div>
</div>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
<div>
<div>
<div>
<p class="MsoNormal">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>
</div>
</div>
</div>
<div>
<div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<div>
<div>
<div>
<p class="MsoNormal">Just my 2c.<o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">[1] <a href="https://blogs.msdn.microsoft.com/vcblog/2018/05/07/announcing-msvc-conforms-to-the-c-standard/" target="_blank">
https://blogs.msdn.microsoft.com/vcblog/2018/05/07/announcing-msvc-conforms-to-the-c-standard/</a><o:p></o:p></p>
</div>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal">On Thu, May 10, 2018 at 11:18 AM Eric Christopher <<a href="mailto:echristo@gmail.com" target="_blank">echristo@gmail.com</a>> wrote:<o:p></o:p></p>
</div>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<div>
<p class="MsoNormal">Once again, I'm totally down for this and think we should do it. I worry about windows, but ...<o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Zach: How's windows c++14 support looking?<o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">-eric<o:p></o:p></p>
</div>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal">On Thu, May 10, 2018 at 10:01 AM JF Bastien 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>
</div>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<div>
<div>
<p class="MsoNormal">Hi folks!<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Six more months have come and gone, and maybe we could move LLVM to C++14 now?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">The issues I picked out from the last discussion:<o:p></o:p></p>
</div>
<div>
<ol start="1" type="1">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
Some folks want an official policy about compiler support before updating the standard version we use.<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
Worries about which GCC version is available in which distro.<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
Worries about MSVC.<o:p></o:p></li></ol>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">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>
</div>
<div>
<ul type="disc">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
WebKit is <a href="https://lists.webkit.org/pipermail/webkit-dev/2018-March/029922.html" target="_blank">moving to C++17</a> (from C++14) right now †<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
Chromium <a href="https://groups.google.com/a/chromium.org/d/msg/cxx/ow7hmdDm4yw/eV6KWL2yAQAJ" target="_blank">started moving to C++14</a> in August of last year<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
Firefox uses <a href="https://developer.mozilla.org/en-US/docs/Mozilla/Using_CXX_in_Mozilla_code" target="_blank">some C++14</a><o:p></o:p></li></ul>
</div>
<div>
<p class="MsoNormal">What I get from this data: if your distro bundles a modern web browser, it already builds some C++14,
<i>somehow</i>.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">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>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Thanks!<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">JF<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">† 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>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<div>
<p class="MsoNormal">> Last time we discussed this, the consensus was "I think we can survive<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> another year without generalized constexpr and variable templates".<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Well, we did indeed survive. And it's been exactly a year! So naturally,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> it only makes sense to revive this :)<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> There's an active conversation going on in IRC right now, and it seems like<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> there is more desire than there was last year.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> What are the main gains from allowing C++14?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * Variable templates<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * Generalized constexpr<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * Return-type Deduction<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * Generic Lambdas<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * std::make_unique<> (the source of many build bot breakages)<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> What are the main gains from allowing C++17? [1]<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * [[nodiscard]] attribute<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * structured bindings<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * constexpr-if<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * guaranteed copy elision<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * numerous new library types: optional, string_view, variant, byte,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * numerous new algorithms: parallel algorithms, too many to list<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * Probably some more, but I just tried to hit the biggest ones.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> First, it seems like if we want to enable C++14 we need GCC >= 5.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> And if we want to enable C++17 we need GCC >= 7.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> With that out of the way, here were some of the issues that were raised<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> last time:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Issue: Ubuntu 14.04 LTS is on GCC 4.8.x, and we have to support it until<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> end of life.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Resolution: LTS is right around the corner, in 6 more months.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Issue: Various other platforms have older GCCs as their system compiler,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> and it's annoying to upgrade.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Question: Do any of these not have a port you can install? For example,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> NetBSD 7 appears to have GCC 5.3 as a port, if DistroWatch is any<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> indication. It could be wrong though and I could also be misinterpreting<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> it.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Issue: If we're going to make people bootstrap a compiler, we might as well<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> go all the way to C++17.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Comment: I'm not opposed.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Some questions / comments of my own:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * Where is this policy about Ubuntu and LTS documented? Does this mean,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> for example, that we will not be able to use C++17 until 2023 (16.04 LTS<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> has only GCC 5.3.1)? That seems a bit unreasonable. And there's no<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> guarantee that 18.04 LTS will even have GCC 7 or higher either, so it could<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> be 2025 or 2027.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * We've asked people in the past to build a modern toolchain. For example,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> we did it with C++11 and Ubuntu 12.04 LTS. Is C++17 compelling enough to<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> justify this again?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * GCC 4.9 probably isn't sufficient to justify an increase for anyone, as<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> it lacks two of the more sought-after features of C++14 (variable templates<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> and generalized constexpr). So IMO we should require a bump to GCC 5 or<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> higher, or not at all.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * Clang 6 supports all of C++20, and it builds with only C++11, so we<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> shouldn't have to worry too much about the problem of needing to "daisy<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> chain" compilers to finally get the latest version of LLVM building. "GCC<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> 4.8 -> Clang 6 - > Clang ToT" should hold up through C++1z.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> * While we obviously can't be tied to the versioning of every single distro<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> out there, some are "bigger" than others. Which are big enough that<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> warrant serious consideration? The ones I found are (and I did my best to<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> aggregate all this, but please correct me if anything is incorrect or<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> misrepresented):<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> OpenBSD - Ships with GCC 4.2.1 anyway. They are already having to<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> bootstrap something, so the proposal here does not change anything, because<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> even current LLVM doesn't compile with GCC 4.2.1<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> CentOS & RHEL - No version of Distro, including trunk, has GCC >= 4.8.5<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> (are there ports?)<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Debian - Minimum version 9 for GCC >= 5 (are there ports for earlier<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> releases?)<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Fedora - Minimum version 24 for GCC >= 5, minimum version 26 for GCC >= 7<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> Ubuntu - Minimum LTS 16.04 for GCC >= 5<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> NetBSD - Version 7 has GCC 4.8.4 by default, but contains port for 5.3.0<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> FreeBSD - Minimum Version 11 for GCC >= 5<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> So, thoughts?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> [1] - Note that we'd need to wait a few more revs for MSVC before allowing<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> C++17, but given that it's becoming easier and easier to bump the minimum<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> MSVC version, I'm discounting this as a factor, as MSVC will not really be<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> the bottleneck in any real sense.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> On Tue, Oct 4, 2016 at 2:15 PM Mehdi Amini <mehdi.amini at
<a href="http://apple.com/" target="_blank">apple.com</a>> wrote:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>> On Oct 4, 2016, at 2:10 PM, Reid Kleckner <rnk at <a href="http://google.com/" target="_blank">
google.com</a>> wrote:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>> On Tue, Oct 4, 2016 at 11:58 AM, Mehdi Amini <mehdi.amini at
<a href="http://apple.com/" target="_blank">apple.com</a>><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>> wrote:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>>> On Oct 4, 2016, at 8:40 AM, Reid Kleckner via llvm-dev <<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>> llvm-dev at <a href="http://lists.llvm.org/" target="_blank">
lists.llvm.org</a>> wrote:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>>> On Tue, Oct 4, 2016 at 8:29 AM, Zachary Turner <zturner at
<a href="http://google.com/" target="_blank">google.com</a>><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>> wrote:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>>>> I ask because many of these LTS distros are notoriously slow at updating<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>>> their packages. While some people may think C++14 doesn't provide enough<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>>> bang for the buck to justify bumping to GCC 4.9, C++17 definitely does. But<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>>> at that point we're going to be talking about GCC 6.1 or 6.2, which is<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>>> going to be significantly harder unless we want to wait 5-7 years, and I<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>>> suspect people won't.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>>> If by "notoriously slow" you mean they don't bump their toolchain<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>> versions at all, then yeah. We just wait until the LTS release is at<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>> end-of-life before dropping it.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>>> That’s the first time I read about this policy: we support every linux<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>> LTS distribution till their end-of-life? Only Ubuntu? Do you have a pointer<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>> where it is documented / discussed?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>> (Note that Ubuntu LTS is 5 years AFAIK.)<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>> Sorry, I didn't mean to refer to the LTS support lifetime. I just meant we<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>> support the last LTS until we can reasonably expect users to have upgraded<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>> to the new one. If there's an LTS release every two years, then we want to<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>> keep supporting them for at least three years to give people a year to<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>> upgrade.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>> OK, got it.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>> Thanks for clarifying!<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>> Mehdi<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">>><o:p> </o:p></p>
</div>
</div>
</div>
<p class="MsoNormal">_______________________________________________<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>
</div>
</div>
</blockquote>
</div>
</div>
</div>
</div>
</blockquote>
</div>
</div>
</div>
</div>
</blockquote>
</div>
</div>
</div>
</body>
</html>