<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Sep 4, 2015, at 12:22 AM, Eric Christopher <<a href="mailto:echristo@gmail.com" class="">echristo@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""><br class=""><div class="gmail_quote"><div dir="ltr" class="">On Thu, Sep 3, 2015 at 11:45 PM Mehdi Amini <<a href="mailto:mehdi.amini@apple.com" class="">mehdi.amini@apple.com</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;">Hi,<br class=""><br class="">> On Sep 2, 2015, at 7:31 PM, Peter Collingbourne via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank" class="">llvm-dev@lists.llvm.org</a>> wrote:<br class="">><br class="">> On Thu, Sep 03, 2015 at 01:10:42AM +0000, Eric Christopher wrote:<br class="">>> On Tue, Sep 1, 2015 at 10:43 AM Duncan P. N. Exon Smith <<br class="">>><span class="Apple-converted-space"> </span><a href="mailto:dexonsmith@apple.com" target="_blank" class="">dexonsmith@apple.com</a>> wrote:<br class="">>><br class="">>>><br class="">>>>> On 2015-Aug-31, at 18:09, Eric Christopher <<a href="mailto:echristo@gmail.com" target="_blank" class="">echristo@gmail.com</a>> wrote:<br class="">>>>><br class="">>>>><br class="">>>>><br class="">>>>> On Mon, Aug 31, 2015 at 5:50 PM Duncan P. N. Exon Smith <<br class="">>>><span class="Apple-converted-space"> </span><a href="mailto:dexonsmith@apple.com" target="_blank" class="">dexonsmith@apple.com</a>> wrote:<br class="">>>>><br class="">>>>>> On 2015-Aug-31, at 12:21, Eric Christopher <<a href="mailto:echristo@gmail.com" target="_blank" class="">echristo@gmail.com</a>> wrote:<br class="">>>>>> Yep. This is where I was going :)<br class="">>>>><br class="">>>>> Glad I found consensus, but I want to double-check that this makes<br class="">>>>> sense to add to the driver. I didn't quite think through the<br class="">>>>> implications myself.<br class="">>>>><br class="">>>>> Since the driver doesn't know if there's any bitcode, or if LTO is<br class="">>>>> going to be invoked, it seems like I'll have to change the noasserts<br class="">>>>> driver to *always* pass the option to the linker just in case we are<br class="">>>>> doing LTO. Is this reasonable?<br class="">>>>><br class="">>>>> Also, I realized that passing `-mllvm -disable-llvm-verifier` to ld64<br class="">>>>> is redundant... so I'm thinking `-mllvm -disable-verify`. Make<br class="">>>>> sense?<br class="">>>>><br class="">>>>> *sigh* Reasons to hate the driver interface again...<br class="">>>>><br class="">>>>> I guess this is ok. Could possibly add it to the existing terrible<br class="">>>> "enable this pass" interface on liblto as well.<br class="">>>><br class="">>>> The linker doesn't know whether clang was built with asserts, though.<br class="">>>><br class="">>>> We could just make it implicit: move the decision to libLTO itself. Given<br class="">>>> that clang and libLTO.dylib are different executables anyway -- and you<br class="">>>> might be interposing an asserts libLTO.dylib to use with an installed clang<br class="">>>> -- maybe it's even better?<br class="">>>><br class="">>>><br class="">>> *nod* We could do that. Seems better than the alternative.<br class="">><br class="">> +1<br class="">><br class="">>>>> I don't suppose ld64 could move to a model like we're talking about with<br class="">>>> lld that pcc is working on?<br class="">>>><br class="">>>> What specifically?<br class="">>><br class="">>><br class="">>> Ah, using the C++ interface to handle everything and not using libLTO at<br class="">>> all.<br class="">>><br class="">>> He can speak more to this though.<br class="">><br class="">> The C++ interface is much more convenient for a C++ program to use, but<br class="">> clients need to revlock themselves to LLVM in order to use it.<br class="">><br class="">> In theory the same does not apply to libLTO, but we do end up changing it<br class="">> occasionally to add new APIs which ld64 promptly starts using, so it isn't<br class="">> clear how much ld64 gains by relying on libLTO,<br class=""><br class="">Backward/Forward compatibility?<br class="">Drop any version of clang/libLTO and still be able to use the system provided linker on any version of OS X?<br class="">Sounds like a valuable feature to me, which is what I believe was (is?) sought by the C API in general (but that’s another story).<br class=""><br class=""></blockquote><div class=""><br class=""></div><div class="">Static linking against the parts of llvm you care about? There's nothing in the ld64 build system that means it can't do this :)</div></div></div></div></blockquote><div><br class=""></div><div>I’m not sure how is that supposed to work?</div><div>I drop a new clang/libLTO on the system, clang generates bitcode, and libLTO handles it.</div><div><br class=""></div><div>If ld64 was statically linked against LLVM, it couldn’t read the new bitcode right?</div><div><br class=""></div><div>— </div><div>Mehdi</div><div><br class=""></div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="gmail_quote"><div class=""><br class=""></div><div class="">And you already don't have forward compatibility because of what Peter said in the first place. :)</div></div></div></div></blockquote><blockquote type="cite" class=""><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="gmail_quote"><div class=""><br class=""></div><div class="">Anyhow, I don't actually expect this to change. Also the C API has to change, but yes that's a different thread.</div><div class=""><br class=""></div><div class="">-eric</div><div class=""> </div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;">—<br class="">Mehdi<br class=""><br class=""><br class="">> or whether the burden on<br class="">> in-tree clients is worth it (there are certainly a number of internal APIs<br class="">> that are more clumsy as a result of needing to support libLTO's API; see<br class="">> e.g. llvm::splitCodeGen's return value).<br class="">><br class="">> Thanks,<br class="">> --<br class="">> Peter<br class="">> _______________________________________________<br class="">> LLVM Developers mailing list<br class="">><span class="Apple-converted-space"> </span><a href="mailto:llvm-dev@lists.llvm.org" target="_blank" class="">llvm-dev@lists.llvm.org</a><br class="">><span class="Apple-converted-space"> </span><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" rel="noreferrer" target="_blank" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a></blockquote></div></div></div></blockquote></div><br class=""></body></html>