<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 18 May 2017, at 01:29, Gábor Horváth via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org" class="">cfe-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class=""><div class=""><div class=""><div class="">Hi!<br class=""><br class=""></div>I wanted to revive the discussion on adding API notes feature to Clang. <br class=""><br class=""></div></div><div class=""><b class="">The description of the feature from the original discussion</b><br class=""><br class="">"API notes solve a not-uncommon problem: we invent some new Clang attribute that would be beneficial to add to some declarations in system headers (e.g., adding a ‘noreturn’ attribute to the C ‘exit’ function), but we can’t go around and fix all of the system headers everywhere. With API notes, we can write a separate YAML file that states that we want to add ‘noreturn’ to the ‘exit’ function: when we feed that YAML file into Clang as part of normal compilation (via a command-line option), Clang will add ‘noreturn’ to the ‘exit’ function when it parses the declaration of ‘exit’."</div><div class=""><br class="">The old discussion can be found here: <a href="http://lists.llvm.org/pipermail/cfe-dev/2015-December/046335.html" class="">http://lists.llvm.org/pipermail/cfe-dev/2015-December/046335.html</a><br class=""><br class=""></div><b class="">The summary of the discussion</b><br class=""><br class=""></div><div class="">* It would be useful for the static analyzer to attach additional info to the functions<br class="">* There were already other trials to get similar feature working, see <a href="https://reviews.llvm.org/D13731" class="">https://reviews.llvm.org/D13731</a><br class=""></div><div class="">* Anna has a nice summary what is the problem with augmented declarations: <a href="http://lists.llvm.org/pipermail/cfe-dev/2015-December/046378.html" class="">http://lists.llvm.org/pipermail/cfe-dev/2015-December/046378.html</a><br class=""></div><div class="">* C++ support is requested by the community, this is missing right now. <br class=""></div><div class="">* Wider range of annotation support is missing. It is also requested by the community. <br class=""></div><div class="">* Parameter annotations are supported<br class=""></div><div class="">* One of the concerns is the performance<br class=""><br class=""></div><div class=""><b class="">The case for adding API Notes</b><br class=""><br class=""></div><div class="">* Importing annotations from external source looks to be an interesting feature for the community<br class=""></div><div class="">* Sean presented some API checkers which works based on special annotations: <a href="http://llvm.org/devmtg/2017-03//2017/02/20/accepted-sessions.html#29" class="">http://llvm.org/devmtg/2017-03//2017/02/20/accepted-sessions.html#29</a><br class=""></div><div class="">* Similar feature can be used to provide fake implementations for functions. It could help to finish a half done feature of the Static Analyzer that was implemented during a GSoC project: <a href="https://www.google-melange.com/archive/gsoc/2014/orgs/llvm/projects/xazax.html" class="">https://www.google-melange.com/archive/gsoc/2014/orgs/llvm/projects/xazax.html</a><br class="">* Performance might be crucial for regular compilation, but less of a problem for the Clang Static Analyzer which tends to be slower than compilations, so it is less likely to be bottlenecked by this phase<br class=""></div><div class="">* It would also be possible to import sanitizer/optimizer/codegen related annotations<br class=""></div><div class=""><br class=""></div><div class=""><b class="">Proposed roadmap</b><br class=""></div><div class=""><br class=""></div><div class="">* Commit the feature as is<br class=""></div><div class="">* Extend it with C++ support (namespaces, overloading, templates..)<br class=""></div><div class="">* Extend it with additional annotations, and attaching custom data (like fake function bodies)<br class=""></div><div class=""><br class=""></div><div class="">What do you think? What are the main concerns with this feature?<br class=""><br class=""></div></div></div></blockquote><div><br class=""></div><div>I'm interested in having something like API notes available in Clang, definitely. I have a few questions though:</div><div><br class=""></div><div>- Is YAML absolutely necessary? What I think I don't understand is what the actual data structure is that it will represent. Is it a configuration for something that will actually imbue the attributes into the IR? Or is it a dump of an in-memory data structure, that specifies a side-table of attributes for the generated IR?</div><div><br class=""></div><div>- What is the overlap with the sanitiser special case list, which provides regular expressions and a simple configuration language? Can one be ported to be built on top of the other? Is there a roadmap/plan for unifying that features?</div><div><br class=""></div><div>- What is the programmatic API for imbuing the attributes before IR generation? Say I'm using clang as a library, is there a data structure (in-memory) that I can programmatically define so that the attributes are applied to the IR as a transformation? If so, should this be part of the LLVM back-end instead? Or should it be a stand-alone library that clang uses in the static analysis phase? I can certainly imagine this being useful in LTO or PGO, not necessarily tied to Clang.</div><div><br class=""></div><div>Cheers</div></div><br class=""><div class="">
<div style="color: rgb(0, 0, 0); letter-spacing: 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; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); letter-spacing: 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; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">-- Dean</div></div>
</div>
<br class=""></body></html>