<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Jul 1, 2020, at 10:52 PM, Michael Kruse <<a href="mailto:llvmdev@meinersbur.de" class="">llvmdev@meinersbur.de</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="Singleton"><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><blockquote type="cite" class=""><blockquote type="cite" class="">Unit tests are very widely used across the industry, and it is certainly true that they are fully general and more flexible. This makes them attractive, but it is a trap. I’d really rather we don’t go down this route, and maintain the approach of only using unit tests for very low level things like apis in ADT etc.<br class=""></blockquote><br class="">Note that we already have unittests for non low-level APIs such as<br class="">passes (VPlan, LICM, Unrolling, ...)<br class=""><br class="">Can you elaborate on what the trap is?<br class=""></blockquote><br class="">I am also opposed to those - I think they have exactly the same problems described above, and we should invest in better testing infra to support them.<br class=""></blockquote><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Except for the linking issue, I don't see them being problems or even</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">being advantages.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">You seem to acknowledge that these kind of unit tests are widely used</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">for supposedly good reasons. </span></div></div></blockquote><div><br class=""></div><div><div class="">To be clear, I am not saying that unit tests are bad, I’m advocating we use them for things like ADT tests. I am just saying there is something better for many purposes and that we should use the better thing instead of the worse thing.</div></div><br class=""><blockquote type="cite" class=""><div class=""><div class="Singleton"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Why is LLVM special?</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""></div></div></blockquote></div><div class=""><br class=""></div><div class="">It depends on what you are comparing it against. A short answer is that LLVM is ahead of most of the rest of the industry in this respect.</div><br class=""><div class="">If you are comparing it against other compilers, one of the founding principles of LLVM is that the IR is round triable to a textual form that does not lose information. I wouldn’t go so far to say that this was novel at the time, but it was certainly unusual: most compilers used lossy dump formats. Even MachineInstr was this way until recent work. This is even mentioned in section 3.6 of <a href="http://llvm.org/pubs/2002-12-LattnerMSThesis.pdf" class="">this thesis</a>.</div><div class=""><br class=""></div><div class="">If you are comparing it to other application level software, you’ll find that testing is much more important for LLVM than for most (not all) app software, and LLVM has a LOT of tests. Individual .ll files end up containing dozens (or sometimes hundreds) of tests, and making this efficient to run, efficient to maintain, and scalable across a growing community is not a trivial matter.</div><div class=""><br class=""></div><div class="">LLVM is also unusual in that it has a very modular design, this design has many benefits including reuse, but also testability.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">-Chris</div></body></html>