<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="">Hi,<div class=""><br class=""></div><div class="">This is hard to answer in the abstract. There are multiple knobs that impact compile time (optimization level, using fast-isel, etc).</div><div class="">Ideally we’d have an example of C output and IR output so that we can reproduce offline and profile what happens.</div><div class=""><br class=""></div><div class="">— </div><div class="">Mehdi</div><div class=""><br class=""><div class=""><div><blockquote type="cite" class=""><div class="">On Oct 12, 2016, at 8:15 AM, Andrew Kelley via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Hello,<div class=""><br class=""></div><div class="">Recently Jonathan Blow posted a short screencast discussing build time of his compiler with when no optimizations are run on the user's code.</div><div class=""><br class=""></div><div class="">Part 1: <a href="https://www.youtube.com/watch?v=HLk4eiGUic8" class="">https://www.youtube.com/watch?v=HLk4eiGUic8</a></div><div class="">Part 2: <a href="https://www.youtube.com/watch?v=mIjGYbol0O4" class="">https://www.youtube.com/watch?v=mIjGYbol0O4</a></div><div class=""><br class=""></div><div class="">He discusses what parts are taking the longest to compile, and the ultimately shows this:</div><div class=""><a href="http://i.imgur.com/BkbKcJK.png" class="">http://i.imgur.com/BkbKcJK.png</a></div><div class="">...which shows that emitting LLVM IR in memory and LLVMTargetMachineEmitToFile is the bottleneck in his compiler toolchain.</div><div class=""><br class=""></div><div class="">In fact, it was significantly faster to emit C to disk and compile with MSVC than to emit LLVM in memory and call LLVMTargetMachineEmitToFile.</div><div class=""><br class=""></div><div class="">His conclusion is that he will not depend on LLVM when his users compile with optimizations off, instead directly emitting x86_64 machine code into an object file.</div><div class=""><br class=""></div><div class="">Needless to say, this is duplicate effort. Is there any way the LLVM project could speed things up when no optimizations are run?</div><div class=""><br class=""></div><div class="">As another compiler author (<a href="http://ziglang.org/" class="">http://ziglang.org/</a>), I want to compete with Jon's speed without having to duplicate the effort that LLVM already solves.</div><div class=""><br class=""></div><div class="">Thanks for your time.</div><div class="">Andrew</div></div>
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