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    <div class="moz-cite-prefix">On 10/25/2017 12:21 PM, Xinliang David
      Li wrote:<br>
    </div>
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cite="mid:CALRgJCM+ZSmBAU0-Z4KF9sS3ufiNOsjCHy1AstudUF_g2f9DLw@mail.gmail.com"
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          <div class="gmail_quote">On Wed, Oct 25, 2017 at 10:19 AM, Hal
            Finkel <span dir="ltr"><<a moz-do-not-send="true"
                href="mailto:hfinkel@anl.gov" target="_blank">hfinkel@anl.gov</a>></span>
            wrote:<br>
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                  <div class="m_3151644750661815301moz-cite-prefix">On
                    10/25/2017 12:16 PM, Xinliang David Li via llvm-dev
                    wrote:<br>
                  </div>
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                      <div class="gmail_extra"><br>
                        <div class="gmail_quote">On Tue, Oct 17, 2017 at
                          11:50 PM, Chandler Carruth via llvm-dev <span
                            dir="ltr"><<a moz-do-not-send="true"
                              href="mailto:llvm-dev@lists.llvm.org"
                              target="_blank">llvm-dev@lists.llvm.org</a>></span>
                          wrote:<br>
                          <blockquote class="gmail_quote"
                            style="margin:0 0 0 .8ex;border-left:1px
                            #ccc solid;padding-left:1ex">
                            <div dir="ltr">Greetings everyone!
                              <div><br>
                              </div>
                              <div>The new pass manager is getting
                                extremely close to the point where I'm
                                not aware of any significant outstanding
                                work needed, and I'd like to see what
                                else would be needed to enable it by
                                default. Here are the current
                                functionality I'm aware of outstanding:</div>
                              <div><br>
                              </div>
                              <div>1) Does not do non-trivial loop
                                unswitching. Majority of this is in <a
                                  moz-do-not-send="true"
                                  href="https://reviews.llvm.org/D34200"
                                  target="_blank">https://reviews.llvm.org/D3420<wbr>0</a> but
                                will need one or two small follow-ups.</div>
                              <div><br>
                              </div>
                              <div>2) Currently, sanitizers don't work
                                correctly with it. Thanks to the work of
                                others, the missing infrastructure has
                                been added and I'll send a patch to wire
                                this up this week.</div>
                              <div><br>
                              </div>
                              <div>3) Missing support for 'optnone'.
                                I've been working on this, but the
                                existing testing wasn't as thorough as I
                                wanted, so it is going slowly. I've got
                                about 1/4 of this implemented and should
                                have patches this week or next.</div>
                              <div><br>
                              </div>
                              <div>4) Missing opt-bisect (or similar)
                                facility. This looks pretty trivial to
                                add, but I've not even started. If
                                anyone is interested in it, go for it.
                                We might even be able to do something
                                simpler using the generic debug counters
                                and get equivalent functionality.</div>
                              <div><br>
                              </div>
                              <div>... that's it?</div>
                            </div>
                          </blockquote>
                          <div><br>
                          </div>
                          <div><br>
                          </div>
                          <div>Missing support of 'print-after-all' or
                            'print-after-passX'  is another major
                            usability loss.</div>
                          <div><br>
                          </div>
                          <div>Regarding the default switch, maybe do it
                            in two steps: </div>
                          <div><br>
                          </div>
                          <div>1) Switch the default for PGO build first</div>
                          <div>2) Switch the default for all modes.</div>
                        </div>
                      </div>
                    </div>
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                  <br>
                </span> Why?<span class="HOEnZb"><font color="#888888"><br>
                    <br>
                  </font></span></div>
            </blockquote>
            <div><br>
            </div>
            <div>1) PGO users benefit from the PM change the most</div>
            <div>2) I suppose incremental changes are always better and
              causes fewer churns?</div>
          </div>
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    <br>
    I'm somewhat nervous about having the PGO builds differ so much from
    the non-PGO builds. My thought is that: (Significant) regressions in
    execution performance or compile time need to be fixed regardless.
    Maybe there's some flexibility on code-size regressions (e.g., such
    that we could delay the transition for -Oz if necessary)?<br>
    <br>
     -Hal<br>
    <br>
    <blockquote
cite="mid:CALRgJCM+ZSmBAU0-Z4KF9sS3ufiNOsjCHy1AstudUF_g2f9DLw@mail.gmail.com"
      type="cite">
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            <div><br>
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            <div>David</div>
            <div> </div>
            <blockquote class="gmail_quote" style="margin:0 0 0
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              <div bgcolor="#FFFFFF" text="#000000"><span class="HOEnZb"><font
                    color="#888888">  -Hal</font></span><span class=""><br>
                  <br>
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                      <div class="gmail_extra">
                        <div class="gmail_quote">
                          <div><br>
                          </div>
                          <div>David</div>
                          <div><br>
                          </div>
                          <div><br>
                          </div>
                          <div> </div>
                          <blockquote class="gmail_quote"
                            style="margin:0 0 0 .8ex;border-left:1px
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                            <div dir="ltr">
                              <div><br>
                              </div>
                              <div>Optimization quality / run-time
                                performance:</div>
                              <div>- We've been using it at Google
                                extensively and are very happy with the
                                optimization quality. Benchmarks look
                                *very* good here.</div>
                              <div>- More data from other users would be
                                important.</div>
                              <div>- You can try it out with
                                `-fexperimental-new-pass-manag<wbr>er`
                                to Clang</div>
                              <div><br>
                              </div>
                              <div>Compile-time performance:</div>
                              <div>- Sometimes *much* better due to
                                cached analyses.</div>
                              <div>- Sometimes worse, typically due to
                                more / different inlining in turn
                                running main pipeline (GVN +
                                InstCombine) more times or over more
                                code.</div>
                              <div>- Overall somewhat a wash, but the
                                increased compile times typically due to
                                the optimizer "trying" harder, so not
                                too concerning on our end.</div>
                              <div>- Again, more feedback from other
                                users good:
                                `-fexperimental-new-pass-manag<wbr>er`
                                to Clang</div>
                              <div><br>
                              </div>
                              <div>Once the four missing things land,
                                I'll also happily work on collecting
                                some of the basics on the test-suite and
                                CTMark. But I suspect more "in the wild"
                                data would really be useful here given
                                the significance of the change.</div>
                              <div><br>
                              </div>
                              <div>Thoughts? What else (beyond the four
                                items above and feedback on run-time and
                                compile-time) would folks like to see?</div>
                              <div><br>
                              </div>
                              <div>Once this happens, I'll also be
                                preparing some batch, mechanical updates
                                to the test suite to primarily use the
                                new pass manager. Also there is lots of
                                documentation updates that will be
                                needed here.</div>
                              <span class="m_3151644750661815301HOEnZb"><font
                                  color="#888888">
                                  <div><br>
                                  </div>
                                  <div>-Chandler</div>
                                </font></span>
                              <div><br>
                              </div>
                              <div>PS: I'll be sending a note to cfe-dev
                                as a "heads up" about this discussion as
                                in some ways, the default flip is mostly
                                a Clang default flip. But hopefully our
                                doc updates will trigger this being
                                "perceived" as the default for other
                                frontends, and I'll try to reach out to
                                other major frontends as well (Swift and
                                Rust are on my radar, and I've already
                                started talking with Philip Reames about
                                their Falcon JIT).</div>
                            </div>
                            <br>
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                            <br>
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</pre>
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    </span><span class=""><pre class="m_3151644750661815301moz-signature" cols="72">-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
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</blockquote>
<pre class="moz-signature" cols="72">-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre></body></html>