<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Apr 18, 2016 at 4:36 PM, Philip Reames <span dir="ltr"><<a href="mailto:listmail@philipreames.com" target="_blank">listmail@philipreames.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
  
    
  
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    <div>On 04/18/2016 04:05 PM, Easwaran Raman
      via llvm-dev wrote:<br>
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          <div class="gmail_quote">On Mon, Apr 18, 2016 at 3:25 PM,
            Chandler Carruth <span dir="ltr"><<a href="mailto:chandlerc@gmail.com" target="_blank"></a><a href="mailto:chandlerc@gmail.com" target="_blank">chandlerc@gmail.com</a>></span>
            wrote:<br>
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                    <div dir="ltr">On Mon, Apr 18, 2016 at 3:20 PM
                      Easwaran Raman <<a href="mailto:eraman@google.com" target="_blank">eraman@google.com</a>>
                      wrote:<br>
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                          <div class="gmail_quote">On Mon, Apr 18, 2016
                            at 3:00 PM, Chandler Carruth via llvm-dev <span dir="ltr"><<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>></span>
                            wrote:<br>
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                                    <div dir="ltr">On Mon, Apr 18, 2016
                                      at 2:48 PM Hal Finkel <<a href="mailto:hfinkel@anl.gov" target="_blank"></a><a href="mailto:hfinkel@anl.gov" target="_blank">hfinkel@anl.gov</a>>
                                      wrote:<br>
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                                          <blockquote style="border-left-width:2px;border-left-style:solid;border-left-color:rgb(16,16,255);margin-left:5px;padding-left:5px;color:rgb(0,0,0);font-weight:normal;font-style:normal;text-decoration:none;font-family:helvetica,arial,sans-serif;font-size:12pt"><b>From:
                                            </b>"Xinliang David Li" <<a href="mailto:davidxl@google.com" target="_blank"></a><a href="mailto:davidxl@google.com" target="_blank">davidxl@google.com</a>><br>
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                                                <div class="gmail_quote">On
                                                  Mon, Apr 18, 2016 at
                                                  2:33 PM, Mehdi Amini <span dir="ltr"><<a href="mailto:mehdi.amini@apple.com" target="_blank"></a><a href="mailto:mehdi.amini@apple.com" target="_blank">mehdi.amini@apple.com</a>></span>
                                                  wrote:
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                                                        <div>In the
                                                          current case
                                                          at stake: the
                                                          issue is that
                                                          we can't make
                                                          the Analysis
                                                          library using
                                                          anything from
                                                          the
                                                          ProfileData
                                                          library.
                                                          Conceptually
                                                          there is a
                                                          problem IMO.</div>
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                                                  <div><br>
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                                                  <div>Yes -- this is a
                                                    very good point.</div>
                                                </div>
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                                        </div>
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                                      <div>
                                        <div style="font-family:arial,helvetica,sans-serif;font-size:10pt;color:rgb(0,0,0)">Independent
                                          of anything else, +1.<br>
                                        </div>
                                      </div>
                                    </span></blockquote>
                                  <div><br>
                                  </div>
                                  <div>The design of ProfileData and
                                    reading profile information in the
                                    entire middle end had a really
                                    fundamental invariant that folks
                                    seem to have lost track of:</div>
                                  <div><br>
                                  </div>
                                  <div>a) There is exactly *one* way to
                                    get at profile information from
                                    general analyses and transforms: a
                                    dedicated analysis pass that manages
                                    access to the profile info.</div>
                                  <div><br>
                                  </div>
                                  <div>b) There is exactly *one* way for
                                    this analysis to compute this
                                    information from an *external*
                                    profile source: profile metadata
                                    attached to the IR.</div>
                                  <div><br>
                                  </div>
                                  <div>c) There could be many external
                                    profile sources, but all of them
                                    should be read and then translated
                                    into metadata annotations on the IR
                                    so that serialization /
                                    deserialization preserve them in a
                                    common format and we can reason
                                    about how they work.</div>
                                  <div><br>
                                  </div>
                                  <div><br>
                                  </div>
                                  <div>This layering is why it is only a
                                    transform that accesses ProfileData
                                    -- it is responsible for annotating
                                    the IR and nothing else. <span style="line-height:1.5">Then the
                                      analysis uses these annotations
                                      and never reads the data directly.</span></div>
                                  <div><span style="line-height:1.5"><br>
                                    </span></div>
                                  <div><span style="line-height:1.5">I
                                      think this is a really important
                                      separation of concerns as it
                                      ensures that we don't get an
                                      explosion of different analyses
                                      supporting various different
                                      subsets of profile sources.</span></div>
                                  <div><span style="line-height:1.5"><br>
                                    </span></div>
                                  <div><span style="line-height:1.5"><br>
                                    </span></div>
                                  <div><span style="line-height:1.5">Now,
                                      the original design only accounted
                                      for profile information *within* a
                                      function body, clearly it needs to
                                      be extended to support
                                      intraprocedural information. But I
                                      would still expect that to follow
                                      a similar layering where we first
                                      read the data into IR annotations,
                                      then have an analysis pass (this
                                      time a module analysis pass in all
                                      likelihood) that brokers access to
                                      these annotations through an API
                                      that can do intelligent things
                                      like synthesizing it from the
                                      "cold" attribute or whatever when
                                      missing.</span></div>
                                  <span><font color="#888888">
                                      <div><span style="line-height:1.5"><br>
                                        </span></div>
                                    </font></span></div>
                              </div>
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                            <div><br>
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                            <div>Invariants b) and c) above are still
                              true, but a) is not since InlineCost
                              directly calls ProfileSummary instead of
                              through an analysis pass.</div>
                          </div>
                        </div>
                      </div>
                    </blockquote>
                    <div><br>
                    </div>
                  </span>
                  <div>Not quite -- ProfileSummary seems to only exist
                    in the profile *reading* code, so it isn't *just* an
                    annotation on the IR.</div>
                </div>
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            <div>Sorry, I'm lost here. There is an IR annotation (module
              flag) called ProfileSummary and this data is represented
              in memory by the ProfileSummary class. . This class
               provides methods to serialize/de-serialize  this data
              into/from metadata. This class has methods to compute this
              summary, but this is used only by the profile readers and
              writers. I am not sure what you mean by "it isn't just* an
              annotation on the IR". <br>
            </div>
          </div>
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    </blockquote></span>
    If this is true, why is this class currently part of ProfileData? 
    Shouldn't this live in IR?  Or to phrase this differently, why is an
    "analysis" over IR mixed in with the parsing code?</div></blockquote><div><br></div><div>ProfileSummary does not have any analysis over IR, so I don't understand that part of your question. As to why this is part of ProfileData, it is partly because initially summary was something that was just displayed by the llvm-profdata tool and partly because it felt natural to keep all profile related code together.  Having said that, I have nothing against moving it to IR if that is the appropriate place.</div><div><br></div><div>- Easwaran</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF"><span class=""><br>
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            <div>- Easwaran</div>
            <div> </div>
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                  <div>I think the problem here is that we have failed
                    to build a proper separate abstraction around the
                    interprocedural profile data that is extracted from
                    IR annotations. That abstraction should have nothing
                    to do with reading profile data and so shouldn't
                    live in the ProifileData library, it should (IMO)
                    live in the Analysis library.</div>
                  <span>
                    <div><br>
                    </div>
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                            <div>  I'll add a module level pass as you
                              suggest, but that still needs breaking the
                              ProfileData->Analysis dependence
                              chain. </div>
                          </div>
                        </div>
                      </div>
                    </blockquote>
                    <div><br>
                    </div>
                  </span>
                  <div>Well, this will also re-highlight the fundamental
                    pass manager problem as you won't have easy access
                    to this analysis pass.</div>
                  <span>
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                      </span></div>
                    <div><span style="line-height:1.5"> </span></div>
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                            <div><br>
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                            <div>- Easwaran</div>
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                                      <div><span style="line-height:1.5"></span></div>
                                      <div><span style="line-height:1.5">-Chandler</span></div>
                                    </font></span></div>
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      <br>
      <pre>_______________________________________________
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