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<div class="moz-cite-prefix">On 02/27/2017 01:47 PM, Daniel Berlin
wrote:<br>
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cite="mid:CAF4BwTX9XUeNd2JZE0=f6Fh=B+dk3w2xX6Tf7xBafi4=65NfQw@mail.gmail.com"
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<div class="gmail_quote">On Mon, Feb 27, 2017 at 11:29 AM,
Adam Nemet <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:anemet@apple.com" target="_blank">anemet@apple.com</a>></span>
wrote:<br>
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<div>On Feb 27, 2017, at 10:11 AM, Hal Finkel
<<a moz-do-not-send="true"
href="mailto:hfinkel@anl.gov"
target="_blank">hfinkel@anl.gov</a>>
wrote:</div>
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<div
class="m_-8094851141848933186moz-cite-prefix">On
02/27/2017 11:47 AM, Adam Nemet wrote:<br>
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<div>On Feb 27, 2017, at 9:39 AM,
Daniel Berlin <<a
moz-do-not-send="true"
href="mailto:dberlin@dberlin.org"
target="_blank">dberlin@dberlin.org</a>>
wrote:</div>
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<div class="gmail_quote">On Mon,
Feb 27, 2017 at 9:29 AM, Adam
Nemet <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:anemet@apple.com"
target="_blank">anemet@apple.com</a>></span>
wrote:<br>
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<div>On Feb 27,
2017, at 7:27 AM,
Hal Finkel <<a
moz-do-not-send="true" href="mailto:hfinkel@anl.gov" target="_blank">hfinkel@anl.gov</a>>
wrote:</div>
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class="m_-8094851141848933186gmail-m_8239107560126363242Apple-interchange-newline">
On 02/27/2017
06:29 AM, Nema,
Ashutosh wrote:<br>
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<div>Thanks
for looking
into this.</div>
<div> </div>
<div>1) Issues
with re
running
vectorizer:</div>
<div>Vectorizer
might generate
redundant
alias checks
while
vectorizing
epilog loop.</div>
<div>Redundant
alias checks
are expensive,
we like to
reuse the
results of
already
computed alias
checks.</div>
<div>With
metadata we
can limit the
width of
epilog loop,
but not sure
about reusing
alias check
result.</div>
<div>Any
thoughts on
rerunning
vectorizer
with reusing
the alias
check result ?</div>
</div>
</blockquote>
<br
style="font-family:helvetica;font-size:10px;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;background-color:rgb(255,255,255)">
<span
style="font-family:helvetica;font-size:10px;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;background-color:rgb(255,255,255);float:none;display:inline">One
way of looking
at this is:
Reusing the
alias-check
result is really
just a
conditional
propagation
problem; if we
don't already
have an
optimization
that can combine
these after the
fact, then we
should.</span><br
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<div>+Danny</div>
<div><br>
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<div>Isn’t Extended SSA
supposed to help with
this?</div>
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<div>Yes, it will solve this
with no issue already. GVN
probably does already too.</div>
<div><br>
</div>
<div>even if if you have</div>
<div><br>
</div>
<div>if (a == b)</div>
<div>
<div>if (a == c)</div>
</div>
<div>
<div> if (a == d)</div>
</div>
<div>
<div> if (a == e)</div>
</div>
<div>
<div> if (a == g)</div>
</div>
<div><br>
</div>
<div><br>
</div>
<div>and we can prove a ... g
equivalent, newgvn will
eliminate them all and set
all the branches true.</div>
<div><br>
</div>
<div>If you need a simpler
clean up pass, we could run
it on sub-graphs.</div>
</div>
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<div>Yes we probably don’t want to run a
full GVN after the “loop-scheduling”
passes.</div>
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<br>
FWIW, we could, just without the
memory-dependence analysis enabled (i.e. set
the NoLoads constructor parameter to true).
GVN is pretty fast in that mode.<br>
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<div>OK. Another data point is that I’ve seen cases
in the past where the alias checks required for the
loop passes could enable GVN to remove redundant
loads/stores. Currently we can only pick these up
with LTO when GVN is rerun.</div>
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</div>
<div>This is just GVN brokenness, newgvn should not have
this problem.</div>
<div>If it does, i'd love to see it.</div>
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<br>
I thought that the problem is that we just don't run GVN after that
point in the pipeline.<br>
<br>
-Hal<br>
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<div>(I'm working on the last few parts of turning it on by
default, but it requires a new getModRefInfo interface to
be able to get the last few testcases)</div>
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<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
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