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<div class="moz-cite-prefix">On 02/27/2017 11:47 AM, Adam Nemet
wrote:<br>
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cite="mid:1808DF46-BCA7-4F08-B707-8996564A9C76@apple.com"
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<div class="">On Feb 27, 2017, at 9:39 AM, Daniel Berlin <<a
moz-do-not-send="true" href="mailto:dberlin@dberlin.org"
class="">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" class=""><<a
moz-do-not-send="true"
href="mailto:anemet@apple.com" target="_blank"
class="">anemet@apple.com</a>></span> wrote:<br
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<div class="">On Feb 27, 2017, at 7:27 AM,
Hal Finkel <<a moz-do-not-send="true"
href="mailto:hfinkel@anl.gov"
target="_blank" class="">hfinkel@anl.gov</a>>
wrote:</div>
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On 02/27/2017 06:29 AM, Nema, Ashutosh
wrote:<br class="">
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<div style="margin:0in 0in
0.0001pt;font-size:12pt;font-family:"times
new roman",serif" class="">Thanks
for looking into this.</div>
<div style="margin:0in 0in
0.0001pt;font-size:12pt;font-family:"times
new roman",serif" class=""> </div>
<div style="margin:0in 0in
0.0001pt;font-size:12pt;font-family:"times
new roman",serif" class="">1)
Issues with re running vectorizer:</div>
<div style="margin:0in 0in
0.0001pt;font-size:12pt;font-family:"times
new roman",serif" class="">Vectorizer
might generate redundant alias
checks while vectorizing epilog
loop.</div>
<div style="margin:0in 0in
0.0001pt;font-size:12pt;font-family:"times
new roman",serif" class="">Redundant
alias checks are expensive, we like
to reuse the results of already
computed alias checks.</div>
<div style="margin:0in 0in
0.0001pt;font-size:12pt;font-family:"times
new roman",serif" class="">With
metadata we can limit the width of
epilog loop, but not sure about
reusing alias check result.</div>
<div style="margin:0in 0in
0.0001pt;font-size:12pt;font-family:"times
new roman",serif" class="">Any
thoughts on rerunning vectorizer
with reusing the alias check result
?</div>
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<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"
class="">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 class="">+Danny</div>
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<div class="">Isn’t Extended SSA supposed to
help with this?</div>
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<div class="">Yes, it will solve this with no issue
already. GVN probably does already too.</div>
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<div class="">even if if you have</div>
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</div>
<div class="">if (a == b)</div>
<div class="">
<div class="">if (a == c)</div>
</div>
<div class="">
<div class=""> if (a == d)</div>
</div>
<div class="">
<div class=""> if (a == e)</div>
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<div class=""> if (a == g)</div>
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<div class="">and we can prove a ... g equivalent,
newgvn will eliminate them all and set all the
branches true.</div>
<div class=""><br class="">
</div>
<div class="">If you need a simpler clean up pass, we
could run it on sub-graphs.</div>
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<div><br class="">
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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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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>
<br>
-Hal<br>
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<div>I guess the pipeline to experiment with for now is opt
-loop-vectorize -loop-vectorize -newgvn.</div>
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<div>Adam</div>
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<div class="">The only thing you'd have to do is write
some code to set "live on entry" subgraph variables
in their own congruence classes.</div>
<div class="">We already do this for incoming
arguments.</div>
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<div class="">Otherwise, it's trivial to make it only
walk things in the subgraph.</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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