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<div class="moz-cite-prefix">On 3/20/20 2:11 PM, Chris Lattner
wrote:<br>
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cite="mid:FEBE85F3-1FCB-4DA0-AB58-82C5B65610DF@nondot.org">
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<div class="">On Mar 19, 2020, at 2:31 PM, Johannes Doerfert
<<a href="mailto:johannesdoerfert@gmail.com" class=""
moz-do-not-send="true">johannesdoerfert@gmail.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class=""><span style="caret-color: rgb(0, 0, 0);
font-family: Helvetica; font-size: 12px; font-style:
normal; font-variant-caps: normal; font-weight: normal;
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0px; text-transform: none; white-space: normal;
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!important;" class="">I think addressing this issue first
makes sense. I would however start</span><br
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class="">
<span style="caret-color: rgb(0, 0, 0); font-family:
Helvetica; font-size: 12px; font-style: normal;
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0px; text-transform: none; white-space: normal;
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!important;" class="">by determining the actual impact of
different design choices here. I</span><br
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<span style="caret-color: rgb(0, 0, 0); font-family:
Helvetica; font-size: 12px; 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;
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!important;" class="">mean, do we know locks will be
heavily contented? If I had to guess I'd</span><br
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class="">
<span style="caret-color: rgb(0, 0, 0); font-family:
Helvetica; font-size: 12px; 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;
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!important;" class="">say most passes will not create or
modify functions nor add or remove</span><br
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class="">
<span style="caret-color: rgb(0, 0, 0); font-family:
Helvetica; font-size: 12px; 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;
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!important;" class="">calls.</span></div>
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<div class="">The problem isn’t constants or functions themselves,
it is that they are instances of llvm::Value. Everything that
walks a use/def list would have to run code that checks for
this, and every call to inst->setOperand() would have to do
locking or conditional locking. This would be a significant
across-the-board slowdown for the compiler even when globals and
constants are not involved.</div>
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<div class="">-Chris</div>
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<br>
Hi Chris,<br>
<br>
Thanks for the comments. Sure that may be true but I would prefer to
get real data to see how shared data actually looks. We can<br>
argue over it at a theoretical level. However with any real
mutli-threading of a code base, real data is required. I've not sure
about<br>
setOperand() or other llvm:Value issues but real data is more my
concern. Sure it may turn out that is the case but I would prefer<br>
to have data as guessing with multi-threaded code in terms of
locking/scaling is always bad or even assuming issues.<br>
<br>
Thanks and if this is a real concern we should get data for it then
or other llvm:Value issues,<br>
Nick<br>
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