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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Seems like something that could be useful, but…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">> Given that this eternal optimizer will respect the initial semantics, one can compile<br>
> a module, test it, and then let the optimizer do its best. The behavior of a module should<br>
> only be faster, no need to re-test.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> This seems extremely dangerous. In theory it shouldn’t change the behavior, but all software has bugs…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal"> Christopher Tetreault<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> <b>On Behalf Of
</b>Stefanos Baziotis via llvm-dev<br>
<b>Sent:</b> Monday, April 13, 2020 9:13 AM<br>
<b>To:</b> llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> [EXT] [llvm-dev] Why we don't have eternal optimizers?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi everyone,<br>
<br>
Lately I've been thinking of the optimization model of almost any optimizer ever.<br>
The optimizer should finish "at a reasonable time". For example,<br>
for a 20k lines program, the optimizer should finish in a couple of minutes and not<br>
e.g. a couple of days.<br>
<br>
And my question is, why? For almost all programs, the period that starts when the program<br>
starts being developed to the day it is released is way bigger than a couple of minutes.<br>
In the meantime, a couple of modules might not have been touched for months.<br>
And an unconstrained optimizer could do its best in all this time.<br>
<br>
Given that this eternal optimizer will respect the initial semantics, one can compile<br>
a module, test it, and then let the optimizer do its best. The behavior of a module should<br>
only be faster, no need to re-test.<o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
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<div>
<p class="MsoNormal">In the meantime of course, we need to test the program as a whole and other modules<br>
might actually change. For that we can already what happens today which is run<br>
"reasonably optimized" builds.<br>
<br>
This is a humble opinion and I'm looking forward to hear the opinion of the LLVM community.<br>
<br>
Best,<br>
Stefanos<o:p></o:p></p>
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