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<div class="moz-cite-prefix">On 01/08/2015 01:15 AM, Chandler
Carruth wrote:<br>
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<div class="gmail_quote">On Wed, Jan 7, 2015 at 11:05 AM,
Peter Collingbourne <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:peter@pcc.me.uk"
target="_blank">peter@pcc.me.uk</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex"><span
class="">> I don't know if this will ever be
necessary, but another option is for llgo to grow its
own IR on top of go/ssa. I'd rather not go there for
this, though.<br>
<br>
<br>
</span>Agreed. FWIW, the long term direction I'd like to
see is attempting to extend go/ssa with what we need (in
this particular case, a native switch instruction).<br>
<span class=""><br>
> I did look to see if there was an existing pass,
but again I couldn't see anything that looked relevant<br>
<br>
<br>
</span>If you grep for
`SimplifyCFGOpt::FoldValueComparisonIntoPredecessors` you
should find something.<br>
<span class=""><br>
> Geo-mean improvement of 0.49% (0.23% - 0.75% @ 95%
CI)<br>
<br>
<br>
</span>Great! I'm a little surprised that we can do better
than LLVM on its own, but maybe I don't understand what
the simplifycfg code is doing.</blockquote>
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Just a peanut gallery comment, but I'm pretty disappointed
that LLVM can't turn if-chains into switches for you. I think
not dealing with switches sounds like a really reasonable
simplification for a frontend to desire. The optimizer should
fix this code, and should both be faster and more powerful in
doing so.</div>
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I agree here.<br>
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<div class="gmail_extra">Any interest in trying to make LLVM's
switch formation powerful enough to catch the cases you care
about? Or at least reducing the test case we missed? If we can
do that, it seems like it would remove the ugliness from the
approach by letting you generate "naive" switches with high
confidence that they optimize appropriately?</div>
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This is close enough to my own interests that if you can create a
small test case, I'll take a serious look at fixing it. I'm not
going to go too far, but if it ends up being a simple fix, I'd like
to have this work. Please file a bug with your IR fragment. <br>
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