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Hey James,<br>
<br>
Feel free to ping me off list if you are wanting to bounce ideas off
of someone!<br>
<br>
(For context - I wrote and maintain a high precision GPU math
library at Codeplay as one of my many hats)<br>
<br>
Cheers,<br>
-Neil.<br>
<br>
<div class="moz-cite-prefix">On 05/04/16 08:00, James Molloy via
llvm-dev wrote:<br>
</div>
<blockquote
cite="mid:CALCTSA0cidDLgVwWb=mP-9LC25Zh_PW2As4hmLsq+OAYy5sFtQ@mail.gmail.com"
type="cite">
<div dir="ltr">Hi,
<div><br>
</div>
<div>OK, writing an APFloat implementation of log and exp is a
far more tractable problem. Thanks for the feedback all!</div>
<div><br>
</div>
<div>James</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Tue, 5 Apr 2016 at 04:06 Chandler Carruth via
llvm-dev <<a moz-do-not-send="true"
href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div class="gmail_quote">
<div dir="ltr">On Mon, Apr 4, 2016 at 10:41 AM Joerg
Sonnenberger via llvm-dev <<a moz-do-not-send="true"
href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">On
Mon, Apr 04, 2016 at 09:49:24AM -0700, Reid Kleckner via
llvm-dev wrote:<br>
> An optional MPFR dependency would also be pretty
painful. I expect it will<br>
> frequently be missing and will not be exercised by
most buildbots.<br>
<br>
IMO if constant folding of transcendental functions
makes a significant<br>
difference for your program, you likely are doing
something strange<br>
already. I don't think it matters much for a lot of use
cases, so having<br>
an optional dependency for this seems to be fine.</blockquote>
<div><br>
</div>
</div>
</div>
<div dir="ltr">
<div class="gmail_quote">
<div>I think that if transcendental functions are
sufficiently unimportant, we shouldn't support them at
all. We should have consistent behavior rather than
ending up with nearly impossible to triage issues
because one person's Clang used MPFR and the other
didn't.</div>
<div><br>
</div>
<div>While I think the optimizer should be able to
constant fold transcendentals as a matter of core
competency, I don't have very strong opinions about it
for the reasons you cite -- I don't have use cases.</div>
</div>
</div>
<div dir="ltr">
<div class="gmail_quote">
<div><br>
</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex"> Note
that the<br>
non-transcendental functions are quite a different deal,
especially<br>
reasonable well behaving functions like log and exp.<br>
</blockquote>
<div><br>
</div>
</div>
</div>
<div dir="ltr">
<div class="gmail_quote">
<div>Agreed, and I feel very strongly that we should
support both log and exp, and it has no business being
optional.</div>
<div><br>
</div>
<div>But clearly the right way to do this is to start from
the bottom and work our way up. We should add the
easiest ones first and incrementally add support. I
particularly like the suggestions from Hal about how to
make this a tractable engineering task.</div>
</div>
</div>
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