[Bug 216770] lang/julia: fails to build with clang 4.0

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=216770

Dimitry Andric <dim at FreeBSD.org> changed:

           What    |Removed                     |Added
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                 CC|                            |emaste at freebsd.org

--- Comment #9 from Dimitry Andric <dim at FreeBSD.org> ---
(In reply to tavert from comment #8)
> Is that working around a compiler bug in clang 4.0, or undefined behavior in
> the source where other compiler versions behaved differently?

It's not entirely clear yet.  It seems that adding that line, or putting some
printf's in the ratio() function "fixes" it, either due to some sort of
undefined behavior or a compiler bug.  So as a quick stopgap it would probably
be OK.

That said, I did some bisecting of upstream llvm/clang, and this revision
causes the trouble:
http://llvm.org/viewvc/llvm-project?view=revision&revision=280351

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r280351 | jamesm | 2016-09-01 12:44:35 +0200 (Thu, 01 Sep 2016) | 22 lines

[SimplifyCFG] Change the algorithm in SinkThenElseCodeToEnd

It shuffles around some code in smisc.c's ratio() function, apparently with
interesting effects.  I still need to figure out some way of transforming this
into a test case for upstream, or if it is actually caused by undefined
behavior, some workaround that can be applied permanently.

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