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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Optimizing switch to jumps"
href="https://bugs.llvm.org/show_bug.cgi?id=42313">42313</a>
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<th>Summary</th>
<td>Optimizing switch to jumps
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>denis.yaroshevskij@gmail.com
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Hi!
There is a nice optimisation for std::merge that I cannot do because std::merge
would soon be required to be constexpr (<a href="https://reviews.llvm.org/D63063">https://reviews.llvm.org/D63063</a>).
I could have replaced my gotos with a switch and write my state machine on it
but unfortunately switch does not get optimised away into jumps.
Here is the code comparison: <a href="https://gcc.godbolt.org/z/8wq6O3">https://gcc.godbolt.org/z/8wq6O3</a>
Could it maybe be possible to optimise the switch away?
I looked at gcc and it seems to produce identical code for both switch and goto
implementation: <a href="https://gcc.godbolt.org/z/HzZHSb">https://gcc.godbolt.org/z/HzZHSb</a> (to be fare - clang manages to
collapse two memmoves into one for the goto implementation, which gcc does not
but gcc's result is identical)</pre>
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