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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Add specializations of small std::tuple to reduce pre-optimization code generation"
href="https://bugs.llvm.org/show_bug.cgi?id=46974">46974</a>
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<th>Summary</th>
<td>Add specializations of small std::tuple to reduce pre-optimization code generation
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<th>Product</th>
<td>libc++
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<th>Version</th>
<td>11.0
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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>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>dsharlet@google.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>I've noticed that if I replace std::make_tuple(a, b) with std::make_pair(a, b)
where I can, I get a few percent reduction in the size of -S -emit-llvm -O0,
and build time with -O2 appears to go down by 3-5%. I didn't change anything
else (kept using std::get<0>/std::get<1> to access these tuples).
The thing is, std::tuple(a, b) where I know there are exactly two elements is
only a very small fraction of the tuple usage in my project. There are still
many usages of std::tuple<T...> where sizeof...(T) is 2, but I don't know that
at compile time. My program makes heavy use of tuple_cat and make_tuple. The
vast majority of the tuple usage is for <= 5 tuple elements.
It seems like if there were a special case implementation of std::tuple<>,
std::tuple<T>, std::tuple<T1, T2>, ... up to some small finite number of types,
it could have a significant impact on the pre-optimization code size and build
time of tuple-using code.</pre>
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