[libcxx-commits] [PATCH] D63063: Bug 42208: speeding up std::merge

[Eric Fiselier via Phabricator via libcxx-commits]

EricWF added inline comments.


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Comment at: include/algorithm:1725
     if (__n > 0)
         _VSTD::memmove(__result, __first, __n * sizeof(_Up));
     return __result + __n;
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`__builtin_memmove` is constexpr, so I think using that is a better approach that branching on `is_constant_evaluated`.


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Comment at: include/algorithm:4394
+        if (__comp(*__first2, *__first1)) goto __takeSecond;
+        *__result = *__first1;
+        ++__first1, (void)++__result;
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Everytime I've seen a duff's device optimization, it's a win is some cases and a loss in others. That makes me skeptical that it's the libraries job to perform the loop unrolling.
Do you know why LLVM is failing to generate comparable code here?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63063/new/

https://reviews.llvm.org/D63063