[libcxx-commits] [PATCH] D116296: [libc++] Add an early return for __partial_sort of an empty range.

[Arthur O'Dwyer via Phabricator via libcxx-commits]

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If `__first == __middle`, then `partial_sort` is a no-op; don't bother to iterate all the way from `__middle` to `__end`.

      

Fixes https://github.com/llvm/llvm-project/issues/49431


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D116296

Files:
  libcxx/include/__algorithm/partial_sort.h


Index: libcxx/include/__algorithm/partial_sort.h
===================================================================
--- libcxx/include/__algorithm/partial_sort.h
+++ libcxx/include/__algorithm/partial_sort.h
@@ -33,6 +33,8 @@
 __partial_sort(_RandomAccessIterator __first, _RandomAccessIterator __middle, _RandomAccessIterator __last,
              _Compare __comp)
 {
+    if (__first == __middle)
+        return;
     _VSTD::__make_heap<_Compare>(__first, __middle, __comp);
     typename iterator_traits<_RandomAccessIterator>::difference_type __len = __middle - __first;
     for (_RandomAccessIterator __i = __middle; __i != __last; ++__i)


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