[libcxx-commits] [libcxx] f6fb7bf - [libc++] Add an early return for __partial_sort of an empty range.

[Arthur O'Dwyer via libcxx-commits]

Author: Arthur O'Dwyer
Date: 2022-01-04T16:14:05-05:00
New Revision: f6fb7bf636e3257a32a629460d447eea76616384

URL: https://github.com/llvm/llvm-project/commit/f6fb7bf636e3257a32a629460d447eea76616384
DIFF: https://github.com/llvm/llvm-project/commit/f6fb7bf636e3257a32a629460d447eea76616384.diff

LOG: [libc++] Add an early return for __partial_sort of an empty range.

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

Fixes #49431.

Differential Revision: https://reviews.llvm.org/D116296

Added: 
    

Modified: 
    libcxx/include/__algorithm/partial_sort.h

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__algorithm/partial_sort.h b/libcxx/include/__algorithm/partial_sort.h
index 017ac90b67142..40e39e2be9741 100644
--- a/libcxx/include/__algorithm/partial_sort.h
+++ b/libcxx/include/__algorithm/partial_sort.h
@@ -33,6 +33,8 @@ _LIBCPP_CONSTEXPR_AFTER_CXX17 void
 __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>::
diff erence_type __len = __middle - __first;
     for (_RandomAccessIterator __i = __middle; __i != __last; ++__i)