[libc++] Fix ambiguous call in {ranges, std}::count (#122529)

This PR fixes an ambiguous call encountered while using the
`std::ranges::count` and `std::count` algorithms with `vector<bool>`
with small `size_type`s.

The ambiguity arises from integral promotions during the internal
bitwise arithmetic of the `count` algorithms for small integral types.
This results in multiple viable candidates:
`__libcpp_popcount(unsigned)`,` __libcpp_popcount(unsigned long)`, and
`__libcpp_popcount(unsigned long long)`, leading to an ambiguous call
error. To resolve this ambiguity, we introduce a dispatcher function,
`__popcount`, which directs calls to the appropriate overloads of
`__libcpp_popcount`. This closes #122528.

1 files changed, 5 insertions, 5 deletions

diff --git a/libcxx/include/__algorithm/count.h b/libcxx/include/__algorithm/count.h
index cd9125779ec6..0cbe9b6e61b9 100644
--- a/libcxx/include/__algorithm/count.h
+++ b/libcxx/include/__algorithm/count.h
@@ -55,18 +55,18 @@ __count_bool(__bit_iterator<_Cp, _IsConst> __first, typename __size_difference_t
   if (__first.__ctz_ != 0) {
     __storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
     __storage_type __dn    = std::min(__clz_f, __n);
-    __storage_type __m     = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
-    __r                    = std::__libcpp_popcount(std::__invert_if<!_ToCount>(*__first.__seg_) & __m);
+    __storage_type __m     = std::__middle_mask<__storage_type>(__clz_f - __dn, __first.__ctz_);
+    __r                    = std::__popcount(__storage_type(std::__invert_if<!_ToCount>(*__first.__seg_) & __m));
     __n -= __dn;
     ++__first.__seg_;
   }
   // do middle whole words
   for (; __n >= __bits_per_word; ++__first.__seg_, __n -= __bits_per_word)
-    __r += std::__libcpp_popcount(std::__invert_if<!_ToCount>(*__first.__seg_));
+    __r += std::__popcount(std::__invert_if<!_ToCount>(*__first.__seg_));
   // do last partial word
   if (__n > 0) {
-    __storage_type __m = ~__storage_type(0) >> (__bits_per_word - __n);
-    __r += std::__libcpp_popcount(std::__invert_if<!_ToCount>(*__first.__seg_) & __m);
+    __storage_type __m = std::__trailing_mask<__storage_type>(__bits_per_word - __n);
+    __r += std::__popcount(__storage_type(std::__invert_if<!_ToCount>(*__first.__seg_) & __m));
   }
   return __r;
 }