[gcc/devel/fortran_unsigned] libstdc++: Remove __find_if unrolling for random access iterators

[Thomas Kﾃｶnig]

https://gcc.gnu.org/g:7ad3d3303bbc2c3fd78f91dee96b1c023f9a2744

commit 7ad3d3303bbc2c3fd78f91dee96b1c023f9a2744
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jul 4 12:01:29 2024 +0100

    libstdc++: Remove __find_if unrolling for random access iterators
    
    As the numbers in PR libstdc++/88545 show, the manual loop unrolling in
    std::__find_if doesn't actually help these days, and it prevents the
    compiler from auto-vectorizing.
    
    Remove the dispatching on iterator_category and just use the simple loop
    for all iterator categories.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/stl_algobase.h (__find_if): Remove overloads for
            dispatching on iterator_category. Do not unroll loop manually.
            * include/bits/stl_algo.h (__find_if_not): Remove
            iterator_category argument from __find_if call.

Diff:
---
 libstdc++-v3/include/bits/stl_algo.h     |  3 +-
 libstdc++-v3/include/bits/stl_algobase.h | 70 ++------------------------------
 2 files changed, 5 insertions(+), 68 deletions(-)

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index d250b2e04d4d..541f588883b2 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -110,8 +110,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		  _Predicate __pred)
     {
       return std::__find_if(__first, __last,
-			    __gnu_cxx::__ops::__negate(__pred),
-			    std::__iterator_category(__first));
+			    __gnu_cxx::__ops::__negate(__pred));
     }
 
   /// Like find_if_not(), but uses and updates a count of the
diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index dec1e4c79d86..27f6c377ad6f 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -2098,77 +2098,15 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
 
 _GLIBCXX_END_NAMESPACE_ALGO
 
-  /// This is an overload used by find algos for the Input Iterator case.
-  template<typename _InputIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
-    inline _InputIterator
-    __find_if(_InputIterator __first, _InputIterator __last,
-	      _Predicate __pred, input_iterator_tag)
-    {
-      while (__first != __last && !__pred(__first))
-	++__first;
-      return __first;
-    }
-
-  /// This is an overload used by find algos for the RAI case.
-  template<typename _RandomAccessIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
-    _RandomAccessIterator
-    __find_if(_RandomAccessIterator __first, _RandomAccessIterator __last,
-	      _Predicate __pred, random_access_iterator_tag)
-    {
-      typename iterator_traits<_RandomAccessIterator>::difference_type
-	__trip_count = (__last - __first) >> 2;
-
-      for (; __trip_count > 0; --__trip_count)
-	{
-	  if (__pred(__first))
-	    return __first;
-	  ++__first;
-
-	  if (__pred(__first))
-	    return __first;
-	  ++__first;
-
-	  if (__pred(__first))
-	    return __first;
-	  ++__first;
-
-	  if (__pred(__first))
-	    return __first;
-	  ++__first;
-	}
-
-      switch (__last - __first)
-	{
-	case 3:
-	  if (__pred(__first))
-	    return __first;
-	  ++__first;
-	  // FALLTHRU
-	case 2:
-	  if (__pred(__first))
-	    return __first;
-	  ++__first;
-	  // FALLTHRU
-	case 1:
-	  if (__pred(__first))
-	    return __first;
-	  ++__first;
-	  // FALLTHRU
-	case 0:
-	default:
-	  return __last;
-	}
-    }
-
+  // Implementation of std::find_if, also used in std::remove_if and others.
   template<typename _Iterator, typename _Predicate>
     _GLIBCXX20_CONSTEXPR
     inline _Iterator
     __find_if(_Iterator __first, _Iterator __last, _Predicate __pred)
     {
-      return __find_if(__first, __last, __pred,
-		       std::__iterator_category(__first));
+      while (__first != __last && !__pred(__first))
+	++__first;
+      return __first;
     }
 
   template<typename _InputIterator, typename _Predicate>