From: Jonathan Wakely <jwakely@redhat.com>
Date: Thu, 4 Jul 2024 11:01:29 +0000 (+0100)
Subject: libstdc++: Remove __find_if unrolling for random access iterators
X-Git-Tag: basepoints/gcc-16~7197
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e69456ff9a54ba3e9c93842b05757b7d8fff6d9d;p=thirdparty%2Fgcc.git

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 --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index d250b2e04d4..541f588883b 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 dec1e4c79d8..27f6c377ad6 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>