From: Jonathan Wakely <jwakely@redhat.com>
Date: Wed, 10 Sep 2025 09:10:07 +0000 (+0100)
Subject: libstdc++: Reuse predicates in std::search and std::is_permutation
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=1cf6cda0554406f3d3ca641de7c4e360953aeb22;p=thirdparty%2Fgcc.git

libstdc++: Reuse predicates in std::search and std::is_permutation

Hoist construction of the call wrappers out of the loop when we're
repeatedly creating a call wrapper with the same bound arguments.

We need to be careful about iterators that return proxy references,
because bind1st(pred, *first) could bind a reference to a prvalue proxy
reference returned by *first. That would then be an invalid reference by
the time we invoked the call wrapper.

If we dereference the iterator first and store the result of that on the
stack, then we don't have a prvalue proxy reference, and can bind it (or
the value it refers to) into the call wrapper:

  auto&& val = *first; // lifetime extension
  auto wrapper = bind1st(pred, val);
  for (;;)
    /* use wrapper */;

This ensures that the reference returned from *first outlives the call
wrapper, whether it's a proxy reference or not.

For C++98 compatibility in __search we can use __decltype(expr) instead
of auto&&.

libstdc++-v3/ChangeLog:

	* include/bits/stl_algobase.h (__search, __is_permutation):
	Reuse predicate instead of creating a new one each time.
	* include/bits/stl_algo.h (__is_permutation): Likewise.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
---

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 7ff5dd84a97..bbd1800af77 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -3531,18 +3531,14 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
 
       for (_ForwardIterator1 __scan = __first1; __scan != __last1; ++__scan)
 	{
-	  if (__scan != std::__find_if(__first1, __scan,
-				       __gnu_cxx::__ops::bind1st(__pred,
-								 *__scan)))
+	  auto&& __scan_val = *__scan;
+	  auto __scaneq = __gnu_cxx::__ops::bind1st(__pred, __scan_val);
+	  if (__scan != std::__find_if(__first1, __scan, __scaneq))
 	    continue; // We've seen this one before.
 
-	  auto __matches = std::__count_if(__first2, __last2,
-					   __gnu_cxx::__ops::bind1st(__pred,
-								     *__scan));
+	  auto __matches = std::__count_if(__first2, __last2, __scaneq);
 	  if (0 == __matches
-	      || std::__count_if(__scan, __last1,
-				 __gnu_cxx::__ops::bind1st(__pred, *__scan))
-	      != __matches)
+		|| std::__count_if(__scan, __last1, __scaneq) != __matches)
 	    return false;
 	}
       return true;
diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index 03f64fb3e6c..443cbef76de 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -2149,21 +2149,21 @@ _GLIBCXX_END_NAMESPACE_ALGO
       if (__first1 == __last1 || __first2 == __last2)
 	return __first1;
 
+      __decltype(*__first2) __first2_val(*__first2);
+      __decltype(__gnu_cxx::__ops::bind2nd(__predicate, __first2_val))
+	__match_first = __gnu_cxx::__ops::bind2nd(__predicate, __first2_val);
+
       // Test for a pattern of length 1.
       _ForwardIterator2 __p1(__first2);
       if (++__p1 == __last2)
-	return std::__find_if(__first1, __last1,
-			      __gnu_cxx::__ops::bind2nd(__predicate,
-							*__first2));
+	return std::__find_if(__first1, __last1, __match_first);
 
       // General case.
       _ForwardIterator1 __current = __first1;
 
       for (;;)
 	{
-	  __first1 =
-	    std::__find_if(__first1, __last1,
-			   __gnu_cxx::__ops::bind2nd(__predicate, *__first2));
+	  __first1 = std::__find_if(__first1, __last1, __match_first);
 
 	  if (__first1 == __last1)
 	    return __last1;
@@ -2184,6 +2184,7 @@ _GLIBCXX_END_NAMESPACE_ALGO
 	}
       return __first1;
     }
+#undef __match_first
 
 #if __cplusplus >= 201103L
   template<typename _ForwardIterator1, typename _ForwardIterator2,
@@ -2208,18 +2209,14 @@ _GLIBCXX_END_NAMESPACE_ALGO
       std::advance(__last2, std::distance(__first1, __last1));
       for (_ForwardIterator1 __scan = __first1; __scan != __last1; ++__scan)
 	{
-	  if (__scan != std::__find_if(__first1, __scan,
-				       __gnu_cxx::__ops::bind1st(__pred,
-								 *__scan)))
+	  auto&& __scan_val = *__scan;
+	  auto __scaneq = __gnu_cxx::__ops::bind1st(__pred, __scan_val);
+	  if (__scan != std::__find_if(__first1, __scan, __scaneq))
 	    continue; // We've seen this one before.
 
-	  auto __matches
-	    = std::__count_if(__first2, __last2,
-			      __gnu_cxx::__ops::bind1st(__pred, *__scan));
-	  if (0 == __matches ||
-	      std::__count_if(__scan, __last1,
-			      __gnu_cxx::__ops::bind1st(__pred, *__scan))
-	      != __matches)
+	  auto __matches = std::__count_if(__first2, __last2, __scaneq);
+	  if (0 == __matches
+		|| std::__count_if(__scan, __last1, __scaneq) != __matches)
 	    return false;
 	}
       return true;