https://gcc.gnu.org/g:ce34fcc572a0dceebcffef76e98064546feebb38
commit r15-1880-gce34fcc572a0dceebcffef76e98064546feebb38
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Sat Jul 6 21:34:29 2024 +0100
libstdc++: Fix std::find for non-contiguous iterators [PR115799]
The r15-1857 change didn't correctly restrict the new optimization to
contiguous iterators.
libstdc++-v3/ChangeLog:
PR libstdc++/115799
* include/bits/stl_algo.h (find): Use 'if constexpr' so that
memchr optimization is a discarded statement for non-contiguous
iterators.
* testsuite/25_algorithms/find/bytes.cc: Check with input
iterators.
Diff:
---
libstdc++-v3/include/bits/stl_algo.h | 44 ++++++++++------------
libstdc++-v3/testsuite/25_algorithms/find/bytes.cc | 7 ++++
2 files changed, 27 insertions(+), 24 deletions(-)
diff --git a/libstdc++-v3/include/bits/stl_algo.h
b/libstdc++-v3/include/bits/stl_algo.h
index 45c3b591326..d250b2e04d4 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -3849,32 +3849,28 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
#if __cpp_if_constexpr && __glibcxx_type_trait_variable_templates
using _ValT = typename iterator_traits<_InputIterator>::value_type;
if constexpr (__can_use_memchr_for_find<_ValT, _Tp>)
- {
- // If converting the value to the 1-byte value_type alters its value,
- // then it would not be found by std::find using equality comparison.
- // We need to check this here, because otherwise something like
- // memchr("a", 'a'+256, 1) would give a false positive match.
- if (!(static_cast<_ValT>(__val) == __val))
- return __last;
- else if (!__is_constant_evaluated())
- {
- const void* __p0 = nullptr;
- if constexpr (is_pointer_v<decltype(std::__niter_base(__first))>)
- __p0 = std::__niter_base(__first);
+ if constexpr (is_pointer_v<decltype(std::__niter_base(__first))>
#if __cpp_lib_concepts
- else if constexpr (contiguous_iterator<_InputIterator>)
- __p0 = std::to_address(__first);
+ || contiguous_iterator<_InputIterator>
#endif
- if (__p0)
- {
- const int __ival = static_cast<int>(__val);
- if (auto __n = std::distance(__first, __last); __n > 0)
- if (auto __p1 = __builtin_memchr(__p0, __ival, __n))
- return __first + ((const char*)__p1 - (const char*)__p0);
- return __last;
- }
- }
- }
+ )
+ {
+ // If conversion to the 1-byte value_type alters the value,
+ // it would not be found by std::find using equality comparison.
+ // We need to check this here, because otherwise something like
+ // memchr("a", 'a'+256, 1) would give a false positive match.
+ if (!(static_cast<_ValT>(__val) == __val))
+ return __last;
+ else if (!__is_constant_evaluated())
+ {
+ const void* __p0 = std::__to_address(__first);
+ const int __ival = static_cast<int>(__val);
+ if (auto __n = std::distance(__first, __last); __n > 0)
+ if (auto __p1 = __builtin_memchr(__p0, __ival, __n))
+ return __first + ((const char*)__p1 - (const char*)__p0);
+ return __last;
+ }
+ }
#endif
return std::__find_if(__first, __last,
diff --git a/libstdc++-v3/testsuite/25_algorithms/find/bytes.cc
b/libstdc++-v3/testsuite/25_algorithms/find/bytes.cc
index f4ac5d4018d..e1d6c01ab21 100644
--- a/libstdc++-v3/testsuite/25_algorithms/find/bytes.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/find/bytes.cc
@@ -3,6 +3,7 @@
#include <algorithm>
#include <cstddef> // std::byte
#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
// PR libstdc++/88545 made std::find use memchr as an optimization.
// This test verifies that it didn't change any semantics.
@@ -113,6 +114,12 @@ test_non_characters()
#endif
}
+void
+test_pr115799c2(__gnu_test::input_iterator_wrapper<char> i)
+{
+ (void) std::find(i, i, 'a');
+}
+
int main()
{
test_char<char>();
