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* [gcc r12-5530] libstdc++: Do not use memset in constexpr calls to ranges::fill_n [PR101608]
@ 2021-11-25 20:03 Jonathan Wakely
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From: Jonathan Wakely @ 2021-11-25 20:03 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:82c3657dd74896b39937bb0a2aaeba9b8ca105fd
commit r12-5530-g82c3657dd74896b39937bb0a2aaeba9b8ca105fd
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Nov 24 13:17:54 2021 +0000
libstdc++: Do not use memset in constexpr calls to ranges::fill_n [PR101608]
libstdc++-v3/ChangeLog:
PR libstdc++/101608
* include/bits/ranges_algobase.h (__fill_n_fn): Check for
constant evaluation before using memset.
* testsuite/25_algorithms/fill_n/constrained.cc: Check
byte-sized values as well.
Diff:
---
libstdc++-v3/include/bits/ranges_algobase.h | 28 ++++++++++++++--------
.../testsuite/25_algorithms/fill_n/constrained.cc | 6 +++--
2 files changed, 22 insertions(+), 12 deletions(-)
diff --git a/libstdc++-v3/include/bits/ranges_algobase.h b/libstdc++-v3/include/bits/ranges_algobase.h
index c8c4d032983..9929e5e828b 100644
--- a/libstdc++-v3/include/bits/ranges_algobase.h
+++ b/libstdc++-v3/include/bits/ranges_algobase.h
@@ -527,17 +527,25 @@ namespace ranges
if (__n <= 0)
return __first;
- // TODO: Generalize this optimization to contiguous iterators.
- if constexpr (is_pointer_v<_Out>
- // Note that __is_byte already implies !is_volatile.
- && __is_byte<remove_pointer_t<_Out>>::__value
- && integral<_Tp>)
- {
- __builtin_memset(__first, static_cast<unsigned char>(__value), __n);
- return __first + __n;
- }
- else if constexpr (is_scalar_v<_Tp>)
+ if constexpr (is_scalar_v<_Tp>)
{
+ // TODO: Generalize this optimization to contiguous iterators.
+ if constexpr (is_pointer_v<_Out>
+ // Note that __is_byte already implies !is_volatile.
+ && __is_byte<remove_pointer_t<_Out>>::__value
+ && integral<_Tp>)
+ {
+#ifdef __cpp_lib_is_constant_evaluated
+ if (!std::is_constant_evaluated())
+#endif
+ {
+ __builtin_memset(__first,
+ static_cast<unsigned char>(__value),
+ __n);
+ return __first + __n;
+ }
+ }
+
const auto __tmp = __value;
for (; __n > 0; --__n, (void)++__first)
*__first = __tmp;
diff --git a/libstdc++-v3/testsuite/25_algorithms/fill_n/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/fill_n/constrained.cc
index 6a015d34a89..1d1e1c104d4 100644
--- a/libstdc++-v3/testsuite/25_algorithms/fill_n/constrained.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/fill_n/constrained.cc
@@ -73,11 +73,12 @@ test01()
}
}
+template<typename T>
constexpr bool
test02()
{
bool ok = true;
- int x[6] = { 1, 2, 3, 4, 5, 6 };
+ T x[6] = { 1, 2, 3, 4, 5, 6 };
const int y[6] = { 1, 2, 3, 4, 5, 6 };
const int z[6] = { 17, 17, 17, 4, 5, 6 };
@@ -94,5 +95,6 @@ int
main()
{
test01();
- static_assert(test02());
+ static_assert(test02<int>());
+ static_assert(test02<unsigned char>()); // PR libstdc++/101608
}
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