[libc++] Make std::numeric_limits<NonPromoted>::traps false
#166724
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@llvm/pr-subscribers-libcxx Author: A. Jiang (frederick-vs-ja) ChangesPer LWG554, the rationale is that even if This is also true for all other non-promoted integer types. As a result, Fixes #166053. Full diff: https://github.com/llvm/llvm-project/pull/166724.diff 2 Files Affected:
diff --git a/libcxx/include/limits b/libcxx/include/limits
index e8581cf9c321d..ae93fcd7164fd 100644
--- a/libcxx/include/limits
+++ b/libcxx/include/limits
@@ -107,6 +107,7 @@ template<> class numeric_limits<cv long double>;
#else
# include <__config>
# include <__type_traits/is_arithmetic.h>
+# include <__type_traits/is_same.h>
# include <__type_traits/is_signed.h>
# if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -220,7 +221,7 @@ protected:
static _LIBCPP_CONSTEXPR const bool is_modulo = !std::is_signed<_Tp>::value;
# if defined(__i386__) || defined(__x86_64__) || defined(__wasm__)
- static _LIBCPP_CONSTEXPR const bool traps = true;
+ static _LIBCPP_CONSTEXPR const bool traps = is_same<decltype(+_Tp(0)), _Tp>::value;
# else
static _LIBCPP_CONSTEXPR const bool traps = false;
# endif
diff --git a/libcxx/test/std/language.support/support.limits/limits/numeric.limits.members/traps.pass.cpp b/libcxx/test/std/language.support/support.limits/limits/numeric.limits.members/traps.pass.cpp
index 66e149bf58d1b..f90bdfea7dcad 100644
--- a/libcxx/test/std/language.support/support.limits/limits/numeric.limits.members/traps.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/limits/numeric.limits.members/traps.pass.cpp
@@ -33,17 +33,17 @@ test()
int main(int, char**)
{
test<bool, false>();
- test<char, integral_types_trap>();
- test<signed char, integral_types_trap>();
- test<unsigned char, integral_types_trap>();
- test<wchar_t, integral_types_trap>();
+ test<char, false>();
+ test<signed char, false>();
+ test<unsigned char, false>();
+ test<wchar_t, false>();
#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
- test<char8_t, integral_types_trap>();
+ test<char8_t, false>();
#endif
- test<char16_t, integral_types_trap>();
- test<char32_t, integral_types_trap>();
- test<short, integral_types_trap>();
- test<unsigned short, integral_types_trap>();
+ test<char16_t, false>();
+ test<char32_t, false>();
+ test<short, false>();
+ test<unsigned short, false>();
test<int, integral_types_trap>();
test<unsigned int, integral_types_trap>();
test<long, integral_types_trap>();
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Per [LWG554](https://cplusplus.github.io/LWG/issue554), the rationale is that even if `true / false` traps, the values causing trap are the converted `int` values produced by usual arithmetic conversion, but not the original `bool` values. This is also true for all other non-promoted integer types. As a result, `std::numeric_limits<I>` should be `false` if `I` is a non non-promoted integer type.
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ldionne
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Nov 8, 2025
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Per LWG554, the rationale is that even if
true / falsetraps, the values causing trap are the convertedintvalues produced by usual arithmetic conversion, but not the originalboolvalues.This is also true for all other non-promoted integer types. As a result,
std::numeric_limits<I>should befalseifIis a non non-promoted integer type.Fixes #166053.