[libc++] Simplify __bitset::__init #121357
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winner245
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@llvm/pr-subscribers-libcxx Author: Peng Liu (winner245) ChangesThis PR simplifies Full diff: https://github.com/llvm/llvm-project/pull/121357.diff 1 Files Affected:
diff --git a/libcxx/include/bitset b/libcxx/include/bitset
index 919d2a0f07e096..57c29f5f85d27c 100644
--- a/libcxx/include/bitset
+++ b/libcxx/include/bitset
@@ -253,26 +253,16 @@ inline _LIBCPP_CONSTEXPR __bitset<_N_words, _Size>::__bitset() _NOEXCEPT
template <size_t _N_words, size_t _Size>
void __bitset<_N_words, _Size>::__init(unsigned long long __v, false_type) _NOEXCEPT {
- __storage_type __t[sizeof(unsigned long long) / sizeof(__storage_type)];
- size_t __sz = _Size;
- for (size_t __i = 0; __i < sizeof(__t) / sizeof(__t[0]); ++__i, __v >>= __bits_per_word, __sz -= __bits_per_word)
- if (__sz < __bits_per_word)
- __t[__i] = static_cast<__storage_type>(__v) & (1ULL << __sz) - 1;
- else
- __t[__i] = static_cast<__storage_type>(__v);
-
- std::copy(__t, __t + sizeof(__t) / sizeof(__t[0]), __first_);
- std::fill(
- __first_ + sizeof(__t) / sizeof(__t[0]), __first_ + sizeof(__first_) / sizeof(__first_[0]), __storage_type(0));
+ const size_t __ull_words = sizeof(unsigned long long) / sizeof(__storage_type);
+ for (size_t __i = 0; __i < __ull_words; ++__i, __v >>= __bits_per_word)
+ __first_[__i] = static_cast<__storage_type>(__v);
+ std::fill(__first_ + __ull_words, __first_ + _N_words, __storage_type(0));
}
template <size_t _N_words, size_t _Size>
inline _LIBCPP_HIDE_FROM_ABI void __bitset<_N_words, _Size>::__init(unsigned long long __v, true_type) _NOEXCEPT {
__first_[0] = __v;
- if (_Size < __bits_per_word)
- __first_[0] &= (1ULL << _Size) - 1;
-
- std::fill(__first_ + 1, __first_ + sizeof(__first_) / sizeof(__first_[0]), __storage_type(0));
+ std::fill(__first_ + 1, __first_ + _N_words, __storage_type(0));
}
# endif // _LIBCPP_CXX03_LANG
@@ -623,7 +613,8 @@ public:
// 23.3.5.1 constructors:
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset() _NOEXCEPT {}
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset(unsigned long long __v) _NOEXCEPT : __base(__v) {}
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset(unsigned long long __v) _NOEXCEPT
+ : __base(sizeof(unsigned long long) * CHAR_BIT <= _Size ? __v : __v & ((1ULL << _Size) - 1)) {}
template <class _CharT, __enable_if_t<_IsCharLikeType<_CharT>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 explicit bitset(
const _CharT* __str,
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winner245
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There was a problem hiding this comment.
I think instead of trying to simplify the C++03 code, we should look into removing __init entirely and replace the code with something like
bitset(unsigned long long __v) : vals() {
vals[0] = static_cast<size_t>(__v);
if (sizeof(size_t) == 4) {
__first_[1] = _Size >= 2 * __bits_per_word
? static_cast<size_t>(__v >> __bits_per_word)
: static_cast<size_t>((__v >> __bits_per_word) &
(__storage_type(1) << (_Size - __bits_per_word)) - 1);
}
}
winner245
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After several attempts with a stage1 (generic-gcc, gcc-14, g++-14) CI failure, I realized that we still have to keep the initialization of the Given this limitation, it seems that we still have to move the initialization back to the constructor initializer list. Since C++03 does not support |
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Gentle ping @philnik777 , there are questions for you here. |
winner245
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I'd like to say "let's just drop GCC C++11 support", but I guess that's not trivial to get through. Could you file a bug against GCC and ask for them to implement the Clang extension? Otherwise LGTM. |
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Shipping despite CI failures cause our CI is super unstable right now. |
4 participants
This PR simplifies
__bitset::__initinto a more compact and readable form, which avoids redundant computations of asize_tvalue and eliminates the overhead of a local array.