[PATCH v2] libstdc++: Use 'if constexpr' to slightly simplify <regex>
Jonathan Wakely
jwakely@redhat.com
Tue Apr 29 08:53:57 GMT 2025
This will hardly make a dent in the very slow compile times for <regex>
but it seems worth doing anyway.
libstdc++-v3/ChangeLog:
* include/bits/regex_compiler.h: Replace _GLIBCXX17_CONSTEXPR
with constexpr and disable diagnostics with pragmas.
(_AnyMatcher::operator()): Use constexpr-if instead of tag
dispatching. Postpone calls to _M_translate until after checking
result of earlier calls.
(_AnyMatcher::_M_apply): Remove both overloads.
(_BracketMatcher::operator(), _BracketMatcher::_M_ready):
Replace tag dispatching with 'if constexpr'.
(_BracketMatcher::_M_apply(_CharT, true_type)): Remove.
(_BracketMatcher::_M_apply(_CharT, false_type)): Remove second
parameter.
(_BracketMatcher::_M_make_cache): Remove both overloads.
* include/bits/regex_compiler.tcc (_BracketMatcher::_M_apply):
Remove second parameter.
* include/bits/regex_executor.tcc: Replace _GLIBCXX17_CONSTEXPR
with constexpr and disable diagnostics with pragmas.
(_Executor::_M_handle_backref): Replace __glibcxx_assert with
constexpr-if and use __builtin_unreachable for non-DFS mode
specialization.
(_Executor::_M_handle_accept): Mark _S_opcode_backref case as
unreachable for non-DFS mode.
---
Tested x86_64-linux.
The v2 patch uses constexpr-if in <bits/regex_executor.tcc> as well, and
optimizes _AnyMatcher so it doesn't do all the _M_translate calls up
front.
libstdc++-v3/include/bits/regex_compiler.h | 67 ++++++++------------
libstdc++-v3/include/bits/regex_compiler.tcc | 2 +-
libstdc++-v3/include/bits/regex_executor.tcc | 62 ++++++++++--------
3 files changed, 64 insertions(+), 67 deletions(-)
diff --git a/libstdc++-v3/include/bits/regex_compiler.h b/libstdc++-v3/include/bits/regex_compiler.h
index f24c7e3baa6..21e7065e066 100644
--- a/libstdc++-v3/include/bits/regex_compiler.h
+++ b/libstdc++-v3/include/bits/regex_compiler.h
@@ -38,6 +38,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
_GLIBCXX_END_NAMESPACE_CXX11
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
namespace __detail
{
/**
@@ -221,9 +223,9 @@ namespace __detail
_CharT
_M_translate(_CharT __ch) const
{
- if _GLIBCXX17_CONSTEXPR (__icase)
+ if constexpr (__icase)
return _M_traits.translate_nocase(__ch);
- else if _GLIBCXX17_CONSTEXPR (__collate)
+ else if constexpr (__collate)
return _M_traits.translate(__ch);
else
return __ch;
@@ -285,7 +287,7 @@ namespace __detail
bool
_M_match_range(_CharT __first, _CharT __last, _CharT __ch) const
{
- if _GLIBCXX17_CONSTEXPR (!__icase)
+ if constexpr (!__icase)
return __first <= __ch && __ch <= __last;
else
return this->_M_in_range_icase(__first, __last, __ch);
@@ -376,26 +378,20 @@ namespace __detail
bool
operator()(_CharT __ch) const
- { return _M_apply(__ch, typename is_same<_CharT, char>::type()); }
-
- bool
- _M_apply(_CharT __ch, true_type) const
{
- auto __c = _M_translator._M_translate(__ch);
- auto __n = _M_translator._M_translate('\n');
- auto __r = _M_translator._M_translate('\r');
- return __c != __n && __c != __r;
- }
-
- bool
- _M_apply(_CharT __ch, false_type) const
- {
- auto __c = _M_translator._M_translate(__ch);
- auto __n = _M_translator._M_translate('\n');
- auto __r = _M_translator._M_translate('\r');
- auto __u2028 = _M_translator._M_translate(u'\u2028');
- auto __u2029 = _M_translator._M_translate(u'\u2029');
- return __c != __n && __c != __r && __c != __u2028 && __c != __u2029;
+ const auto __c = _M_translator._M_translate(__ch);
+ if (__c == _M_translator._M_translate('\n'))
+ return false;
+ if (__c == _M_translator._M_translate('\r'))
+ return false;
+ if constexpr (!is_same<_CharT, char>::value)
+ {
+ if (__c == _M_translator._M_translate(u'\u2028')) // line sep
+ return false;
+ if (__c == _M_translator._M_translate(u'\u2029')) // para sep
+ return false;
+ }
+ return true;
}
_TransT _M_translator;
@@ -441,7 +437,10 @@ namespace __detail
operator()(_CharT __ch) const
{
_GLIBCXX_DEBUG_ASSERT(_M_is_ready);
- return _M_apply(__ch, _UseCache());
+ if constexpr (_UseCache::value)
+ if (!(__ch & 0x80)) [[__likely__]]
+ return _M_cache[static_cast<_UnsignedCharT>(__ch)];
+ return _M_apply(__ch);
}
void
@@ -512,7 +511,9 @@ namespace __detail
std::sort(_M_char_set.begin(), _M_char_set.end());
auto __end = std::unique(_M_char_set.begin(), _M_char_set.end());
_M_char_set.erase(__end, _M_char_set.end());
- _M_make_cache(_UseCache());
+ if constexpr (_UseCache::value)
+ for (unsigned __i = 0; __i < 128; __i++) // Only cache 7-bit chars
+ _M_cache[__i] = _M_apply(static_cast<_CharT>(__i));
_GLIBCXX_DEBUG_ONLY(_M_is_ready = true);
}
@@ -531,22 +532,7 @@ namespace __detail
using _UnsignedCharT = typename std::make_unsigned<_CharT>::type;
bool
- _M_apply(_CharT __ch, false_type) const;
-
- bool
- _M_apply(_CharT __ch, true_type) const
- { return _M_cache[static_cast<_UnsignedCharT>(__ch)]; }
-
- void
- _M_make_cache(true_type)
- {
- for (unsigned __i = 0; __i < _M_cache.size(); __i++)
- _M_cache[__i] = _M_apply(static_cast<_CharT>(__i), false_type());
- }
-
- void
- _M_make_cache(false_type)
- { }
+ _M_apply(_CharT __ch) const;
private:
_GLIBCXX_STD_C::vector<_CharT> _M_char_set;
@@ -565,6 +551,7 @@ namespace __detail
///@} regex-detail
} // namespace __detail
+#pragma GCC diagnostic pop
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
diff --git a/libstdc++-v3/include/bits/regex_compiler.tcc b/libstdc++-v3/include/bits/regex_compiler.tcc
index cd0db2761b5..59b79fdd106 100644
--- a/libstdc++-v3/include/bits/regex_compiler.tcc
+++ b/libstdc++-v3/include/bits/regex_compiler.tcc
@@ -598,7 +598,7 @@ namespace __detail
template<typename _TraitsT, bool __icase, bool __collate>
bool
_BracketMatcher<_TraitsT, __icase, __collate>::
- _M_apply(_CharT __ch, false_type) const
+ _M_apply(_CharT __ch) const
{
return [this, __ch]
{
diff --git a/libstdc++-v3/include/bits/regex_executor.tcc b/libstdc++-v3/include/bits/regex_executor.tcc
index e887e28854f..f310291b4c4 100644
--- a/libstdc++-v3/include/bits/regex_executor.tcc
+++ b/libstdc++-v3/include/bits/regex_executor.tcc
@@ -32,6 +32,8 @@ namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
namespace __detail
{
template<typename _BiIter, typename _Alloc, typename _TraitsT,
@@ -217,7 +219,7 @@ namespace __detail
}
else // Non-greedy mode
{
- if (__dfs_mode)
+ if constexpr (__dfs_mode)
{
// vice-versa.
_M_dfs(__match_mode, __state._M_next);
@@ -322,7 +324,7 @@ namespace __detail
if (_M_current == _M_end)
return;
- if (__dfs_mode)
+ if constexpr (__dfs_mode)
{
if (__state._M_matches(*_M_current))
{
@@ -393,32 +395,35 @@ namespace __detail
void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
_M_handle_backref(_Match_mode __match_mode, _StateIdT __i)
{
- __glibcxx_assert(__dfs_mode);
-
- const auto& __state = _M_nfa[__i];
- auto& __submatch = _M_cur_results[__state._M_backref_index];
- if (!__submatch.matched)
- return;
- auto __last = _M_current;
- for (auto __tmp = __submatch.first;
- __last != _M_end && __tmp != __submatch.second;
- ++__tmp)
- ++__last;
- if (_Backref_matcher<_BiIter, _TraitsT>(
- _M_re.flags() & regex_constants::icase,
- _M_re._M_automaton->_M_traits)._M_apply(
- __submatch.first, __submatch.second, _M_current, __last))
+ if constexpr (__dfs_mode)
{
- if (__last != _M_current)
+ const auto& __state = _M_nfa[__i];
+ auto& __submatch = _M_cur_results[__state._M_backref_index];
+ if (!__submatch.matched)
+ return;
+ auto __last = _M_current;
+ for (auto __tmp = __submatch.first;
+ __last != _M_end && __tmp != __submatch.second;
+ ++__tmp)
+ ++__last;
+ if (_Backref_matcher<_BiIter, _TraitsT>(
+ _M_re.flags() & regex_constants::icase,
+ _M_re._M_automaton->_M_traits)._M_apply(
+ __submatch.first, __submatch.second, _M_current, __last))
{
- auto __backup = _M_current;
- _M_current = __last;
- _M_dfs(__match_mode, __state._M_next);
- _M_current = __backup;
+ if (__last != _M_current)
+ {
+ auto __backup = _M_current;
+ _M_current = __last;
+ _M_dfs(__match_mode, __state._M_next);
+ _M_current = __backup;
+ }
+ else
+ _M_dfs(__match_mode, __state._M_next);
}
- else
- _M_dfs(__match_mode, __state._M_next);
}
+ else
+ __builtin_unreachable();
}
template<typename _BiIter, typename _Alloc, typename _TraitsT,
@@ -426,7 +431,7 @@ namespace __detail
void _Executor<_BiIter, _Alloc, _TraitsT, __dfs_mode>::
_M_handle_accept(_Match_mode __match_mode, _StateIdT)
{
- if _GLIBCXX17_CONSTEXPR (__dfs_mode)
+ if constexpr (__dfs_mode)
{
__glibcxx_assert(!_M_has_sol);
if (__match_mode == _Match_mode::_Exact)
@@ -529,7 +534,11 @@ namespace __detail
case _S_opcode_match:
_M_handle_match(__match_mode, __i); break;
case _S_opcode_backref:
- _M_handle_backref(__match_mode, __i); break;
+ if constexpr (__dfs_mode)
+ _M_handle_backref(__match_mode, __i);
+ else
+ __builtin_unreachable();
+ break;
case _S_opcode_accept:
_M_handle_accept(__match_mode, __i); break;
case _S_opcode_alternative:
@@ -564,6 +573,7 @@ namespace __detail
return __left_is_word != __right_is_word;
}
} // namespace __detail
+#pragma GCC diagnostic pop
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
--
2.49.0
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