Re: [committed] libstdc++: Reduce template instantiations in <regex>

[Stephan Bergmann <sbergman@redhat.com>]

On 05/01/2022 14:47, Jonathan Wakely via Libstdc++ wrote:
> Tested powerpc64le-linux, pushed to trunk.
> 
> 
> This moves the last two template parameters of __regex_algo_impl to be
> runtime function parameters instead, so that we don't need four
> different instantiations for the possible ways to call it. Most of the
> function (and what it instantiates) is the same in all cases, so making
> them compile-time choices doesn't really have much benefit.
> 
> Use  'if constexpr' for conditions that check template parameters, so
> that when we do depend on a compile-time condition we only instantiate
> what we need to.
> 
> libstdc++-v3/ChangeLog:
> 
> 	* include/bits/regex.h (__regex_algo_impl): Change __policy and
> 	__match_mode template parameters to be function parameters.
> 	(regex_match, regex_search): Pass policy and match mode as
> 	function arguments.
> 	* include/bits/regex.tcc (__regex_algo_impl): Change template
> 	parameters to function parameters.
> 	* include/bits/regex_compiler.h (_RegexTranslatorBase): Use
> 	'if constexpr' for conditions using template parameters.
> 	(_RegexTranslator): Likewise.
> 	* include/bits/regex_executor.tcc (_Executor::_M_handle_accept):
> 	Likewise.
> 	* testsuite/util/testsuite_regex.h (regex_match_debug)
> 	(regex_search_debug): Move template arguments to function
> 	arguments.
> ---
>   libstdc++-v3/include/bits/regex.h             | 33 +++++++++----------
>   libstdc++-v3/include/bits/regex.tcc           |  8 ++---
>   libstdc++-v3/include/bits/regex_compiler.h    |  9 ++---
>   libstdc++-v3/include/bits/regex_executor.tcc  |  2 +-
>   libstdc++-v3/testsuite/util/testsuite_regex.h | 24 +++++++-------
>   5 files changed, 37 insertions(+), 39 deletions(-)

Clang now fails #include <regex> with

> In file included from gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/12.0.0/../../../../include/c++/12.0.0/regex:66:
> gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/12.0.0/../../../../include/c++/12.0.0/bits/regex.h:799:9: error: unknown type name '_RegexExecutorPolicy'; did you mean '__detail::_RegexExecutorPolicy'?
>                                     _RegexExecutorPolicy, bool);
>                                     ^
> gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/12.0.0/../../../../include/c++/12.0.0/bits/regex.h:45:14: note: '__detail::_RegexExecutorPolicy' declared here
>   enum class _RegexExecutorPolicy : int { _S_auto, _S_alternate };
>              ^
> gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/12.0.0/../../../../include/c++/12.0.0/bits/regex.h:2070:9: error: unknown type name '_RegexExecutorPolicy'; did you mean '__detail::_RegexExecutorPolicy'?
>                                     _RegexExecutorPolicy, bool);
>                                     ^
> gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/12.0.0/../../../../include/c++/12.0.0/bits/regex.h:45:14: note: '__detail::_RegexExecutorPolicy' declared here
>   enum class _RegexExecutorPolicy : int { _S_auto, _S_alternate };
>              ^

and

> diff --git a/libstdc++-v3/include/bits/regex.h b/libstdc++-v3/include/bits/regex.h
> index 7480b0a5f97..46c168010bf 100644
> --- a/libstdc++-v3/include/bits/regex.h
> +++ b/libstdc++-v3/include/bits/regex.h
> @@ -796,7 +796,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>         __detail::__regex_algo_impl(_Bp, _Bp, match_results<_Bp, _Ap>&,
>                                     const basic_regex<_Cp, _Rp>&,
>                                     regex_constants::match_flag_type,
> -                                   _RegexExecutorPolicy, bool);
> +                                   __detail::_RegexExecutorPolicy, bool);
>  
>        template<typename, typename, typename, bool>
>         friend class __detail::_Executor;
> @@ -2067,7 +2067,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>         __detail::__regex_algo_impl(_Bp, _Bp, match_results<_Bp, _Ap>&,
>                                     const basic_regex<_Cp, _Rp>&,
>                                     regex_constants::match_flag_type,
> -                                   _RegexExecutorPolicy, bool);
> +                                   __detail::_RegexExecutorPolicy, bool);
>  
>        // Reset contents to __size unmatched sub_match objects
>        // (plus additional objects for prefix, suffix and unmatched sub).

would fix that.