[gcc r12-9462] libstdc++: Optimize std::try_facet and std::use_facet [PR103755]

[gcc r12-9462] libstdc++: Optimize std::try_facet and std::use_facet [PR103755]

[Jonathan Wakely]

https://gcc.gnu.org/g:8caf5805ad76125b84430b8653003f4776489d46

commit r12-9462-g8caf5805ad76125b84430b8653003f4776489d46
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Apr 20 21:02:22 2023 +0100

    libstdc++: Optimize std::try_facet and std::use_facet [PR103755]
    
    The std::try_facet and std::use_facet functions were optimized in
    r13-3888-gb3ac43a3c05744 to avoid redundant checking for all facets that
    are required to always be present in every locale.
    
    This performs a simpler version of the optimization that only applies to
    std::ctype<char>, std::num_get<char>, std::num_put<char>, and the
    wchar_t specializations of those facets. Those are the facets that are
    cached by std::basic_ios, which means they're used on construction for
    every iostream object. This smaller change is suitable for the gcc-12
    branch, and mitigates the performance loss for powerpc64le-linux on the
    gcc-12 branch caused by r12-9454-g24cf9f4c6f45f7 for PR 103387. It also
    greatly improves the performance of constructing iostreams objects, for
    all targets.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/103755
            * include/bits/locale_classes.tcc (try_facet, use_facet): Do not
            check array index or dynamic type when accessing required
            specializations of std::ctype, std::num_get, or std::num_put.
            * testsuite/22_locale/ctype/is/string/89728_neg.cc: Adjust
            expected errors.

Diff:
---
 libstdc++-v3/include/bits/locale_classes.tcc       | 23 ++++++++++++++++++++++
 .../22_locale/ctype/is/string/89728_neg.cc         |  1 +
 2 files changed, 24 insertions(+)

diff --git a/libstdc++-v3/include/bits/locale_classes.tcc b/libstdc++-v3/include/bits/locale_classes.tcc
index 64cd7534dc6..e6ce07ae8b7 100644
--- a/libstdc++-v3/include/bits/locale_classes.tcc
+++ b/libstdc++-v3/include/bits/locale_classes.tcc
@@ -103,6 +103,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     bool
     has_facet(const locale& __loc) throw()
     {
+      if _GLIBCXX17_CONSTEXPR (__is_same(_Facet, ctype<char>)
+				 || __is_same(_Facet, num_get<char>)
+				 || __is_same(_Facet, num_put<char>))
+	return true;
+#ifdef _GLIBCXX_USE_WCHAR_T
+      else if _GLIBCXX17_CONSTEXPR (__is_same(_Facet, ctype<wchar_t>)
+				      || __is_same(_Facet, num_get<wchar_t>)
+				      || __is_same(_Facet, num_put<wchar_t>))
+	return true;
+#endif
+
       const size_t __i = _Facet::id._M_id();
       const locale::facet** __facets = __loc._M_impl->_M_facets;
       return (__i < __loc._M_impl->_M_facets_size
@@ -133,6 +144,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       const size_t __i = _Facet::id._M_id();
       const locale::facet** __facets = __loc._M_impl->_M_facets;
+
+      if _GLIBCXX17_CONSTEXPR (__is_same(_Facet, ctype<char>)
+				 || __is_same(_Facet, num_get<char>)
+				 || __is_same(_Facet, num_put<char>))
+	return static_cast<const _Facet&>(*__facets[__i]);
+#ifdef _GLIBCXX_USE_WCHAR_T
+      else if _GLIBCXX17_CONSTEXPR (__is_same(_Facet, ctype<wchar_t>)
+				      || __is_same(_Facet, num_get<wchar_t>)
+				      || __is_same(_Facet, num_put<wchar_t>))
+	return static_cast<const _Facet&>(*__facets[__i]);
+#endif
+
       if (__i >= __loc._M_impl->_M_facets_size || !__facets[__i])
         __throw_bad_cast();
 #if __cpp_rtti
diff --git a/libstdc++-v3/testsuite/22_locale/ctype/is/string/89728_neg.cc b/libstdc++-v3/testsuite/22_locale/ctype/is/string/89728_neg.cc
index 77bb1a64f45..baed67d64f4 100644
--- a/libstdc++-v3/testsuite/22_locale/ctype/is/string/89728_neg.cc
+++ b/libstdc++-v3/testsuite/22_locale/ctype/is/string/89728_neg.cc
@@ -18,6 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-error "complete" "" { target *-*-* } 0 }
+// { dg-error "invalid .static_cast." "" { target c++14_down } 0 }
 
 #include <locale>