[libc++] Speed up certain locale functions on Windows

The issue is that __libcpp_locale_guard makes some slow calls to setlocale().
This change avoids using __libcpp_locale_guard in snprintf_l().

Fixes https://bugs.llvm.org/show_bug.cgi?id=41131

Differential Revision: https://reviews.llvm.org/D59525

llvm-svn: 356512

1 files changed, 6 insertions, 0 deletions

diff --git a/libcxx/src/support/win32/locale_win32.cpp b/libcxx/src/support/win32/locale_win32.cpp
index c11adfe4cda..d02d7ffc3cd 100644
--- a/libcxx/src/support/win32/locale_win32.cpp
+++ b/libcxx/src/support/win32/locale_win32.cpp
@@ -87,10 +87,16 @@ int wctob_l( wint_t c, locale_t loc )
 
 int snprintf_l(char *ret, size_t n, locale_t loc, const char *format, ...)
 {
+#if !defined(_LIBCPP_MSVCRT)
     __libcpp_locale_guard __current(loc);
+#endif
     va_list ap;
     va_start( ap, format );
+#if defined(_LIBCPP_MSVCRT)
+    int result = _vsnprintf_l( ret, n, format, loc, ap );
+#else
     int result = vsnprintf( ret, n, format, ap );
+#endif
     va_end(ap);
     return result;
 }