Q{Any,}StringView: remove the GCC-specific compile-time content

Because GCC isn't really working them out at compile time. First, for
both lengthHelperPointer(), they don't get called on string literals
such as

  return QStringView(u"Hello");

because the type hasn't decayed to a pointer, but is instead a
char16_t[6]. No one writes

  constexpr auto str = u"Hello";
  return QStringView(str);

Second, even when you do write that, GCC is emitting the code to search
for the null or non-ASCII byte at runtime, instead of pre-calculating
it. That's not worth it because the code is not vectorized, even at -O3
and with a long string. Instead, let it get the length at runtime with
QtPrivate::qustrlen(), which has vector code.

Drive-by fix the QAnyStringView::lengthPointerHelper() to be constexpr,
avoiding the same GCC warning that was fixed for QStringView in commit
4fd4082c3ab682f14911e6308ec5ccb400de34f9.

Change-Id: Ieab617d69f3b4b54ab30fffd175c505cb66eac02
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

1 files changed, 0 insertions, 3 deletions

diff --git a/src/corelib/text/qstringview.h b/src/corelib/text/qstringview.h
index 3dc8b5ce0b..24a860c1a6 100644
--- a/src/corelib/text/qstringview.h
+++ b/src/corelib/text/qstringview.h
@@ -108,9 +108,6 @@ private:
 #if defined(__cpp_lib_is_constant_evaluated)
         if (std::is_constant_evaluated())
             return std::char_traits<Char>::length(str);
-#elif defined(Q_CC_GNU) && !defined(Q_CC_CLANG)
-        if (__builtin_constant_p(*str))
-            return std::char_traits<Char>::length(str);
 #endif
         return QtPrivate::qustrlen(reinterpret_cast<const char16_t *>(str));
     }