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>