> Em qui., 31 de ago. de 2023 às 10:12, Dagfinn Ilmari Mannsåker < > ilmari@ilmari.org> escreveu: > >> Andrew Dunstan <andrew@dunslane.net> writes: >> >> > On 2023-08-31 Th 07:41, John Naylor wrote: >> >> >> >> On Thu, Aug 31, 2023 at 6:07 PM Ranier Vilela <ranier.vf@gmail.com> >> wrote: >> >> > >> >> > Em qui., 31 de ago. de 2023 às 00:22, Michael Paquier >> >> <michael@paquier.xyz> escreveu: >> >> >> >> >> >> On Wed, Aug 30, 2023 at 03:00:13PM -0300, Ranier Vilela wrote: >> >> >> > cstring_to_text has a small overhead, because call strlen for >> >> >> > pointer to char parameter. >> >> >> > >> >> >> > Is it worth the effort to avoid this, where do we know the size >> >> of the >> >> >> > parameter? >> >> >> >> >> >> Are there workloads where this matters? >> >> > >> >> > None, but note this change has the same spirit of 8b26769bc. >> >> >> >> - return cstring_to_text(""); >> >> + return cstring_to_text_with_len("", 0); >> >> >> >> This looks worse, so we'd better be getting something in return. >> > >> > >> > I agree this is a bit ugly. I wonder if we'd be better off creating a >> > function that returned an empty text value, so we'd just avoid >> > converting the empty cstring altogether and say: >> > >> > return empty_text(); >> >> Or we could generalise it for any string literal (of which there are >> slightly more¹ non-empty than empty in calls to >> cstring_to_text(_with_len)): >> >> #define literal_to_text(str) cstring_to_text_with_len("" str "", >> sizeof(str)-1) >> > I do not agree, I think this will get worse.
How exactly will it get worse? It's exactly equivalent to cstring_to_text_with_len("", 0), since sizeof() is a compile-time construct, and the string concatenation makes it fail if the argument is not a literal string.
I think that concatenation makes the strings twice bigger, doesn't it?
Whether we want an even-more-optimised version for an empty text value is another matter, but I doubt it'd be worth it. Another option would be to make cstring_to_text(_with_len) static inline functions, which lets the compiler eliminate the memcpy() call when len == 0.
In fact, after playing around a bit (https://godbolt.org/z/x51aYGadh), it seems like GCC, Clang and MSVC all eliminate the strlen() and memcpy() calls for cstring_to_text("") under -O2 if it's static inline.
In that case, it seems to me that would be good too. Compilers removing memcpy would have the same as empty_text.
Without the burden of a new function and all its future maintenance.