https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56888
--- Comment #47 from David Brown <david at westcontrol dot com> --- (In reply to M Welinder from comment #46) > Should "-std=c99" imply turning off these optimizations? > > Creating calls to, say, strlen is incompatible with the C99 standard and > perhaps better limited to "-std=gnu-something" or an opt-in f-flag. How is it incompatible with C99 to create calls to library functions? I can think of a two possibilities: 1. If the function implementation plays with errno (allowed in 7.5p3), in a way that is visible to the code. 2. If the function is called with parameters that may invoke undefined behaviour (such as calling "strlen" without being sure that the parameter points to a null-terminated string), where such undefined behaviour is not already present. If the user writes code that acts like a call to strlen (let's assume the implementation knows strlen does not change errno), then the compiler can replace it with a library call. Similarly, if the user writes a call to strlen, then the compiler can replace it with inline code. As long as there is no difference in the observable behaviour, the transformation is allowed. Or am I missing something here?
