On Thu, 4 Dec 2014, Richard Biener wrote: > OTOH this also means the user cannot provide a conforming > implementation on his own and get that used by GCC without editing > system headers or including a header with -isystem or similar > tricks.
Well - you could have a pragma / attribute for that purpose (declaring "this program is providing a version of function X that has the semantics GCC expects for function X", so GCC can both generate and optimize calls). Such a pragma / attribute could also override targetm.libc_has_function (for the case of the user providing their own definition of something missing from their system's standard libraries). A related case would be declaring somehow "I will be linking in libm, even though this translation unit doesn't appear to be using libm functions, so calls to libm functions can be implicitly generated", if GCC were made to avoid introducing uses of libm. (Again, this would be a matter of providing a cleaner interface rather than something that currently can't be expressed at all - the proposed definition of what it means to use libm explicitly implies that "if (0) (void) sqrt (0);" says that libm is being used.) -- Joseph S. Myers jos...@codesourcery.com
