On Thu, Sep 05, 2019 at 04:23:11PM +0200, Rasmus Villemoes wrote: > On 05/09/2019 15.45, Segher Boessenkool wrote: > > On Thu, Sep 05, 2019 at 01:07:11PM +0200, Rasmus Villemoes wrote: > >> Perhaps something like below, though that > >> won't affect the already released gcc 9.1 and 9.2, of course. > > > > That is one reason to not want such a predefined macro. Another reason > > is that you usually need to compile some test programs *anyway*, to see if > > some bug is present for example, or to see if the exact implementation of > > the feature is beneficial (or harmful) to your program in some way. > > OK, I think I'll just use a version check for now, and then switch to a > Kconfig test if and when clang grows support. > > >> gcc maintainers, WDYT? Can we add a feature test macro for asm inline()? > > > > Why would GCC want to have macros for all features it has? > > Well, gcc has implemented __has_attribute() which is similar - one could > detect support by compiling a trivial test program.
It is not a macro, it doesn't spill over the place, and it is for detecting things that are already fixed strings, much easier to do :-) > Or the same could be > said for many of the predefined macros that are conditionally defined, > e.g. __HAVE_SPECULATION_SAFE_VALUE. That one happened because of the Great Security Scare of 2017/2018, it's not a good precedent. And, how it is set is target-specific, it can depend on CPU model selected, target code generation options, or whatnot. > But I was just throwing the question into the air, I won't pursue this > further. Maybe GCC should have a has_feature thing, it might fit in well there. As preprocessor macros, not so much, IMO. Segher
