On 31.12.2010, at 05:34, Jakob Stoklund Olesen wrote: > On Dec 30, 2010, at 4:08 PM, Benjamin Kramer wrote: >> >> I'm not very happy with this fix. Using such a pinned variable with inline >> asm looks like an edge case. > > It is all that is required for local variables, see > http://gcc.gnu.org/onlinedocs/gcc/Local-Reg-Vars.html > >> Most code (e.g. ruby 1.9) uses this as a (premature) optimization so it >> shouldn't hurt there but on the other hand >> the linux kernel uses this extension to access the stack pointer like a >> variable. >> >> register unsigned long current_stack_pointer asm("esp"); >> foo = current_stack_pointer; > > Presumably this is a global variable, otherwise it could legally be compiled > to: > > foo = undef > > I think we can support global variables like this one by replacing all reads > and writes with empty inline assembly statements. > > That will work for reserved registers like %esp. As for using allocatable > registers for global variables, I really hope we can avoid that.
Okay, the kernel indeed uses a global variable and that still gives an error with clang. Sorry for the noise. *phew* To sum this up, should we consider using local register vars outside of asm statements unsafe and just ignore them (as we do now)? While GCC supports them to some extent I don't think it's worth to support it just to enable some premature optimizations. We don't even need a warning in that case. _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
