On Wed, Nov 26, 2008 at 07:51:04AM +0000, Ralf Baechle wrote: > On Wed, Nov 26, 2008 at 06:50:53AM +0100, Manuel Lauss wrote: > > > > The probe routines in cpu-probe.c should get at least some of that correct. > > > How about just overriding the things that cpu-probe.c doesn't get right? > > > > CPU detection gets them all right, it's just that somehow GCC does not use > > the information correctly; i.e. in the __fls() case it blindly falls back > > on the C version instead of using the asm macro with clz in it. I scanned > > a few callsites of __fls() and there's not 'clz' to be found anywhere. With > > this addition the clz is used and the binary is a _lot_ smaller. > > > > You should define all values as constants, as far as known. GCC will > then be able to use constant propagation and dead code elemination to > optimize the code for a particular target system. > > The way fls() is written it will only use of CLZ if the expression > cpu_has_mips_r is a constant, that is if the kernel is being built > exclusivly for MIPS32 / MIPS64 revision 1 or higher. The reason that Ah, so the __builtin_constat_p() is a compiletime check as to whether a given symbol is a constant or needs to be evaluated at runtime? That explains a lot. Thanks, Manuel Lauss
