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 __fls is written this way is that both it's legacy and R1 variants using CLZ/DCLZ the function body will be compiled into something relativly small. There is not such much point in adding even more code for a runtime decission between two variants. > I believe this is a gcc thing, but this seemed to be the obvious quick > remedy. GCC does correct. Ralf
