| Message ID | 20240902100355.3032079-2-andrew.cooper3@citrix.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | ARM: Cleanup following bitops improvements | expand |
On 02/09/2024 12:03, Andrew Cooper wrote: > > > Following the improvements to Xen's bitops, fls() does constant propagation in > all cases. Use it, and drop the local opencoded helper. > > No functional change. > > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Michal Orzel <michal.orzel@amd.com> > --- > CC: Stefano Stabellini <sstabellini@kernel.org> > CC: Julien Grall <julien@xen.org> > CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com> > CC: Bertrand Marquis <bertrand.marquis@arm.com> > CC: Michal Orzel <michal.orzel@amd.com> > > ARM32 gets a very minor code generation improvement: > > xen.git/xen$ ../scripts/bloat-o-meter xen-syms-arm32-{before,after} > add/remove: 0/0 grow/shrink: 0/6 up/down: 0/-48 (-48) > Function old new delta > wallclock_time 288 280 -8 > printk_start_of_line 560 552 -8 > domain_vtimer_init 472 464 -8 > do_settime 376 368 -8 > burn_credits 760 752 -8 > __printk_ratelimit 424 416 -8 > > But it's just a couple of operations improvement and no real change in code > structure. I expect that the constant propagation being done through > __builtin_clz(), rather than pure C, is giving the optimiser a bit more > information to work with. > > This file also has an __GNUC__ < 4 case which seems ripe for removing... Agree and noted. ~Michal
diff --git a/xen/arch/arm/include/asm/div64.h b/xen/arch/arm/include/asm/div64.h index 0459d5cc0122..da1f1fcbd503 100644 --- a/xen/arch/arm/include/asm/div64.h +++ b/xen/arch/arm/include/asm/div64.h @@ -102,7 +102,7 @@ /* preserve low part of n for reminder computation */ \ __r = __n; \ /* determine number of bits to represent __b */ \ - __p = 1 << __div64_fls(__b); \ + __p = 1 << fls(__b); \ /* compute __m = ((__p << 64) + __b - 1) / __b */ \ __m = (~0ULL / __b) * __p; \ __m += (((~0ULL % __b + 1) * __p) + __b - 1) / __b; \ @@ -150,8 +150,8 @@ __p /= (__m & -__m); \ __m /= (__m & -__m); \ } else { \ - __p >>= __div64_fls(__bits); \ - __m >>= __div64_fls(__bits); \ + __p >>= fls(__bits); \ + __m >>= fls(__bits); \ } \ /* No correction needed. */ \ __c = 0; \ @@ -217,18 +217,6 @@ __r; \ }) -/* our own fls implementation to make sure constant propagation is fine */ -#define __div64_fls(bits) \ -({ \ - unsigned int __left = (bits), __nr = 0; \ - if (__left & 0xffff0000) __nr += 16, __left >>= 16; \ - if (__left & 0x0000ff00) __nr += 8, __left >>= 8; \ - if (__left & 0x000000f0) __nr += 4, __left >>= 4; \ - if (__left & 0x0000000c) __nr += 2, __left >>= 2; \ - if (__left & 0x00000002) __nr += 1; \ - __nr; \ -}) - #endif /* GCC version */ #endif /* BITS_PER_LONG */
Following the improvements to Xen's bitops, fls() does constant propagation in all cases. Use it, and drop the local opencoded helper. No functional change. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: Stefano Stabellini <sstabellini@kernel.org> CC: Julien Grall <julien@xen.org> CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com> CC: Bertrand Marquis <bertrand.marquis@arm.com> CC: Michal Orzel <michal.orzel@amd.com> ARM32 gets a very minor code generation improvement: xen.git/xen$ ../scripts/bloat-o-meter xen-syms-arm32-{before,after} add/remove: 0/0 grow/shrink: 0/6 up/down: 0/-48 (-48) Function old new delta wallclock_time 288 280 -8 printk_start_of_line 560 552 -8 domain_vtimer_init 472 464 -8 do_settime 376 368 -8 burn_credits 760 752 -8 __printk_ratelimit 424 416 -8 But it's just a couple of operations improvement and no real change in code structure. I expect that the constant propagation being done through __builtin_clz(), rather than pure C, is giving the optimiser a bit more information to work with. This file also has an __GNUC__ < 4 case which seems ripe for removing... --- xen/arch/arm/include/asm/div64.h | 18 +++--------------- 1 file changed, 3 insertions(+), 15 deletions(-)