| Date | Wed, 31 Aug 2022 01:51:49 -0700 | From | Yury Norov <> | Subject | Re: [PATCH v6 0/2] x86/asm/bitops: optimize ff{s,z} functions for constant expressions |
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On Wed, Aug 31, 2022 at 04:57:40PM +0900, Vincent Mailhol wrote: > The compilers provide some builtin expression equivalent to the ffs(), > __ffs() and ffz() functions of the kernel. The kernel uses optimized > assembly which produces better code than the builtin > functions. However, such assembly code can not be folded when used > with constant expressions. > > This series relies on __builtin_constant_p to select the optimal solution: > > * use kernel assembly for non constant expressions > > * use compiler's __builtin function for constant expressions. > > > ** Statistics ** > > Patch 1/2 optimizes 26.7% of ffs() calls and patch 2/2 optimizes 27.9% > of __ffs() and ffz() calls (details of the calculation in each patch).
Hi Vincent,
Can you please add a test for this? We've recently added a very similar test_bitmap_const_eval() in lib/test_bitmap.c.
dc34d5036692c ("lib: test_bitmap: add compile-time optimization/evaluations assertions")
Would be nice to have something like this for ffs() and ffz() in lib/test_bitops.c.
Please keep me in loop in case of new versions.
Thanks, Yury
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