On Fri, Jun 24, 2022 at 02:13:10PM +0200, Alexander Lobakin wrote: > Currently, many architecture-specific non-atomic bitop > implementations use inline asm or other hacks which are faster or > more robust when working with "real" variables (i.e. fields from > the structures etc.), but the compilers have no clue how to optimize > them out when called on compile-time constants. That said, the > following code: > > DECLARE_BITMAP(foo, BITS_PER_LONG) = { }; // -> unsigned long foo[1]; > unsigned long bar = BIT(BAR_BIT); > unsigned long baz = 0; > > __set_bit(FOO_BIT, foo); > baz |= BIT(BAZ_BIT); > > BUILD_BUG_ON(!__builtin_constant_p(test_bit(FOO_BIT, foo)); > BUILD_BUG_ON(!__builtin_constant_p(bar & BAR_BIT)); > BUILD_BUG_ON(!__builtin_constant_p(baz & BAZ_BIT)); > > triggers the first assertion on x86_64, which means that the > compiler is unable to evaluate it to a compile-time initializer > when the architecture-specific bitop is used even if it's obvious. > In order to let the compiler optimize out such cases, expand the > bitop() macro to use the "constant" C non-atomic bitop > implementations when all of the arguments passed are compile-time > constants, which means that the result will be a compile-time > constant as well, so that it produces more efficient and simple > code in 100% cases, comparing to the architecture-specific > counterparts. > > The savings are architecture, compiler and compiler flags dependent, > for example, on x86_64 -O2: > > GCC 12: add/remove: 78/29 grow/shrink: 332/525 up/down: 31325/-61560 (-30235) > LLVM 13: add/remove: 79/76 grow/shrink: 184/537 up/down: 55076/-141892 (-86816) > LLVM 14: add/remove: 10/3 grow/shrink: 93/138 up/down: 3705/-6992 (-3287) > > and ARM64 (courtesy of Mark): > > GCC 11: add/remove: 92/29 grow/shrink: 933/2766 up/down: 39340/-82580 (-43240) > LLVM 14: add/remove: 21/11 grow/shrink: 620/651 up/down: 12060/-15824 (-3764) > > Cc: Mark Rutland <mark.rutland@xxxxxxx> > Signed-off-by: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx> > Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Building i386:allyesconfig ... failed -------------- Error log: arch/x86/platform/olpc/olpc-xo1-sci.c: In function 'send_ebook_state': arch/x86/platform/olpc/olpc-xo1-sci.c:83:63: error: logical not is only applied to the left hand side of comparison Bisect log attached. Guenter --- # bad: [4662b7adea50bb62e993a67f611f3be625d3df0d] Add linux-next specific files for 20220713 # good: [32346491ddf24599decca06190ebca03ff9de7f8] Linux 5.19-rc6 git bisect start 'HEAD' 'v5.19-rc6' # good: [8b7e002d8bc6e17c94092d25e7261db4e6e5f2cc] Merge branch 'drm-next' of git://git.freedesktop.org/git/drm/drm.git git bisect good 8b7e002d8bc6e17c94092d25e7261db4e6e5f2cc # good: [07f6d21d6e33c1e28e24ae84e9d26e4e7d4853f5] Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux.git git bisect good 07f6d21d6e33c1e28e24ae84e9d26e4e7d4853f5 # good: [5ff085e5d4f6700e03635d5e700f52163a6dc2a7] Merge branch 'staging-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git git bisect good 5ff085e5d4f6700e03635d5e700f52163a6dc2a7 # good: [eb9e3fdbdd8b61ef0f4bee23259fe6ab69e463ab] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git git bisect good eb9e3fdbdd8b61ef0f4bee23259fe6ab69e463ab # good: [9f2183cd961e5ddb7954eafb6bb01a495c6a9c7b] hexagon/mm: enable ARCH_HAS_VM_GET_PAGE_PROT git bisect good 9f2183cd961e5ddb7954eafb6bb01a495c6a9c7b # bad: [e878aa5faf9ac8c0b5d0c3f293389c194c250fff] Merge branch 'mm-nonmm-stable' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm git bisect bad e878aa5faf9ac8c0b5d0c3f293389c194c250fff # good: [cf95d50205f62c4f5f538676def847292cf39fa9] fs: don't call ->writepage from __mpage_writepage git bisect good cf95d50205f62c4f5f538676def847292cf39fa9 # good: [5103cbfd92d3587713476f94f9485b96e02f0146] Merge branch 'for-next/execve' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git git bisect good 5103cbfd92d3587713476f94f9485b96e02f0146 # good: [ee56c3e8eec166f4e4a2ca842b7804d14f3a0208] Merge branch 'master' into mm-nonmm-stable git bisect good ee56c3e8eec166f4e4a2ca842b7804d14f3a0208 # bad: [dc34d5036692c614eef23c1130ee42a201c316bf] lib: test_bitmap: add compile-time optimization/evaluations assertions git bisect bad dc34d5036692c614eef23c1130ee42a201c316bf # good: [bb7379bfa680bd48b468e856475778db2ad866c1] bitops: define const_*() versions of the non-atomics git bisect good bb7379bfa680bd48b468e856475778db2ad866c1 # bad: [b03fc1173c0c2bb8fad61902a862985cecdc4b1b] bitops: let optimize out non-atomic bitops on compile-time constants git bisect bad b03fc1173c0c2bb8fad61902a862985cecdc4b1b # good: [e69eb9c460f128b71c6b995d75a05244e4b6cc3e] bitops: wrap non-atomic bitops with a transparent macro git bisect good e69eb9c460f128b71c6b995d75a05244e4b6cc3e # first bad commit: [b03fc1173c0c2bb8fad61902a862985cecdc4b1b] bitops: let optimize out non-atomic bitops on compile-time constants