On Mon, Jun 20, 2022 at 05:08:55PM +0200, Alexander Lobakin wrote: > From: Mark Rutland <mark.rutland@xxxxxxx> > Date: Mon, 20 Jun 2022 15:19:42 +0100 > > > On Fri, Jun 17, 2022 at 04:40:24PM +0200, Alexander Lobakin wrote: > > > > > 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[0]): > > > > > > 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) > > > > Hmm... with *this version* of the series, I'm not getting results nearly as > > good as that when building defconfig atop v5.19-rc3: > > > > GCC 8.5.0: add/remove: 83/49 grow/shrink: 973/1147 up/down: 32020/-47824 (-15804) > > GCC 9.3.0: add/remove: 68/51 grow/shrink: 1167/592 up/down: 30720/-31352 (-632) > > GCC 10.3.0: add/remove: 84/37 grow/shrink: 1711/1003 up/down: 45392/-41844 (3548) > > GCC 11.1.0: add/remove: 88/31 grow/shrink: 1635/963 up/down: 51540/-46096 (5444) > > GCC 11.3.0: add/remove: 89/32 grow/shrink: 1629/966 up/down: 51456/-46056 (5400) > > GCC 12.1.0: add/remove: 84/31 grow/shrink: 1540/829 up/down: 48772/-43164 (5608) > > > > LLVM 12.0.1: add/remove: 118/58 grow/shrink: 437/381 up/down: 45312/-65668 (-20356) > > LLVM 13.0.1: add/remove: 35/19 grow/shrink: 416/243 up/down: 14408/-22200 (-7792) > > LLVM 14.0.0: add/remove: 42/16 grow/shrink: 415/234 up/down: 15296/-21008 (-5712) > > > > ... and that now seems to be regressing codegen with recent versions of GCC as > > much as it improves it LLVM. > > > > I'm not sure if we've improved some other code and removed the benefit between > > v5.19-rc1 and v5.19-rc3, or whether something else it at play, but this doesn't > > look as compelling as it did. > > Mostly likely it's due to that in v1 I mistakingly removed > `volatile` from gen[eric]_test_bit(), so there was an impact for > non-constant cases as well. > +5 Kb sounds bad tho. Do you have CONFIG_TEST_BITMAP enabled, does > it work? I didn't have it enabled, but I tried that just nw with GCC 12.1.0 and it builds cleanly, and test_bitmap_const_eval() gets optimized away entirely. If i remove the `static` from that, GCC generates: | <test_bitmap_const_eval>: | paciasp | autiasp | ret ... which is a trivial stub. > Probably the same reason as for m68k, more constant > optimization -> more aggressive inlining or inlining rebalance -> > larger code. OTOH I've no idea why sometimes compiler decides to > uninline really tiny functions where due to this patch series some > bitops have been converted to constants, like it goes on m68k. Hmm.... it'd be interesting to take a look at a few architectures and see what the common case is. Thanks, Mark.
