Christophe Leroy f83647d642 powerpc: Discard ffs()/__ffs() function and use builtin functions instead ... With the ffs() function as defined in arch/powerpc/include/asm/bitops.h GCC will not optimise the code in case of constant parameter, as shown by the small exemple below. int ffs_test(void) { return 4 << ffs(31); } c0012334 <ffs_test>: c0012334: 39 20 00 01 li r9,1 c0012338: 38 60 00 04 li r3,4 c001233c: 7d 29 00 34 cntlzw r9,r9 c0012340: 21 29 00 20 subfic r9,r9,32 c0012344: 7c 63 48 30 slw r3,r3,r9 c0012348: 4e 80 00 20 blr With this patch, the same function will compile as follows: c0012334 <ffs_test>: c0012334: 38 60 00 08 li r3,8 c0012338: 4e 80 00 20 blr The same happens with __ffs() For non constant calls, the generated code is doing the same, allthought it is slightly different on 64 bits for ffs(): unsigned long test__ffs(unsigned long x) { return __ffs(x); } int testffs(int x) { return ffs(x); } On PPC32, before the patch: 0000003c <test__ffs>: 3c: 7d 23 00 d0 neg r9,r3 40: 7d 23 18 38 and r3,r9,r3 44: 7c 63 00 34 cntlzw r3,r3 48: 20 63 00 1f subfic r3,r3,31 4c: 4e 80 00 20 blr 00000050 <testffs>: 50: 7d 23 00 d0 neg r9,r3 54: 7d 23 18 38 and r3,r9,r3 58: 7c 63 00 34 cntlzw r3,r3 5c: 20 63 00 20 subfic r3,r3,32 60: 4e 80 00 20 blr On PPC32, after the patch: 0000002c <test__ffs>: 2c: 7d 23 00 d0 neg r9,r3 30: 7d 23 18 38 and r3,r9,r3 34: 7c 63 00 34 cntlzw r3,r3 38: 20 63 00 1f subfic r3,r3,31 3c: 4e 80 00 20 blr 00000040 <testffs>: 40: 7d 23 00 d0 neg r9,r3 44: 7d 23 18 38 and r3,r9,r3 48: 7c 63 00 34 cntlzw r3,r3 4c: 20 63 00 20 subfic r3,r3,32 50: 4e 80 00 20 blr On PPC64, before the patch: 0000000000000060 <.test__ffs>: 60: 7c 03 00 d0 neg r0,r3 64: 7c 03 18 38 and r3,r0,r3 68: 7c 63 00 74 cntlzd r3,r3 6c: 20 63 00 3f subfic r3,r3,63 70: 7c 63 07 b4 extsw r3,r3 74: 4e 80 00 20 blr 0000000000000080 <.testffs>: 80: 7c 03 00 d0 neg r0,r3 84: 7c 03 18 38 and r3,r0,r3 88: 7c 63 00 74 cntlzd r3,r3 8c: 20 63 00 40 subfic r3,r3,64 90: 7c 63 07 b4 extsw r3,r3 94: 4e 80 00 20 blr On PPC64, after the patch: 0000000000000050 <.test__ffs>: 50: 7c 03 00 d0 neg r0,r3 54: 7c 03 18 38 and r3,r0,r3 58: 7c 63 00 74 cntlzd r3,r3 5c: 20 63 00 3f subfic r3,r3,63 60: 4e 80 00 20 blr 0000000000000070 <.testffs>: 70: 7c 03 00 d0 neg r0,r3 74: 7c 03 18 38 and r3,r0,r3 78: 7c 63 00 34 cntlzw r3,r3 7c: 20 63 00 20 subfic r3,r3,32 80: 7c 63 07 b4 extsw r3,r3 84: 4e 80 00 20 blr (ffs() operates on an int so cntlzw is equivalent to cntlzd) In addition, when reading the generated vmlinux, we can observe that with the builtin functions, GCC sometimes efficiently spreads the instructions within the generated functions while the inline assembly force them to remain grouped together. __builtin_ffs() is already used in arch/powerpc/include/asm/page_32.h Those builtins have been in GCC since at least 3.4.6 (see https://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/Other-Builtins.html ) Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>		2017-06-02 19:23:54 +10:00
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asm	powerpc: Discard ffs()/__ffs() function and use builtin functions instead	2017-06-02 19:23:54 +10:00
uapi/asm	powerpc: Use uapi/asm-generic/sockios.h	2017-05-30 14:59:51 +10:00