1 /* SPDX-License-Identifier: GPL-2.0-only */ 2 #ifndef __ASM_UNROLL_H__ 3 #define __ASM_UNROLL_H__ 4 5 /* 6 * Explicitly unroll a loop, for use in cases where doing so is performance 7 * critical. 8 * 9 * Ideally we'd rely upon the compiler to provide this but there's no commonly 10 * available means to do so. For example GCC's "#pragma GCC unroll" 11 * functionality would be ideal but is only available from GCC 8 onwards. Using 12 * -funroll-loops is an option but GCC tends to make poor choices when 13 * compiling our string functions. -funroll-all-loops leads to massive code 14 * bloat, even if only applied to the string functions. 15 */ 16 #define unroll(times, fn, ...) do { \ 17 extern void bad_unroll(void) \ 18 __compiletime_error("Unsupported unroll"); \ 19 \ 20 /* \ 21 * We can't unroll if the number of iterations isn't \ 22 * compile-time constant. Unfortunately clang versions \ 23 * up until 8.0 tend to miss obvious constants & cause \ 24 * this check to fail, even though they go on to \ 25 * generate reasonable code for the switch statement, \ 26 * so we skip the sanity check for those compilers. \ 27 */ \ 28 BUILD_BUG_ON(!__builtin_constant_p(times)); \ 29 \ 30 switch (times) { \ 31 case 32: fn(__VA_ARGS__); /* fall through */ \ 32 case 31: fn(__VA_ARGS__); /* fall through */ \ 33 case 30: fn(__VA_ARGS__); /* fall through */ \ 34 case 29: fn(__VA_ARGS__); /* fall through */ \ 35 case 28: fn(__VA_ARGS__); /* fall through */ \ 36 case 27: fn(__VA_ARGS__); /* fall through */ \ 37 case 26: fn(__VA_ARGS__); /* fall through */ \ 38 case 25: fn(__VA_ARGS__); /* fall through */ \ 39 case 24: fn(__VA_ARGS__); /* fall through */ \ 40 case 23: fn(__VA_ARGS__); /* fall through */ \ 41 case 22: fn(__VA_ARGS__); /* fall through */ \ 42 case 21: fn(__VA_ARGS__); /* fall through */ \ 43 case 20: fn(__VA_ARGS__); /* fall through */ \ 44 case 19: fn(__VA_ARGS__); /* fall through */ \ 45 case 18: fn(__VA_ARGS__); /* fall through */ \ 46 case 17: fn(__VA_ARGS__); /* fall through */ \ 47 case 16: fn(__VA_ARGS__); /* fall through */ \ 48 case 15: fn(__VA_ARGS__); /* fall through */ \ 49 case 14: fn(__VA_ARGS__); /* fall through */ \ 50 case 13: fn(__VA_ARGS__); /* fall through */ \ 51 case 12: fn(__VA_ARGS__); /* fall through */ \ 52 case 11: fn(__VA_ARGS__); /* fall through */ \ 53 case 10: fn(__VA_ARGS__); /* fall through */ \ 54 case 9: fn(__VA_ARGS__); /* fall through */ \ 55 case 8: fn(__VA_ARGS__); /* fall through */ \ 56 case 7: fn(__VA_ARGS__); /* fall through */ \ 57 case 6: fn(__VA_ARGS__); /* fall through */ \ 58 case 5: fn(__VA_ARGS__); /* fall through */ \ 59 case 4: fn(__VA_ARGS__); /* fall through */ \ 60 case 3: fn(__VA_ARGS__); /* fall through */ \ 61 case 2: fn(__VA_ARGS__); /* fall through */ \ 62 case 1: fn(__VA_ARGS__); /* fall through */ \ 63 case 0: break; \ 64 \ 65 default: \ 66 /* \ 67 * Either the iteration count is unreasonable \ 68 * or we need to add more cases above. \ 69 */ \ 70 bad_unroll(); \ 71 break; \ 72 } \ 73 } while (0) 74 75 #endif /* __ASM_UNROLL_H__ */ 76