/* SPDX-License-Identifier: GPL-2.0-only */ #ifndef __ASM_UNROLL_H__ #define __ASM_UNROLL_H__ /* * Explicitly unroll a loop, for use in cases where doing so is performance * critical. * * Ideally we'd rely upon the compiler to provide this but there's no commonly * available means to do so. For example GCC's "#pragma GCC unroll" * functionality would be ideal but is only available from GCC 8 onwards. Using * -funroll-loops is an option but GCC tends to make poor choices when * compiling our string functions. -funroll-all-loops leads to massive code * bloat, even if only applied to the string functions. */ #define unroll(times, fn, ...) do { \ extern void bad_unroll(void) \ __compiletime_error("Unsupported unroll"); \ \ /* \ * We can't unroll if the number of iterations isn't \ * compile-time constant. Unfortunately clang versions \ * up until 8.0 tend to miss obvious constants & cause \ * this check to fail, even though they go on to \ * generate reasonable code for the switch statement, \ * so we skip the sanity check for those compilers. \ */ \ BUILD_BUG_ON(!__builtin_constant_p(times)); \ \ switch (times) { \ case 32: fn(__VA_ARGS__); fallthrough; \ case 31: fn(__VA_ARGS__); fallthrough; \ case 30: fn(__VA_ARGS__); fallthrough; \ case 29: fn(__VA_ARGS__); fallthrough; \ case 28: fn(__VA_ARGS__); fallthrough; \ case 27: fn(__VA_ARGS__); fallthrough; \ case 26: fn(__VA_ARGS__); fallthrough; \ case 25: fn(__VA_ARGS__); fallthrough; \ case 24: fn(__VA_ARGS__); fallthrough; \ case 23: fn(__VA_ARGS__); fallthrough; \ case 22: fn(__VA_ARGS__); fallthrough; \ case 21: fn(__VA_ARGS__); fallthrough; \ case 20: fn(__VA_ARGS__); fallthrough; \ case 19: fn(__VA_ARGS__); fallthrough; \ case 18: fn(__VA_ARGS__); fallthrough; \ case 17: fn(__VA_ARGS__); fallthrough; \ case 16: fn(__VA_ARGS__); fallthrough; \ case 15: fn(__VA_ARGS__); fallthrough; \ case 14: fn(__VA_ARGS__); fallthrough; \ case 13: fn(__VA_ARGS__); fallthrough; \ case 12: fn(__VA_ARGS__); fallthrough; \ case 11: fn(__VA_ARGS__); fallthrough; \ case 10: fn(__VA_ARGS__); fallthrough; \ case 9: fn(__VA_ARGS__); fallthrough; \ case 8: fn(__VA_ARGS__); fallthrough; \ case 7: fn(__VA_ARGS__); fallthrough; \ case 6: fn(__VA_ARGS__); fallthrough; \ case 5: fn(__VA_ARGS__); fallthrough; \ case 4: fn(__VA_ARGS__); fallthrough; \ case 3: fn(__VA_ARGS__); fallthrough; \ case 2: fn(__VA_ARGS__); fallthrough; \ case 1: fn(__VA_ARGS__); fallthrough; \ case 0: break; \ \ default: \ /* \ * Either the iteration count is unreasonable \ * or we need to add more cases above. \ */ \ bad_unroll(); \ break; \ } \ } while (0) #endif /* __ASM_UNROLL_H__ */
