| 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475 |
- /* 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__ */
|
