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Diffstat (limited to 'arch/mips/include/asm/unroll.h')
| -rw-r--r-- | arch/mips/include/asm/unroll.h | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/arch/mips/include/asm/unroll.h b/arch/mips/include/asm/unroll.h new file mode 100644 index 000000000..6f4ac854b --- /dev/null +++ b/arch/mips/include/asm/unroll.h @@ -0,0 +1,75 @@ +/* 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__ */ |