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-rw-r--r--arch/mips/include/asm/unroll.h75
1 files changed, 75 insertions, 0 deletions
diff --git a/arch/mips/include/asm/unroll.h b/arch/mips/include/asm/unroll.h
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+++ b/arch/mips/include/asm/unroll.h
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+/* 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__ */