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authorAlexander Lobakin <alexandr.lobakin@intel.com>2022-06-24 15:13:08 +0300
committerYury Norov <yury.norov@gmail.com>2022-07-01 05:52:41 +0300
commitbb7379bfa680bd48b468e856475778db2ad866c1 (patch)
tree83565d30d7fb5f3da1a099cb2b3192d9d7a6088f /include/asm-generic
parent0e862838f290147ea9c16db852d8d494b552d38d (diff)
downloadlinux-bb7379bfa680bd48b468e856475778db2ad866c1.tar.xz
bitops: define const_*() versions of the non-atomics
Define const_*() variants of the non-atomic bitops to be used when the input arguments are compile-time constants, so that the compiler will be always able to resolve those to compile-time constants as well. Those are mostly direct aliases for generic_*() with one exception for const_test_bit(): the original one is declared atomic-safe and thus doesn't discard the `volatile` qualifier, so in order to let optimize code, define it separately disregarding the qualifier. Add them to the compile-time type checks as well just in case. Suggested-by: Marco Elver <elver@google.com> Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> Reviewed-by: Marco Elver <elver@google.com> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: Yury Norov <yury.norov@gmail.com>
Diffstat (limited to 'include/asm-generic')
-rw-r--r--include/asm-generic/bitops/generic-non-atomic.h31
1 files changed, 31 insertions, 0 deletions
diff --git a/include/asm-generic/bitops/generic-non-atomic.h b/include/asm-generic/bitops/generic-non-atomic.h
index b85b8a2ac239..3d5ebd24652b 100644
--- a/include/asm-generic/bitops/generic-non-atomic.h
+++ b/include/asm-generic/bitops/generic-non-atomic.h
@@ -127,4 +127,35 @@ generic_test_bit(unsigned long nr, const volatile unsigned long *addr)
return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
}
+/*
+ * const_*() definitions provide good compile-time optimizations when
+ * the passed arguments can be resolved at compile time.
+ */
+#define const___set_bit generic___set_bit
+#define const___clear_bit generic___clear_bit
+#define const___change_bit generic___change_bit
+#define const___test_and_set_bit generic___test_and_set_bit
+#define const___test_and_clear_bit generic___test_and_clear_bit
+#define const___test_and_change_bit generic___test_and_change_bit
+
+/**
+ * const_test_bit - Determine whether a bit is set
+ * @nr: bit number to test
+ * @addr: Address to start counting from
+ *
+ * A version of generic_test_bit() which discards the `volatile` qualifier to
+ * allow a compiler to optimize code harder. Non-atomic and to be called only
+ * for testing compile-time constants, e.g. by the corresponding macros, not
+ * directly from "regular" code.
+ */
+static __always_inline bool
+const_test_bit(unsigned long nr, const volatile unsigned long *addr)
+{
+ const unsigned long *p = (const unsigned long *)addr + BIT_WORD(nr);
+ unsigned long mask = BIT_MASK(nr);
+ unsigned long val = *p;
+
+ return !!(val & mask);
+}
+
#endif /* __ASM_GENERIC_BITOPS_GENERIC_NON_ATOMIC_H */