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Message-Id: <20220621191553.69455-5-alexandr.lobakin@intel.com>
Date: Tue, 21 Jun 2022 21:15:49 +0200
From: Alexander Lobakin <alexandr.lobakin@...el.com>
To: Arnd Bergmann <arnd@...db.de>, Yury Norov <yury.norov@...il.com>
Cc: Alexander Lobakin <alexandr.lobakin@...el.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Mark Rutland <mark.rutland@....com>,
Matt Turner <mattst88@...il.com>,
Brian Cain <bcain@...cinc.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
Rich Felker <dalias@...c.org>,
"David S. Miller" <davem@...emloft.net>,
Kees Cook <keescook@...omium.org>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Marco Elver <elver@...gle.com>, Borislav Petkov <bp@...e.de>,
Tony Luck <tony.luck@...el.com>,
Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
Jesse Brandeburg <jesse.brandeburg@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-alpha@...r.kernel.org, linux-hexagon@...r.kernel.org,
linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 4/8] 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@...gle.com>
Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
Reviewed-by: Marco Elver <elver@...gle.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
.../asm-generic/bitops/generic-non-atomic.h | 31 +++++++++++++++++++
include/linux/bitops.h | 1 +
2 files changed, 32 insertions(+)
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 */
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 87087454a288..d393297287d5 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -37,6 +37,7 @@ extern unsigned long __sw_hweight64(__u64 w);
/* Check that the bitops prototypes are sane */
#define __check_bitop_pr(name) \
static_assert(__same_type(arch_##name, generic_##name) && \
+ __same_type(const_##name, generic_##name) && \
__same_type(name, generic_##name))
__check_bitop_pr(__set_bit);
--
2.36.1
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