From: Alexander Lobakin <alexandr.lobakin@intel.com>
To: Arnd Bergmann <arnd@arndb.de>, Yury Norov <yury.norov@gmail.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Mark Rutland <mark.rutland@arm.com>,
Matt Turner <mattst88@gmail.com>, Brian Cain <bcain@quicinc.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Rich Felker <dalias@libc.org>,
"David S. Miller" <davem@davemloft.net>,
Kees Cook <keescook@chromium.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Marco Elver <elver@google.com>, Borislav Petkov <bp@suse.de>,
Tony Luck <tony.luck@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-alpha@vger.kernel.org, linux-hexagon@vger.kernel.org,
linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org,
linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 4/6] bitops: define const_*() versions of the non-atomics
Date: Fri, 10 Jun 2022 13:34:25 +0200 [thread overview]
Message-ID: <20220610113427.908751-5-alexandr.lobakin@intel.com> (raw)
In-Reply-To: <20220610113427.908751-1-alexandr.lobakin@intel.com>
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 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 the 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>
---
.../asm-generic/bitops/generic-non-atomic.h | 31 +++++++++++++++++++
include/linux/bitops.h | 3 +-
2 files changed, 33 insertions(+), 1 deletion(-)
diff --git a/include/asm-generic/bitops/generic-non-atomic.h b/include/asm-generic/bitops/generic-non-atomic.h
index 3ce0fa0ab35f..9a77babfff35 100644
--- a/include/asm-generic/bitops/generic-non-atomic.h
+++ b/include/asm-generic/bitops/generic-non-atomic.h
@@ -121,4 +121,35 @@ 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 the compiler to optimize code harder. Non-atomic and to be used only
+ * for testing compile-time constants, e.g. from the corresponding macro, or
+ * when you really know what you are doing.
+ */
+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..51c22b8667b4 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -36,7 +36,8 @@ 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) && \
+ static_assert(__same_type(const_##name, generic_##name) && \
+ __same_type(arch_##name, generic_##name) && \
__same_type(name, generic_##name))
__check_bitop_pr(__set_bit);
--
2.36.1
next prev parent reply other threads:[~2022-06-10 11:36 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-10 11:34 [PATCH v2 0/6] bitops: let optimize out non-atomic bitops on compile-time constants Alexander Lobakin
2022-06-10 11:34 ` [PATCH v2 1/6] ia64, processor: fix -Wincompatible-pointer-types in ia64_get_irr() Alexander Lobakin
2022-06-10 12:18 ` David Laight
2022-06-10 13:46 ` Andy Shevchenko
2022-06-15 2:59 ` Yury Norov
2022-06-10 11:34 ` [PATCH v2 2/6] bitops: always define asm-generic non-atomic bitops Alexander Lobakin
2022-06-10 13:50 ` Andy Shevchenko
2022-06-10 16:02 ` Luck, Tony
2022-06-10 16:32 ` Marco Elver
2022-06-13 14:19 ` Alexander Lobakin
2022-06-13 14:33 ` Marco Elver
2022-06-15 2:47 ` Yury Norov
2022-06-15 7:46 ` Marco Elver
2022-06-13 16:26 ` Luck, Tony
2022-06-13 21:29 ` David Laight
2022-06-10 11:34 ` [PATCH v2 3/6] bitops: unify non-atomic bitops prototypes across architectures Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin [this message]
2022-06-10 13:56 ` [PATCH v2 4/6] bitops: define const_*() versions of the non-atomics Andy Shevchenko
2022-06-13 14:30 ` Alexander Lobakin
2022-06-15 2:57 ` Yury Norov
2022-06-15 13:55 ` Alexander Lobakin
2022-06-15 15:52 ` David Laight
2022-06-10 11:34 ` [PATCH v2 5/6] bitops: wrap non-atomic bitops with a transparent macro Alexander Lobakin
2022-06-10 11:34 ` [PATCH v2 6/6] bitops: let optimize out non-atomic bitops on compile-time constants Alexander Lobakin
2022-06-15 3:26 ` Yury Norov
2022-06-15 14:00 ` Alexander Lobakin
2022-06-13 7:35 ` [PATCH v2 0/6] " Geert Uytterhoeven
2022-06-13 14:26 ` Alexander Lobakin
2022-06-13 15:22 ` Geert Uytterhoeven
2022-06-15 14:17 ` Alexander Lobakin
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