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Peter Anvin" Subject: [PATCH 2/2] x86/bootflag: Use __builtin_parity() when available Date: Wed, 29 Jan 2025 16:47:51 +0100 Message-ID: <20250129154920.6773-2-ubizjak@gmail.com> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20250129154920.6773-1-ubizjak@gmail.com> References: <20250129154920.6773-1-ubizjak@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Compilers (GCC and clang) provide optimized __builtin_parity() function that returns the parity of X, i.e. the number of 1-bits in X modulo 2. Use __builtin_parity() built-in function to optimize parity(). This improves generated parity code to just: 57: 84 db test %bl,%bl 59: 7a 5c jp b7 where TEST instruction sets parity flag (PF) in EFLAGS, exercised by the follow-up jump instruction. Signed-off-by: Uros Bizjak Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" --- arch/x86/kernel/bootflag.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/bootflag.c b/arch/x86/kernel/bootflag.c index 4d89a2d80d0f..d63247d7abd4 100644 --- a/arch/x86/kernel/bootflag.c +++ b/arch/x86/kernel/bootflag.c @@ -22,6 +22,9 @@ int sbf_port __initdata = -1; /* set via acpi_boot_init() */ static bool __init parity(u8 v) { +#if __has_builtin(__builtin_parity) + int x = __builtin_parity(v); +#else int x = 0; int i; @@ -29,7 +32,7 @@ static bool __init parity(u8 v) x ^= (v & 1); v >>= 1; } - +#endif return !!x; } -- 2.42.0