From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
dan.j.williams@intel.com, linux-cxl@vger.kernel.org,
linux-kernel@vger.kernel.org,
David Lechner <dlechner@baylibre.com>,
Ingo Molnar <mingo@kernel.org>,
"Fabio M. De Francesco"
<fabio.maria.de.francesco@linux.intel.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Jonathan Cameron <jonathan.cameron@huawei.com>,
Dave Jiang <dave.jiang@intel.com>,
Alison Schofield <alison.schofield@intel.com>,
Vishal Verma <vishal.l.verma@intel.com>,
Ira Weiny <ira.weiny@intel.com>
Subject: Re: [PATCH 1/7] cleanup: Introduce DEFINE_ACQUIRE() a CLASS() for conditional locking
Date: Tue, 13 May 2025 21:06:19 +0100 [thread overview]
Message-ID: <20250513200619.GJ2023217@ZenIV> (raw)
In-Reply-To: <CAHk-=wjBiAqaWnXG_44ajMCqU3nNQOC1RQ6SUmKYC03Y1G=r1g@mail.gmail.com>
On Tue, May 13, 2025 at 12:46:29PM -0700, Linus Torvalds wrote:
> Right now IS_ERR_OR_NULL() generates pretty disgusting code, with
> clang doing things like this:
>
> testq %rdi, %rdi
> sete %al
> cmpq $-4095, %rdi # imm = 0xF001
> setae %cl
> orb %al, %cl
> je .LBB3_1
>
> in order to avoid two jumps, while gcc generates that
>
> testq %rdi, %rdi
> je .L189
> cmpq $-4096, %rdi
> ja .L189
>
> pattern.
FWIW (unsigned long)v - 1 >= (unsigned long)(-MAX_ERRNO-1) yields
leaq -1(%rdi), %rax
cmpq $-4097, %rax
ja .L4
from gcc and
leaq 4095(%rdi), %rax
cmpq $4095, %rax # imm = 0xFFF
ja .LBB0_1
from clang...
next prev parent reply other threads:[~2025-05-13 20:06 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-05-07 7:21 [PATCH 0/7] Introduce DEFINE_ACQUIRE(), a scoped_cond_guard() replacement Dan Williams
2025-05-07 7:21 ` [PATCH 1/7] cleanup: Introduce DEFINE_ACQUIRE() a CLASS() for conditional locking Dan Williams
2025-05-07 9:32 ` Peter Zijlstra
2025-05-07 21:18 ` Dan Williams
2025-05-08 11:00 ` Peter Zijlstra
2025-05-09 5:04 ` Dan Williams
2025-05-09 10:40 ` Peter Zijlstra
2025-05-10 1:11 ` dan.j.williams
2025-05-12 10:50 ` Peter Zijlstra
2025-05-12 18:25 ` Peter Zijlstra
2025-05-12 18:58 ` Peter Zijlstra
2025-05-12 20:39 ` Linus Torvalds
2025-05-13 7:09 ` Peter Zijlstra
2025-05-13 8:50 ` Peter Zijlstra
2025-05-13 19:46 ` Linus Torvalds
2025-05-13 20:06 ` Al Viro [this message]
2025-05-13 20:31 ` Al Viro
2025-05-13 21:28 ` Linus Torvalds
2025-05-17 9:17 ` David Laight
2025-05-14 6:46 ` Peter Zijlstra
2025-05-13 3:32 ` dan.j.williams
2025-05-09 19:10 ` kernel test robot
2025-05-07 7:21 ` [PATCH 2/7] cxl/decoder: Move decoder register programming to a helper Dan Williams
2025-05-07 7:21 ` [PATCH 3/7] cxl/decoder: Drop pointless locking Dan Williams
2025-05-07 7:21 ` [PATCH 4/7] cxl/region: Split commit_store() into __commit() and queue_reset() helpers Dan Williams
2025-05-07 7:21 ` [PATCH 5/7] cxl/region: Move ready-to-probe state check to a helper Dan Williams
2025-05-07 7:21 ` [PATCH 6/7] cxl/region: Introduce CLASS(cxl_decoder_detach...) consolidate multiple paths Dan Williams
2025-05-08 7:44 ` kernel test robot
2025-05-07 7:21 ` [PATCH 7/7] cleanup: Create an rwsem conditional acquisition class Dan Williams
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