From: Kanna Scarlet <knscarlet@gnuweeb.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: Borislav Petkov <bp@alien8.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
Ard Biesheuvel <ardb@kernel.org>,
Bill Metzenthen <billm@melbpc.org.au>,
Brijesh Singh <brijesh.singh@amd.com>,
Joerg Roedel <jroedel@suse.de>,
Josh Poimboeuf <jpoimboe@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Mark Rutland <mark.rutland@arm.com>,
Michael Roth <michael.roth@amd.com>,
Peter Zijlstra <peterz@infradead.org>,
Sean Christopherson <seanjc@google.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ammar Faizi <ammarfaizi2@gnuweeb.org>,
GNU/Weeb Mailing List <gwml@vger.gnuweeb.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/1] x86: Change mov $0, %reg with xor %reg, %reg
Date: Mon, 8 Aug 2022 23:38:34 +0700 [thread overview]
Message-ID: <97c052a1-44e4-3c59-d4c8-34176d1d601a@gnuweeb.org> (raw)
In-Reply-To: <126271e264204581a42b079b51481740@AcuMS.aculab.com>
On 8/5/22 4:26 PM, David Laight wrote:
> Use "xor %rax,%rax" instead of "xor %eax,%eax" to save
> the 'reg' prefix.
hello David Laight
"xor %rax,%rax" is bigger because of rex prefix, "xor %eax,%eax" is smaller
because it doesn't need rex prefix.
asm:
0: 48 31 c0 xor %rax,%rax
3: 31 c0 xor %eax,%eax
so i think to save from rex prefix, use xor %eax,%eax instead of xor %rax,%rax.
Best regards,
--
Kanna Scarlet
next prev parent reply other threads:[~2022-08-08 16:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-04 15:26 [PATCH 0/1] x86 change mov 0, %reg to " Kanna Scarlet
2022-08-04 15:26 ` [PATCH 1/1] x86: Change mov $0, %reg with " Kanna Scarlet
2022-08-04 15:53 ` Borislav Petkov
2022-08-04 18:08 ` Kanna Scarlet
2022-08-05 9:26 ` David Laight
2022-08-05 9:42 ` Joerg Roedel
2022-08-08 16:45 ` Kanna Scarlet
2022-08-08 18:59 ` H. Peter Anvin
2022-08-08 16:38 ` Kanna Scarlet [this message]
2022-08-08 18:59 ` H. Peter Anvin
2022-08-09 7:38 ` David Laight
2022-08-05 9:54 ` Borislav Petkov
2022-08-08 16:57 ` Kanna Scarlet
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