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Date: Fri, 18 Mar 2022 15:47:49 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
To: David Laight <David.Laight@ACULAB.COM>,
        "'Segher Boessenkool'" <segher@kernel.crashing.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
CC: Andy Lutomirski <luto@kernel.org>,
        Andrew Cooper <Andrew.Cooper3@citrix.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Bill Wendling <morbo@google.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>, Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "llvm@lists.linux.dev" <llvm@lists.linux.dev>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-toolchains <linux-toolchains@vger.kernel.org>
Subject: RE: [PATCH v5] x86: use builtins to read eflags
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On March 18, 2022 3:36:48 PM PDT, David Laight <David=2ELaight@ACULAB=2ECOM=
> wrote:
>From: Segher Boessenkool
>> Sent: 18 March 2022 22:09
>=2E=2E=2E
>> It generally is a very good idea to
>> have a redzone though, without it you pay much more than necessary for
>> frame setup and teardown in leaf functions (similar to some of what the
>> misnamed "shrink-wrapping" optimisation does, but the two are mostly
>> independent, the benefits add up)=2E
>
>Are there really leaf functions that need to spill data to stack
>where the cost of setting up a stack frame is significant?
>
>I'd have thought that was relatively rare=2E
>
>	David
>
>-
>Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1=
 1PT, UK
>Registration No: 1397386 (Wales)
>
>

Yes=2E