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From: Denys Vlasenko <vda.linux@googlemail.com>
Newsgroups: gmane.linux.lib.musl.general
Subject: Re: [PATCH] x86_64/memset: use "small block" code for blocks
 up to 30 bytes long
Date: Mon, 16 Feb 2015 11:09:25 +0100
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On Sun, Feb 15, 2015 at 11:55 PM, Rich Felker <dalias@libc.org> wrote:
>> "sub $8,%rcx" can be folded into lea.
>
> No, it can't, for the above reason.

Why can't?

lea -9(%rdx), %rcx

will also underflow for %rdx == 0, just like "lea -1".