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Re: [Emacs-diffs] emacs-25 3eb93c0: Rely on conservative stack scanning

From: Daniel Colascione
Subject: Re: [Emacs-diffs] emacs-25 3eb93c0: Rely on conservative stack scanning to find "emacs_value"s
Date: Fri, 1 Apr 2016 11:34:16 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 03/31/2016 02:29 PM, Stefan Monnier wrote:
>> That's cheap: you can do it with linear allocation out of an array.
>> Why would that be expensive?
> That's very expensive compared to doing nothing.
> It means that you have to allocate a new array, 


> loop through the old one
> calling your "cheap allocation" function on each element, instead of
> just passing the array pointer untouched.

It's a pointer comparison of something that will be in L1 cache anyway.

Of course it's slower than doing nothing. But you have not demonstrated
that it is meaningfully slower, meanwhile, you're ignoring the
compatibility benefits and consigning everyone to stack scanning forever.

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