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Re: Lisp_Marker size on 32bit systems

From: Stefan Monnier
Subject: Re: Lisp_Marker size on 32bit systems
Date: Fri, 07 Sep 2018 08:16:51 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

> Although the first attached patch shrinks sizeof (struct Lisp_Maker) from 32
> to 24 bytes on x86 as requested, allocate_pseudovector still *allocates* 32
> bytes for the struct, as it rounds the size up to the next multiple of
> alignof (max_align_t), which is 16 on x86. It's not hard to change that to
> 8 (please see 2nd attached patch) but this causes a 20% CPU performance hit
> (!) to 'make compile-always' on my platform (AMD Phenom II X4 910e circa
> 2010, Fedora 28 x86-64, gcc -m32 -march=native), so I didn't install and
> can't recommend the 2nd attached patch.

Where does this 20% slow down come from?


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