linux-kernel - Re: [PATCH 2/2] include/linux: apply _

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Message-ID: <87mvplukii.fsf@rasmusvillemoes.dk>
Date:	Sat, 26 Mar 2016 20:06:13 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 2/2] include/linux: apply __malloc attribute

On Thu, Mar 24 2016, Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Thu, 24 Mar 2016 00:42:32 +0100 Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
>
>> Attach the malloc attribute to a few allocation functions. This helps
>> gcc generate better code by telling it that the return value doesn't
>> alias any existing pointers (which is even more valuable given the
>> pessimizations implied by -fno-strict-aliasing).
>> 
> Shaves 6 bytes off my 1MB i386 defconfig vmlinux.  Winner!

Well, the full bloat-o-meter summary is

add/remove: 0/0 grow/shrink: 72/155 up/down: 1165/-1674 (-509)

which sure still isn't much, but this isn't (just) about saving a few
bytes, but more about allowing gcc to generate better code; sometimes by
not having to reload, but also by enabling it to reorder instructions
(e.g. hoisting a load above a store) - the simple example was chosen
because it was very easy to see the relationship between the source and
the generated code.

Anyway, thanks for picking them up.

Rasmus