Re: [Ksummit-discuss] [TECH TOPIC] Compiler shopping list

[David Woodhouse <dwmw2@infradead.org>]

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On Fri, 2016-07-22 at 17:52 +0200, Christian Borntraeger wrote:
> On 07/22/2016 12:41 PM, David Howells wrote:
> > Are there additional things we can get the compiler to do for us?  Some
> > things I've seen brought up:
> > 
> >  (1) Additional __atomic_*() ops could be useful.  Suggestions I've heard
> >      include direct LL/SC support - though the compiler people don't seem so
> >      keen on that.
> > 
> >  (2) -mmodel=kernel flag so that the compiler can optimise better for the
> >      kernel memory model.
> 
> Some years ago (actually many) Linus proposed to have an endianess attribute to data
> types, so that the compiler can do the bswap automatically. For some reason this
> was never implemented, but this might be a good idea anyway.
> 
> e.g. 
> 
> unsigned long x[10] __attribute__(("bigendian"));

I'm not sure Linus proposed that. I certainly did, many times.

With the work I put in to make use of __builtin_bswapXX() we do have a
*certain* amount of the functionality that full endianness attribution
would give us — the compiler can see and optimise certain
load/mask/save operations, and can use movbe and equivalent
instructions.

But a full implementation that let us just do assignment without
jumping through the hoops might still be nice.

-- 
dwmw2

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