Re: [RFC] gcc feature request: Moving blocks into sections

From: Richard Henderson
Date: Mon Aug 05 2013 - 16:48:17 EST

On 08/05/2013 09:57 AM, Jason Baron wrote:
> On 08/05/2013 03:40 PM, Marek Polacek wrote:
>> On Mon, Aug 05, 2013 at 11:34:55AM -0700, Linus Torvalds wrote:
>>> On Mon, Aug 5, 2013 at 11:24 AM, Linus Torvalds
>>> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>>> Ugh. I can see the attraction of your section thing for that case, I
>>>> just get the feeling that we should be able to do better somehow.
>>> Hmm.. Quite frankly, Steven, for your use case I think you actually
>>> want the C goto *labels* associated with a section. Which sounds like
>>> it might be a cleaner syntax than making it about the basic block
>>> anyway.
>> FWIW, we also support hot/cold attributes for labels, thus e.g.
>> if (bar ())
>> goto A;
>> /* ... */
>> A: __attribute__((cold))
>> /* ... */
>> I don't know whether that might be useful for what you want or not though...
>> Marek
> It certainly would be.
> That was how I wanted to the 'static_key' stuff to work, but unfortunately the
> last time I tried it, it didn't move the text out-of-line any further than it
> was already doing. Would that be expected? The change for us, if it worked
> would be quite simple. Something like:

It is expected. One must use -freorder-blocks-and-partition, and use real
profile feedback to get blocks moved completely out-of-line.

Whether that's a sensible default or not is debatable.

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