[llvm] r190773 - Implement function prefix data as an IR feature.

[David Blaikie]

On Mon, Sep 23, 2013 at 1:14 PM, Richard Mitton <richard at codersnotes.com>wrote:

> Hi,
>
> I have a small question about this -
>
> Why does the prefix data have to begin with a jump?
> Couldn't you just make the entry point label appear after the prefix data?
> And then use negative offsets to access it given the function's address? It
> seems like the jump adds a performance hit which isn't needed.
>

How would you know if there's prefix data on a given function at runtime?
If you just start accessing negative offsets, you might segfault.


>
> e.g.
>
> .word 0x1234 // prefix data
> myfunction:
>     push rbp
>     // etc
>     ret
>
> Richard Mitton
> richard at codersnotes.com
>
>
> On 09/23/2013 01:07 PM, Peter Collingbourne wrote:
>
>> On Mon, Sep 23, 2013 at 10:01:18AM -0700, Chris Lattner wrote:
>>
>>> On Sep 15, 2013, at 6:08 PM, Peter Collingbourne <peter at pcc.me.uk>
>>> wrote:
>>>
>>>  Author: pcc
>>>> Date: Sun Sep 15 20:08:15 2013
>>>> New Revision: 190773
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-**project?rev=190773&view=rev<http://llvm.org/viewvc/llvm-project?rev=190773&view=rev>
>>>> Log:
>>>> Implement function prefix data as an IR feature.
>>>>
>>>> Previous discussion:
>>>> http://lists.cs.uiuc.edu/**pipermail/llvmdev/2013-July/**063909.html<http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-July/063909.html>
>>>>
>>>> Differential Revision: http://llvm-reviews.chandlerc.**com/D1191<http://llvm-reviews.chandlerc.com/D1191>
>>>>
>>> Cool, thanks Peter.
>>>
>>> Can I entice you to write a blog post about this? :-)
>>>
>> Please ask me again in a couple of weeks.  There are a number of
>> higher priority tasks that I have to take care of this week...
>>
>> Thanks,
>>
>
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