r220493 - Add a "signature" to AST files to verify that they haven't changed

[Chandler Carruth]

On Mon, Mar 23, 2015 at 10:37 PM, Ben Langmuir <blangmuir at apple.com> wrote:

> On Mar 23, 2015, at 10:21 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
>
>
> On Mon, Mar 23, 2015 at 9:54 PM, Ben Langmuir <blangmuir at apple.com> wrote:
>
>> On Mar 23, 2015, at 5:38 PM, Chandler Carruth <chandlerc at google.com>
>> wrote:
>>
>> Digging this thread back up, I'm starting to work on deterministic
>> output of modules. This is *really* important. Unfortunately, it's
>> almost impossible to make progress as long as this code is actually firing
>> because it kind of makes things definitively non-deterministic. ;]
>>
>>
>> Ben, do you have any concerns about only emitting the signature record
>> for implicit modules? This would omit it for explicit modules (where I'm
>> working), PCH files, etc. Based on your commit message and explanation, it
>> doesn't really make sense outside of implicit modules AFAICT, and we're
>> hoping it will go away completely.
>>
>>
>> SGTM although I would prefer we continue to check the /expected/
>> signature when an AST file imports an implicit module (and in particular
>> when a PCH imports an implicit module).  Thanks for working on this!
>>
>
> I'm not planning to change the checking code path at all. All the tests
> pass if I just restrict the emission to be when generating implicit
> modules
>
>
> Perfect, that’s what I was hoping for.  Sorry I didn’t phrase it clearly.
>

This is in as part of r233115 with the minimal test case for deterministic
output. More to come.
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