[PATCH] Make .bc en/decoding of AttrKind stable

[Tobias Grosser]

On 07/25/2013 05:29 PM, Nick Lewycky wrote:
> On 17 July 2013 15:54, Tobias Grosser <tobias at grosser.es> wrote:
>
>> Hi,
>>
>> I would like to commit the following patch:
>>
>> ----------------------
>> Make .bc en/decoding of AttrKind stable
>>
>> The bitcode representation attribute kinds are encoded into / decoded from
>> should be independent of the current set of LLVM attributes and their
>> position in the AttrKind enum. This patch explicitly encodes attributes to
>> fixed bitcode values.
>>
>> With this patch applied, LLVM does not silently misread attributes written
>> by LLVM 3.3. We also enhance the decoding slightly such that an error
>> message is printed if an unknown AttrKind encoding was dected.
>>
>> Bonus: Dropping bitcode attributes from AttrKind is now easy, as old
>> AttrKinds do not need to be kept to support the Bitcode reader.
>> ----------------------
>>
>> I also considered assigning fixed numbers directly in the AttrKind enum
>> (or keeping the enum stable), but convinced myself that the bitcode
>> encoding should really not part of the IR interface.
>>
>> OK to commit?
>>
>
> Thanks for working on this.

Thanks for the review.

> +  default:
> +    return Error("Unknown attribute kind");
>
> Any chance we could get the value of the attribute kind in there? I know, I
> know, but I forsee a future Nick debugging exactly this.

We now print:

"Unknown attribute kind (43)"

>
> +; RUN:  llvm-dis < %s.bc| FileCheck %s
>
> Space before pipe please. :)

Fixed.

Patch committed in r187186.

Cheers,
Tobias