[llvm] [TableGen] Emit better error message for duplicate Subtarget features. (PR #102090)

[Rahul Joshi via llvm-commits]

jurahul wrote:

The test has been disabled temporarily now.

On Wed, Aug 7, 2024 at 4:00 AM Rahul Joshi ***@***.***> wrote:

> Thanks for reporting this. I suspect the issue is that llvm::sort is not
> stable, so the 2 records can end up in any order in the sorted list,
> leading to non determinism in the error message. The fix would be to use a
> secondary key for sorting to make it deterministic (Record name if “Name”
> field values are same).
>
> I am working on a follow on patch for this and will incorporate that fix
> in that. Meanwhile let me disable the test.
>
> Thanks,
> Rahul
>
> On Wed, Aug 7, 2024 at 2:56 AM Haojian Wu ***@***.***>
> wrote:
>
>> Hi, I see a flaky issue when integrating this change into our internal
>> codebase.
>>
>> The newly-added test is flaky under ASAN. Sometimes it passes, sometimes
>> it fails.
>> The symptom I observed is that the line number of the emitted warning is
>> non-deterministic:
>>
>>    1. Line 10: ***@***.***+2]]:5: error: Feature 'NameA' already defined.
>>    (expected: 12)
>>    2. Line 11: ***@***.***]:5: note: Previous definition here. (expected:
>>    8)
>>
>> Under ASAN, the line number of the first diagnostic can sometimes be 8,
>> and the second one can be 12—they just swap. It is very subtle, and I don't
>> see any problem in your patch.
>>
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https://github.com/llvm/llvm-project/pull/102090