[PATCH] D141625: [DeclContext] Sort the Decls before adding into DeclContext

Tue Jan 31 14:22:34 PST 2023

dblaikie added a comment.

In D141625#4094742 <https://reviews.llvm.org/D141625#4094742>, @steven_wu wrote:

> In D141625#4067225 <https://reviews.llvm.org/D141625#4067225>, @dblaikie wrote:
>
>> In D141625#4066961 <https://reviews.llvm.org/D141625#4066961>, @steven_wu wrote:
>>
>>> No, reverse iteration will not break diff test for a small number of decls. Everything will be in reverse order so it is the same.
>>
>> Hmm, I'm not sure I'm following why that is - could you explain this in more detail? The usual problem is that, say, we're outputting based on an unstable order - even two items would be enough to cause a test of that to fail in either forward or reverse iteration mode until the order is stabilized.
>>
>> Is that not the case here? Is there some interaction between iteration order that's part of the nondeterminism here?
>
> In order to make a test that will break before the change with reverse iteration, the test needs to check that the decls/records are serialized into the module in a pre deterministic order. It can't be just diff the output of two runs with a small input because small input will not overflow the smallptrset, thus the reverse iteration outputs from two runs will very likely to be identical, just in a different order from forward iteration.

Sure, I think I'm with you there - but the current test checks that the decls/records are serialized into the module in a pre-deterministic order, right? So it doesn't seem like a reverse iteration-failing test would be more involved/brittle/less robust than the test being added here?

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