[PATCH] D112016: [IR] Introduce load assume operand bundle

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

In D112016#3073235 <https://reviews.llvm.org/D112016#3073235>, @jdoerfert wrote:

> In D112016#3072158 <https://reviews.llvm.org/D112016#3072158>, @nikic wrote:
>
>> Thus the "as long as the load is speculatable" caveat. It works if you add a `dereferenceable(1)` attribute. Though now that I think about this, I have no idea why speculatability is even a requirement for ephemeral values -- shouldn't side-effect freedom be sufficient? In that case your example would work without the `dereferenceable(1)`.
>
> I think side-effect free is sufficient, though, haven't thought long about it. (When you say deref(1) you mean deref(sizeof(access)), right?)

Right, this was referring to @aeubanks' particular example, which happened to use access size 1.

I gave this a try (https://gist.github.com/nikic/531267d972ce71edf3896e25bc50456a) and it seems to work fine (i.e. no test failures). The precise condition would be `wouldInstructionBeTriviallyDead()`, which we can approximate by `!mayHaveSideEffect() && !isTerminator()`.


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