[bjornsing]

But that works on a different level, right? At least as I understand it data speculation is about prefetching from memory into cache. This trick is about using the branch predictor as an ultra-fast ”L0” cache you could say. At least that’s how I understand it.

[stinkbeetle]

This is doing value speculation in software, using the branch predictor. The hardware of course does do that and instead uses different tables for deriving a predicted value, and misprediction will be detected and flushed in a slightly different way.

But the effect on the main sequence of instructions in the backend will be quite similar. In neither case is it a "prefetch" as such, it is actually executing the load with the predicted value and the result will be consumed by other instructions, decoupling address generation from dependency on previous load result.

[bjornsing]

Yeah that’s sort of how I understand the OP too: The CPU will execute speculatively on the assumption that the next element in the linked list is consecutive in memory, so it doesn’t have to wait for L1 cache. It needs to check the real value in L1 of course, but not synchronously.