[dzaima]

I don't think crossing cache lines is particularly much of a concern? You'll necessarily be fetching the next cache line in the next cycle anyway to decode further instructions (not even an unconditional branch could stop this I'd think), at which point you can just "prepend" the chopped tail of the preceding bundle (and you'd want some inter-bundle communication for fusion regardless).

This does of course delay decoding this one instruction by a cycle, but you already have that for instructions which are fully in the next line anyways (and aligning branch targets at compile time improves both, even if just to a fixed 4 or 8 bytes).

[inkyoto]

> I don't think crossing cache lines is particularly much of a concern?

It is a concern if a branch prediction has failed, and the current cache line has to be discarded or has been invalidated. If the instruction crosses the cache line boundary, both lines have to be discarded. For a high-performance CPU core, it is a significant and, most importantly, unnecessary performance penalty. It is not a concern for a microcontroller or a low power design, though.

[dzaima]

Why does an instruction crossing cache lines have anything to do with invalidation/discarding? RISC-V doesn't require instruction cache coherency so the core doesn't have much restriction on behavior if the line was modified, so all restrictions go to just explicit synchronization instructions. And if you have multiple instructions in the pipeline, you'll likely already have instructions from multiple cache lines anyways. I don't understand what "current cache line" even entails in the context of a misprediction, where the entire nature of the problem is that you did not have any idea where to run code from, and thus shouldn't know of any related cache lines.