GeezerVison

So I'm trying to reason about what happens if we miss something, say a branch instruction that we did not include in our branch table?

Or is everything in the x64 spec already included in the table above?

If we miss it, it won't be optimised and I don't think it will break the logic anyway.

Everything is already included (but one was misspelled, thanks for making me double-check).

If we miss one, we will accidentally create a superblock instead of a basic block, and will miss one outgoing edge. This could cause _invert_hot_branches to miscount the number of predecessors for the jump after the branch, and perform an invalid optimization. It could also make our hot-cold splitting incorrect.

So bad things could happen, but those would just be bugs that need fixing.

(Not detecting any branches is a special case, since _invert_hot_branches will never run, so everything is fine. That's why AArch64 works fine now, even though we haven't taught its optimizer about branches yet.)

We have already discuss this, but can we find a better name for this? Noise implies something irrelevant or random data that can be discarded, eliminated or filtered out. We don't do this here, on the contrary we include all these lines otherwise we end up with a broken file.
I would vote for something like:

• non_instructions: this is very explicit and clear
• metadata: still good enough
• other: this is fairly generic

I've renamed to noninstructions.

Does this still only apply to aarch64 Linux? Just curious why we dropped the platform specificity in the comment?

yes, it's in the branch "aarch64-.*-linux-gnu" and the previous comment was just saying that :)

Yeah, it just seemed redundant given the surrounding context!