[vim] Improve iskeyword for LLVM IR

[frasercrmck]

This patch sets the 'iskeyword' variable to characters found in LLVM IR identifiers. Keywords are used in many places in vim, most notably being treated as word boundaries for commands like 'w' and '*'. The aim with this is to improve the navigability and editability of LLVM IR files as now one is able to: skip over entire identifiers with motions (e.g., w/e/b); yank/delete whole identifiers (e.g., diw); highlight/search for the identifier under the cursor (*), etc.

More complicated LLVM identifiers including quotation marks are not supported. The 'iskeyword' variable is just a list of characters, not a regex, and including quotation marks and all the characters permitted in quoted identifiers would expand the scope to almost everything and become less usable. These types of identifiers are rare by comparison.

Note that this does change how words are considered across the entire LLVM IR file, so including strings, comments, names, etc. Given that the majority of editing/navigating LLVM IR is working with and across values, this is arguably a worthwhile trade-off.

[nickdesaulniers]

Just so I understand the issue being addressed by this issue, is it that variable identifiers that begin with % or @ are treated currently as two words, such that motions don't act on the whole identifier?

[ldrumm]

I'm a big fan of this. Like you say: it's not perfect, but it makes following SSA values so much easier that I think it's definitely worth it despite not covering all complex identifiers.

I'll let someone with more vim chops chime in, but big +1 from me

[frasercrmck]

Just so I understand the issue being addressed by this issue, is it that variable identifiers that begin with % or @ are treated currently as two words, such that motions don't act on the whole identifier?

Yes, partially. However, it's more than that; since . is treated as a word separator, I find IR values very cumbersome to work with. For example, word-based motions on a %foo.i.i.0 b currently take 9 ws to move the cursor from a to b. With this patch it'd be 2, as with any other "word" in any other language. You can also have your cursor anywhere on %foo.i.i.0 and * will take you to the next occurrence. This was my primary motivation for the patch. Yes, you have capital-w Word motions to combat some of what I'm saying, but operators like * can't work with those.

It's a balance, however, since it becomes harder to move through these sub-components of identifiers. You'd probably have to start using motions based on finding the next/previous . character. Ultimately, people can change this to suit their needs. This is about a sensible default. I could always leave in a comment explaining to comment this iskeyword out to have such-and-such behaviour.

All that said, I was thinking I should add the non-latin alphanumeric characters back to the list. That keeps strings just as easy to navigate through (we don't want something like hübsch to become more difficult to navigate through)