cmd/compile: eliminate base.Pos and ir.CurFunc

[mdempsky]

This is an umbrella issue for eliminating the global lineno variable from package gc. Filing as a HelpWanted issue because I think it's a relatively low-barrier-to-entry issue that people can usefully contribute to the compiler with small incremental improvements.

Here's the general algorithm:

1. Identify a function Bar that uses lineno.
2. Split it into two functions Bar and Barl; Barl takes an additional pos src.XPos parameter, and Bar just calls Barl with lineno.
3. Change callers of Bar to use Barl. Ideally, the caller can supply the position information directly (e.g., via n.Pos or something); but if necessary, just use lineno and later we'll recursively apply this procedure on the caller function.

An example of this is yyerror and Warn now have yyerrorl and `Warnl' functions that we're trying to use instead.

Note: sometimes uses of lineno should just go away entirely (e.g., CL 38393 / 80c4b53). I suggest pinging here to discuss instances and/or express interest in working on this to avoid duplicating work (e.g., @josharian and I are looking at this in the backend for #15756).

[josharian]

One caveat. If the function in question calls nod, then it might need to accept both pos srx.XPos and curfn *Node, since both those globals are used in nod. Just as lineno can be the default value of the pos arg, the global Curfn can be the default value of the curfn arg.

I'll send an example CL of this soon, which also introduces nodl.

Unless, @mdempsky, you dislike this, in which case we need another strategy. :)

[griesemer]

Presumably many functions don't need an extra src.XPos because they can get the info from any of the nodes they are working with?

[mdempsky]

@josharian I was thinking about that, and I think we can push the Curfn logic into callers. We don't actually need Curfn for OPACK or OLABEL, just ONAME and for setting IsHiddenClosure.

I think ONAME can be handled by refactoring all the n := nod(ONAME, nil, nil); n.Sym = s instances to n := newname(s).

The IsHiddenClosure logic can probably just be set as appropriate in closure.go instead.

[mdempsky]

@griesemer Yeah, if the position information can be obtained using existing parameters, that's preferable. But there are a lot of helper functions in dcl.go that construct Nodes, though none of their parameters include position information currently. Some of those will probably need to be extended (e.g., newname?), and others can probably just use src.NoPos (e.g., typenod?).

[josharian]

I think we can push the Curfn logic into callers. ...

SGTM. Do you want to tackle this set of things, or shall I?

[mdempsky]

@josharian I can look into it.

[gopherbot]

CL https://golang.org/cl/38592 mentions this issue.

[gopherbot]

CL https://golang.org/cl/38597 mentions this issue.

[josharian]

@mdempsky nod/Curfn is top of my queue now. Looks like the remaining item there is:

I think ONAME can be handled by refactoring all the n := nod(ONAME, nil, nil); n.Sym = s instances to n := newname(s).

Are you actively working on this? If not, I will start on it.

[mdempsky]

@josharian I've got a CL for it, then got side tracked pondering what Node.Addable signifies and whether we could get rid of it.

I'll finish up the CL and mail it in just a sec.

[gopherbot]

CL https://golang.org/cl/38770 mentions this issue.