String allocations from fullNameOfEntitityRef when used in ItemsAreEffectivelyEqual - necessary?

[cartermp]

I took a sample of editing some code across several in FSharp.Editor.dll and noticed that there's a lot of string allocations happening in ItemsAreEffectivelyEqual. In only 37 seconds it allocated 84 MB. Most of these are small and short-lived, but it still feels excessive.

Two routines are involved, both allocating a lot:

Looking at the code, this happens when checking Item.ModuleOrNamespaces here:

fsharp/src/fsharp/NameResolution.fs

Lines 1813 to 1816 in 2571fe7

	| Item.ModuleOrNamespaces modrefs1, Item.ModuleOrNamespaces modrefs2 ->
	modrefs1 |> List.exists (fun modref1 -> modrefs2 |> List.exists (fun r -> tyconRefDefnEq g modref1 r || fullDisplayTextOfModRef modref1 = fullDisplayTextOfModRef r))
	| _ -> false

And it appears to be a "only do this if everything else failed" check.

Is it necessary? This is a lot of string allocations, and when combined makes up the bulk registered by profiling when editing code. Note that the source of these allocations is unused opens analysis.

[cartermp]

@dsyme @TIHan would be good to get your opinion on this