cleanup: Remove fallback post-lowering global resolution #57051
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vtjnash
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Jan 15, 2025
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LGTM. Particularly the rename so this function finally is named after what its actual purpose is for 😅
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| if (e->head == jl_call_sym && jl_expr_nargs(e) == 3 && | ||
| jl_is_globalref(jl_exprarg(e, 0)) && |
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Do we still care about this hack (replacing the syntax a.b with GlobalRef(a, :b) if a appears to be a module?
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I think that hack has been broken for a long time.
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okay, yeah, do we just clean this up by deleting it too?
julia> @eval Base f() = Base.x
f (generic function with 1 method)
julia> @code_lowered Base.f()
CodeInfo(
@ REPL[10]:1 within `unknown scope`
1 ─ %1 = Base.Base
│ %2 = dynamic Base.getproperty(%1, :x)
└── return %2
)
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Fine by me. We could consider putting it into lowering though.
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Lowering doesn't know the symbol will refers to a module constant, so it had to be when we evaluate the expression here
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Alright, fair enough. In that case, I don't think we can really do this at all. With binding redefinition, our semantics do not allow us to make that decision here.
After recent changes, essentially all global symbol scopes are resolved by lowering, so the code in method.c that replaces symbols by globalrefs is no longer necessary. The one small exception to this were symbols resulting from closure conversion, because these get inserted after the point at which lowering converts symbols to globalrefs. However, in the current design, I think that's basically a bug (and easily addressed by inserting `globalref`s where appropriate). Removing this extra resolution step is not particularly necessary, but for the upcoming binding partition backedges, it removes an ambiguity as to which version of the lowered code to scan. It also partially resolves a very old todo about not performing post-hoc mutation of lowered code (although we still do this for ccall).
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…57648) As discovered in #57547, lowering isn't resolving references to captured variables when a global of the same name is declared in any scope in the current function: ``` julia> let g = 1 function f() let; global g = 2; end; return g # g is not resolved end; f() end ERROR: Found raw symbol in code returned from lowering. Expected all symbols to have been resolved to GlobalRef or slots. ``` `resolve-scopes` correctly detects that we're returning the local, but scope-blocks are removed in this pass. As a result, `analyze-vars-lambda` finds more globals than `resolve-scopes` did when calling `find-global-decls` (which does not peek inside nested scopes) on `f`. `analyze-vars-lambda` then calculates the set of captured variables in `f` to be: ``` captvars = (current_env ∩ free_vars) - (new_staticparams ∪ wrong_globals) ``` so `g` in this case is never captured. This bug was introduced (revealed, maybe) in #57051---the whole resolution step used to happen after lowering, so lowering passes disagreeing on scopes would be less visible. Fix: omit globals from the free variable list in `analyze-vars-lambda` in the first place. This way we don't need to call the scope-block-dependent `find-global-decls`.
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After recent changes, essentially all global symbol scopes are resolved by lowering, so the code in method.c that replaces symbols by globalrefs is no longer necessary. The one small exception to this were symbols resulting from closure conversion, because these get inserted after the point at which lowering converts symbols to globalrefs. However, in the current design, I think that's basically a bug (and easily addressed by inserting
globalrefs where appropriate). Removing this extra resolution step is not particularly necessary, but for the upcoming binding partition backedges, it removes an ambiguity as to which version of the lowered code to scan. It also partially resolves a very old todo about not performing post-hoc mutation of lowered code (although we still do this for ccall).