lowering: Canonicalize to builtins for global assignment (JuliaLang#56713)

This adjusts lowering to emit `setglobal!` for assignment to globals,
thus making the `=` expr head used only for slots in `CodeInfo` and
entirely absent in `IRCode`. The primary reason for this is just to
reduce the number of special cases that compiler passes have to reason
about. In IRCode, `=` was already essentially equivalent to
`setglobal!`, so there's no good reason not to canonicalize.

Finally, the `=` syntax form for globals already gets recognized
specially to insert `convert` calls to their declared binding type, so
this doesn't impose any additional requirements on lowering to
distinguish local from global assignments. In general, I'd also like to
separate syntax and intermediate forms as much as possible where their
semantics differ, which this accomplises by just using the builtin.

This change is mostly semantically invisible, except that spliced-in
GlobalRefs now declare their binding because they are indistinguishable
from ordinary assignments at the stage where I inserted the lowering. If
we want to, we can preserve the difference, but it'd be a bit more
annoying for not much benefit, because:
1. The spliced in version was only recently made to work anyway, and
2. The semantics of when exactly bindings are declared is still messy on
master anyway and will get tweaked shortly in further binding partitions
work.

Author: Keno

src/abstractinterpretation.jl

@@ -4050,13 +4050,7 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState, nextr
                 end
                 effects === nothing || merge_override_effects!(interp, effects, frame)
                 if lhs !== nothing && rt !== Bottom
-                    if isa(lhs, SlotNumber)
-                        changes = StateUpdate(lhs, VarState(rt, false))
-                    elseif isa(lhs, GlobalRef)
-                        handle_global_assignment!(interp, frame, currsaw_latestworld, lhs, rt)
-                    else
-                        merge_effects!(interp, frame, EFFECTS_UNKNOWN)
-                    end
+                    changes = StateUpdate(lhs::SlotNumber, VarState(rt, false))
                 end
             end
             if !has_curr_ssaflag(frame, IR_FLAG_NOTHROW)

src/optimize.jl

@@ -1408,16 +1408,7 @@ function statement_cost(ex::Expr, line::Int, src::Union{CodeInfo, IRCode}, sptyp
         extyp = line == -1 ? Any : argextype(SSAValue(line), src, sptypes)
         return extyp === Union{} ? 0 : UNKNOWN_CALL_COST
     elseif head === :(=)
-        if ex.args[1] isa GlobalRef
-            cost = UNKNOWN_CALL_COST
-        else
-            cost = 0
-        end
-        a = ex.args[2]
-        if a isa Expr
-            cost = plus_saturate(cost, statement_cost(a, -1, src, sptypes, params))
-        end
-        return cost
+        return statement_cost(ex.args[2], -1, src, sptypes, params)
     elseif head === :copyast
         return 100
     end

src/ssair/EscapeAnalysis.jl

@@ -642,13 +642,6 @@ function analyze_escapes(ir::IRCode, nargs::Int, 𝕃ₒ::AbstractLattice, get_e
                     escape_invoke!(astate, pc, stmt.args)
                 elseif head === :new || head === :splatnew
                     escape_new!(astate, pc, stmt.args)
-                elseif head === :(=)
-                    lhs, rhs = stmt.args
-                    if isa(lhs, GlobalRef) # global store
-                        add_escape_change!(astate, rhs, ⊤)
-                    else
-                        unexpected_assignment!(ir, pc)
-                    end
                 elseif head === :foreigncall
                     escape_foreigncall!(astate, pc, stmt.args)
                 elseif head === :throw_undef_if_not # XXX when is this expression inserted ?
@@ -981,11 +974,6 @@ function escape_unanalyzable_obj!(astate::AnalysisState, @nospecialize(obj), obj
     return objinfo
 end
 
-@noinline function unexpected_assignment!(ir::IRCode, pc::Int)
-    @eval Main (ir = $ir; pc = $pc)
-    error("unexpected assignment found: inspect `Main.pc` and `Main.pc`")
-end
-
 is_nothrow(ir::IRCode, pc::Int) = has_flag(ir[SSAValue(pc)], IR_FLAG_NOTHROW)
 
 # NOTE if we don't maintain the alias set that is separated from the lattice state, we can do

src/ssair/verify.jl

@@ -363,14 +363,8 @@ function verify_ir(ir::IRCode, print::Bool=true,
             isforeigncall = false
             if isa(stmt, Expr)
                 if stmt.head === :(=)
-                    if stmt.args[1] isa SSAValue
-                        @verify_error "SSAValue as assignment LHS"
-                        raise_error()
-                    end
-                    if stmt.args[2] isa GlobalRef
-                        # undefined GlobalRef as assignment RHS is OK
-                        continue
-                    end
+                    @verify_error "Assignment should have been removed during SSA conversion"
+                    raise_error()
                 elseif stmt.head === :isdefined
                     if length(stmt.args) > 2 || (length(stmt.args) == 2 && !isa(stmt.args[2], Bool))
                         @verify_error "malformed isdefined"

test/inline.jl

@@ -2111,7 +2111,7 @@ for run_finalizer_escape_test in (run_finalizer_escape_test1, run_finalizer_esca
     global finalizer_escape::Int = 0
 
     let src = code_typed1(run_finalizer_escape_test, Tuple{Bool, Bool})
-        @test any(x->isexpr(x, :(=)), src.code)
+        @test any(iscall((src, Core.setglobal!)), src.code)
     end
 
     let