Core.declare_global is hoisted out of if/else at the top level #59755
Description
Found by @christiangnrd in JuliaMath/BFloat16s.jl#111.
Notice how without assigning the result of the if/else to a variable, the Core.declare_global isn't executed unless the condition is true (1.12 behaviour):
o | Version 1.13.0-DEV.1272 (2025-10-06)
o o | Commit 406027e7212 (0 days old master)
julia> Meta.@lower if cond()
global x
1
end
:($(Expr(:thunk, CodeInfo(
1 ─ %1 = Main.cond
│ %2 = dynamic (%1)()
└── goto #3 if not %2
@ none within `unknown scope`
┌ @ REPL[1]:2 within `macro expansion`
2 ─│ builtin Core.declare_global(Main, :x, false)
│ │ $(Expr(:latestworld))
└──│ return 1
3 ─│ return nothing
└
))))
If we set a variable to the result of the expression, the Core.declare_global happens unconditionally:
julia> Meta.@lower y = if cond()
global x
1
end
:($(Expr(:thunk, CodeInfo(
1 ─ builtin Core.declare_global(Main, :x, false)
│ $(Expr(:latestworld))
│ builtin Core.declare_global(Main, :y, true)
│ $(Expr(:latestworld))
│ %5 = Main.cond
│ %6 = dynamic (%5)()
└── goto #3 if not %6
@ none within `unknown scope`
┌ @ REPL[2]:3 within `macro expansion`
2 ─│ @_2 = 1
└──│ goto #4
3 ─│ @_2 = nothing
4 ┄│ %11 = @_2
│ │ %12 = builtin Core.get_binding_type(Main, :y)
│ │ #s2 = %11
│ │ %14 = #s2
│ │ %15 = builtin %14 isa %12
└──│ goto #6 if not %15
5 ─│ goto #7
6 ─│ %18 = #s2
└──│ #s2 = Base.convert(%12, %18)
7 ┄│ %20 = #s2
│ │ builtin Core.setglobal!(Main, :y, %20)
└──│ return %11
└
))))
Introduced by #58279.