inference: prevent nested slot wrappers in abstract_call_builtin (#58249)

Author: aviatesk

Compiler/src/abstractinterpretation.jl

@@ -1402,8 +1402,9 @@ function matching_cache_argtypes(𝕃::AbstractLattice, mi::MethodInstance,
             if slotid !== nothing
                 # using union-split signature, we may be able to narrow down `Conditional`
                 sigt = widenconst(slotid > nargs ? argtypes[slotid] : cache_argtypes[slotid])
-                thentype = tmeet(cnd.thentype, sigt)
-                elsetype = tmeet(cnd.elsetype, sigt)
+                ⊓ = meet(𝕃)
+                thentype = cnd.thentype ⊓ sigt
+                elsetype = cnd.elsetype ⊓ sigt
                 if thentype === Bottom && elsetype === Bottom
                     # we accidentally proved this method match is impossible
                     # TODO bail out here immediately rather than just propagating Bottom ?
@@ -2119,7 +2120,7 @@ function abstract_call_builtin(interp::AbstractInterpreter, f::Builtin, (; fargs
                 else
                     thentype = form_partially_defined_struct(𝕃ᵢ, argtype2, argtypes[3])
                     if thentype !== nothing
-                        elsetype = argtype2
+                        elsetype = widenslotwrapper(argtype2)
                         if rt === Const(false)
                             thentype = Bottom
                         elseif rt === Const(true)
@@ -3254,7 +3255,7 @@ function abstract_eval_isdefined_expr(interp::AbstractInterpreter, e::Expr, ssta
         elseif !vtyp.undef
             rt = Const(true) # definitely assigned previously
         else # form `Conditional` to refine `vtyp.undef` in the then branch
-            rt = Conditional(sym, vtyp.typ, vtyp.typ; isdefined=true)
+            rt = Conditional(sym, widenslotwrapper(vtyp.typ), widenslotwrapper(vtyp.typ); isdefined=true)
         end
         return RTEffects(rt, Union{}, EFFECTS_TOTAL)
     end

Compiler/test/inference.jl

@@ -2264,12 +2264,18 @@ struct AliasableFields{S,T}
     f1::S
     f2::T
 end
+struct NullableAliasableFields{S,T}
+    f1::S
+    f2::T
+    NullableAliasableFields(f1::S, f2::T) where {S,T} = new{S,T}(f1, f2)
+    NullableAliasableFields(f1::S) where {S} = new{S,Union{}}(f1)
+end
 mutable struct AliasableConstField{S,T}
     const f1::S
     f2::T
 end
 
-import .Compiler:
+using .Compiler:
     InferenceLattice, MustAliasesLattice, InterMustAliasesLattice,
     BaseInferenceLattice, SimpleInferenceLattice, IPOResultLattice, typeinf_lattice, ipo_lattice, optimizer_lattice
 
@@ -2282,7 +2288,7 @@ Compiler.optimizer_lattice(::MustAliasInterpreter) = SimpleInferenceLattice.inst
 # lattice
 # -------
 
-import .Compiler: MustAlias, Const, PartialStruct, ⊑, tmerge
+using .Compiler: MustAlias, Const, PartialStruct, ⊑, tmerge
 let 𝕃ᵢ = InferenceLattice(MustAliasesLattice(BaseInferenceLattice.instance))
     ⊑(@nospecialize(a), @nospecialize(b)) = Compiler.:⊑(𝕃ᵢ, a, b)
     tmerge(@nospecialize(a), @nospecialize(b)) = Compiler.tmerge(𝕃ᵢ, a, b)
@@ -2520,6 +2526,15 @@ jet509_hasitems(list) = length(list) >= 1
     error("list is empty")
 end |> only == Vector{Int}
 
+# don't form nested slot wrappers
+@test Base.infer_return_type((NullableAliasableFields{NullableAliasableFields},); interp=MustAliasInterpreter()) do x
+    y = getfield(x, :f1)
+    if isdefined(y, :f2) && isa(getfield(y, :f2), Int)
+        return getfield(y, :f2)
+    end
+    return 0
+end == Int
+
 # === constraint
 # --------------