inference: refine PartialStruct lattice tmerge

Be more aggressive about merging fields to greatly accelerate
convergence, but also compute anyrefine more correctly as we do now
elsewhere (since #42831, a121721)

Move the tmeet algorithm, without changes, since it is a precise lattice
operation, not a heuristic limit like tmerge.

Close #43784

base/compiler/typelattice.jl

@@ -425,3 +425,45 @@ function stupdate1!(state::VarTable, change::StateUpdate)
     end
     return false
 end
+
+# compute typeintersect over the extended inference lattice,
+# as precisely as we can,
+# where v is in the extended lattice, and t is a Type.
+function tmeet(@nospecialize(v), @nospecialize(t))
+    if isa(v, Const)
+        if !has_free_typevars(t) && !isa(v.val, t)
+            return Bottom
+        end
+        return v
+    elseif isa(v, PartialStruct)
+        has_free_typevars(t) && return v
+        widev = widenconst(v)
+        if widev <: t
+            return v
+        end
+        ti = typeintersect(widev, t)
+        valid_as_lattice(ti) || return Bottom
+        @assert widev <: Tuple
+        new_fields = Vector{Any}(undef, length(v.fields))
+        for i = 1:length(new_fields)
+            vfi = v.fields[i]
+            if isvarargtype(vfi)
+                new_fields[i] = vfi
+            else
+                new_fields[i] = tmeet(vfi, widenconst(getfield_tfunc(t, Const(i))))
+                if new_fields[i] === Bottom
+                    return Bottom
+                end
+            end
+        end
+        return tuple_tfunc(new_fields)
+    elseif isa(v, Conditional)
+        if !(Bool <: t)
+            return Bottom
+        end
+        return v
+    end
+    ti = typeintersect(widenconst(v), t)
+    valid_as_lattice(ti) || return Bottom
+    return ti
+end

base/compiler/typelimits.jl

@@ -404,6 +404,7 @@ function tmerge(@nospecialize(typea), @nospecialize(typeb))
         aty = widenconst(typea)
         bty = widenconst(typeb)
         if aty === bty
+            # must have egal here, since we do not create PartialStruct for non-concrete types
             typea_nfields = nfields_tfunc(typea)
             typeb_nfields = nfields_tfunc(typeb)
             isa(typea_nfields, Const) || return aty
@@ -412,18 +413,38 @@ function tmerge(@nospecialize(typea), @nospecialize(typeb))
             type_nfields === typeb_nfields.val::Int || return aty
             type_nfields == 0 && return aty
             fields = Vector{Any}(undef, type_nfields)
-            anyconst = false
+            anyrefine = false
             for i = 1:type_nfields
                 ai = getfield_tfunc(typea, Const(i))
                 bi = getfield_tfunc(typeb, Const(i))
-                ity = tmerge(ai, bi)
-                if ai === Union{} || bi === Union{}
-                    ity = widenconst(ity)
+                ft = fieldtype(aty, i)
+                if is_lattice_equal(ai, bi)
+                    # Since ai===bi, the given type has no restrictions on complexity.
+                    # and can be used to refine ft
+                    tyi = ai
+                else
+                    # Otherwise choose between using the fieldtype or some other simple merged type.
+                    # The wrapper type never has restrictions on complexity,
+                    # so try to use that to refine the estimated type too.
+                    tni = _typename(widenconst(ai))
+                    if tni isa Const && tni === _typename(widenconst(bi))
+                        # A tmeet call may cause tyi to become complex, but since the inputs were
+                        # strictly limited to being egal, this has no restrictions on complexity.
+                        # (Otherwise, we would need to use <: and take the narrower one without
+                        # intersection. See the similar comment in abstract_call_method.)
+                        tyi = typeintersect(ft, (tni.val::Core.TypeName).wrapper)
+                    else
+                        # Since aty===bty, the fieldtype has no restrictions on complexity.
+                        tyi = ft
+                    end
+                end
+                fields[i] = tyi
+                if !anyrefine
+                    anyrefine = has_nontrivial_const_info(tyi) || # constant information
+                                tyi ⋤ ft                          # just a type-level information, but more precise than the declared type
                 end
-                fields[i] = ity
-                anyconst |= has_nontrivial_const_info(ity)
             end
-            return anyconst ? PartialStruct(aty, fields) : aty
+            return anyrefine ? PartialStruct(aty, fields) : aty
         end
     end
     if isa(typea, PartialOpaque) && isa(typeb, PartialOpaque) && widenconst(typea) == widenconst(typeb)
@@ -610,44 +631,3 @@ function tuplemerge(a::DataType, b::DataType)
     end
     return Tuple{p...}
 end
-
-# compute typeintersect over the extended inference lattice
-# where v is in the extended lattice, and t is a Type
-function tmeet(@nospecialize(v), @nospecialize(t))
-    if isa(v, Const)
-        if !has_free_typevars(t) && !isa(v.val, t)
-            return Bottom
-        end
-        return v
-    elseif isa(v, PartialStruct)
-        has_free_typevars(t) && return v
-        widev = widenconst(v)
-        if widev <: t
-            return v
-        end
-        ti = typeintersect(widev, t)
-        valid_as_lattice(ti) || return Bottom
-        @assert widev <: Tuple
-        new_fields = Vector{Any}(undef, length(v.fields))
-        for i = 1:length(new_fields)
-            vfi = v.fields[i]
-            if isvarargtype(vfi)
-                new_fields[i] = vfi
-            else
-                new_fields[i] = tmeet(vfi, widenconst(getfield_tfunc(t, Const(i))))
-                if new_fields[i] === Bottom
-                    return Bottom
-                end
-            end
-        end
-        return tuple_tfunc(new_fields)
-    elseif isa(v, Conditional)
-        if !(Bool <: t)
-            return Bottom
-        end
-        return v
-    end
-    ti = typeintersect(widenconst(v), t)
-    valid_as_lattice(ti) || return Bottom
-    return ti
-end

test/compiler/inference.jl

@@ -3999,15 +3999,33 @@ end
     @test ⊑(a, c)
     @test ⊑(b, c)
 
-    @test @eval Module() begin
-        const ginit = Base.ImmutableDict{Any,Any}()
-        Base.return_types() do
-            g = ginit
+    init = Base.ImmutableDict{Number,Number}()
+    a = Const(init)
+    b = Core.PartialStruct(typeof(init), Any[Const(init), Any, ComplexF64])
+    c = Core.Compiler.tmerge(a, b)
+    @test ⊑(a, c) && ⊑(b, c)
+    @test c === typeof(init)
+
+    a = Core.PartialStruct(typeof(init), Any[Const(init), ComplexF64, ComplexF64])
+    c = Core.Compiler.tmerge(a, b)
+    @test ⊑(a, c) && ⊑(b, c)
+    @test c.fields[2] === Any # or Number
+    @test c.fields[3] === ComplexF64
+
+    b = Core.PartialStruct(typeof(init), Any[Const(init), ComplexF32, Union{ComplexF32,ComplexF64}])
+    c = Core.Compiler.tmerge(a, b)
+    @test ⊑(a, c)
+    @test ⊑(b, c)
+    @test c.fields[2] === Complex
+    @test c.fields[3] === Complex
+
+    global const ginit43784 = Base.ImmutableDict{Any,Any}()
+    @test Base.return_types() do
+            g = ginit43784
             while true
                 g = Base.ImmutableDict(g, 1=>2)
             end
         end |> only === Union{}
-    end
 end
 
 # Test that purity modeling doesn't accidentally introduce new world age issues