inference: avoid inferring unreachable code methods (#51317)

Author: vtjnash

base/compiler/abstractinterpretation.jl

@@ -485,7 +485,10 @@ function abstract_call_method(interp::AbstractInterpreter,
         return MethodCallResult(Any, false, false, nothing, Effects())
     end
     sigtuple = unwrap_unionall(sig)
-    sigtuple isa DataType || return MethodCallResult(Any, false, false, nothing, Effects())
+    sigtuple isa DataType ||
+        return MethodCallResult(Any, false, false, nothing, Effects())
+    all(@nospecialize(x) -> valid_as_lattice(unwrapva(x), true), sigtuple.parameters) ||
+        return MethodCallResult(Union{}, false, false, nothing, EFFECTS_THROWS) # catch bad type intersections early
 
     if is_nospecializeinfer(method)
         sig = get_nospecializeinfer_sig(method, sig, sparams)
@@ -1365,25 +1368,35 @@ function precise_container_type(interp::AbstractInterpreter, @nospecialize(itft)
     end
     if isa(tti, Union)
         utis = uniontypes(tti)
-        if any(@nospecialize(t) -> !isa(t, DataType) || !(t <: Tuple) || !isknownlength(t), utis)
-            return AbstractIterationResult(Any[Vararg{Any}], nothing, Effects())
-        end
-        ltp = length((utis[1]::DataType).parameters)
-        for t in utis
-            if length((t::DataType).parameters) != ltp
-                return AbstractIterationResult(Any[Vararg{Any}], nothing)
+        # refine the Union to remove elements that are not valid tags for objects
+        filter!(@nospecialize(x) -> valid_as_lattice(x, true), utis)
+        if length(utis) == 0
+            return AbstractIterationResult(Any[], nothing) # oops, this statement was actually unreachable
+        elseif length(utis) == 1
+            tti = utis[1]
+            tti0 = rewrap_unionall(tti, tti0)
+        else
+            if any(@nospecialize(t) -> !isa(t, DataType) || !(t <: Tuple) || !isknownlength(t), utis)
+                return AbstractIterationResult(Any[Vararg{Any}], nothing, Effects())
             end
-        end
-        result = Any[ Union{} for _ in 1:ltp ]
-        for t in utis
-            tps = (t::DataType).parameters
-            _all(valid_as_lattice, tps) || continue
-            for j in 1:ltp
-                result[j] = tmerge(result[j], rewrap_unionall(tps[j], tti0))
+            ltp = length((utis[1]::DataType).parameters)
+            for t in utis
+                if length((t::DataType).parameters) != ltp
+                    return AbstractIterationResult(Any[Vararg{Any}], nothing)
+                end
+            end
+            result = Any[ Union{} for _ in 1:ltp ]
+            for t in utis
+                tps = (t::DataType).parameters
+                for j in 1:ltp
+                    @assert valid_as_lattice(tps[j], true)
+                    result[j] = tmerge(result[j], rewrap_unionall(tps[j], tti0))
+                end
             end
+            return AbstractIterationResult(result, nothing)
         end
-        return AbstractIterationResult(result, nothing)
-    elseif tti0 <: Tuple
+    end
+    if tti0 <: Tuple
         if isa(tti0, DataType)
             return AbstractIterationResult(Any[ p for p in tti0.parameters ], nothing)
         elseif !isa(tti, DataType)
@@ -1647,7 +1660,7 @@ end
     return isa_condition(xt, ty, max_union_splitting)
 end
 @inline function isa_condition(@nospecialize(xt), @nospecialize(ty), max_union_splitting::Int)
-    tty_ub, isexact_tty = instanceof_tfunc(ty)
+    tty_ub, isexact_tty = instanceof_tfunc(ty, true)
     tty = widenconst(xt)
     if isexact_tty && !isa(tty_ub, TypeVar)
         tty_lb = tty_ub # TODO: this would be wrong if !isexact_tty, but instanceof_tfunc doesn't preserve this info
@@ -1657,7 +1670,7 @@ end
                 # `typeintersect` may be unable narrow down `Type`-type
                 thentype = tty_ub
             end
-            valid_as_lattice(thentype) || (thentype = Bottom)
+            valid_as_lattice(thentype, true) || (thentype = Bottom)
             elsetype = typesubtract(tty, tty_lb, max_union_splitting)
             return ConditionalTypes(thentype, elsetype)
         end
@@ -1903,7 +1916,7 @@ function abstract_invoke(interp::AbstractInterpreter, (; fargs, argtypes)::ArgIn
     ft′ = argtype_by_index(argtypes, 2)
     ft = widenconst(ft′)
     ft === Bottom && return CallMeta(Bottom, EFFECTS_THROWS, NoCallInfo())
-    (types, isexact, isconcrete, istype) = instanceof_tfunc(argtype_by_index(argtypes, 3))
+    (types, isexact, isconcrete, istype) = instanceof_tfunc(argtype_by_index(argtypes, 3), false)
     isexact || return CallMeta(Any, Effects(), NoCallInfo())
     unwrapped = unwrap_unionall(types)
     if types === Bottom || !(unwrapped isa DataType) || unwrapped.name !== Tuple.name
@@ -2322,7 +2335,7 @@ function abstract_eval_statement_expr(interp::AbstractInterpreter, e::Expr, vtyp
         (; rt, effects) = abstract_eval_call(interp, e, vtypes, sv)
         t = rt
     elseif ehead === :new
-        t, isexact = instanceof_tfunc(abstract_eval_value(interp, e.args[1], vtypes, sv))
+        t, isexact = instanceof_tfunc(abstract_eval_value(interp, e.args[1], vtypes, sv), true)
         ut = unwrap_unionall(t)
         consistent = noub = ALWAYS_FALSE
         nothrow = false
@@ -2387,7 +2400,7 @@ function abstract_eval_statement_expr(interp::AbstractInterpreter, e::Expr, vtyp
         end
         effects = Effects(EFFECTS_TOTAL; consistent, nothrow, noub)
     elseif ehead === :splatnew
-        t, isexact = instanceof_tfunc(abstract_eval_value(interp, e.args[1], vtypes, sv))
+        t, isexact = instanceof_tfunc(abstract_eval_value(interp, e.args[1], vtypes, sv), true)
         nothrow = false # TODO: More precision
         if length(e.args) == 2 && isconcretedispatch(t) && !ismutabletype(t)
             at = abstract_eval_value(interp, e.args[2], vtypes, sv)

base/compiler/abstractlattice.jl

@@ -98,16 +98,18 @@ is_valid_lattice_norec(::InferenceLattice, @nospecialize(elem)) = isa(elem, Limi
 """
     tmeet(𝕃::AbstractLattice, a, b::Type)
 
-Compute the lattice meet of lattice elements `a` and `b` over the lattice `𝕃`.
-If `𝕃` is `JLTypeLattice`, this is equivalent to type intersection.
+Compute the lattice meet of lattice elements `a` and `b` over the lattice `𝕃`,
+dropping any results that will not be inhabited at runtime.
+If `𝕃` is `JLTypeLattice`, this is equivalent to type intersection plus the
+elimination of results that have no concrete subtypes.
 Note that currently `b` is restricted to being a type
 (interpreted as a lattice element in the `JLTypeLattice` sub-lattice of `𝕃`).
 """
 function tmeet end
 
 function tmeet(::JLTypeLattice, @nospecialize(a::Type), @nospecialize(b::Type))
     ti = typeintersect(a, b)
-    valid_as_lattice(ti) || return Bottom
+    valid_as_lattice(ti, true) || return Bottom
     return ti
 end
 

base/compiler/optimize.jl

@@ -243,7 +243,7 @@ function new_expr_effect_flags(𝕃ₒ::AbstractLattice, args::Vector{Any}, src:
     Targ = args[1]
     atyp = argextype(Targ, src)
     # `Expr(:new)` of unknown type could raise arbitrary TypeError.
-    typ, isexact = instanceof_tfunc(atyp)
+    typ, isexact = instanceof_tfunc(atyp, true)
     if !isexact
         atyp = unwrap_unionall(widenconst(atyp))
         if isType(atyp) && isTypeDataType(atyp.parameters[1])
@@ -335,7 +335,7 @@ function stmt_effect_flags(𝕃ₒ::AbstractLattice, @nospecialize(stmt), @nospe
         elseif head === :new_opaque_closure
             length(args) < 4 && return (false, false, false)
             typ = argextype(args[1], src)
-            typ, isexact = instanceof_tfunc(typ)
+            typ, isexact = instanceof_tfunc(typ, true)
             isexact || return (false, false, false)
             ⊑(𝕃ₒ, typ, Tuple) || return (false, false, false)
             rt_lb = argextype(args[2], src)

base/compiler/ssair/inlining.jl

@@ -1200,7 +1200,7 @@ function handle_invoke_call!(todo::Vector{Pair{Int,Any}},
 end
 
 function invoke_signature(argtypes::Vector{Any})
-    ft, argtyps = widenconst(argtypes[2]), instanceof_tfunc(widenconst(argtypes[3]))[1]
+    ft, argtyps = widenconst(argtypes[2]), instanceof_tfunc(widenconst(argtypes[3]), false)[1]
     return rewrap_unionall(Tuple{ft, unwrap_unionall(argtyps).parameters...}, argtyps)
 end
 

base/compiler/ssair/passes.jl

@@ -1756,7 +1756,7 @@ function adce_pass!(ir::IRCode, inlining::Union{Nothing,InliningState}=nothing)
         else
             if is_known_call(stmt, typeassert, compact) && length(stmt.args) == 3
                 # nullify safe `typeassert` calls
-                ty, isexact = instanceof_tfunc(argextype(stmt.args[3], compact))
+                ty, isexact = instanceof_tfunc(argextype(stmt.args[3], compact), true)
                 if isexact && ⊑(𝕃ₒ, argextype(stmt.args[2], compact), ty)
                     compact[idx] = nothing
                     continue