inference: Relax constprop recursion detection

At the moment, we restrict const prop whenever we see a cycle in
methods being called. However, I think this condition can be relaxed
slightly: In particular, if the type complexity limiting did not
decide to limit the growth of the type in question, I think it
should be fine to constant prop as long as there is no cycle in
*method instances* (rather than just methods).

Fixes #39915, replaces #39918

Co-Authored-By: Keno Fisher <[email protected]>

base/compiler/abstractinterpretation.jl

@@ -137,12 +137,12 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
         if splitunions
             splitsigs = switchtupleunion(sig)
             for sig_n in splitsigs
-                rt, edgecycle, edge = abstract_call_method(interp, method, sig_n, svec(), multiple_matches, sv)
+                rt, edgecycle, edgelimited, edge = abstract_call_method(interp, method, sig_n, svec(), multiple_matches, sv)
                 if edge !== nothing
                     push!(edges, edge)
                 end
                 this_argtypes = applicable_argtypes === nothing ? argtypes : applicable_argtypes[i]
-                const_rt, const_result = abstract_call_method_with_const_args(interp, rt, f, this_argtypes, match, sv, edgecycle, false)
+                const_rt, const_result = abstract_call_method_with_const_args(interp, rt, f, this_argtypes, match, sv, edgecycle, edgelimited, false)
                 if const_rt !== rt && const_rt ⊑ rt
                     rt = const_rt
                 end
@@ -156,14 +156,14 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
                 end
             end
         else
-            this_rt, edgecycle, edge = abstract_call_method(interp, method, sig, match.sparams, multiple_matches, sv)
+            this_rt, edgecycle, edgelimited, edge = abstract_call_method(interp, method, sig, match.sparams, multiple_matches, sv)
             if edge !== nothing
                 push!(edges, edge)
             end
             # try constant propagation with argtypes for this match
             # this is in preparation for inlining, or improving the return result
             this_argtypes = applicable_argtypes === nothing ? argtypes : applicable_argtypes[i]
-            const_this_rt, const_result = abstract_call_method_with_const_args(interp, this_rt, f, this_argtypes, match, sv, edgecycle, false)
+            const_this_rt, const_result = abstract_call_method_with_const_args(interp, this_rt, f, this_argtypes, match, sv, edgecycle, edgelimited, false)
             if const_this_rt !== this_rt && const_this_rt ⊑ this_rt
                 this_rt = const_this_rt
             end
@@ -315,14 +315,15 @@ const RECURSION_MSG = "Bounded recursion detected. Call was widened to force con
 function abstract_call_method(interp::AbstractInterpreter, method::Method, @nospecialize(sig), sparams::SimpleVector, hardlimit::Bool, sv::InferenceState)
     if method.name === :depwarn && isdefined(Main, :Base) && method.module === Main.Base
         add_remark!(interp, sv, "Refusing to infer into `depwarn`")
-        return Any, false, nothing
+        return Any, false, false, nothing
     end
     topmost = nothing
     # Limit argument type tuple growth of functions:
     # look through the parents list to see if there's a call to the same method
     # and from the same method.
     # Returns the topmost occurrence of that repeated edge.
     edgecycle = false
+    edgelimited = false
     # The `method_for_inference_heuristics` will expand the given method's generator if
     # necessary in order to retrieve this field from the generated `CodeInfo`, if it exists.
     # The other `CodeInfo`s we inspect will already have this field inflated, so we just
@@ -383,7 +384,7 @@ function abstract_call_method(interp::AbstractInterpreter, method::Method, @nosp
                     # we have a self-cycle in the call-graph, but not in the inference graph (typically):
                     # break this edge now (before we record it) by returning early
                     # (non-typically, this means that we lose the ability to detect a guaranteed StackOverflow in some cases)
-                    return Any, true, nothing
+                    return Any, true, true, nothing
                 end
                 topmost = nothing
                 edgecycle = true
@@ -432,14 +433,15 @@ function abstract_call_method(interp::AbstractInterpreter, method::Method, @nosp
                 # since it's very unlikely that we'll try to inline this,
                 # or want make an invoke edge to its calling convention return type.
                 # (non-typically, this means that we lose the ability to detect a guaranteed StackOverflow in some cases)
-                return Any, true, nothing
+                return Any, true, true, nothing
             end
             add_remark!(interp, sv, RECURSION_MSG)
             topmost = topmost::InferenceState
             parentframe = topmost.parent
             poison_callstack(sv, parentframe === nothing ? topmost : parentframe)
             sig = newsig
             sparams = svec()
+            edgelimited = true
         end
     end
 
@@ -471,14 +473,14 @@ function abstract_call_method(interp::AbstractInterpreter, method::Method, @nosp
 
     rt, edge = typeinf_edge(interp, method, sig, sparams, sv)
     if edge === nothing
-        edgecycle = true
+        edgecycle = edgelimited = true
     end
-    return rt, edgecycle, edge
+    return rt, edgecycle, edgelimited, edge
 end
 
 function abstract_call_method_with_const_args(interp::AbstractInterpreter, @nospecialize(rettype),
                                               @nospecialize(f), argtypes::Vector{Any}, match::MethodMatch,
-                                              sv::InferenceState, edgecycle::Bool,
+                                              sv::InferenceState, edgecycle::Bool, edgelimited::Bool,
                                               va_override::Bool)
     mi = maybe_get_const_prop_profitable(interp, rettype, f, argtypes, match, sv, edgecycle)
     mi === nothing && return Any, nothing
@@ -489,7 +491,11 @@ function abstract_call_method_with_const_args(interp::AbstractInterpreter, @nosp
         # if there might be a cycle, check to make sure we don't end up
         # calling ourselves here.
         if edgecycle && _any(InfStackUnwind(sv)) do infstate
-                return match.method === infstate.linfo.def && any(infstate.result.overridden_by_const)
+                # if the type complexity limiting didn't decide to limit the call signature (`edgelimited = false`)
+                # we can relax the cycle detection by comparing `MethodInstance`s and allow inference to
+                # propagate different constant elements if the recursion is finite over the lattice
+                return (edgelimited ? match.method === infstate.linfo.def : mi === infstate.linfo) &&
+                       any(infstate.result.overridden_by_const)
             end
             add_remark!(interp, sv, "[constprop] Edge cycle encountered")
             return Any, nothing
@@ -1231,15 +1237,15 @@ end
 function abstract_call_opaque_closure(interp::AbstractInterpreter, closure::PartialOpaque, argtypes::Vector{Any}, sv::InferenceState)
     pushfirst!(argtypes, closure.env)
     sig = argtypes_to_type(argtypes)
-    rt, edgecycle, edge = abstract_call_method(interp, closure.source::Method, sig, Core.svec(), false, sv)
+    rt, edgecycle, edgelimited, edge = abstract_call_method(interp, closure.source::Method, sig, Core.svec(), false, sv)
     edge !== nothing && add_backedge!(edge, sv)
     tt = closure.typ
     sigT = unwrap_unionall(tt).parameters[1]
     match = MethodMatch(sig, Core.svec(), closure.source::Method, sig <: rewrap_unionall(sigT, tt))
     info = OpaqueClosureCallInfo(match)
     if !edgecycle
         const_rettype, result = abstract_call_method_with_const_args(interp, rt, closure, argtypes,
-            match, sv, edgecycle, closure.isva)
+            match, sv, edgecycle, edgelimited, closure.isva)
         if const_rettype ⊑ rt
            rt = const_rettype
         end

test/compiler/inference.jl

@@ -3270,3 +3270,25 @@ end == [Union{Some{Float64}, Some{Int}, Some{UInt8}}]
         true
     end
 end
+
+# Make sure that const prop doesn't fall into cycles that aren't problematic
+# in the type domain
+f_recurse(x) = x > 1000000 ? x : f_recurse(x+1)
+@test Base.return_types() do
+    f_recurse(1)
+end |> first === Int
+
+# issue #39915
+function f33915(a_tuple, which_ones)
+    rest = f33915(Base.tail(a_tuple), Base.tail(which_ones))
+    if first(which_ones)
+        (first(a_tuple), rest...)
+    else
+        rest
+    end
+end
+f33915(a_tuple::Tuple{}, which_ones::Tuple{}) = ()
+g39915(a_tuple) = f33915(a_tuple, (true, false, true, false))
+@test Base.return_types() do
+    g39915((1, 1.0, "a", :a))
+end |> first === Tuple{Int, String}