inference: always use const-prop'ed result (#44001)

Previously, for `invoke`/opaque closure callsite, we use constant-prop'ed
method body only when the inferred return type gets strictly improved
by const-prop. But since the inliner is now able to inline the method
body from `InferenceResult`, I believe it is always better to use method
body shaped up by const-prop' no matter if the return type is improved
(as we already do for ordinal call sites).

> use constant prop' result even when the return type doesn't get refined
```julia
const Gx = Ref{Any}()
Base.@constprop :aggressive function conditional_escape!(cnd, x)
    if cnd
        Gx[] = x
    end
    return nothing
end
@test fully_eliminated((String,)) do x
    Base.@invoke conditional_escape!(false::Any, x::Any)
end
```

Author: aviatesk

base/compiler/abstractinterpretation.jl

@@ -85,10 +85,7 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
                 this_arginfo = ArgInfo(fargs, this_argtypes)
                 const_result = abstract_call_method_with_const_args(interp, result, f, this_arginfo, match, sv, false)
                 if const_result !== nothing
-                    const_rt, const_result = const_result
-                    if const_rt !== rt && const_rt ⊑ rt
-                        rt = const_rt
-                    end
+                    rt, const_result = const_result
                 end
                 push!(const_results, const_result)
                 if const_result !== nothing
@@ -125,10 +122,7 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
             this_arginfo = ArgInfo(fargs, this_argtypes)
             const_result = abstract_call_method_with_const_args(interp, result, f, this_arginfo, match, sv, false)
             if const_result !== nothing
-                const_this_rt, const_result = const_result
-                if const_this_rt !== this_rt && const_this_rt ⊑ this_rt
-                    this_rt = const_this_rt
-                end
+                this_rt, const_result = const_result
             end
             push!(const_results, const_result)
             if const_result !== nothing
@@ -622,7 +616,7 @@ function abstract_call_method_with_const_args(interp::AbstractInterpreter, resul
     # if constant inference hits a cycle, just bail out
     isa(result, InferenceState) && return nothing
     add_backedge!(mi, sv)
-    return result, inf_result
+    return Pair{Any,InferenceResult}(result, inf_result)
 end
 
 # if there's a possibility we could get a better result (hopefully without doing too much work)
@@ -1364,12 +1358,9 @@ function abstract_invoke(interp::AbstractInterpreter, (; fargs, argtypes)::ArgIn
     # end
     const_result = abstract_call_method_with_const_args(interp, result, singleton_type(ft′), arginfo, match, sv, false)
     if const_result !== nothing
-        const_rt, const_result = const_result
-        if const_rt !== rt && const_rt ⊑ rt
-            rt, res = const_rt, const_result
-        end
+        rt, const_result = const_result
     end
-    return CallMeta(from_interprocedural!(rt, sv, arginfo, sig), InvokeCallInfo(match, res))
+    return CallMeta(from_interprocedural!(rt, sv, arginfo, sig), InvokeCallInfo(match, const_result))
 end
 
 function invoke_rewrite(xs::Vector{Any})
@@ -1491,18 +1482,15 @@ function abstract_call_opaque_closure(interp::AbstractInterpreter, closure::Part
     tt = closure.typ
     sigT = (unwrap_unionall(tt)::DataType).parameters[1]
     match = MethodMatch(sig, Core.svec(), closure.source, sig <: rewrap_unionall(sigT, tt))
-    res = nothing
+    const_result = nothing
     if !result.edgecycle
         const_result = abstract_call_method_with_const_args(interp, result, closure,
             arginfo, match, sv, closure.isva)
         if const_result !== nothing
-            const_rettype, const_result = const_result
-            if const_rettype ⊑ rt
-               rt, res = const_rettype, const_result
-            end
+            rt, const_result = const_result
         end
     end
-    info = OpaqueClosureCallInfo(match, res)
+    info = OpaqueClosureCallInfo(match, const_result)
     return CallMeta(from_interprocedural!(rt, sv, arginfo, match.spec_types), info)
 end
 

test/compiler/inline.jl

@@ -895,3 +895,15 @@ end
 # sqrt not considered volatile
 f_sqrt() = sqrt(2)
 @test fully_eliminated(f_sqrt, Tuple{})
+
+# use constant prop' result even when the return type doesn't get refined
+const Gx = Ref{Any}()
+Base.@constprop :aggressive function conditional_escape!(cnd, x)
+    if cnd
+        Gx[] = x
+    end
+    return nothing
+end
+@test fully_eliminated((String,)) do x
+    Base.@invoke conditional_escape!(false::Any, x::Any)
+end