inference: override return type inference by const-prop more carefully

A return type derived by const-prop' inference can be wider than that of
non const-prop' inference in rare cases e.g. when there are cycles but
cached result is still accurate. This commit checks if the const-prop'ed
result is really more accurate than non-const result.

fix Ferrite-FEM/Tensors.jl#178

base/compiler/abstractinterpretation.jl

@@ -97,7 +97,11 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
                 const_result = abstract_call_method_with_const_args(interp, result, f, this_arginfo, match, sv)
                 effects = result.edge_effects
                 if const_result !== nothing
-                    (; rt, effects, const_result) = const_result
+                    const_rt = const_result.rt
+                    if const_rt ⊑ rt
+                        rt = const_rt
+                    end
+                    (; effects, const_result) = const_result
                 end
                 tristate_merge!(sv, effects)
                 push!(const_results, const_result)
@@ -136,7 +140,12 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
             const_result = abstract_call_method_with_const_args(interp, result, f, this_arginfo, match, sv)
             effects = result.edge_effects
             if const_result !== nothing
-                this_rt = const_result.rt
+                this_const_rt = const_result.rt
+                # return type of const-prop' inference can be wider than  that of non const-prop' inference
+                # e.g. in cases when there are cycles but cached result is still accurate
+                if this_const_rt ⊑ this_rt
+                    this_rt = this_const_rt
+                end
                 (; effects, const_result) = const_result
             end
             tristate_merge!(sv, effects)
@@ -1485,7 +1494,11 @@ 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)
     if const_result !== nothing
-        (;rt, const_result) = const_result
+        const_rt = const_result.rt
+        if const_rt ⊑ rt
+            rt = const_rt
+        end
+        const_result = const_result.const_result
     end
     return CallMeta(from_interprocedural!(rt, sv, arginfo, sig), InvokeCallInfo(match, const_result))
 end
@@ -1633,7 +1646,11 @@ function abstract_call_opaque_closure(interp::AbstractInterpreter, closure::Part
         const_result = abstract_call_method_with_const_args(interp, result, nothing,
             arginfo, match, sv)
         if const_result !== nothing
-            (;rt, const_result) = const_result
+            const_rt = const_result.rt
+            if const_rt ⊑ rt
+                rt = const_rt
+            end
+            const_result = const_result.const_result
         end
     end
     info = OpaqueClosureCallInfo(match, const_result)