add deepcopy to Cached constructor

src/Compiler.jl

@@ -12,7 +12,8 @@ import ..Reactant:
     make_tracer,
     TracedToConcrete,
     append_path,
-    TracedType
+    TracedType,
+    Cached
 using ScopedValues
 import ReactantCore: enable_tracing
 
@@ -284,7 +285,7 @@ function compile_mlir(f, args; kwargs...)
     @ccall MLIR.API.mlir_c.RegisterDialects(ctx::MLIR.API.MlirContext)::Cvoid
     MLIR.IR.context!(ctx) do
         mod = MLIR.IR.Module(MLIR.IR.Location())
-        callcache = Dict()
+        callcache = Dict{Cached, @NamedTuple{f_name::String, mlir_result_types::Vector{MLIR.IR.Type}, traced_result::Any}}()
         evalinfo = compile_mlir!(mod, f, args, callcache; kwargs...)
         return mod, evalinfo...
     end

src/ControlFlow.jl

@@ -227,6 +227,9 @@ end
 
 struct Cached
     obj
+    # `deepcopy` is needed for when a Cached object is used as a key in a Dict.
+    # If the original object is mutated, the key should stay the same:
+    Cached(obj) = new(deepcopy(obj))
 end
 Base.:(==)(a::Cached, b::Cached) = recursive_equal(a.obj, b.obj)
 Base.hash(a::Cached, h::UInt) = recursive_hash(a.obj, h)