Can I suppress F# compiler making copy of function in IL code?

I want to create a JIT GPU compiler. You give an F# function, and we JIT compile it. The key of JIT compiling is to be able to cache the compiling result. I tried to use the MethodInfo as the caching key, but it won't work. It seems that F# compiler will make a copy of the function instead of referencing the origin function. Is there a way to suppress this behavior?

Here is a test code, ideally, it should be just compiled twice, but it did it 4 times.

let compileGpuCode (m:MethodInfo) =
    printfn "JIT compiling..."
    printfn "Type  : %A" m.ReflectedType
    printfn "Method: %A" m
    printfn ""
    "fake gpu code"

let gpuCodeCache = ConcurrentDictionary<MethodInfo, string>()

let launchGpu (func:int -> int -> int) =
    let m = func.GetType().GetMethod("Invoke", [| typeof<int>; typeof<int> |])
    let gpuCode = gpuCodeCache.GetOrAdd(m, compileGpuCode)
    // launch gpuCode
    ()

let myGpuCode (a:int) (b:int) = a + 2 * b

[<Test>]
let testFSFuncReflection() =
    launchGpu (+)
    launchGpu (+)
    launchGpu myGpuCode
    launchGpu myGpuCode