Annotation to elide function call if the return value is unused

General Usage Performance
5

The macro as written doesn’t resolve the variables correctly:

@macroexpand function compute(input, callback)
         x = @elidable foo(input)
         y = @elidable bar(input)
         z = @elidable baz(x, y)
         return callback((;x, y, z))
       end
:(function compute(input, callback)
      #= REPL[3]:1 =#
      #= REPL[3]:2 =#
      x = $(Expr(:unnecessary, :(Main.foo(Main.input))))
      #= REPL[3]:3 =#
      y = $(Expr(:unnecessary, :(Main.bar(Main.input))))
      #= REPL[3]:4 =#
      z = $(Expr(:unnecessary, :(Main.baz(Main.x, Main.y))))
      #= REPL[3]:5 =#
      return callback((; x, y, z))
  end)

defining it as

macro elidable(ex)
    @show ex
    return Expr(:unnecessary, esc(ex))
end

seems to do the trick.

I know that all bets are off at this point, but I’m not getting the desired behavior:

function foo(input)
    println("foo")
    2 * input
end

function bar(input)
    println("bar")
    2 + input
end

function baz(x, y)
    println("baz")
    x / y
end

function compute(input, callback)
  x = @elidable foo(input)
  y = @elidable bar(input)
  z = @elidable baz(x, y)
  return callback((;x, y, z))
end

@inline callback_xyz(nt) = nt.x + nt.y + nt.z
@inline callback_xy(nt) = nt.x + nt.y
@inline callback_xz(nt) = nt.x + nt.z
@inline callback_x(nt) = nt.x

julia> @code_typed compute(20, callback_x)
CodeInfo(
1 ─      invoke Main.println("foo"::String)::Any
│   %2 = Base.mul_int(2, input)::Int64
│        invoke Main.println("bar"::String)::Any
│        invoke Main.println("baz"::String)::Any
└──      return %2
) => Int64

(@yha as I mentioned in my original post, I’m not looking to do memoization.)