RDV: private main2.

gistfile1.txt

there's another bug in remove-dead-values. 
the problem is liveness analysis depends on  mlir::dataflow::DeadCodeAnalysis. 
without any reference of @main2, it doesn't participate progation of liveness. As a result, it has no idea arg0 and %arg1 of @immutable_fn_return_void_with_unused_argument. 

RDV needs to delete @main2 entirely. 

➜  build git:(backward_remove_dead_values) cat in3.mlir
// /bin/mlir-opt --remove-dead-values --debug-only=remove-dead-values --debug-only=liveness-analysis  --debug-only=dataflow ./in3.mlir
  func.func public @immutable_fn_return_void_with_unused_argument(%arg0: i32, %arg1: memref<4xf32>) -> () {
    return
  }
  func.func private @main2(%arg: i32) -> () {
    %one = arith.constant 1 : i32
    %scalar = arith.addi %arg, %one: i32
    %mem = memref.alloc() : memref<4xf32>

    call @immutable_fn_return_void_with_unused_argument(%scalar, %mem) : (i32, memref<4xf32>) -> ()
    return
  }
  //func.func @main(%arg: i32) -> () {
  //  call @main2(%arg): (i32) -> ()
  //  return
  //}