Conditional stateful function call will not handle shiftstate position properly

[tomoyanonymous]

Continued from #63 .

I found the reason for the bug of the segfault. Function that calls stateful function only on the one side of the if-else branch generate bytecodes that may shift different amount of state position depending on the branch path.

The function bar is compiled to

fn some_self_fun() {
  self + 1.0
}
fn foo() {
  0.0
}
fn bar(){
  let _ = some_self_fun()

  if (1.0) {
    0.0
  } else {
    foo()
  }
}

fn dsp(){
  bar()
}

like this.

fn bar []
upindexes:[]upper:0 state_size: 1(=[number])
  block 0
  reg(9)  := alloc number
  reg(7)  := uint 1
  reg(8)  := call reg(7) [] ->number
  reg(10) := store reg(9), reg(8), number
  reg(11) := float 1
  reg(12) := jmpif reg(11) 1 2 3

  block 1
  reg(13) := float 0

  block 2
             pushstateidx 1(=[number])
  reg(14) := uint 2
  reg(15) := call reg(14) [] ->number

  block 3
  reg(16) := phi reg(13) reg(15)
             popstateidx  1(=[number])
  reg(17) := ret reg(16) number

If the condition was true, pushstate(1) and popstate(1) will be called but only popstate(1) is called when the condition was false.

[tomoyanonymous]

In the current implementation, popstate is inserted at the end of the function with the sum of the statesize within the function, but is should be inserted right after the non-closure function call. Or, maybe new instruction like callstatefulfn address [arguments] statesize should be introduced at the MIR level and push/popstate instruction should be removed.

[tomoyanonymous]

Hmm, I'm thinking a bit more subtle cases like this.

fn dsp(){
 if (random()){
   gen_a() 
 }else{
   gen_b()
}
}

gen_a and gen_b are stateful functions which have a different state size, 4 and 5 respectively for instance.

The state size of the dsp function should be 9 and shiftstate(4) should be inserted at the beginning of else block.

Also, it maybe problematic because only one side of branches are evaluated and then samplerate becomes inconsistent...