swap arguments for functions with more than 3 arguments

[fyrchik]

Proposed changes in this pull request

Functions with more than 3 arguments are not working now.

func Main() {
	a := [4]int{0,0,0,0}
	a[0] = 0
	f1(a, 1, 2, 3)
}

func f1(a [4]int, x int, y int, z int) {
	a[1] = x
}

I think, I have fixed it with this pull request. What do you think?
make test still passes all tests

Type (put an x where ever applicable)

• Bug fix: Link to the issue
• Feature (Non-breaking change)
• Feature (Breaking change)
• Documentation Improvement

Checklist

Please put an x against the checkboxes. Write a small comment explaining if its N/A (not applicable)

• Read the CONTRIBUTION guidelines.
• All the tests are passing after the introduction of new changes.
• Added tests respective to the part of code I have written.
• Added proper documentation where ever applicable (in code and README.md).

Extra information

Any extra information related to this pull request.

[anthdm]

UPDATE: More then 3 needs some adustment. Sorry was looking at 3 arguments.

When looking in the neo-boa compiler I see the exact same thing in converting 3 functions arguments.

https://github.com/CityOfZion/neo-boa/blob/master/boa/code/vmtoken.py#L424

[anthdm]

This is working for me:

// Main in the contract entry point.
func Main() int {
    return someFunction(0, 1, 2, 3, 4, 5) // 6
}

func someFunction(a int, b int, c int, d int, e int, f int) int {
    // Make sure the compiler not flatten the arguments in a single result.
    va := a
    vb := b
    vc := c
    vd := d
    ve := e
    vf := f

    return va + vb + vc + vd + ve + vf
}

Testinvoke

{
  "state": "HALT, BREAK",
  "gas_consumed": "0.076",
  "script": "51c56b0051525354556506006c75665dc56b6a00527ac46a51527ac46a52527ac46a53527ac46a54527ac46a55527ac46a00c36a56527ac46a51c36a57527ac46a52c36a58527ac46a53c36a59527ac46a54c36a5a527ac46a55c36a5b527ac46a56c36a57c3936a58c3936a59c3936a5ac3936a5bc3936c7566",
  "Stack": [
    {
      "type": "Integer",
      "value": "15"
    }
  ]
}

[fyrchik]

@anthdm I think the way neo-boa does this is suboptimal (5 bytes per argument vs 2 in my PR if it is correct)
Regarding your example, it can behave good, because return value is symmetric in relation to function arguments. I was using [4]int with ints.

[anthdm]

@fyrchik If you test this with your fix, there is indeed no VM.FAULT, however, the stack is not looking too good.

[anthdm]

@fyrchik After testing your example with neo-boa I get the exact same result as with neo-storm after your fix. But like I said the stack is not cleaned up properly.

[anthdm]

@fyrchik UPDATE:

Your fix is correct after looking at the result for this example which only works after your fix.

func Main() string {
    c := f1(0, 1, 2, "foo")
    return c
}

func f1(a int, b int, c int, d string) string {
    return d
}

{
  "state": "HALT, BREAK",
  "gas_consumed": "0.03",
  "script": "52c56b00515203666f6f650e006a00527ac46a00c36c756655c56b6a00527ac46a51527ac46a52527ac46a53527ac46a53c36c7566",
  "Stack": [
    {
      "type": "ByteArray",
      "value": "666f6f"
    }
  ]
}

[fyrchik]

@anthdm could you please provide an example which leaves stack dirty? For me all your examples are working fine.