[OPTIMISATION] Better conditions transcriptions from AST inside if/while/!/bool()

[denis-migdal]

Hi,

The logical operators are, rightfully, converted as follow, as they need to return the value (and not just True/False) :

1 and 2
3 or 4

(! $B.$bool(locals.$test = 1) ? locals.$test : 2)
($B.$bool(locals.$test = 3) ? locals.$test : 4)

However, in direct children of nodes :

• !
• if
• while
• bool()

We don't care about the value.
For example if 1 and 2: is converted as :

if($B.set_lineno(frame, 1) && $B.$bool((! $B.$bool(locals.$test = 1) ? locals.$test : 2))){  .... }

When it could be converted to :

if($B.set_lineno(frame, 1) && ( $B.$bool(1) &&  $B.$bool(2)  )   ){  .... }

Resulting on smaller, cleaner, and faster code.

Hence I suggest the following behavior :

1. let N the current node. If N isn't if or while or ! or bool(), stops here.
2. let n the direct child of N.
   1. if n is a comparison operator (e.g. > or not in or in), write : ($B.rich_comp('__gt__', 1, 3)) instead of $B.$bool($B.rich_comp('__gt__', 1, 3)) (indeed it already returns a boolean.)
   2. if n is ! or and or or or bool(), write e.g. : ( [LEFT_VALUE] && [RIGHT_VALUE] ) instead of $B.$bool((! $B.$bool(locals.$test = [LEFT_VALUE]) ? locals.$test : [RIGHT_VALUE]))
      1. if [LEFT_VALUE] (or [RIGHT_VALUE]) isn't a ! or and or or or bool(), write it as : $B.bool([THE_VALUE]) (we need to convert it).
      2. else, put N = [LEFT_VALUE] and go step 2. to determine how to write [LEFT_VALUE].

Note : I think adding === true in if and while can very slightly increase execution speed as JS/the browser would knows it doesn't have to try casting the types :

if($B.set_lineno(frame, 1) && ( $B.$bool(1) &&  $B.$bool(2)  ) === true  ){  .... }

Cordially,

[denis-migdal]

Also, there are a lot of temporary variables that aren't used.

E.g.

a = 2
b = a

Is translated as :

  var v1380 = 2
  locals_exec.a = v1380
  var v1381 = locals_exec.a
  locals_exec.b = v1381

Could be rewritten :

let v1380 = locals_exec.a = 2;
locals_exec.b = v1380; // avoid doing locals_exec.a which can be a little costly

or

locals_exec.a = 2;
locals_exec.b = locals_exec.a;

[PierreQuentel]

Removing $B.$bool()) is not possible, because Python allows a rich comparison method to return something else than a boolean. If we removed $B.$bool(), the code below

class A:

  def __eq__(self, other):
    return []

if A() == 'xy':
    print('ok')

would not give the same result as CPython.

[PierreQuentel]

I implemented the second suggestion in commit b1383ca

[denis-migdal]

Removing $B.$bool()) is not possible, because Python allows a rich comparison method to return something else than a boolean. If we removed $B.$bool(), the code below

Hum, I think we can still do it by removing the 2.i step.

Pretty sure :

if 1 and 2:

Instead of :

if( $B.$bool( (! $B.$bool(locals.$test = 1) ? locals.$test : 2) )   ){  .... }

can be rewritten as :

if( ( $B.$bool(1) &&  $B.$bool(2)  )  ){  .... }

Because the if doesn't care about the real return value of a and b, it just care whether the expression evaluate to True or False. So in this context, the traduction of a and b, in JS, can be simplified.

[denis-migdal]

I also wonder if using a function would be faster or slower for the general case (would requires to test that) :

function and(a,b) {
     if( $B.bool(a) )
          a;
     return b;
}

EDIT : it seems 1.57x faster, but the test is very very limited.
https://jsperf.app/nanebi/2

EDIT: I'm an idiot, I forgot that the second operand must not be evaluated if "a" is evaluated to False.

[PierreQuentel]

Implemented in the commit above. Do you think we can close this issue ?

[denis-migdal]

Hi,

Sorry for the late answer.

I am currently in the middle of an house moving so I currently doesn't have a lot of time.
I'll check on that when I'll have more time ;)

[PierreQuentel]

Pas de problème Denis, bon courage pour le déménagement !