837832 - Labeled breaks slower than normal breaks in emscripten code

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine, defect)

Description

[Alon Zakai (:azakai)]

Attachment: smaller but slower

Attached are two versions of fasta, run them with

  file.js 19000000

The only difference between them is that one has

label: do {
  if (..) {
  }
} while(0);

while the other has

label: if(..) {
  ...
}

the second is more compact which is good for code size. However it runs much more slowly, 2.5x.

Aside from putting the label directly on the if, the other change which is necessary is to make all breaks to that label labeled breaks, since a do-while can have a raw |break| but an if cannot. Are labeled breaks slower perhaps?

Comment 1

[Alon Zakai (:azakai)]

Attachment: bigger but faster

Comment 2

[Alon Zakai (:azakai)]

Note: diff -w is useful to see that only the do-while vs if and labeled breaks have changed, -w makes it ignore the changed indentation.

Comment 3

[Alon Zakai (:azakai)]

Forgot to say, there is no speed difference in v8 between the two versions.

Comment 4

[Jan de Mooij [:jandem]]

IonMonkey currently only handles labeled breaks if the label is immediately followed by a loop (bug 684384). So we abort compilation of incoming.js:2608:

[Abort] could not find the target of a break
[Abort] aborted @ /Users/jan/dev/incoming.js:2653