Closed Bug 1383364 Opened 7 years ago Closed 8 months ago

for..of significantly slower in certain testcases

Categories

(Core :: JavaScript Engine: JIT, defect, P3)

defect

Tracking

()

RESOLVED INCOMPLETE
Performance Impact low
Tracking Status
firefox57 --- wontfix

People

(Reporter: yfdyh000, Unassigned)

References

(Blocks 1 open bug)

Details

(Keywords: perf, testcase)

For example:

https://jsperf.com/pk-for-of-vs-for-each
For Of
30,885
±0.61%
97% slower

For Each
1,183,367
±0.32%
fastest


https://jsperf.com/for-of-vs-for-short-arr
for
515,049
±4.44%
fastest

for..of
21,891
±6.85%
96% slower
Blocks: es6perf
> https://jsperf.com/pk-for-of-vs-for-each

this case ignores the return value of the function call, and looks like the whole loop gets optimized away in forEach case.
(between "func05-pass15-De-Beta-mir.gv" and "func05-pass16-RA check UCE-mir.gv", in iongraph)

but the loop is still there in for-of case.
See Also: → 1355874
Priority: -- → P3
Whiteboard: [qf:p3]
Type: enhancement → defect
Status: UNCONFIRMED → NEW
Ever confirmed: true
Performance Impact: --- → P3
Whiteboard: [qf:p3]
Severity: normal → S3

Unfortunately the test case has been lost to the sands of time, rendering this bug unactionable, and our performance efforts are currently focused elsewhere.

If this test case can be recovered, we could re-check the current state of the world and re-open.

We've done work in this area of the last few years, and it may well be improved.

Status: NEW → RESOLVED
Closed: 8 months ago
Resolution: --- → INCOMPLETE
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