200848 - Slow access of global variables

Status: VERIFIED DUPLICATE of bug 169559

(Core :: Security, defect)

Description

[Tim Powell]

Accessing a JavaScript global variable is extremely slow in Mozilla 1.3. I don't
understand why this is. The slowest is to use global variables outside a
function, which I would imagine is quite common. Global variables are about 3
times slower than local variables in a function. Globals in functions in IE are
also somewhat slower, but only about 1.5 times slower than its local variables.

Comment 1

[Tim Powell]

Attachment: Testcase comparing local and global variables in loops

I'm using this testcase to compare performance. Here's the results on the same
computer (Pentium II 300MHz, 364M RAM):

Mozilla 1.3: Local: 770ms  Global: 2310ms  Global not Function: 3960ms
   MS IE5.5: Local: 880ms  Global: 1430ms  Global not Function: 2190ms

Comment 2

[Tim Powell]

Note that the testcase may load somewhat slowly initially because it tests
globals outside a function when the page loads. Click the test button to test
local and global variables in functions.

Comment 3

[Phil Schwartau]

This is due to DOM security checks on global variables. That is,
Mozilla does a security check on every global variable access;
IE does not.

Reassigning to Security:General to see if this cost can be mitigated
in any way, and cc'ing jst -

Comment 4

[Phil Schwartau]

Actually, this bug is a duplicate of bug 169559. Tim, you will be
cc'ed on that one so you can follow progress on this issue -

*** This bug has been marked as a duplicate of 169559 ***

Comment 5

[Charles Rosendahl]

v