Closed Bug 692847 Opened 8 years ago Closed 8 years ago

Speed up Array.shift, and Array.{pop,shift} on empty arrays

Categories

(Core :: JavaScript Engine, defect)

x86
macOS
defect
Not set

Tracking

()

RESOLVED FIXED
mozilla10

People

(Reporter: bhackett1024, Assigned: bhackett1024)

References

(Blocks 1 open bug)

Details

Attachments

(1 file, 1 obsolete file)

Attached patch patch against 15bfad783467 (obsolete) — Splinter Review
Peacekeeper 2.0's arrayCombine test is broken and does many of its operations on an empty array, with a bunch of pop and shift calls costing the most.  V8 has a fast path for pop() on an empty array, so I don't feel too bad benchmark-gaming this one.

Attached patch allows the pop() inline path to handle empty arrays (only when the call is known to produce undefined), and generalizes this path to also handle shift() (which calls a stub to memmove() in the non-empty case).  This gives a good speedup to non-empty shift() too:

function foo(x) {
  for (var i = 0; i < 10; i++)
    x.push(i);
  for (var i = 0; i < 10000000; i++)
    x.push(x.shift());
}
foo([]);

js -m -n (old): 625
js -m -n (new): 322
js -m -j -p: 805
d8: 592
Attachment #565575 - Flags: review?(dvander)
Brian, I get an error about ‘js::mjit::Assembler::storeValueFromComponents(JSValueType&, JSC::X86Registers::RegisterID, JSC::AbstractMacroAssembler<JSC::X86Assembler>::Address&) not being defined when I build this on top of rev 15bfad783467.  This is in a 64-bit build.  A 32-bit build works fine.
Attached patch updatedSplinter Review
Oops, was missing a coercion that was necessary on x64.
Assignee: general → bhackett1024
Attachment #565575 - Attachment is obsolete: true
Attachment #565575 - Flags: review?(dvander)
Attachment #565591 - Flags: review?(dvander)
Attachment #565591 - Flags: review?(dvander) → review+
As an aside, according to https://bugzilla.mozilla.org/show_bug.cgi?id=499198#c32 Peacekeeper doesn't do a bunch of operations on empty arrays any more, in arrayCombined.
https://hg.mozilla.org/mozilla-central/rev/882404096d65
Status: NEW → RESOLVED
Closed: 8 years ago
Resolution: --- → FIXED
Target Milestone: --- → mozilla10
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