813727 - IonMonkey: Implement atom inequalities.

Status: RESOLVED DUPLICATE of bug 813836

(Core :: JavaScript Engine, defect)

Description

[Zibi Braniecki [:zbraniecki][:gandalf]]

Attachment: demo html

when iterating over string and doing character comparison the JS engine is two times slower than V8.

Comment 1

[Tom S [:evilpie]]

v8 generates code for character compares. We only have one very simple optimization for ==/!=. Which checks for ptr==ptr, atoms and string length. I think optimizing this very case could be simple. Last time I tried implementing a whole string compare path everything got very ugly, because of register pressure.

Comment 2

[Nicolas B. Pierron [:nbp]]

The problem is that IonMonkey does not yet provide a fast path for atom inequalities (see MCompare::infer in ion/MIR.cpp), so currently the result of  charAt  returns another atom which is boxed and pushed twice to call into a VM function which unbox its operands and compare the atoms.

Note: x2 times slower does not seems too bad knowing the overhead of VM function calls, both in terms of spilling and it terms of number of instructions.

Comment 3

[André Bargull [:anba]]

Fixed through bug 813836.