1573643 - [meta] XDR writes multiple copies of the same atom to XDR buffer

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect, P1)

Description

[Caroline Cullen [:caroline]]

When encoding JS to bytecode to be stored in the XDR buffer, atoms get written to the buffer after each script gets encoded. This is an issue for the case when a top level function
and an inner function share the same atoms. In this case atoms get copied into the XDR buffer multiple times. Such as in the example below:

function foo() {
    var i = 1;
    function bar() {
        for (var j = 0; j < 5; ++j) {
            print(i);
        }
    }
}
foo();

If foo and bar both get encoded then their shared atoms will be written to the XDR buffer multiple times. Removing these additional buffer writes has the potential to save both buffer space and time writing to the buffer.