512813 - build symbol analysis tool to monitor template code bloat

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect)

Description

[Luke Wagner [:luke]]

Recent patches (bug 200505, bug 506410) are introducing STL-style containers into the JS engine for great performance wins.  Unchecked, templates can produce a lot of code which can indirectly reduce these wins or other badness.  There are techniques to combat this, but they involve writing more code and often "ungenericizing" things, which can reduce some of the template performance benefits.  Hence, we should build a tool that provides clear information on how much code is being generated so that we can go about fighting it on an as-needed basis.  At the moment there are only a handful of instantiations, so we can accept this as a "baseline" against which to monitor future growth.

Ideally, a tool would analyze a binary with symbols, like the js/shell, and, at the minimum, produce for each template function or member function of template class:
 - the number of instantiations
 - an argument tuple for each instantiation
 - the average binary size of each instantiation (I'm assuming low variance, but I could be wrong)