Slow-Code-Detector

Tool to show slow calls in your code runned by v8.

Install

npm i -g slow-code-detector

How to use

scd your-index-js-file.js – it creates bunch of files in current directory code.asm hydrogen.cfg out.txt code.html

code.html – is what you need, open it in the browser.

Also you can generate markdown file code.md, just run with --md option: scd --md index.js

Generated code.html groupped by files and functions.

code.html

Every runtime call highlighted by gray. Call cost ~4ns.

Pink highlight is LoadGeneric or StoreGeneric. Generic read or write cost ~9ns.

If function in code is inlined it highlighted by blue, you can show its code by click.

If function is not inlined you can show non inline reason by a hint on call function name.

If function deoptimized, it colored by red.

Every function reoptimization marked by ~recompile~ – max 10 times, else deopt: Optimize too many times

How it works

The scd execute node with some v8 trace options and parse given logs to find slow path calls.

node --trace-inlining --trace-hydrogen --trace-phase=Z --trace-deopt

IRHydra

You can use hydrogen.cfg and code.asm with IRHydra to investigate internal representation of your code