Comment #3 on issue 2179 by [email protected]: Breakpoint of not
executed function slows down javascript performance
http://code.google.com/p/v8/issues/detail?id=2179
Running the same code in d8 (slightly modified):
Debug = debug.Debug;
var BreakPointPerformance = function() {
}
BreakPointPerformance.prototype.breakFunc = function() {
return 0;
}
BreakPointPerformance.prototype.mathFunc = function() {
var a = Math.sqrt(Math.random());
return a;
}
BreakPointPerformance.prototype.runLoop = function() {
var start = new Date();
var b = 0;
for(var i=0;i<10000000;i++) {
b+=this.mathFunc();
}
print("time: " + (new Date() - start) + "ms");
}
var p = new BreakPointPerformance();
Debug.setBreakPoint(BreakPointPerformance.prototype.breakFunc, 1, 0);
p.runLoop();
takes ~680ms (vs. ~120ms without the breakpoint). In comparison, running
without crankshaft takes ~580ms, so this seems alright. Enabling debug mode
triggers a recompile of all code with the non-optimizing compiler (so that
loop-hoisting, inlining etc. that are not compatible with debugging are not
done.)
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