DFG should compile a little sooner
https://bugs.webkit.org/show_bug.cgi?id=113835

Reviewed by Michael Saboff.

2% speedup on SunSpider.

2% speedup on JSRegress.

Neutral on Octane, v8, and Kraken.

The worst-hit single sub-test is kraken-stanford-crypto-ccm.js, which gets
18% slower. Since Kraken is neutral overall in its preferred mean, I
think that's OK for now.

(Our array indexing speculation fails pathologically on
kraken-stanford-crypto-ccm.js. Compiling sooner is a regression because
it triggers those failures sooner. I'm going to file some follow-up bugs
explaining how to fix our speculations on this sub-test, at which point
compiling earlier should become a slight speedup on Kraken overall.)

* bytecode/CodeBlock.cpp:
(JSC::CodeBlock::optimizationThresholdScalingFactor): I experimented
with a few different options, including reducing the coefficient 'a'.
A simple linear reduction on instruction count worked best.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147511 268f45cc-cd09-0410-ab3c-d52691b4dbfc