Slow evaluation of large javascript sources (>1.4Mb) like extjs

Since Version 5.2.1 of QT the loading of large javascript libraries in webkit is really slow:

• 260ms on version 5.2.1
  + 1800ms on version 5.4.1 (same machine / same options)

I think this is a regression.

Here is a idea to speed up things:

in qtwebkit\Source\JavaScriptCore\jit\JIT.cpp line 77, replace
, m_labels( codeBlock ? codeBlock->numberOfInstructions() : 0 )
by
, m_labels( 0 ),

then line 178, insert this code in method privateCompileMainPass()
m_labels.resize( instructionCount );

This avoid an unnecessary creation of a large array of labels (175111 on extjs) each time the jit is created (this is a lazy init)

I can explain why if you need it