https://bugs.webkit.org/show_bug.cgi?id=126047

Reviewed by Filip Pizlo.

* dfg/DFGSpeculativeJIT.cpp:
(JSC::DFG::SpeculativeJIT::storeToWriteBarrierBuffer): Use the register allocator to 
determine which registers need saving instead of saving every single one of them.
(JSC::DFG::SpeculativeJIT::osrWriteBarrier): We don't need to save live register state 
because the write barriers during OSR execute when there are no live registers. Also we  
don't need to use pushes to pad the stack pointer for pokes on x86; we can just use an add.
(JSC::DFG::SpeculativeJIT::writeBarrier):
* dfg/DFGSpeculativeJIT.h:
* jit/Repatch.cpp:
(JSC::emitPutReplaceStub):
(JSC::emitPutTransitionStub):
* runtime/VM.h: Get rid of writeBarrierRegisterBuffer since it's no longer used.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160919 268f45cc-cd09-0410-ab3c-d52691b4dbfc