Bytecode liveness analysis should have more lambdas and fewer sets

Bytecode liveness analysis should have more lambdas and fewer sets
https://bugs.webkit.org/show_bug.cgi?id=142647

Reviewed by Mark Lam.

Source/JavaScriptCore:

In bug 141174 I'll need to identify all of the bytecode kill sites. This requires hooking into
the bytecode analysis' stepOverFunction method, except in such a way that we observe uses that
are not in outs. This refactors stepOverFunction so that you can pass it use/def functors that
can either be used to propagate outs (as we do right now) or to additionally detect kills or
whatever else.

In order to achieve this, the liveness analysis was moved off of maintaining uses/defs
bitvectors. This wasn't helping the abstraction and was probably inefficient. The new code
should be a bit faster since we don't have to clear uses/defs bitvectors on each instruction. On
the other hand, being able to intercept each use means that our code for exception handlers is
no longer a bitwise-merge; it requires finding set bits. Fortunately, this code only kicks in
for instructions inside a try, and its performance is O(live at catch), so that's probably not
bad.

* bytecode/BytecodeLivenessAnalysis.cpp:
(JSC::indexForOperand):
(JSC::stepOverInstruction):
(JSC::computeLocalLivenessForBytecodeOffset):
(JSC::BytecodeLivenessAnalysis::computeFullLiveness):
(JSC::setForOperand): Deleted.
* bytecode/BytecodeUseDef.h:
(JSC::computeUsesForBytecodeOffset):
(JSC::computeDefsForBytecodeOffset):
* bytecode/CodeBlock.cpp:

Source/WTF:

Add a method for iterating each set bit in a FastBitVector. Uses a functor as a callback since
this allows for a more efficient algorithm.

* wtf/FastBitVector.h:
(WTF::FastBitVector::forEachSetBit):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@181467 268f45cc-cd09-0410-ab3c-d52691b4dbfc