https://bugs.webkit.org/show_bug.cgi?id=118152

Reviewed by Mark Hahnenberg.

There are a bunch of things we can do when we know where the loops are.
Previously we didn't. With this patch, we do.

This patch adds the classic dominator based natural loop finder.

The only client of this right now is the DFG::Disassembler. It prints out
a summary of the analysis for each block.

This will become more important when I do
https://bugs.webkit.org/show_bug.cgi?id=118151, which definitely requires
this kind of analysis, at least if we want to do the optimization over
DFG IR (and I'm pretty sure we do).

* JavaScriptCore.xcodeproj/project.pbxproj:
* dfg/DFGAnalysis.h: Added.
(DFG):
(Analysis):
(JSC::DFG::Analysis::Analysis):
(JSC::DFG::Analysis::invalidate):
(JSC::DFG::Analysis::computeIfNecessary):
(JSC::DFG::Analysis::isValid):
* dfg/DFGCFGSimplificationPhase.cpp:
(JSC::DFG::CFGSimplificationPhase::run):
* dfg/DFGDisassembler.cpp:
(JSC::DFG::Disassembler::createDumpList):
* dfg/DFGDominators.cpp:
(JSC::DFG::Dominators::Dominators):
(JSC::DFG::Dominators::compute):
* dfg/DFGDominators.h:
(Dominators):
* dfg/DFGGraph.cpp:
(JSC::DFG::Graph::dumpBlockHeader):
(JSC::DFG::Graph::invalidateCFG):
(DFG):
* dfg/DFGGraph.h:
(Graph):
* dfg/DFGNaturalLoops.cpp: Added.
(DFG):
(JSC::DFG::NaturalLoop::dump):
(JSC::DFG::NaturalLoops::NaturalLoops):
(JSC::DFG::NaturalLoops::~NaturalLoops):
(JSC::DFG::NaturalLoops::compute):
(JSC::DFG::NaturalLoops::loopsOf):
(JSC::DFG::NaturalLoops::dump):
* dfg/DFGNaturalLoops.h: Added.
(DFG):
(NaturalLoop):
(JSC::DFG::NaturalLoop::NaturalLoop):
(JSC::DFG::NaturalLoop::addBlock):
(JSC::DFG::NaturalLoop::header):
(JSC::DFG::NaturalLoop::size):
(JSC::DFG::NaturalLoop::at):
(JSC::DFG::NaturalLoop::operator[]):
(JSC::DFG::NaturalLoop::contains):
(NaturalLoops):
(JSC::DFG::NaturalLoops::numLoops):
(JSC::DFG::NaturalLoops::loop):
(JSC::DFG::NaturalLoops::headerOf):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153257 268f45cc-cd09-0410-ab3c-d52691b4dbfc