https://bugs.webkit.org/show_bug.cgi?id=117920

Source/JavaScriptCore:

Reviewed by Sam Weinig.

This is a 20% speed-up for string equality comparisons when both strings are
identifiers.

This is important for two reasons:

1) Using strings as enumerations is an idiom. A great example is typeof. It
   would be great if this performed better.

2) When I implement switch_string in the DFG, it would be great to optimize
   the case where the switched-on value is an identifier. That would involve
   a simple binary switch rather than a more complicated trie-switch over
   characters.

* bytecode/SpeculatedType.cpp:
(JSC::dumpSpeculation):
(JSC::speculationToAbbreviatedString):
(JSC::speculationFromCell):
* bytecode/SpeculatedType.h:
(JSC):
(JSC::isStringIdentSpeculation):
(JSC::isStringSpeculation):
* dfg/DFGAbstractState.cpp:
(JSC::DFG::AbstractState::executeEffects):
* dfg/DFGFixupPhase.cpp:
(JSC::DFG::FixupPhase::fixupNode):
* dfg/DFGNode.h:
(JSC::DFG::Node::shouldSpeculateStringIdent):
(Node):
* dfg/DFGSpeculativeJIT.cpp:
(JSC::DFG::SpeculativeJIT::compilePeepHoleBranch):
(JSC::DFG::SpeculativeJIT::compare):
(JSC::DFG::SpeculativeJIT::compileStrictEq):
(JSC::DFG::SpeculativeJIT::compileStringEquality):
(JSC::DFG::SpeculativeJIT::compileStringIdentEquality):
(DFG):
(JSC::DFG::SpeculativeJIT::speculateString):
(JSC::DFG::SpeculativeJIT::speculateStringIdentAndLoadStorage):
(JSC::DFG::SpeculativeJIT::speculateStringIdent):
(JSC::DFG::SpeculativeJIT::speculate):
* dfg/DFGSpeculativeJIT.h:
(SpeculativeJIT):
* dfg/DFGUseKind.cpp:
(WTF::printInternal):
* dfg/DFGUseKind.h:
(JSC::DFG::typeFilterFor):
(JSC::DFG::isCell):

LayoutTests:

Reviewed by Sam Weinig.

Add a benchmark for string equality where there is a long identifier, and
also add a benchmark for non-identifier string equality (since the previous
test for string equality was really identifier equality).

* fast/js/regress/script-tests/string-long-ident-equality.js: Added.
(foo):
* fast/js/regress/script-tests/string-var-equality.js: Added.
(addFoo):
(foo):
* fast/js/regress/string-long-ident-equality-expected.txt: Added.
* fast/js/regress/string-long-ident-equality.html: Added.
* fast/js/regress/string-var-equality-expected.txt: Added.
* fast/js/regress/string-var-equality.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153245 268f45cc-cd09-0410-ab3c-d52691b4dbfc