FTL should support CompareEq(String:, String:)

FTL should support CompareEq(String:, String:)
https://bugs.webkit.org/show_bug.cgi?id=154269
rdar://problem/24499921

Reviewed by Benjamin Poulain.

Looks like a slight pdfjs slow-down, probably because we're having some recompilations. I
think we should land the increased coverage first and fix the issues after, especially since
the regression is so small and doesn't have a statistically significant effect on the overall
score.

* ftl/FTLCapabilities.cpp:
(JSC::FTL::canCompile):
* ftl/FTLLowerDFGToLLVM.cpp:
(JSC::FTL::DFG::LowerDFGToLLVM::compileCompareEq):
(JSC::FTL::DFG::LowerDFGToLLVM::compileCompareStrictEq):
(JSC::FTL::DFG::LowerDFGToLLVM::nonSpeculativeCompare):
(JSC::FTL::DFG::LowerDFGToLLVM::stringsEqual):
* tests/stress/ftl-string-equality.js: Added.
* tests/stress/ftl-string-ident-equality.js: Added.
* tests/stress/ftl-string-strict-equality.js: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@196685 268f45cc-cd09-0410-ab3c-d52691b4dbfc