Invariant hoisting for CheckFixedFields
Invariant hoisting for CheckFixedFields

Fixed initial value loading and loop invariant hoisting to enable hoisting of CheckFixedFields.
Improves a few benchmarks in Octane (0.6% overall): DeltaBlue 3.2%, Mandreel 1.6%, Richards 2.2%, Splay 3.5%

Microsoft/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore