Just like what is done for getprop we can look to the baseline caches to decide to use monomorphic/polymorphic instruction. Atm for GWT linpack we are at 2.74s. Quick and dirty implementing this monomorphic thing for getelem improves the score to 2.1s (30% faster). Couldn't test it quickly for setelem. But if it has the same improvement we will be at 1.6s (comparison: chrome is at 1s).
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