This patch adds a fast path to the PutByValue bytecode op that bypasses
a ton of things *if* a set of assumptions hold:
- The property key must be a non-negative Int32
- The base object must not interfere with indexed property access
- The base object must have simple indexed property storage
- The property key must already be present as an own property
- The existing value must not have any accessors defined
If this holds (which it should in many common cases), we can skip all
kinds of checks and poke directly at the property storage, saving time.
16% speed-up on the entire Kraken benchmark :^)
(including: 88% speed-up on Kraken/imaging-desaturate.js)
(including: 55% speed-up on Kraken/audio-fft.js)
(including: 54% speed-up on Kraken/audio-beat-detection.js)
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