Sorry if there was any confusion earlier, but throw-on-OOB semantics is easier from an AOT/asm.js-compilation POV. Ideally, typed arrays would throw on all OOB, but I realize that isn't web compatible at this point.
On Wed, Feb 25, 2015 at 6:40 PM, Jeff Walden <jwalden...@mit.edu> wrote: > Currently, the behavior of IntegerIndexedElementSet is to return false if > the index being set is outside the array bounds. This return-false > directly feeds into the result of [[Set]] on a typed array. The result is > that in strict mode code, setting an out-of-bounds array element throws a > TypeError. > > I've heard claims from other SpiderMonkey implementers that this > requirement makes it difficult to implement high-performance JIT > optimizations for code that assigns into typed arrays, except in the case > that the array length is observable in context, the typed array never > escapes anywhere, its backing ArrayBuffer never escapes anywhere, etc. > Restrictions that generally aren't very easy to determine with local > information observable by a JIT. And while quite often such > high-performance code isn't strict mode code, it's doubtful that will be > true far into the future. > > From that point of view, it would be better if IntegerIndexedElementSet > just returned true in this case -- indicate success without doing > anything. What are the compelling reasons to not do this? > > Jeff >
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