Updates:
Summary: Crankshaft should generate special case code for
Array.prototype.append where the receiver is not live after the call
Labels: Priority-Low Type-FeatureRequest
Comment #1 on issue 2117 by erik.corry: Crankshaft should generate special
case code for Array.prototype.append where the receiver is not live after
the call
http://code.google.com/p/v8/issues/detail?id=2117
Push will modify an existing array, while append creates a new one. This
bug report is thus complaining about the difference between an algorithm
that is O(n2) and one that is O(n log n) amortized. In order for the VM to
convert one algorithm to another it would have to recognize that the old
version of 'one' does not escape and is dead when you do
one = one.concat(record.one)
this is a pretty difficult optimization to do in JS, since any access to an
array element can at any time trigger a getter which can cause the
old 'one' array to be captured. But with the correct map checks I think it
could be done in Crankshaft.
Given that the bug report contains a reasonable workaround I don't think
this should have high priority. Note that apply has limits on the array
length (long arrays will trigger a stack overflow) so you may have to use a
loop if the input arrays have arbitrary length.
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