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499fc0976b
The IPDL compiler generates code like this in DestroySubtree methods:
// Recursively shutting down PAPZ kids
nsTArray<PAPZChild*> kids((mManagedPAPZChild).Count());
// Accumulate kids into a stable structure to iterate over
ManagedPAPZChild(kids);
for (uint32_t i = 0; (i) < ((kids).Length()); (++(i))) {
// Guarding against a child removing a sibling from the list during the iteration.
if ((mManagedPAPZChild).Contains(kids[i])) {
(kids[i])->DestroySubtree(subtreewhy);
}
}
There are three problems with this code:
1) We initialize |kids| with a capacity, which is wasted work;
ManagedPAPZChild() is going to resize the array for us anyway.
2) We're constantly reading from |kids.Length()| in the loop, when we
only really need to read from it once.
3) We're repeatedly accessing kids[i], and doing needless bounds checks.
Let's fix those three problems.