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LLVM backend for 6502
1f0cde9fd7
There are two main reasons why a linked-list makes sense for
`DIEValueList`.
1. We want `DIE` to be on a `BumpPtrAllocator` to improve teardown
efficiency. Making `DIEValueList` array-based would make that much
more complicated.
2. The singly-linked list is fairly memory efficient. The histogram
[1] shows that most DIEs have relatively few values, so we often pay
less than the 2/3-pointer static overhead of a vector. Furthermore,
we don't know ahead of time exactly how many values a `DIE` needs,
so a vector-like scheme will on average over-allocate by ~50%. As
it happens, that's the same memory overhead as the linked list node.
[1]: http://lists.cs.uiuc.edu/pipermail/llvmdev/2015-May/085910.html
The comment I added to the code is a little more succinct, but I think
it's enough to give the idea.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240868 91177308-0d34-0410-b5e6-96231b3b80d8
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