[llvm] [DataLayout] Specialize the getTypeAllocSize() implementation (PR #156687)

[Nikita Popov via llvm-commits]

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nikic wrote:

Here we can see that this is not NFC. The reason is that this implementation does not always go through the size in bits, which may end up discarding high bits of the type. As such, the new implementation is technically "more correct". But really type sizes the overflow when converting bits <-> bytes are not really something we can sensibly support -- we should probably try to make the IR verifier reject these.

https://github.com/llvm/llvm-project/pull/156687