[llvm-dev] Indices for extractvalue and insertvalue

[Xin Tong via llvm-dev]

Hi

Can someone explain to me why we cant use uint64_t for extractvalue
and insertvalue indices, while GEP on arrays can have indices of any
integer type. Basically if I load an array with UINT_MAX+O (O>=2)
elements, I can not extract its last element.

Given this restriction I feel we have a bug here (uint64_t is passed
as a unsigned). This cant happen because of the if (NumElements >
1024) guard, but its a bug anyways.

https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp#L634

Thanks,
-Xin
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[Reid Kleckner via llvm-dev]

I think originally insertvalue / extractvalue were only intended to work on struct values. LLVM struct types can have up to 2**32 element types, and the insertvalue/extractvalue indices match that.

I hope people aren't actually trying to load a >4GB array and hoping to do something good with it.

[Xin Tong via llvm-dev]

That makes sense.

Then it seems to me that there is some unclearness about what the
language ref says, i.e.
http://llvm.org/docs/LangRef.html#extractvalue-instruction says
extractvalue indices work in a similar manner as indices for
getelementptr, and what the the compiler supports (extractvalue
indices are unsigned or smaller while getelementptr indices can be
uint64_t).

What would be the problem if we make extractvalue and insertvalue use
uint64_t indices, other than the compiler potentially uses a bit more
memory ?

-Xin