[LLVMdev] LLVM IR in DAG form

[Jeehoon Kang]

Hi all,
this is Jeehoon Kang, a CS PhD student and a newbie to LLVM.

I am wondering why LLVM IR's basic block consists of a list of instructions,
rather than a DAG of instruction as in the low level (ISelectionDAG).

My gut feeling tells me that LLVM IR in DAG form may admit more
optimisations in a systematic manner. This is because data dependence is
more explicit in a DAG of instructions than in a list of those.

However, I found an exact opposite proposal: removing DAG structure at all (
http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-April/061238.html). I am a
newbie to LLVM (and compiler in general), so I could not understand the
rationale behind the proposal.

Would you please give me some advice on this matter?

Thanks,
Jeehoon

-- 
Jeehoon Kang (Ph.D. student) <http://sf.snu.ac.kr/jeehoon.kang>
Software Foundations Laboratory <http://sf.snu.ac.kr>
Seoul National University <http://www.snu.ac.kr>
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