[llvm-dev] Selection DAG adding node question

[Ryan Taylor via llvm-dev]

It is my understanding that you cannot create a clone in the DAG. This is
due to common sub tree from what I understand.

This is a problem for direct mem architectures, seems more and more people
are having issues with this but it can be worked around.

LLVM assumes a LD/ST architecture.

I'd love to hear otherwise.

-Ryan

On Wed, Oct 12, 2016 at 12:31 PM, SiliconValleyEmployee - via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I am having trouble adding a node to the selection DAG (e.g. during
> combine)
>
> E.g. node1 -> use1, use2
>
> Now if you add a node2, with node1 -> node2 with node2 number of output
> values equal node1 number of output values, then combine as well as e.g.
> promotion pass with replace all of node1's uses with node2, leaving node1
> dead. While this is kind of expected, does this mean
>
> a) always create new node (can you clone node, e.g. node1 above)?
> b) is this something that selection DAG is not intended for at all?
> c) sometimes it is not straight forward to create a new load, e.g. for
> loads, as DAG.getLoad will return "old" node if identical => a) can I clone
> a node?
>
> Thanks! Hendrik
>
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