[LLVMdev] Making Sense of ISel DAG Output

[Dan Gohman]

On Fri, October 3, 2008 9:10 am, David Greene wrote:
> On Thursday 02 October 2008 19:32, Dan Gohman wrote:
>
>> Looking at your dump() output above, it looks like the pre-selection
>> loads have multiple uses, so even though you've managed to match a
>> larger pattern that incorporates them, they still need to exist to
>> satisfy some other users.
>
> Yes, I looked at that too.  It looks like these other uses end up being
> chains to TokenFactor nodes that don't go anywhere.  They're really,
> truly,
> dead.  Who is supposed to clean those up?

DAGCombine will zap dead nodes, but nodes can also become dead
during selection. Some parts of selection know how to clean up
nodes that become dead during selection, but my guess is that
it's missing some cases.

Dan