llvm dev - May 2018 - How jump－table representated in DAG

Hi, all


I am  interested in how jump-table representated in DAG.
I find the method  visitJumpTable will Emit JumpTable node in the current MBB.
 visitJumpTableHeader - This function emits necessary code to produce index in
the JumpTable from switch case.
but how  switch case emits? 


I would like to make this clearly.


Thanks,
yaoxiao
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Hi Yao,

On Tue, May 22, 2018 at 4:30 AM, yao via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi, all
>
> I am  interested in how jump-table representated in DAG.
> I find the method  visitJumpTable will Emit JumpTable node in the current
> MBB.
>  visitJumpTableHeader - This function emits necessary code to produce index
> in the JumpTable from switch case.
> but how  switch case emits?
>
> I would like to make this clearly.
It sounds like you're already looking in the right places.

The switch lowering starts in SelectionDAGBuilder::visitSwitch which
analyses the switch and decides how to lower it. For jump tables, it
calls SelectionDAGBuilder::buildJumpTable which creates and populates
the JumpTable and JumpTableHeader

Hope this helps,
Hans