[LLVMdev] RFC: implicit null checks in llvm

[Reid Kleckner]

On Thu, Apr 23, 2015 at 3:31 PM, Andrew Trick <atrick at apple.com> wrote:
>
> It would be really nice to just emit a label next to an instruction and
> assume the stackmap entry will end up at the right address. I don’t think
> the backend can make that guarantee. Any Machine pass can insert
> instructions wherever it wants without looking for labels.
>
> I think labels are only employed just before code emission. Is there any
> existing example of labels being used earlier (I think GCRootLowering is
> the earliest)?
>

SelectionDAGBuilder::lowerInvokable() inserts EH_LABELs into the DAG for
normal invokes, and it more or less works out.

I don't know much about what transformations MI passes typically do, but my
guess is that you're concerned that some pass might re-schedule possibly
trapping operations inside the label range?
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