[llvm-dev] How to inhibit jump table range check

[bagel via llvm-dev]

Thank you for your prompt reply.  I will take a look at what you have done and 
hopefully it will work for me.  I would have preferred to eliminate the range 
check at the point where it was generated instead of adding a pass later to 
eliminate it.  But I guess we have to live with what ever the implementers of 
the two major architectures allow us to do.

Regards,
brian

On 6/20/20 12:52 AM, Thomas Lively wrote:
> Hi Brian,
> 
> I actually solved this exact problem for the upstream WebAssembly backend in 
> the last couple of weeks. I was originally going to use the OmitRangeCheck 
> field, but after prompting from my reviewers on 
> https://reviews.llvm.org/D80778 I ended up removing the range checks in the 
> backend instead. You can see the pass I added to do that here: 
> https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp I 
> think it probably wouldn't be too hard to adapt that pass to a different 
> backend, but feel free to reach out if you have any questions about it!
> 
> Best,
> 
> Thomas
> 
> On Fri, Jun 19, 2020 at 12:55 PM Bagel via llvm-dev <llvm-dev at lists.llvm.org 
> <mailto:llvm-dev at lists.llvm.org>> wrote:
> 
>     I am working on a back end for an architecture whose jump via table
>     instruction
>     includes the range check.  Therefore I don't need the range check
>     generated (in
>     SelectionDAGBuilder ?).
> 
>     There appears to be a struct JumpTableHeader which contains a field
>     OmitRangeCheck which, when true, does what I want.  However, there doesn't
>     appear to be a mechanism for a back end to set it.
> 
>     Anyone have any ideas?
> 
>     Thanks,
>     brian
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