[llvm-dev] Handling argument for an intrinsic

[Philip Reames via llvm-dev]

On 12/01/2016 04:01 PM, Louis Li via llvm-dev wrote:
> Hi, I'm trying to implement a target-agnostic intrinsic, first 
> targeting X86. I'm trying to map the intrinsic SD node to an 
> instruction with a certain target opcode that I've introduced. The 
> issue that I'm running into is what the correct way to lower the 
> argument is. I've done a couple loops on the docs so any help would be 
> appreciated!
I'm really confused by the way you're asking the question.  Assuming 
you're adding code to SelectionDAGBuilder, handling the argument should 
just be a getValue(Value*) call.  Take a look at the lowering for ctlz 
(or one of many other examples), how are your arguments different than 
what's done here?  Do you need to vary the psuedo op emitted depending 
on the argument or something like that?
>
> Some options I've explored but have been missing some crucial 
> step/concept:
> - tablegen matching?
> - SelectionDAGBuilder.cpp + BuildMI call (but then this runs into the 
> issue of lowering the argument correctly - not sure if that's feasible 
> at this point in instruction selection)
> - X86ISelLowering -- same confusion as above
>
> Here's how the dag currently looks (before erroring out, since I 
> haven't handled the intrinsic)
> https://drive.google.com/file/d/0B5G4m_mQneSjRWQzRVltdDJOQnM/view?usp=sharing
> Would it be problematic if I somehow extracted the pointer address arg 
> to the intrisic from TargetConstant and passed it as MachineOperand to 
> the MachineInstruction?
>
> Opcode definition (Target/Target.td)
> ==============
> +def PATCHABLE_LOG_CALL : Instruction {
> +  let OutOperandList = (outs);
> +  let InOperandList = (ins unknown:$entry);
> +  let AsmString = "# XRay Custom Log.";
> +  let usesCustomInserter = 1;
> +  let hasSideEffects = 1;
> +}
>
> Example IR for the graph above
> ===========
> define i32 @caller() nounwind noinline uwtable 
> "function-instrument"="xray-always" {
>     %logentryptr = alloca i8
>     call void @llvm.xray.customlog(i8* %logentryptr)
>     ret i32 0
> }
>
> declare void @llvm.xray.customlog(i8*)
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161202/cf1cf3cf/attachment.html>