llvm dev - Dec 2016 - Handling argument for an intrinsic

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!

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*)
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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

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Hi Philip, thanks for the response. No, I don't need to vary the pseudo op
-- I did follow the other intrinsics but what happens now (after tinkering
some more) is that my instruction actually gets optimized out (after
debugging by showing the selection dag after various rounds of
optimization). It might help if I send a patch along -- I uploaded it to
phabricator with a link to selectiondagbuilder.

https://reviews.llvm.org/D27503#58aa05e8

On Fri, Dec 2, 2016 at 5:35 PM Philip Reames <listmail at
philipreames.com>
wrote:
> 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 listllvm-dev at
lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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