[llvm-dev] Help required, Target Specifc SDNode getting optimized by ISel DAG

[Krzysztof Parzyszek via llvm-dev]

Hi Vivek,
Make sure that you return the correct chain from LowerReturn.

-Krzysztof


On 2/22/2017 7:17 AM, vivek pandya via llvm-dev wrote:
> Hello LLVM Devs,
>
> I am trying to compile following simple program for an experimental backend
>
> int main()
> {
>    printf("Hello World \n");
>     return 0;
> }
>
> I have added code to lower return instruction in the backend however in
> assembly I don't find return instruction generated.
> In the debug-only=isel dump I can see that my target specific SDNode for
> RET_FLAG is added but it gets removed during DAG
> optimization phase.
>
>
> Initial selection DAG: BB#0 'main:entry'
> SelectionDAG has 18 nodes:
>   t5: i32 = GlobalAddress<i32 (i8*, ...)* @printf> 0
>         t0: ch = EntryToken
>       t4: ch = store<ST4[%retval]> t0, Constant:i32<0>,
> FrameIndex:i32<0>, undef:i32
>     t8: ch,glue = callseq_start t4, TargetConstant:i32<0>
>
>   t10: ch,glue = CopyToReg t8, Register:i32 %R5, GlobalAddress:i32<[14 x
> i8]* @.str> 0
>   t12: ch,glue = DummyArchISD::CALL t10, TargetGlobalAddress:i32<i32
> (i8*, ...)* @printf> 0, Register:i32 %R5, t10:1
>   t13: ch,glue = callseq_end t12, TargetConstant:i32<0>,
> TargetConstant:i32<0>, t12:1
>     t15: i32,ch,glue = CopyFromReg t13, Register:i32 %R3, t13:1
>
>   t16: ch,glue = CopyToReg t15:1, Register:i32 %R3, Constant:i32<0>
>
>   t17: ch = DummyArchISD::RET_FLAG t16, Register:i32 %R3, t16:1
>
>   t15: i32,ch,glue = CopyFromReg t13, Register:i32 %R3, t13:1
>
>
> Optimized lowered selection DAG: BB#0 'main:entry'
> SelectionDAG has 15 nodes:
>         t0: ch = EntryToken
>       t4: ch = store<ST4[%retval]> t0, Constant:i32<0>,
> FrameIndex:i32<0>, undef:i32
>     t8: ch,glue = callseq_start t4, TargetConstant:i32<0>
>
>   t10: ch,glue = CopyToReg t8, Register:i32 %R5, GlobalAddress:i32<[14 x
> i8]* @.str> 0
>   t12: ch,glue = DummyArchISD::CALL t10, TargetGlobalAddress:i32<i32
> (i8*, ...)* @printf> 0, Register:i32 %R5, t10:1
>   t13: ch,glue = callseq_end t12, TargetConstant:i32<0>,
> TargetConstant:i32<0>, t12:1
>   t15: i32,ch,glue = CopyFromReg t13, Register:i32 %R3, t13:1
>
>
>
> Can someone please guide me how to furhter debug this situation? Or any
> hints.
>
> Sincerely,
> Vivek
>
>
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