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

[vivek pandya via llvm-dev]

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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