[PATCH] D45341: [DebugInfo] Convert intrinsic llvm.dbg.label to MachineInstr.

[Hsiangkai Wang via Phabricator via llvm-commits]

HsiangKai added a comment.

In https://reviews.llvm.org/D45341#1060380, @aprantl wrote:

> Thanks, this looks mostly fine! Have you considered just allowing the DBG_VALUE MachineInstr to carry a DILabel insetad of just DILocalVariables? Would that simplify the code or make it harder to understand?


The formats of DBG_VALUE are

DBG_VALUE Reg, 0, DILocalVariable, DIExpression
DBG_VALUE FrameIndex, Imm, DILocalVariable, DIExpression
DBG_VALUE Imm, Imm, DILocalVariable, DIExpression

When processing DBG_VALUE, there are assumptions about these operands. Take a snippet from lib/CodeGen/PrologEpilogInserter.cpp as an example,

if (MI.isDebugValue()) {

  assert(i == 0 && "Frame indices can only appear as the first "
                   "operand of a DBG_VALUE machine instruction");
  unsigned Reg;
  int64_t Offset =
      TFI->getFrameIndexReference(Fn, MI.getOperand(0).getIndex(), Reg);
  MI.getOperand(0).ChangeToRegister(Reg, false /*isDef*/);
  auto *DIExpr = DIExpression::prepend(MI.getDebugExpression(),
                                       DIExpression::NoDeref, Offset);
  MI.getOperand(3).setMetadata(DIExpr);
  continue;

}

If we add the possibility of operand(0) as DILabel, it will complicate the implementation.

I think to create DBG_LABEL is easier to understand and easier to maintain.


Repository:
  rL LLVM

https://reviews.llvm.org/D45341