[PATCH] D147506: [DebugLine] save one debug line entry for empty prologue

[ChenZheng via Phabricator via llvm-commits]

shchenz added a comment.

> That way if two recordSourceLine calls happen with no instruction between them, no emitDwarfLocDirective is called - but on the next insntruction that's emitted, the source line info would be emitted at that point.

  recordSourceLine() {
    this->lineInfo = {line, file};
  }
  beginInstruction() {
    if (this->lineInfo) {
      emitDwarfLocDirective(this->lineInfo)
      this->lineInfo = std::nullopt;
    }
    ...
  }

Thanks! I know your point now. This should be able to handle duplicated lines for the empty prologue case. But seems it also has same issue for the case when generating `loc` for instructions. (Currently, when starting to handle instructions, `recordSourceLine` is always called by a new instruction emitting, so there are always instructions between two `recordSourceLine()` calls in `beginInstruction()`). For example:

  Inst1;  // line1
  Inst2;  // line2

When handle `Inst1`, in the `DwarfDebug::beginInstruction()`, the line info for `Inst1` is cached to `this->lineInfo()` in `recordSourceLine()` and then `Inst1` is emitted to assembly file. This delay will cause issue, `loc` for `Inst1` is supposed to be in front of `Inst1`. Even at the very beginning of `beginInstruction()` for `Instr2`, we call `emitDwarfLocDirective()` for `Inst1`, it is still put the `.loc` after `Inst1`.


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  https://reviews.llvm.org/D147506/new/

https://reviews.llvm.org/D147506