[PATCH] D53657: [DEBUG_INFO][NVPTX]Fix processing of DBG_VALUES.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added inline comments.


================
Comment at: lib/Target/NVPTX/NVPTXRegisterInfo.cpp:122-129
+  int Offset = MF.getFrameInfo().getObjectOffset(FrameIndex);
 
   // Using I0 as the frame pointer
-  MI.getOperand(FIOperandNum).ChangeToRegister(NVPTX::VRFrame, false);
+  MI.getOperand(FIOperandNum).ChangeToRegister(NVPTX::VRFrame, /*isDef=*/false);
+  // Special processing of dbg_value instructions.
+  if (!MI.isDebugValue())
+    Offset += MI.getOperand(FIOperandNum + 1).getImm();
----------------
tra wrote:
> I'm not sure I understand this change.  What is in getOperand(FIOperandNum + 1) for DebugValue instructions? Other instructions carry FI-based offset, but your change appears to ignore it and effectively treats it as if it's always zero.
> 
> It may be worth adding more details about *why* debug values need to be handled this way.
> 
DebugValue does not have FI-based offset. That's why it causes compiler crash. For DebugValue it is enough just to have the base object offset. 
Some other targets, like ARC, Thumb have same kind of processing.
Alternatively, we can use the code similar to one existing in `lib/CodeGen/PrologEpilogInserter.cpp` for special handling of the debug values:
```
      // Frame indices in debug values are encoded in a target independent
      // way with simply the frame index and offset rather than any
      // target-specific addressing mode.
      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(MF, MI.getOperand(0).getIndex(), Reg);
        MI.getOperand(0).ChangeToRegister(Reg, false /*isDef*/);
        MI.getOperand(0).setIsDebug();
        auto *DIExpr = DIExpression::prepend(MI.getDebugExpression(),
                                             DIExpression::NoDeref, Offset);
        MI.getOperand(3).setMetadata(DIExpr);
        continue;
      }

```


Repository:
  rL LLVM

https://reviews.llvm.org/D53657