Assertion in MachineFrameInfo::getObjectOffset() when emitting debug info

[llvmbot]

Bugzilla Link	11105
Resolution	FIXED
Resolved on	Oct 11, 2011 08:12
Version	trunk
OS	Linux
Attachments	bugpoint-reduced-simplified.ll
Reporter	LLVM Bugzilla Contributor

Extended Description

Running llc at -O1 or above with the attached testcase results in the following assertion:

llc: /homelocal/richard/llvm_svn/include/llvm/CodeGen/MachineFrameInfo.h:378: int64_t llvm::MachineFrameInfo::getObjectOffset(int) const: Assertion `unsigned(ObjectIdx+NumFixedObjects) < Objects.size() && "Invalid Object Idx!"' failed.

[llvmbot]

The problem is as follows. In XCoreRegisterInfo::eliminateFrameIndex() we replace the frame index of a dbg_value machine instruction with the frame register and set the next operand to the offset:

// Special handling of DBG_VALUE instructions.
if (MI.isDebugValue()) {
MI.getOperand(i).ChangeToRegister(FrameReg, false /isDef/);
MI.getOperand(i+1).ChangeToImmediate(Offset);
return;
}

This results in the second operand of the dbg_value being set to the byte offset from the frame register.

However in CompileUnit::constructVariableDIE it seems to expect the second operand of dbg_value to be the frame index since it passes it to TargetFrameLowering::getFrameIndexReference:

if (DVInsn->getNumOperands() == 3) {
  if (DVInsn->getOperand(0).isReg()) {
    const MachineOperand RegOp = DVInsn->getOperand(0);
    const TargetRegisterInfo *TRI = Asm->TM.getRegisterInfo();
    if (DVInsn->getOperand(1).isImm() &&
        TRI->getFrameRegister(*Asm->MF) == RegOp.getReg()) {
      unsigned FrameReg = 0;
      const TargetFrameLowering *TFI = Asm->TM.getFrameLowering();
      int Offset = 
        TFI->getFrameIndexReference(*Asm->MF, 
                                    DVInsn->getOperand(1).getImm(), 
                                    FrameReg);

In the testcase in this bug the byte offset of the variable is larger than biggest frame index and so MachineFrameInfo::getObjectOffset() asserts.

[llvmbot]

Fixed in r141666 by implementing the emitFrameIndexDebugValue() and getDebugValueLocation() hooks.