[NVPTX] Backend crash on byval reference to external constant

[jhuber6]

The following code was regressed since the LLVM 20 release and now crashes in the libc test suite. The reproducer is at https://godbolt.org/z/Pjc4nT88P. If you remove the byval it works, so I'm assuming that's where the error lies.

[jhuber6]

@AlexMaclean Was anything here changed recently? Trying to get the libc tests back to green.

[AlexMaclean]

I've just confirmed locally that #138015 will fix this.

The problem is that in NVPTXISelDAGtoDAG we fail to account for the fact that N->getMemOperand()->getValue() may return a nullptr. This underlying issue was exposed by 56910a8 which improved address-space propagation for byval, allowing the logic in NVPTXISelDAGtoDAG to progress further.

llvm-project/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp

Line 801 in 4768173

getUnderlyingObjects(N->getMemOperand()->getValue(), Objs);

[jhuber6]

I've just confirmed locally that #138015 will fix this.

The problem is that in NVPTXISelDAGtoDAG we fail to account for the fact that N->getMemOperand()->getValue() may return a nullptr. This underlying issue was exposed by 56910a8 which improved address-space propagation for byval, allowing the logic in NVPTXISelDAGtoDAG to progress further.

llvm-project/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp

Line 801 in 4768173
getUnderlyingObjects(N->getMemOperand()->getValue(), Objs);

SG, please merge when you can so that the libc tests are green again.