Commit c2e62c7 updated the ReduceDIMetadata pass to be able to remove
DIGlobalVariableExpressions from MDNode operands; it also accidentally
prevented null operands from being preserved, which results in an
assertion being triggered:
`Targets == NoChunksCounter.count() && "number of chunks changes when
reducing"'
This patch allows us to correctly preserve null operands once again.
I've not got a test case for this yet - I'm hoping this patch is just
trivially correct as-is, because I've not got the hang of reducing a
test case for llvm-reduce yet, but I can get a test case generated if
needed.
58211f55c5