llvm dev - Sep 2021 - opt -dot-callgraph filename on windows

I'm trying to generate a callgraph with clang++ -Iinclude -std=c++17 -S
-emit-llvm demo.cpp -o - | opt -analyze -dot-callgraph but I am getting the
following error:

Writing '<stdin>.callgraph.dot'...  error opening file for
writing!
Printing analysis 'Print call graph to 'dot' file':
Pass::print not implemented for pass: 'Print call graph to 'dot'
file'!

I'm using clang 12 on windows. I cannot find a way to supply an alternative
filename (-o doesn't seem to work). Have I missed something in the docs or
is this not supported? Either way, this may be enhancement / bug worthy.

Thank you,
Jeremy
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