[clang] [Clang][MicrosoftMangle] Implement mangling for ConstantMatrixType (PR #134930)

[Reid Kleckner via cfe-commits]

rnk wrote:

We do a similar mangling for our extended vector types, so I would start by copying the clang/test/CodeGenCXX/mangle-ms-vector-types.cpp file to mangle-ms-matrix.cpp, and add a second RUN line that pipes the result to `llvm-cxxfilt` and uses a second FileCheck invocation to validate that the right names come back. Hopefully that is enough info to get started. :)

https://github.com/llvm/llvm-project/pull/134930