[llvm] Add metadata pointer regex substitution to MIR update script (PR #163253)

[via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 6
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saxlungs wrote:

Ah okay I follow. I will name the test to indicate that it's an AMDGPU-specific example then

https://github.com/llvm/llvm-project/pull/163253