[llvm] [FuzzMutate] Prevent the mutator from generating illegal memory operations (PR #144885)

[Peter Rong via llvm-commits]

DataCorrupted wrote:

Can you attach an AMDGCN specific test case? IIUC the `isAMDGCN` branch you added won't be tested by current test cases at all.

https://github.com/llvm/llvm-project/pull/144885