Worked on the ROCm/llvm-project repository to enhance the stability and correctness of the AArch64 backend, focusing on compiler reliability. Addressed a bug in the AArch64PostCoalescerPass by ensuring that the 'undef' flag is properly propagated when registers are replaced, which prevents undefined flag loss and reduces compilation crashes. Introduced a new field in AArch64MachineFunctionInfo to accurately track streaming mode changes, supporting correct context propagation. The solution involved updating all uses of a destination register when the source is undefined, improving code generation stability. Utilized C++, LLVM IR, and expertise in AArch64 architecture and LLVM pass development throughout the process.