[llvm] [AMDGPU] Add MachineVerifer check to detect illegal copies from VGPR to SGPR (PR #105494)

[Aditi Medhane via llvm-commits]

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+# RUN: not --crash llc  -mtriple=amdgcn -mcpu=gfx900 -verify-machineinstrs -run-pass=si-fix-sgpr-copies -o - %s 2>&1 | FileCheck -check-prefix=GCN %s
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AditiRM wrote:

In this specific testcase(phi-vgpr-input-moveimm.mir) it is throwing illegal copy error as expected, and it is because isSSA considers subreg defs invalid in SSA. So I have extracted the specific subtest & converted it into not crash. Please let me know if this is valid.

Reference : https://github.com/llvm/llvm-project/blob/main/llvm/lib/CodeGen/MIRParser/MIRParser.cpp#L361

https://github.com/llvm/llvm-project/pull/105494