[llvm] AMDGPU: Add testcase for materializing sgpr frame indexes (PR #101306)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> These tests written with inline asm constraints are extremely difficult to maintain in terms of retaining the original test scenario. At some point in the future, we are forced to modify them to avoid extreme register pressure (for instance patches like wwm-regalloc) or to make them compilable resulting in losing the purpose of the original test. 

Possibly, but not having tests is worse than having tests that need maintenance 

> Because these forced scenarios might disappear and thereafter, these handpicked volatile tests become irrelevant.

They'll never be irrelevant. We should always have torture tests like this. If there's a change they should be updated to maintain what they were testing 

https://github.com/llvm/llvm-project/pull/101306