[llvm] [AMDGCN] Allow unscheduling of bundled insns (PR #129769)

[Matt Arsenault via llvm-commits]

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+; RUN: llc -mtriple=amdgcn -mcpu=gfx90a -verify-machineinstrs -O1 -stop-after=machine-scheduler < %s | FileCheck -check-prefix=DEBUG %s
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arsenm wrote:

Don't need -verify-machieninstrs. Does this really require -O1 specifically? 

Probably should also include a mir test that only runs scheduling (and pick an explicit scheduler strategy)

https://github.com/llvm/llvm-project/pull/129769