[llvm] [MachinePipeliner] Fix fragile tests (PR #123169)

[Ryotaro Kasuga via llvm-commits]

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+# RUN: llc -mtriple=hexagon -mcpu=hexagonv73 -O2 -mattr=+hvxv73,hvx-length64b \
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kasuga-fj wrote:

Added a new test `swp-initiation-interval.mir` to verify that the pipeline is applied. Is it enough to check the initiation interval? If a small change in the order of instructions is acceptable, I would prefer to avoid making sure that the schedule results match perfectly.

https://github.com/llvm/llvm-project/pull/123169