[llvm] [AMDGPU] Support bottom-up postRA scheduing. (PR #135295)

[Jay Foad via llvm-commits]

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+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -run-pass=postmisched -verify-misched -o - %s | FileCheck -check-prefix=TopDown %s
+# RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -run-pass=postmisched -misched-postra-direction=bottomup -verify-misched -o - %s | FileCheck -check-prefix=BottomUp %s
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jayfoad wrote:

Nit: it is more common for check prefixes to be all capitals:
```suggestion
# RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -run-pass=postmisched -verify-misched -o - %s | FileCheck -check-prefix=TOPDOWN %s
# RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -run-pass=postmisched -misched-postra-direction=bottomup -verify-misched -o - %s | FileCheck -check-prefix=BOTTOMUP %s
```

https://github.com/llvm/llvm-project/pull/135295