[llvm] [MachinePipeliner] Detect a cycle in PHI dependencies early on (PR #167095)

[Ryotaro Kasuga via llvm-commits]

================
@@ -0,0 +1,22 @@
+; RUN: llc -mtriple=hexagon-unknown-linux-gnu -enable-pipeliner -debug-only=pipeliner < %s 2>&1 | FileCheck %s
----------------
kasuga-fj wrote:

```suggestion
; RUN: llc -mtriple=hexagon-unknown-linux-gnu -enable-pipeliner -debug-only=pipeliner < %s 2>&1 | FileCheck %s
; REQUIRES: asserts
```

It's necessary to check debug output.

https://github.com/llvm/llvm-project/pull/167095