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

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``````````diff
diff --git a/llvm/lib/CodeGen/MachinePipeliner.cpp b/llvm/lib/CodeGen/MachinePipeliner.cpp
index b327ba890..ad6fd0d20 100644
--- a/llvm/lib/CodeGen/MachinePipeliner.cpp
+++ b/llvm/lib/CodeGen/MachinePipeliner.cpp
@@ -485,7 +485,8 @@ void MachinePipeliner::setPragmaPipelineOptions(MachineLoop &L) {
   }
 }
 
-bool hasPHICycle(const MachineBasicBlock *LoopHeader, const MachineRegisterInfo &MRI) {
+bool hasPHICycle(const MachineBasicBlock *LoopHeader,
+                 const MachineRegisterInfo &MRI) {
   DenseMap<unsigned, SmallVector<unsigned, 2>> PhiDeps;
   SmallSet<unsigned, 8> PhiRegs;
 
@@ -507,7 +508,7 @@ bool hasPHICycle(const MachineBasicBlock *LoopHeader, const MachineRegisterInfo
   SmallSet<unsigned, 8> Visited, RecStack;
 
   std::function<bool(unsigned)> DFS = [&](unsigned Reg) -> bool {
-  if (!PhiRegs.count(Reg))
+    if (!PhiRegs.count(Reg))
       return false;
     if (RecStack.count(Reg))
       return true;

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