[llvm] [AMDGPU] Prevent cyclic behaviour in SIFoldOperands (PR #82099)

[Pierre van Houtryve via llvm-commits]

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@@ -783,6 +784,10 @@ void SIFoldOperands::foldOperand(
       if (RSUse.getSubReg() != RegSeqDstSubReg)
         continue;
 
+      if (seenMI.count(RSUseMI) != 0)
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Pierre-vh wrote:

If using `DenseSet` this just becomes `contains(RSUseMI)`


https://github.com/llvm/llvm-project/pull/82099