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

[Pierre van Houtryve via llvm-commits]

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@@ -772,7 +773,7 @@ void SIFoldOperands::foldOperand(
   if (UseMI->isRegSequence()) {
     Register RegSeqDstReg = UseMI->getOperand(0).getReg();
     unsigned RegSeqDstSubReg = UseMI->getOperand(UseOpIdx + 1).getImm();
-
+    static std::unordered_set<MachineInstr *> seenMI;
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Pierre-vh wrote:

Use a `DenseSet` instead (better for pointers) and `CamelCase` in var name

Also don't use a static var for this, use something you pass as argument and that's reset/recreated for every function, or use some field in the pass. You can even make the field `mutable` to avoid removing `const`

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