[llvm] [RISCV][VLOPT] Look through PHI instructions (PR #132236)

[Michael Maitland via llvm-commits]

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@@ -1340,6 +1341,17 @@ RISCVVLOptimizer::checkUsers(const MachineInstr &MI) const {
       continue;
     }
 
+    if (UserMI.isPHI() && PHISeen.insert(&UserMI).second) {
+      LLVM_DEBUG(dbgs() << "    Peeking through uses of PHI\n");
+      for (auto &PhiUse : MRI->use_operands(UserMI.getOperand(0).getReg())) {
+        // If UserMI has a PHI cycle, don't analyze it.
+        if (PhiUse.getParent() == &UserMI)
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michaelmaitland wrote:

I think I handle that case too in the if statement with the `insert` check. I added a test for it.

https://github.com/llvm/llvm-project/pull/132236