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

[Luke Lau via llvm-commits]

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@@ -1340,6 +1340,13 @@ RISCVVLOptimizer::checkUsers(const MachineInstr &MI) const {
       continue;
     }
 
+    if (UserMI.isPHI()) {
+      LLVM_DEBUG(dbgs() << "    Peeking through uses of PHI\n");
+      for (auto &PhiUse : MRI->use_operands(UserMI.getOperand(0).getReg()))
+        Worklist.insert(&PhiUse);
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lukel97 wrote:

Do you have a test for a recurrence phi? I think locally I needed a "seen" set of pointers otherwise you ended up with infinite loops: https://github.com/lukel97/llvm-project/blob/a82b6466715ae03e5698a323cb2daae45dd2bded/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp#L1331-L1353

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