[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:

Oops I forgot to add context to that link. That branch is a WIP patch I have that generalizes the RISCVVLOptimizer pass to a dataflow analysis. I originally added it because I thought we needed to handle recurrences when removing vp intrinsics. But I didn't pursue it any further because it didn't have any impact on SPEC.

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