[llvm] [RISCV][VLOPT] Compute demanded VLs up front (PR #124530)

[Michael Maitland via llvm-commits]

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@@ -1285,9 +1290,9 @@ std::optional<MachineOperand> RISCVVLOptimizer::checkUsers(MachineInstr &MI) {
 bool RISCVVLOptimizer::tryReduceVL(MachineInstr &MI) {
   LLVM_DEBUG(dbgs() << "Trying to reduce VL for " << MI << "\n");
 
-  auto CommonVL = checkUsers(MI);
-  if (!CommonVL)
+  if (!DemandedVLs.contains(&MI))
     return false;
+  auto CommonVL = std::make_optional(DemandedVLs.at(&MI));
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michaelmaitland wrote:

Are we just using CommonVL as an optional that always has a value below? I think we could be using it as a MachineOperand.

https://github.com/llvm/llvm-project/pull/124530