[llvm] [RISCV][VLOPT] Allow users that are passthrus if tail elements aren't demanded (PR #124066)

[Luke Lau via llvm-commits]

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@@ -53,7 +53,7 @@ class RISCVVLOptimizer : public MachineFunctionPass {
   std::optional<MachineOperand> getMinimumVLForUser(MachineOperand &UserOp);
   /// Returns the largest common VL MachineOperand that may be used to optimize
   /// MI. Returns std::nullopt if it failed to find a suitable VL.
-  std::optional<MachineOperand> checkUsers(MachineInstr &MI);
+  std::optional<MachineOperand> checkUsers(const MachineInstr &MI);
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lukel97 wrote:

Needed to tweak the signature here since UserMI is const

https://github.com/llvm/llvm-project/pull/124066