Use correct VL operand with masked vleff

Author: lukel97

llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp

@@ -1470,7 +1470,7 @@ bool RISCVVLOptimizer::tryReduceVL(MachineInstr &MI) const {
     const MachineInstr *VLMI = MRI->getVRegDef(CommonVL->getReg());
     if (RISCVInstrInfo::isFaultOnlyFirstLoad(*VLMI) &&
         !MDT->dominates(VLMI, &MI))
-      CommonVL = VLMI->getOperand(4);
+      CommonVL = VLMI->getOperand(RISCVII::getVLOpNum(VLMI->getDesc()));
   }
 
   if (!RISCV::isVLKnownLE(*CommonVL, VLOp)) {

llvm/test/CodeGen/RISCV/rvv/vl-opt.mir

@@ -649,4 +649,15 @@ body: |
     %y:vr, %vl:gprnox0 = PseudoVLE8FF_V_M1 $noreg, $noreg, %avl, 3 /* e8 */, 3 /* ta, ma */
     PseudoVSE8_V_M1 %x, $noreg, %vl, 3 /* e8 */
 ...
-
+---
+name: vleff_mask_imm
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: vleff_mask_imm
+    ; CHECK: %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, 1, 3 /* e8 */, 3 /* ta, ma */
+    ; CHECK-NEXT: %y:vrnov0, %vl:gprnox0 = PseudoVLE8FF_V_M1_MASK $noreg, $noreg, $noreg, 1, 3 /* e8 */, 3 /* ta, ma */
+    ; CHECK-NEXT: PseudoVSE8_V_M1 %x, $noreg, %vl, 3 /* e8 */
+    %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 3 /* ta, ma */
+    %y:vrnov0, %vl:gprnox0 = PseudoVLE8FF_V_M1_MASK $noreg, $noreg, $noreg, 1, 3 /* e8 */, 3 /* ta, ma */
+    PseudoVSE8_V_M1 %x, $noreg, %vl, 3 /* e8 */
+...