Ignore LIs

Author: lukel97

llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp

@@ -1422,7 +1422,8 @@ getMinimumVLForVSLIDEDOWN_VX(const MachineOperand &UserOp,
     return std::nullopt;
   MachineInstr *SlideAmtDef = MRI->getUniqueVRegDef(SlideAmt.getReg());
   if (SlideAmtDef->getOpcode() != RISCV::ADDI ||
-      SlideAmtDef->getOperand(2).getImm() != -AVL.getImm())
+      SlideAmtDef->getOperand(2).getImm() != -AVL.getImm() ||
+      !SlideAmtDef->getOperand(1).getReg().isVirtual())
     return std::nullopt;
   return SlideAmtDef->getOperand(1);
 }

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

@@ -796,3 +796,20 @@ body: |
     %v:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 5 /* e32 */, 0 /* tu, mu */
     %w:vr = PseudoVSLIDEDOWN_VX_M1 $noreg, %v, %y, 1, 5 /* e32 */, 0 /* tu, mu */
 ...
+---
+# Make sure we ignore LIs (ADDI $x0, -1)
+name: vslidedown_vx_li
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: $x8
+    ; CHECK-LABEL: name: vslidedown_vx_li
+    ; CHECK: liveins: $x8
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %y:gprnox0 = ADDI $x0, -1
+    ; CHECK-NEXT: %v:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 5 /* e32 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %w:vr = PseudoVSLIDEDOWN_VX_M1 $noreg, %v, %y, 1, 5 /* e32 */, 0 /* tu, mu */
+    %y:gprnox0 = ADDI $x0, -1
+    %v:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 5 /* e32 */, 0 /* tu, mu */
+    %w:vr = PseudoVSLIDEDOWN_VX_M1 $noreg, %v, %y, 1, 5 /* e32 */, 0 /* tu, mu */
+...