[RISCV] Deduplicate AVL forwarding in RISCVInsertVSETVLI. NFC

We do the AVL forwarding trick in both getInfoForVSETVLI and
computeInfoForInstr, but there's a bug with this that I plan on fixing
in an upcoming patch. This factors it out to so we only need to fix it
in one place.

Author: lukel97

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -927,6 +927,7 @@ class RISCVInsertVSETVLI : public MachineFunctionPass {
 
   VSETVLIInfo getInfoForVSETVLI(const MachineInstr &MI) const;
   VSETVLIInfo computeInfoForInstr(const MachineInstr &MI) const;
+  void forwardVSETVLIAVL(VSETVLIInfo &Info) const;
 };
 
 } // end anonymous namespace
@@ -937,6 +938,26 @@ char &llvm::RISCVInsertVSETVLIID = RISCVInsertVSETVLI::ID;
 INITIALIZE_PASS(RISCVInsertVSETVLI, DEBUG_TYPE, RISCV_INSERT_VSETVLI_NAME,
                 false, false)
 
+// If the AVL is defined by a vsetvli's output vl with the same VLMAX, we can
+// replace the AVL operand with the AVL of the defining vsetvli. E.g.
+//
+// %vl = PseudoVSETVLI %avl:gpr, SEW=32, LMUL=M1
+// $x0 = PseudoVSETVLI %vl:gpr, SEW=32, LMUL=M1
+// ->
+// %vl = PseudoVSETVLI %avl:gpr, SEW=32, LMUL=M1
+// $x0 = PseudoVSETVLI %avl:gpr, SEW=32, LMUL=M1
+void RISCVInsertVSETVLI::forwardVSETVLIAVL(VSETVLIInfo &Info) const {
+  if (!Info.hasAVLReg())
+    return;
+  const MachineInstr *DefMI = Info.getAVLDefMI(LIS);
+  if (!DefMI || !isVectorConfigInstr(*DefMI))
+    return;
+  VSETVLIInfo DefInstrInfo = getInfoForVSETVLI(*DefMI);
+  if (!DefInstrInfo.hasSameVLMAX(Info))
+    return;
+  Info.setAVL(DefInstrInfo);
+}
+
 // Return a VSETVLIInfo representing the changes made by this VSETVLI or
 // VSETIVLI instruction.
 VSETVLIInfo
@@ -962,16 +983,7 @@ RISCVInsertVSETVLI::getInfoForVSETVLI(const MachineInstr &MI) const {
   }
   NewInfo.setVTYPE(MI.getOperand(2).getImm());
 
-  // If AVL is defined by a vsetvli with the same VLMAX, we can replace the
-  // AVL operand with the AVL of the defining vsetvli.
-  if (NewInfo.hasAVLReg()) {
-    if (const MachineInstr *DefMI = NewInfo.getAVLDefMI(LIS);
-        DefMI && isVectorConfigInstr(*DefMI)) {
-      VSETVLIInfo DefInstrInfo = getInfoForVSETVLI(*DefMI);
-      if (DefInstrInfo.hasSameVLMAX(NewInfo))
-        NewInfo.setAVL(DefInstrInfo);
-    }
-  }
+  forwardVSETVLIAVL(NewInfo);
 
   return NewInfo;
 }
@@ -1060,16 +1072,7 @@ RISCVInsertVSETVLI::computeInfoForInstr(const MachineInstr &MI) const {
 #endif
   InstrInfo.setVTYPE(VLMul, SEW, TailAgnostic, MaskAgnostic);
 
-  // If AVL is defined by a vsetvli with the same VLMAX, we can replace the
-  // AVL operand with the AVL of the defining vsetvli.
-  if (InstrInfo.hasAVLReg()) {
-    if (const MachineInstr *DefMI = InstrInfo.getAVLDefMI(LIS);
-        DefMI && isVectorConfigInstr(*DefMI)) {
-      VSETVLIInfo DefInstrInfo = getInfoForVSETVLI(*DefMI);
-      if (DefInstrInfo.hasSameVLMAX(InstrInfo))
-        InstrInfo.setAVL(DefInstrInfo);
-    }
-  }
+  forwardVSETVLIAVL(InstrInfo);
 
   return InstrInfo;
 }