[VPlan] Move onlyFirstLaneUsed to VPWidenInductionRecipe (NFC).

Move onlyFirstLaneUsed from VPWidenIntOrFpInductionRecipe and
VPWidenPointerInduction to VPWidenInductionRecipe. Also mark step value
as having only its first lane used.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -1755,6 +1755,16 @@ class VPWidenInductionRecipe : public VPHeaderPHIRecipe {
     llvm_unreachable(
         "VPWidenIntOrFpInductionRecipe generates its own backedge value");
   }
+
+  /// Returns true if the recipe only uses the first lane of operand \p Op.
+  bool onlyFirstLaneUsed(const VPValue *Op) const override {
+    assert(is_contained(operands(), Op) &&
+           "Op must be an operand of the recipe");
+    // The recipe creates its own wide start value, so it only requests the
+    // first lane of the operand.
+    // TODO: Remove once creating the start value is modeled separately.
+    return Op == getStartValue() || Op == getStepValue();
+  }
 };
 
 /// A recipe for handling phi nodes of integer and floating-point inductions,
@@ -1831,16 +1841,6 @@ class VPWidenIntOrFpInductionRecipe : public VPWidenInductionRecipe {
   VPValue *getLastUnrolledPartOperand() {
     return getNumOperands() == 5 ? getOperand(4) : this;
   }
-
-  /// Returns true if the recipe only uses the first lane of operand \p Op.
-  bool onlyFirstLaneUsed(const VPValue *Op) const override {
-    assert(is_contained(operands(), Op) &&
-           "Op must be an operand of the recipe");
-    // The recipe creates its own wide start value, so it only requests the
-    // first lane of the operand.
-    // TODO: Remove once creating the start value is modeled separately.
-    return Op == getStartValue();
-  }
 };
 
 class VPWidenPointerInductionRecipe : public VPWidenInductionRecipe,
@@ -1873,13 +1873,6 @@ class VPWidenPointerInductionRecipe : public VPWidenInductionRecipe,
   /// Returns true if only scalar values will be generated.
   bool onlyScalarsGenerated(bool IsScalable);
 
-  /// Returns true if the recipe only uses the first lane of operand \p Op.
-  bool onlyFirstLaneUsed(const VPValue *Op) const override {
-    assert(is_contained(operands(), Op) &&
-           "Op must be an operand of the recipe");
-    return Op == getOperand(0);
-  }
-
   /// Returns the VPValue representing the value of this induction at
   /// the first unrolled part, if it exists. Returns itself if unrolling did not
   /// take place.