[VPlan] VPInterleaveRecipe only requires the first lane of the address.

[fhahn]

Summary

VPInterleaveRecipe only uses the first lane of the address. Add
onlyFirstLaneUsed implementation. This is needed for a follow-up patch.

[Ayal]

Ship it!
Address clearly uses first lane only, as evident in VPInterleaveGroup::execute(), and the other operands Stored values and Mask clearly use all lanes.
This will be exercised/tested by follow-up patch only?

[fhahn]

In D121612#3382470, @Ayal wrote:

Ship it!
Address clearly uses first lane only, as evident in VPInterleaveGroup::execute(), and the other operands Stored values and Mask clearly use all lanes.

Thanks!

This will be exercised/tested by follow-up patch only?

Yes unfortunately it will only be exercised by a follow up patch. I'll land them close together.

llvm/lib/Transforms/Vectorize/VPlan.h

#endif
 
   const InterleaveGroup<Instruction> *getInterleaveGroup() { return IG; }
 
   /// Returns the number of stored operands of this interleave group. Returns 0
   /// for load interleave groups.
   unsigned getNumStoreOperands() const {
     return getNumOperands() - (HasMask ? 2 : 1);
   }
+
+  /// The recipe only uses the first lane of the address.
+  bool onlyFirstLaneUsed(const VPValue *Op) const override {
+    assert(is_contained(operands(), Op) &&
+           "Op must be an operand of the recipe");
+    return Op == getAddr();
+  }
 };
 
 /// A recipe to represent inloop reduction operations, performing a reduction on
 /// a vector operand into a scalar value, and adding the result to a chain.
 /// The Operands are {ChainOp, VecOp, [Condition]}.
 class VPReductionRecipe : public VPRecipeBase, public VPValue {
   /// The recurrence decriptor for the reduction in question.
   const RecurrenceDescriptor *RdxDesc;