[AArch64][SVE2] Delete an unused parameter for isExtPartOfAvgExpr, NFC

Depend on D157628, which set the cost of extends 0 because they will fold into
the s/urhadd.

Reviewed By: kmclaughlin
Differential Revision: https://reviews.llvm.org/D159273

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -2049,10 +2049,8 @@ bool AArch64TTIImpl::isWideningInstruction(Type *DstTy, unsigned Opcode,
 //   %y = (zext i8 -> i16)
 //   trunc i16 (lshr (add %x, %y), 1) -> i8
 //
-bool AArch64TTIImpl::isExtPartOfAvgExpr(const Instruction *ExtUser,
-                                        const CastInst *Ext, Type *Dst,
+bool AArch64TTIImpl::isExtPartOfAvgExpr(const Instruction *ExtUser, Type *Dst,
                                         Type *Src) {
-
   // The source should be a legal vector type.
   if (!Src->isVectorTy() || !TLI->isTypeLegal(TLI->getValueType(DL, Src)) ||
       (Src->isScalableTy() && !ST->hasSVE2()))
@@ -2120,7 +2118,7 @@ InstructionCost AArch64TTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
 
     // The cast will be free for the s/urhadd instructions
     if ((isa<ZExtInst>(I) || isa<SExtInst>(I)) &&
-        isExtPartOfAvgExpr(SingleUser, cast<CastInst>(I), Dst, Src))
+        isExtPartOfAvgExpr(SingleUser, Dst, Src))
       return 0;
   }
 

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h

@@ -163,8 +163,7 @@ class AArch64TTIImpl : public BasicTTIImplBase<AArch64TTIImpl> {
                                          TTI::TargetCostKind CostKind,
                                          const Instruction *I = nullptr);
 
-  bool isExtPartOfAvgExpr(const Instruction *ExtUser, const CastInst *Ext,
-                          Type *Dst, Type *Src);
+  bool isExtPartOfAvgExpr(const Instruction *ExtUser, Type *Dst, Type *Src);
 
   InstructionCost getCastInstrCost(unsigned Opcode, Type *Dst, Type *Src,
                                    TTI::CastContextHint CCH,