[ConstantFold] Remove redundant zero index gep fold (NFCI)

We already handle the more general case of zero index GEPs above,
so we don't need to also handle GEPs with null based and zero
indices. (Strictly speaking, this code could handle the special
case of an inrange gep with null base and zero indices, but that
has no practical relevance.)

Author: nikic

llvm/lib/IR/ConstantFold.cpp

@@ -1617,39 +1617,6 @@ Constant *llvm::ConstantFoldGetElementPtr(Type *PointeeTy, Constant *C,
                      cast<VectorType>(GEPTy)->getElementCount(), C)
                : C;
 
-  if (C->isNullValue()) {
-    bool isNull = true;
-    for (Value *Idx : Idxs)
-      if (!isa<UndefValue>(Idx) && !cast<Constant>(Idx)->isNullValue()) {
-        isNull = false;
-        break;
-      }
-    if (isNull) {
-      PointerType *PtrTy = cast<PointerType>(C->getType()->getScalarType());
-      Type *Ty = GetElementPtrInst::getIndexedType(PointeeTy, Idxs);
-
-      assert(Ty && "Invalid indices for GEP!");
-      Type *OrigGEPTy = PointerType::get(Ty, PtrTy->getAddressSpace());
-      Type *GEPTy = PointerType::get(Ty, PtrTy->getAddressSpace());
-      if (VectorType *VT = dyn_cast<VectorType>(C->getType()))
-        GEPTy = VectorType::get(OrigGEPTy, VT->getElementCount());
-
-      // The GEP returns a vector of pointers when one of more of
-      // its arguments is a vector.
-      for (Value *Idx : Idxs) {
-        if (auto *VT = dyn_cast<VectorType>(Idx->getType())) {
-          assert((!isa<VectorType>(GEPTy) || isa<ScalableVectorType>(GEPTy) ==
-                                                 isa<ScalableVectorType>(VT)) &&
-                 "Mismatched GEPTy vector types");
-          GEPTy = VectorType::get(OrigGEPTy, VT->getElementCount());
-          break;
-        }
-      }
-
-      return Constant::getNullValue(GEPTy);
-    }
-  }
-
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
     if (auto *GEP = dyn_cast<GEPOperator>(CE))
       if (Constant *C = foldGEPOfGEP(GEP, PointeeTy, InBounds, Idxs))