Dependent IV not simplified

[nikic]

https://alive2.llvm.org/ce/z/hfmwgf

The following fold is not performed. Same can be done with GEPs.

define void @src2(i64 %base, i64 %end) {
entry:
  br label %loop

loop:
  %iv2 = phi i64 [ %iv2.next, %loop ], [ %base, %entry ]
  %iv = phi i64 [ %iv.next, %loop ], [ 0, %entry ]
  call void @use.i64(i64 %iv2)
  %iv.next = add nuw nsw i64 %iv, 4
  %iv2.next = add i64 %base, %iv.next
  %cmp = icmp eq i64 %iv.next, %end
  br i1 %cmp, label %exit, label %loop

exit:
  ret void
}

define void @tgt2(i64 %base, i64 %end) {
entry:
  br label %loop

loop:
  %iv = phi i64 [ %iv.next, %loop ], [ 0, %entry ]
  %iv2 = add i64 %base, %iv
  call void @use.i64(i64 %iv2)
  %iv.next = add nuw nsw i64 %iv, 4
  %cmp = icmp eq i64 %iv.next, %end
  br i1 %cmp, label %exit, label %loop

exit:
  ret void
}

iv2 here is basically just iv+base but written as phi(base, iv.next+base)