Hello, I’m trying add `conv2d`

operation(maybe simiplied version) in Toy dialect and lower to affine Dialect.This is Affine code I wrote handly (%arg2 and %arg3 are result index,%arg4 and %arg5 are filter index)

```
affine.for %arg2 = 0 to 2 {
affine.for %arg3 = 0 to 2 {
affine.for %arg4 = 0 to 2 {
affine.for %arg5 = 0 to 2 {
%3 = affine.load %1[%arg4, %arg5]
%4 = affine.load %2[ %arg4+%arg2, %arg5+%arg3]
%5 = mulf %3, %4
%6 = affine.load %0[%arg2, %arg3]
%7 = addf %5,%6
affine.store %7, %0[%arg2, %arg3]
}
}
}
}
```

I have trouble in implementing `%4 = affine.load %2[ %arg4+%arg2, %arg5+%arg3]`

.Firstly,I tried get the sum of two index and use the sum as index to create `AffineLoad`

but I get the Error message `'affine.load' op index must be a dimension or symbol identifier`

.Then I was told I should `When you call create<AffineLoadOp>, you can pass an instance of AffineMap between the memref value and the subscript values.`

I am not familiar with AffineMap(doesn’t show up in Toy Tutorial) .Can someone demostrate how to code that?

Another question is when I first call `%6 = affine.load %0[%arg2, %arg3]`

(%0 is memref value of result),%6 is 0 or not? should I initialize %0 with zero?