[Binding] Support for general if condition

[chhzh123]

Sometimes we may put array element comparison as the condition of if operation, but current implementation only allows passing in AffineExpr as condition and generate affine.if operation, which has big limitations.

Thus, to generate more generalized code, we can use scf.if as follows.

module {
    func @kernel(%A: memref<1024xi32>) -> memref<1024xi32>
    {
        affine.for %i = 0 to 1024 {
            %zero = arith.constant 0 : i32
            %load = affine.load %A[%i] : memref<1024xi32>
            %cond = arith.cmpi "sgt", %load, %zero : i32
            scf.if %cond {
                %a = affine.load %A[%i] : memref<1024xi32>
                %add = arith.addi %a, %a: i32
                affine.store %add, %A[%i] : memref<1024xi32>
            }
        }
        return %A : memref<1024xi32>
    }
}

[chhzh123]

The Python binding of scf.if has some problems. See the discussion in the LLVM discourse.

[chhzh123]

Submitted upstream LLVM patch in D121076.