Question: Without the cast operation, malloc cannot be correctly identified.

[sybs5968]

void Cast1() {
    void *mem = malloc(100);
    char *arr = (char *)mem;
    arr[0] = '%'; arr[1] = '#'; arr[2] = '\0';
    printf("%s\n" , arr);
    free(mem);
}

/*
 func.func @Cast1() attributes {llvm.linkage = #llvm.linkage<external>} {
    %c0_i8 = arith.constant 0 : i8
    %c35_i8 = arith.constant 35 : i8
    %c37_i8 = arith.constant 37 : i8
    %c100_i64 = arith.constant 100 : i64
    %0 = call @malloc(%c100_i64) : (i64) -> memref<?xi8>
    affine.store %c37_i8, %0[0] : memref<?xi8>
    affine.store %c35_i8, %0[1] : memref<?xi8>
    affine.store %c0_i8, %0[2] : memref<?xi8>
    %1 = llvm.mlir.addressof @str0 : !llvm.ptr
    %2 = llvm.getelementptr %1[0, 0] : (!llvm.ptr) -> !llvm.ptr, !llvm.array<4 x i8>
    %3 = "polygeist.memref2pointer"(%0) : (memref<?xi8>) -> !llvm.ptr
    %4 = llvm.call @printf(%2, %3) vararg(!llvm.func<i32 (ptr, ...)>) : (!llvm.ptr, !llvm.ptr) -> i32
    memref.dealloc %0 : memref<?xi8>
    return
  }
  func.func private @malloc(i64) -> memref<?xi8> attributes {llvm.linkage = #llvm.linkage<external>}
*/

I noticed that your malloc conversion is done in VisitCastExpr, so you can only recognize malloc as a custom function if you have a special case like above.