Lower reads and writes in Rust backend

• Refactor HerculesBox.
• Implement Read and Write in RT backend.

hercules_cg/src/cpu.rs

@@ -665,7 +665,7 @@ impl<'a> CPUContext<'a> {
                         get_type_alignment(&self.types, fields[*idx]),
                         body,
                     )?;
-                    acc_ptr = Self::gep(collect_name, &acc_offset, body)?;
+                    acc_ptr = Self::gep(&acc_ptr, &acc_offset, body)?;
                 }
                 Index::Variant(_) => {
                     // The tag of a summation is at the end of the summation, so
@@ -690,7 +690,7 @@ impl<'a> CPUContext<'a> {
 
                     // Convert offset in # elements -> # bytes.
                     acc_offset = Self::multiply(&acc_offset, &elem_size, body)?;
-                    acc_ptr = Self::gep(collect_name, &acc_offset, body)?;
+                    acc_ptr = Self::gep(&acc_ptr, &acc_offset, body)?;
                 }
             }
         }