[IR] Added special-purpose dequantize instruction (#759)

It is currently necessary for optimal performance in quantized workloads to add a special-purpose instruction in the IR. Backward compatibility with this instruction is *NOT* guaranteed.

lib/ir/builder.cc

@@ -120,6 +120,14 @@ value *builder::create_ret(value* val) {
   return insert(return_inst::create(ctx_, val));
 }
 
+//===----------------------------------------------------------------------===//
+//                               dequantize instructions
+//===----------------------------------------------------------------------===//
+
+value* builder::create_dequantize(value *src, value *scale, value *shift, type *dst_ty){
+  return insert(dequantize_inst::create(src, scale, shift, dst_ty));
+}
+
 //===----------------------------------------------------------------------===//
 //                               cast instructions
 //===----------------------------------------------------------------------===//