Is it possible to reduce a file size and how to do it?
Yes, use an efficient compiler.

Keil and Raisonance (and maybe others) have developed compilers specifically for the '51 SDCC (and maybe others) are "general purpose" compilers adapted for the '51

The data usage by IAR (1) makes me suspicious that the IAR (while reasonably compact in code size) is using the stack for parameter passing which, regardless of the resulting code size, result in a throughput penalty.

Erik

PS
The concern for code size should, in my opinion, be replaced by a concern for throughput speed. With todays price of flash (ST micro 2 megabytes <$3) the need for a few more k of program storage seems a lot less important than a few years ago.