Compiler optimisation

Hello,

1.when i use printf with no var_args then the compiler should call puts instead of printf.

ex1:

#include <REGX51.H>
#include <stdio.h>

void main(void)
{
        printf("This must call puts instead of printf");
}

Program Size: data=30.1 xdata=0 code=1103

ex2:

#include <REGX51.H>
#include <stdio.h>

void main(void)
{
        puts("This must call puts instead of printf");
}

Program Size: data=9.0 xdata=0 code=168

The above code links the printf function from the library which is huge(produces 1103 bytes).But the compiler can use puts when there is no var_args given which is much smaller than printf(produces 168 bytes).

2.The Compiler must find and remove the duplicate constant strings

ex3:

#include <REGX51.H>
#include <stdio.h>

void main(void)
{
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
        puts("This string gets duplicated as many time as i use it");
}

Program Size: data=9.0 xdata=0 code=334

ex4:

#include <REGX51.H>
#include <stdio.h>

void main(void)
{
        puts("This string gets duplicated as many time as i use it");
}

Program Size: data=9.0 xdata=0 code=183

3.Bit Test instructions are not used when i actually test for the bit

ex5:

#include <REGX51.H>
#include <stdio.h>


void main(void)
{
        if(P0^1)
        {
                P1 = 10;
        }

}


ASSEMBLY LISTING OF GENERATED OBJECT CODE

             ; FUNCTION main (BEGIN)
                                           ; SOURCE LINE # 6
                                           ; SOURCE LINE # 7
                                           ; SOURCE LINE # 8
0000 E580              MOV     A,P0
0002 6401              XRL     A,#01H
0004 6003              JZ      ?C0002
                                           ; SOURCE LINE # 9
                                           ; SOURCE LINE # 10
0006 75900A            MOV     P1,#0AH
                                           ; SOURCE LINE # 11
                                           ; SOURCE LINE # 13
0009         ?C0002:
0009 22                RET
             ; FUNCTION main (END)

In the above assembly output it should have used a single instruction JNB instead of three MOV,XRL and JZ.This is very basic anybody would object the assembly code produced.

I have not used the compiler much.But the compiler needs a look by the programmers at keil.

The above programs were all compiled with compiler optimisation level set to 9 & favour speed.

About 5 years back i compiled a c51 source code using keil.
Now i recompiled the same source code with the latest compiler from keil and compared the two output .hex files.
Unfortunately it produced exactly the same output.Here i was expecting some code and data size reduction as the compiler must be capable of optimising more.

It seems there was no improvement on the compiler side.

It is not a complaint but in the interest of improving the compiler.

regards,

S.Sheik mohamed