How much optimize depend on optimization level of compiler?

"How much would the output file change if we compiled C code using the XC8 compiler?"

So I tried to compile C code that I made and compared the each output HEX file depend on each optimization level.

pic16_optimizationText.X.zip

I will use below C code, It will be friendly if you learned C language

/* TODO <INSERT USER APPLICATION CODE HERE> */         for(i=2;i<=9;i++){             for(j=2;j<=9;j++){                 LATA = i*j;             }         }

Now let's see the result! XC8 Compiler has three kinds of optimization level such as Free, Standard, and Professional mode

• XC8 Compiler version: v1.45

	Free mode	Standard mode	Professional mode
Flash memory used	80 bytes	69 bytes	50 bytes
rate	1	0.86	0.65

• Free mode

Memory Summary:     Program space        used    50h (    80) of  2000h words   (  1.0%)     Data space           used     Ah (    10) of   3F0h bytes   (  1.0%)     EEPROM space         used     0h (     0) of   100h bytes   (  0.0%)     Data stack space     used     0h (     0) of   3F0h bytes   (  0.0%)     Configuration bits   used     0h (     0) of     4h words   (  0.0%)     ID Location space    used     0h (     0) of     4h bytes   (  0.0%)

• Standard mode

Memory Summary:     Program space        used    45h (    69) of  2000h words   (  0.8%)     Data space           used     Ah (    10) of   3F0h bytes   (  1.0%)     EEPROM space         used     0h (     0) of   100h bytes   (  0.0%)     Data stack space     used     0h (     0) of   3F0h bytes   (  0.0%)     Configuration bits   used     0h (     0) of     4h words   (  0.0%)     ID Location space    used     0h (     0) of     4h bytes   (  0.0%)

• Professional mode

Memory Summary:     Program space        used    32h (    50) of  2000h words   (  0.6%)     Data space           used     7h (     7) of   3F0h bytes   (  0.7%)     EEPROM space         used     0h (     0) of   100h bytes   (  0.0%)     Data stack space     used     0h (     0) of   3F0h bytes   (  0.0%)     Configuration bits   used     0h (     0) of     4h words   (  0.0%)     ID Location space    used     0h (     0) of     4h bytes   (  0.0%)

As we see the result of compiler depend on the optimization level, In case of Standard mode, The size of hex file can be reduced to 0.85 ratio. In case of Professional mode, The size of hex file can be reduced to 0.65 ratio. 

As you may expect, As the size of an Hex file decreases, it will execute much more faster and save the flash memory which stores the hex file.

I think that Free mode also can use for embedded programming but if you use the standard version or professional version, you can save the flash memory and execute code much more faster.