MSP-CGT: Potential optimisation in MSP430 C compiler

Michal Durec

Part Number: MSP-CGT

Hello,

First of all, sorry for not putting this into MSP microcontrollers forum - the MSP-CGT seems to be under (incorrect?) ARM-based MCUs...

I think there is an opportunity for a small optimisation of the following C snippet. After checking the return value of function "boolean_test_func" (in register R12), the generated instructions should not need to clear R12 before returning from "func" as this has already been cleared by "boolean_test_func".

bool func(...)

{
...

if ( ! boolean_test_func())

{

return false;

}

...

return true;

}

Generated instructions from a similar code as the snippet above:

func()
...
0x0E066 12B0 E00E           CALL    #boolean_test_func
0x0E06A 934C                TST.B   R12
0x0E06C 2416                JEQ     ($C$L46)
...
0x0E096 435C                MOV.B   #1,R12
0x0E098 4130                RET
$C$L46
0x0E09A 434C                CLR.B   R12
0x0E09C 4130                RET

The code generated could omit the last two instructions altogether and jump to the preceding RET instruction instead:

func()
...
0x0E066 12B0 E00E           CALL    #boolean_test_func
0x0E06A 934C                TST.B   R12
0x0E06C 2416                JEQ     ($C$L46)
...
0x0E096 435C                MOV.B   #1,R12
$C$L46
0x0E098 4130                RET

Four bytes saved