Whole program optimization / Link time optimization

Hi,

Can anybody comment on LTO or WPO’s effect on optimizing for space  - I have run out of flash memory and would rather not refactor my code at the moment. I only need 10 more bytes or so, for today at least... Yes it’s not ideal, such is life.

I am using mspgcc 20120406-p20120911 and when I pass `–flto` in both the compilation and link stages it compiles fine but the linker complains “unrecognized option '-plugin'”. I assume LTO isn’t supported at this time?

So then I skipped intermediate .o files altogether and used the following command:
msp430-gcc -mmcu=msp430f233 -Os -Wall -Werror -o Coyote.elf <all c files>

I get the expected message that my code does not fit.

Using –fwhole-program:
msp430-gcc -mmcu=msp430f233 -Os -Wall -Werror -fwhole-program -o Coyote.elf <all c files>

I get the following output:
C:\Users\WAYNEU~1\AppData\Local\Temp\cclYmoCC.o: In function `main':
main.c:(.init9+0x2): undefined reference to `systemDisableInterrupts'
main.c:(.init9+0x6): undefined reference to `PlatformInit'
main.c:(.init9+0xc): undefined reference to `systemEnableCrystalClock'
main.c:(.init9+0x2a): undefined reference to `delay'
main.c:(.init9+0x44): undefined reference to `delay'
main.c:(.init9+0x5e): undefined reference to `delay'
main.c:(.init9+0x78): undefined reference to `delay'
main.c:(.init9+0x80): undefined reference to `delay'
C:\Users\WAYNEU~1\AppData\Local\Temp\cclYmoCC.o:main.c:(.init9+0xa4): more undefined references to `delay' follow
C:\Users\WAYNEU~1\AppData\Local\Temp\cclYmoCC.o: In function `main':
main.c:(.init9+0xf8): undefined reference to `batteryGetStateOfCharge'
main.c:(.init9+0x104): undefined reference to `chargeIsPresent'
main.c:(.init9+0x118): undefined reference to `delay'
main.c:(.init9+0x134): undefined reference to `delay'
main.c:(.init9+0x138): undefined reference to `infomemValidate'
main.c:(.init9+0x13c): undefined reference to `logicMainLoop'
collect2: ld returned 1 exit status


I then created two files, test1.c and test2.c

test1.c:
-------------------------------
void test2(void);

void test1(void)
{
    test2();
}

int main()
{
    test2();
    return 0;
}

-------------------------------

test2.c:
-------------------------------
void test1(void);

void test2(void)
{
    test1();
}

-------------------------------

Compiling them:
msp430-gcc -mmcu=msp430f233 -Os -Wall -Werror -fwhole-program -o test.elf test1.c test2.c

C:\Users\WAYNEU~1\AppData\Local\Temp\ccs3TYlw.o: In function `main':
test1.c:(.init9+0x2): undefined reference to `test2'
collect2: ld returned 1 exit status

Have I done something wrong?

In the meantime, I will refactor. I don’t even expect WPO/LTO to give me much of a space saving anyway.

- Wayne

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