Re: Whole program optimization / Link time optimization

I've never tested mspgcc for any whole-program optimizations.  A common and
supported way to reduce space by eliminating unused material is
-ffunction-sections -fdata-sections during compilation and -Wl,-gc-sections
during linking.

Peter


On Sun, Apr 21, 2013 at 8:13 PM, Wayne Uroda <[email protected]> wrote:

> 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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Precog is a next-generation analytics platform capable of advanced
analytics on semi-structured data. The platform includes APIs for building
apps and a phenomenal toolset for data science. Developers can use
our toolset for easy data analysis & visualization. Get a free account!
http://www2.precog.com/precogplatform/slashdotnewsletter

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