Re: Whole program optimization / Link time optimization

Thanks, it works great!

- Wayne

From: Peter Bigot 
Sent: Monday, April 22, 2013 11:17 AM
To: Wayne Uroda 
Cc: MSPGCC list 
Subject: Re: [Mspgcc-users] 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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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!
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