Re: powercp-linux cross GCC 4.2 vs GCC 4.0.0: -Os code size regression? [Emcraft #11717]

[Sergei Poselenov <sposelenov at emcraft dot com>]

Hello Andrew,

Andrew Haley wrote:
> Sergei Poselenov writes:
>  > Hello Andrew,
>  > 
>  > > Now, I sympathize that in your particular case you have a code size
>  > > regression.  This happens: when we do optimization in gcc, some code
>  > > bases will lose out.  All that we can promise is that we try not to
>  > > make it worse for most users.
>  > > 
>  > > What we can do is compare your code that has got much worse, and try
>  > > to figure out why.
>  > > 
>  > 
>  > Would the generated asm listings be enough? Or should I send
>  > the preprocessed sources as well?
>
> Both.
>
> Rather than sending stuff, best to stick it on a web site if you can.

Here it is:
Preprocessed and assembler code generated by the GCC 4.2.2 ppc-linux
cross-compiler:
http://www.emcraft.com/codesize/gcc-4.2.2/interrupts.i
http://www.emcraft.com/codesize/gcc-4.2.2/interrupts.s

The same code built with gcc-4.0.0 cross-compiler:
http://www.emcraft.com/codesize/gcc-4.0.0/interrupts.i
http://www.emcraft.com/codesize/gcc-4.0.0/interrupts.s

Again, for convenience, the compilation string is:
ppc-linux-gcc -g  -Os   -fPIC -D__KERNEL__ -DTEXT_BASE=0xfffc0000 
-I/work/psl/tmp/u-boot/include -fno-builtin -nostdinc -isystem 
/opt/eldk-4.2-01-08/usr/bin/../lib/gcc/powerpc-linux/4.2.2/include 
-pipe  -DCONFIG_PPC -D__powerpc__ -DCONFIG_4xx -msoft-float -Wa,-m440 
-mcpu=440 -DCONFIG_440=1 -Wall -Wstrict-prototypes -c  interrupts.c

The 'size' output for both the cases:
   text    data     bss     dec     hex filename
   2696      60    1536    4292    10c4 interrupts.o
and
   text    data     bss     dec     hex filename
   2424      88    1536    4048     fd0 interrupts.o


> Having said that, your example is tiny, so it's likely that it won't
> be very representative, and the less representative the code is the
> less likely a gcc maintainer will be interested.  But at least we'll
> be able to see the difference.

I agree. Actually, the CSiBE results are impressive: I've built the 
bzip2 library for powerpc and got similar results.

I wonder why GCC maintainers are ignoring the -Os regression for
most of their cases (at least for powerpc).

Thanks,
Sergei

> Andrew.