[LLVMdev] Executable file size comparison

[Richard Pennington]

On Friday, December 09, 2011 02:53:25 AM Csaba Raduly wrote:
> On Thu, Dec 8, 2011 at 11:46 PM, Richard Pennington  wrote:
> > On Thursday, December 08, 2011 02:46:39 AM Csaba Raduly wrote:
> >> On Wed, Dec 7, 2011 at 9:43 PM, Richard Pennington  wrote:
> >> > I compiled a program and standard library using clang/LLVM and found
> >> > the results interesting:
> >> > 
> >> >   text    data     bss     dec     hex filename
> >> >  141312    4076   16668  162056   27908 bzip2.arm
> >> >  131764    4076   16668  152508   253bc bzip2.armv7
> >> >  134748    4048   16624  155420   25f1c bzip2.i386
> >> >  259112    4028   16732  279872   44540 bzip2.microblaze
> >> >  168044    4040   16816  188900   2e1e4 bzip2.mips
> >> >  167860    4040   16816  188716   2e12c bzip2.mips32r2
> >> >  179032    4040   16816  199888   30cd0 bzip2.mips32r2elsf
> >> >  179008    4040   16816  199864   30cb8 bzip2.mips32r2sf
> >> >  168060    4040   16816  188916   2e1f4 bzip2.mipsel
> >> >  156312    4028   16784  177124   2b3e4 bzip2.ppc
> >> >  163572   10896   19280  193748   2f4d4 bzip2.ppc64
> >> >  145443    4696   19368  169507   29623 bzip2.x86_64
> >> > 
> >> > The libraries were compiled with -O1 and the program was compiled with
> >> > -O2. The whole thing was statically linked. I verified that each
> >> > executable was correct by running the bzip2 test cases under QEMU.
> >> > 
> >> > It is interesting to see how the architecture (and maybe maturity of
> >> > the code generator) affects code size.
> >> 
> >> What could be so different in ppc64 that causes "data" to be more than
> >> twice the size than on any other platform?
> >> 
> >> Csaba
> > 
> > Csaba,
> > 
> > It turns out that most of the data space used by the ppc64 is for a
> > little table created for each function defined in the program. The table
> > has two 64 bit pointers in it, one is the address of the function. This
> > is how Linux ppc64 executables are built: the table is used to
> > indirectly call functions. There are many of these little tables in the
> > program because it is statically linked with the standard library.
> 
> Can you try with GCC? Does it present the same symptom (data more than
> 2x as large than other platforms)?
> 
> Csaba

Csaba,

I'm setting up the library for a gcc build now (for a friend). When I get that 
going, I'll try to find a ppc64 version of gcc to test it. The beauty of 
clang/LLVM is that I only need to build it once and I get all the targets. :-)

-Rich