[LLVMdev] Executable file size comparison

[Csaba Raduly]

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
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