GCC-4.0 vs GCC-3.3.6 ia32 -Os: code size increase from 261 to5339 bytes

[Giovanni Bajo]

Daniel Berlin <dberlin@dberlin.org> wrote:

>> $ ./xgcc -c -Os -B. btst.c && size btst.o
>>    text    data     bss     dec     hex filename
>>    5339       0       0    5339    14db btst.o
>> $ ./xgcc -c -Os -fno-tree-sra -B. btst.c && size btst.o
>>    text    data     bss     dec     hex filename
>>     224       0       0     224      e0 btst.o
>> 
>> So we're actually better than 3.3, after we disable -ftree-sra. I
>> guess SRA should be tuned (disabled?) for -Os.
> 
> Structure aliasing should be able to make up for turning off SRA, i'm
> guessing, at least as far as propagating constants and DCE is
> concerned. 
> 
> You could test this by seeing if -fno-tree-sra -fno-tree-salias
> produces 
> an increased code size over the above.

Not really: with -fno-tree-salias I get exactly the same result (224 bytes).

Giovanni Bajo