Re: Optimization flags not working (GCC 4.2.4)

[slnc <s@slnc.me>]

David Daney wrote:
> slnc wrote:
>> Hi John,
>>
>> Thank you but -O0 makes no difference.
>>
> 
> That's what he just said.  If you use -O0 (the implied default) none of 
> the optimizations are done.  Use -O1 (or -O2 or -O3) if you want 
> optimizations done.

Oh, I misunderstood him, sorry. It also doesn't work if I omit 
-O<anything>. So to sum it up, there is no way to compile a program in 
gcc enabling only one specific optimization flag. The only option is to 
use the "pre-packaged" sets of flags (-O1, -O2 or -O3) right?

I have tried disabling all -O1 flags just to check if I could select 
only one by disabling all the others but:

gcc -c -O1 -fno-defer-pop -fno-delayed-branch 
-fno-guess-branch-probability -fno-cprop-registers -fno-if-conversion 
-fno-if-conversion2 -fno-tree-ccp -fno-tree-dce -fno-tree-dominator-opts 
-fno-tree-dse -fno-tree-ter -fno-tree-lrs -fno-tree-sra 
-fno-tree-copyrename -fno-tree-fre -fno-tree-ch -fno-unit-at-a-time 
-fno-merge-constants main.c
objdump -d dce.o

generates an optimized version. So why are the flags there if they 
cannot be selected individually? (I feel like I am missing something 
completely obvious..)

Thank you,
-- 
slnc