* gcc compile for code size
@ 2012-11-11 19:47 Xin Tong
2012-11-11 19:54 ` Andrew Haley
0 siblings, 1 reply; 6+ messages in thread
From: Xin Tong @ 2012-11-11 19:47 UTC (permalink / raw)
To: gcc-help
when gcc is set to compile for minimal code size, what kind of
optimizations does gcc apply in comparison to compile for performance
? or it is just gcc spends more time doing the compilation, selecting
instruction sequences that are optimal for code size.
Xin
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: gcc compile for code size
2012-11-11 19:47 gcc compile for code size Xin Tong
@ 2012-11-11 19:54 ` Andrew Haley
2012-11-11 19:59 ` Xin Tong
0 siblings, 1 reply; 6+ messages in thread
From: Andrew Haley @ 2012-11-11 19:54 UTC (permalink / raw)
To: Xin Tong; +Cc: gcc-help
On 11/11/2012 07:47 PM, Xin Tong wrote:
> when gcc is set to compile for minimal code size, what kind of
> optimizations does gcc apply in comparison to compile for performance
> ? or it is just gcc spends more time doing the compilation, selecting
> instruction sequences that are optimal for code size.
No. GCC does all optimizations *except* those known to increase
program size. This usually works pretty well, but isn't perfect.
Andrew.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: gcc compile for code size
2012-11-11 19:54 ` Andrew Haley
@ 2012-11-11 19:59 ` Xin Tong
2012-11-11 21:01 ` Andrew Haley
0 siblings, 1 reply; 6+ messages in thread
From: Xin Tong @ 2012-11-11 19:59 UTC (permalink / raw)
To: Andrew Haley; +Cc: gcc-help
so as to how the instructions are selected. compiling for code size
does not have an effect ?
Xin
On Sun, Nov 11, 2012 at 2:54 PM, Andrew Haley <aph@redhat.com> wrote:
> On 11/11/2012 07:47 PM, Xin Tong wrote:
>> when gcc is set to compile for minimal code size, what kind of
>> optimizations does gcc apply in comparison to compile for performance
>> ? or it is just gcc spends more time doing the compilation, selecting
>> instruction sequences that are optimal for code size.
>
> No. GCC does all optimizations *except* those known to increase
> program size. This usually works pretty well, but isn't perfect.
>
> Andrew.
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: gcc compile for code size
2012-11-11 19:59 ` Xin Tong
@ 2012-11-11 21:01 ` Andrew Haley
2012-11-11 21:09 ` Jeff Law
0 siblings, 1 reply; 6+ messages in thread
From: Andrew Haley @ 2012-11-11 21:01 UTC (permalink / raw)
To: Xin Tong; +Cc: gcc-help
On 11/11/2012 07:59 PM, Xin Tong wrote:
> On Sun, Nov 11, 2012 at 2:54 PM, Andrew Haley <aph@redhat.com> wrote:
>> On 11/11/2012 07:47 PM, Xin Tong wrote:
>>> when gcc is set to compile for minimal code size, what kind of
>>> optimizations does gcc apply in comparison to compile for performance
>>> ? or it is just gcc spends more time doing the compilation, selecting
>>> instruction sequences that are optimal for code size.
>>
>> No. GCC does all optimizations *except* those known to increase
>> program size. This usually works pretty well, but isn't perfect.
>>
> so as to how the instructions are selected. compiling for code size
> does not have an effect ?
Please don't top-post on this list.
Any target could, in principle, select instructions based on size
and -OS, but I don't know any that do.
Andrew.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: gcc compile for code size
2012-11-11 21:01 ` Andrew Haley
@ 2012-11-11 21:09 ` Jeff Law
2012-11-11 21:32 ` Andrew Haley
0 siblings, 1 reply; 6+ messages in thread
From: Jeff Law @ 2012-11-11 21:09 UTC (permalink / raw)
To: Andrew Haley; +Cc: Xin Tong, gcc-help
On 11/11/2012 02:01 PM, Andrew Haley wrote:
> On 11/11/2012 07:59 PM, Xin Tong wrote:
>>> No. GCC does all optimizations *except* those known to increase
>>> program size. This usually works pretty well, but isn't perfect.
>>>
>> so as to how the instructions are selected. compiling for code size
>> does not have an effect ?
>
> Please don't top-post on this list.
>
> Any target could, in principle, select instructions based on size
> and -OS, but I don't know any that do.
Many ports look at at -Os and change their instruction selections,
alignment requests, etc.
grep for "optimize_size" in the machine descriptions...
jeff
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: gcc compile for code size
2012-11-11 21:09 ` Jeff Law
@ 2012-11-11 21:32 ` Andrew Haley
0 siblings, 0 replies; 6+ messages in thread
From: Andrew Haley @ 2012-11-11 21:32 UTC (permalink / raw)
To: Jeff Law; +Cc: Xin Tong, gcc-help
On 11/11/2012 09:08 PM, Jeff Law wrote:
> On 11/11/2012 02:01 PM, Andrew Haley wrote:
>> On 11/11/2012 07:59 PM, Xin Tong wrote:
>>>> No. GCC does all optimizations *except* those known to increase
>>>> program size. This usually works pretty well, but isn't perfect.
>>>>
>>> so as to how the instructions are selected. compiling for code size
>>> does not have an effect ?
>>
>> Please don't top-post on this list.
>>
>> Any target could, in principle, select instructions based on size
>> and -OS, but I don't know any that do.
> Many ports look at at -Os and change their instruction selections,
> alignment requests, etc.
>
> grep for "optimize_size" in the machine descriptions...
Oops, sorry. While "I don't know" was true, it wasn't very helpful.
I do now!
Andrew.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2012-11-11 21:32 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2012-11-11 19:47 gcc compile for code size Xin Tong
2012-11-11 19:54 ` Andrew Haley
2012-11-11 19:59 ` Xin Tong
2012-11-11 21:01 ` Andrew Haley
2012-11-11 21:09 ` Jeff Law
2012-11-11 21:32 ` Andrew Haley
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