On Tue, Apr 26, 2011 at 3:39 PM, cirrus75 <cirru...@uol.com.br> wrote:
>
> Hi,
>
> Actually, I would like to ask if all this should be tree level optimization
> or there would be something to do at backend. I am asking because I am trying
> to write a new backend.
It should be dealt with at the tree level by lowering bitfield accesses.
Richard.
> thanks,
> Alex R. Prado
>
>
> Em 25/04/2011 14:47, Ian Lance Taylor < i...@google.com > escreveu:
> cirrus75 writes:
>
>> For the fllowing code:
>>
>> typedef struct {
>> int f1:1;
>> int f2:1;
>> int f3:1;
>> int f4:29;
>> } t1;
>>
>> typedef struct {
>> int f1:1;
>> int f2:1;
>> int f3:30;
>> } t2;
>>
>> t1 s1;
>> t2 s2;
>>
>> void func1(void)
>> {
>> s1.f1 = s2.f1;
>> s1.f2 = s2.f2;
>> }
>>
>> we get (x86_64 target):
>>
>> movzbl s2(%rip), %edx
>> movzbl s1(%rip), %eax
>> movl %edx, %ecx
>> andl $-4, %eax
>> andl $2, %edx
>> andl $1, %ecx
>> orl %ecx, %eax
>> orl %edx, %eax
>> movb %al, s1(%rip)
>> ret
>>
>>
>> Could gcc optimize two or more operations in adjacent bitfields into one
>> operation ?
>
> This question looks more appropriate for the mailing list
> gcc-h...@gcc.gnu.org rather than the mailing list gcc@gcc.gnu.org.
>
> I agree that this looks like suboptimal code. Please consider filing a
> missed-optimization bug report. See http://gcc.gnu.org/bugs/ . Thanks.
>
> Ian
>
>
