regarding assembling branch instruction

[Sivaprasad.pv]

Hi Nick,

Is there any specific example case where assembler relaxation was used ?

Thanks,
Siva Prasad

Nick Clifton wrote:
> Hi Siva,
>
>> If we implement method a)
>>   Label address (or offset) depends on size of the branch 
>> instruction.so I think, it is  need to adjust each instruction offset 
>> after selecting opcode of branch instruction(nested branches) in 
>> second pass .
>
> Correct - this is known as assembler relaxation.
>
>> I think linker relaxation also do the same thing but during the 
>> linking process.
>
>> If both are same, Then which is better option?
>
> Well, they are not exactly the same, since one takes place in the 
> assembler and one in the linker.  There is no hard and fast rule to 
> say which option is better, and in fact some ports implement both.  
> Which you choose is really up to you.  If you only have a branch 
> instruction to relax (and not a function call instruction) then it is 
> reasonable to assume that all branches will be to targets within the 
> same object file, and so you will probably find assembler based 
> relaxation easier to implement.
>
> The advantages of assembler based relaxation are:
>
>   * Smaller object files.  (When compared to linker based
>     relaxation, since for that you have to pass extra information
>     in the object files).
>
>   * Simpler to code.
>
> The advantages of linker based relaxation are:
>
>   * It detects more opportunities for relaxation since it can
>     reduce the length of branches between locations in different
>     object files.
>
> Cheers
>   Nick
>
>