Issue group

[Ian Lance Taylor]

ranjith kumar <ranjit_kumar_b4u@yahoo.co.uk> writes:

>    1)What is an "issues group" ?
> 
>   I think its definition is :
>              " Processors contain more than one
> execution units like integer execution unit, floating
> exection unit, memory read/write execution
> units.....etc.
> An issue group is a list of assembly instructions
> which can be issued simultaneously to different
> execution units at same time so that all execution
> units are busy."
> 
> 
> Am I right???

More or less.  An issue group is a group of instructions which can all
be issued at the same time.  It is not a requirement that *all*
execution units be busy.

> 2) Compilers can make use of it by reodering
> instructions so that all execution units are busy.
> Is GCC exploiting such feature????

In general, this is target dependent: it requires somebody to write
the scheduler description in the MD file.  It has been done for most
targets, though, including all popular targets.

Ian