Re: How to describe function units allocation

["Pranav Bhandarkar" <pranav dot bhandarkar at gmail dot com>]

> Hi,
> For the backend TI DSP TMS320C6x, There are four types of functional
> units which are .L unit, .M unit, .S unit and .D unit, and each type
> consists of two units named .X1 and .X2 respectively. Namely, there are
> total 8 units. Except the .M units surve only for multiply, other units
> share many functions. For example, they both enable 32 bits arithmetical
> operation. And in the assembly, which functional unit is used to perform
> operation must be explicitly indicated. For example, ADD .S1 A0, A1, A2;
> ADD .L1 A0, A1, A2; ADD .D1 A0, A1, A2 achieve the same goal by using
> different units. Surely, when producing assembly, a functional unit
> allocation somewhat like register allocation is needed. I wonder how can
> I describe the relationship in the machine description file, and whether
> I need write a functional unit allocation algorithm or it is done by a
> general purpose allocation algorithm embedded in GCC, like register
> allocation, I only need give some architecture descriptions? Thanks in
> advance for your kind assistance.

IMHO. the functional units that accompany the assembly instruction are
optional. However, for c6x-gcc the reason cc1 doesnt allocate
functional units is that the assembler ( as part of the c6x binutils )
does the functional unit allocation on its own. There are some notes
about how the assembler does this in Extending the GNU Assembler for
Texas Instruments TMS320C6x-DSP.pdf

HTH,
Pranav

>
> Regards,
> Li Wang
>