While reading the USIII Cu manual (Version 2.2 May 2003),
I found this interesting comment in section 3.1.1, page 3-25:

(after describing the RAS' use as indirect branch predictor)
"For other indirect branches (branches whose targets are
determined by a register value), the software can provide
a branch target prediction with a jump target preparation
instruction."

This is the first I've heard of SPARC having a jump target
preparation instruction. The manual doesn't seem to describe
it any further.

Can anyone sched some light on this?
--
Mikael Pettersson (mikpe@csd.uu.se)
Computing Science Department, Uppsala University

>>>>> "Mikael" == Mikael Pettersson <mikpe@harpo.csd.uu.se> writes:

Mikael> While reading the USIII Cu manual (Version 2.2 May 2003),
Mikael> I found this interesting comment in section 3.1.1, page 3-25:

Mikael> (after describing the RAS' use as indirect branch predictor)
Mikael> "For other indirect branches (branches whose targets are
Mikael> determined by a register value), the software can provide
Mikael> a branch target prediction with a jump target preparation
Mikael> instruction."

Mikael> This is the first I've heard of SPARC having a jump target
Mikael> preparation instruction. The manual doesn't seem to describe
Mikael> it any further.

Maybe it's refering to the BPN instruction (branch never with
prediction). The Sparc V9 manual says this can be a prefetch for
instructions, fetching from the branch target. It can also be just a
nop. Maybe the US-III actually makes it a prefetch.

Ray

In article <4nk784sva5.fsf@edgedsp4.rtp.ericsson.se>,
Raymond Toy <toy@rtp.ericsson.se> wrote:
>>>>>> "Mikael" == Mikael Pettersson <mikpe@harpo.csd.uu.se> writes:
>
> Mikael> While reading the USIII Cu manual (Version 2.2 May 2003),
> Mikael> I found this interesting comment in section 3.1.1, page 3-25:
>
> Mikael> (after describing the RAS' use as indirect branch predictor)
> Mikael> "For other indirect branches (branches whose targets are
> Mikael> determined by a register value), the software can provide
> Mikael> a branch target prediction with a jump target preparation
> Mikael> instruction."
>
> Mikael> This is the first I've heard of SPARC having a jump target
> Mikael> preparation instruction. The manual doesn't seem to describe
> Mikael> it any further.
>
>Maybe it's refering to the BPN instruction (branch never with
>prediction). The Sparc V9 manual says this can be a prefetch for
>instructions, fetching from the branch target. It can also be just a
>nop. Maybe the US-III actually makes it a prefetch.

Hmm (checking V9 manual) Nope, I don't think so. BPN is a regular
branch with immediate displacement, which makes it useless as a
"prepare" instruction for indirect branches.

I suspect they added a new instruction.
--
Mikael Pettersson (mikpe@csd.uu.se)
Computing Science Department, Uppsala University