Re: Doubt about filling delay slot

["Mohamed Shafi" <shafitvm at gmail dot com>]

On Thu, Apr 3, 2008 at 7:35 PM, Ian Lance Taylor <iant@google.com> wrote:
> "Mohamed Shafi" <shafitvm@gmail.com> writes:
>
>
> > Say the target has two delay slots for call instructions.
>  > So we can have something like this
>  > (define_attr "slottable" "no,yes,has_slot" (const_string "yes"))
>  >
>  > (define_delay (eq_attr "slottable" "has_slot")
>  >   [(eq_attr "slottable" "yes") (nil) (nil)
>  >    (eq_attr "slottable" "yes") (nil) (nil)])
>  >
>  > So in define_insn for call i can have
>  > (set_attr "slottable" "has_slot")
>  >
>  >
>  > Now imagine that i have 3 patterns : Pattern A with two instructions
>  > in its template, Pattern B and Pattern C with only one instruction in
>  > its template.
>  > When it comes to filling the call instruction delay slot if slot 1 is
>  > filled with Pattern A then there is no need to fill slot 2. But if its
>  > filled with Pattern C or Pattern B, then slot 2 should be filled with
>  > Pattern B or Pattern C, but not Pattern A.
>  > Will i be able to do this in the back-end?
>
>  Ah, OK.  It's easy enough to say that you can't put pattern A in slot
>  2.  But there is no way to say that if pattern A is in slot 1, then
>  slot 2 is not available.
>
Ok i guess you are saying that this is not possible.
But then this should be something that all the targets should deal
with. How are they doing it?

May be i can set the attribute "slottable" as 'no' for patterns with 3
or more instructions and in DBR_OUTPUT_SEQEND or in
TARGET_MACHINE_DEPENDENT_REORG check the delay slots and reorder the
instructions if the slots are filled with 3 instructions ?

Are there any other solutions?

Regards,
Shafi
PS : Why is this not implemented? This seems like a standard
requirement for the delay slots