"Mohamed Shafi" <[EMAIL PROTECTED]> writes: > On Thu, Apr 3, 2008 at 7:35 PM, Ian Lance Taylor <[EMAIL PROTECTED]> wrote: >> "Mohamed Shafi" <[EMAIL PROTECTED]> 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?
It's not a standard problem. On most machines a single insn does not take up two slots. To put it another way, you say that pattern A has two instructions in its template, and I assumed that that was a requirement for some reason. If the instructions can be executed independently, then the normal approach would be to use a define_split which runs after reload to produce two insns for scheduling and delay slot filling. > 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 ? I wouldn't hold out a lot of hope for that approach. I guess it might work, but I think that jump threading would give you no end of trouble. > PS : Why is this not implemented? This seems like a standard > requirement for the delay slots On most machines define_split suffices. I assumed that it wouldn't work for you--if it does, do that. I worked on a machine where certain instructions were required to come in pairs. In that case those instructions were uncommon, and I just marked them as ineligible for delay slots. Ian
