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Scheduling and inserting NOPs


Hi!

My next GCC-adventure is scheduling:

1) As far as I can see some levels of optimization do not schedule the code. To generate correct code I have to insert NOP-operations to fill the delays (the architecture has no interlocks), but I can't find a function/hook to generate these NOPs. Could someone point me to the functions in the internals document? I tried TARGET_SCHED_DFA_NEW_CYCLE but this one can't write to the output.

2) The scheduling depends on the producer/consumer. An operation can consume a register-operand without any difficult scheduling:

cycle 1: MOV R1, #4711	;; r1 := 4711
cycle 2: ADD R1, R1, R1	;; r1 := r1 + r1

But if an operation reads the memory via an address register, then the register must be written some cycles before the operation:

cycle 1: MOV A1, _label_a	;; get address of var a
cycle 2: NOP
..
cycle 5: ADD (A1), (A1), (A1)	;; *a := *a + *a

I tried to solve this with (define_bypass 4 ..) with my own guard- function, but the ADD-operation appears before cycle 5 (same problem as no.1?)

Hm, these are FAQs? Is there a collection of all answers to these FAQs?

Every idea is welcome,
thanks,
Boris


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