Hello All,
I need some help with setting the pipeline hazard recognizer (I am
working with gcc v4.5.1 for a private target).
A brief pipeline description of my target:
We have 2 functional units
1) For multiplication.
2) For All other instructions.
a) Multiply instructions are not pipelined.
b) It takes 4 cycles to execute a multiply instruction.
c) The result of multiply instruction will be available after 4 cycles.
So there should be a 4 cycle gap between 2 multiply instructions
(independent/dependent) and also its depend instructions (other than
multiply).
e.g.1:
mult R3, R4, R5 -- (A)
add R0, R1, R2
mult R7, R8, R9 -- (B)
A) & (B) are independent.
This is a pipeline error.
Need to add 2 NOP's or schedule 2 other independent instructions before
(B).
e.g.2:
mult R3, R4, R5 --(A)
add R7, R8, R9
add R5, R1, R2 --(B)
(A) & (B) are dependent.
Even though there is no pipeline error, the value of "R5" used will
not be the updated one as 'mult' takes 4 cycles for the result to be
available.
Need to add 2 NOP's or schedule 2 other independent instructions before
(B).
I have done the following, but not sure if this will take care of:
A) 4 cycle gap between 2 Independent multiply instructions
B) 4 cycle gap beween multiply and any other dependent instruction.
(define_automaton "pipeline")
(define_cpu_unit "simple" "pipeline")
(define_cpu_unit "mult" "pipeline")
(define_insn_reservation "any_insn" 1 (eq_attr "type" "!mul") "simple")
(define_insn_reservation "mult" 4 (eq_attr "type" "mul") "mult*4")
In case other independent instructions are not available to be
scheduled for this latency, i will be inserting NOP's from the
backend. But i want to make sure the correct info is passed to the
scheduler.
Any comments/suggestions?
Thanks,
Rohit
