[LLVMdev] specializing hybrid_ls_rr_sort (was: Re: Bottom-Up Scheduling?)
atrick at apple.com
Mon Dec 19 23:20:15 PST 2011
On Dec 19, 2011, at 10:53 PM, Hal Finkel wrote:
> Here's my "thought experiment" (from PR11589): I have a bunch of
> load-fadd-store chains to schedule. A store takes two cycles to clear
> its last pipeline stage. The fadd takes longer to compute its result
> (say 5 cycles), but can sustain a rate of 1 independent add per cycle.
> As the scheduling is bottom-up, it will schedule a store, then it has a
> choice: it can schedule another store (at a 1 cycle penalty), or it can
> schedule the fadd associated with the store it just scheduled (with a 4
> cycle penalty due to operand latency). It seems that the current hybrid
> scheduler will choose the fadd, I want a scheduler that will make the
> opposite choice.
That's just wrong. You may need to look at -debug-only=pre-RA-sched and debug your itinerary.
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