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Re: [RFC] sched: Do not move expensive insns speculatively (PR68664)

On 01/27/2017 02:19 AM, Segher Boessenkool wrote:


But what is "insn cost"?  Latency is no good at all -- we *want* insns
with higher latency to be earlier.  fsqrt is not pipelined, and that is
what makes it so costly.  (This isn't modeled in the scheduling
description btw: that would make the automata sizes explode, the usual
problem).
On other machines sqrt might be pipelined, so the patch as-is clearly isn't suitable. rtx_cost/insn_cost probably also won't do, since it doesn't model that property either.
Maybe instead of a hook you could have an insn attribute that the scheduler looks for. 


Bernd
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