[llvm-dev] scheduler options documentation?

Phil Tomson via llvm-dev llvm-dev at lists.llvm.org
Mon Sep 12 10:41:09 PDT 2016

As a follow on question: which of these options are already enabled when
compiling with -O3?


On Mon, Sep 12, 2016 at 10:37 AM, Phil Tomson <phil.a.tomson at gmail.com>

> I see that there are several options to influence instruction scheduling,
> but there doesn't seem to be a lot of information about what they do, for
> example:
> -misched-topdown -misched-bottomup
> The description in MachineScheduler.cpp says:
> "Force top-down list scheduling" and "Force bottom-up list scheduling"
> Which isn't too helpful - where might I want to use these? Under what
> conditions might they improve an instruction schedule?
> Similar questions for the instruction scheduler strategies:
> -misched=(default, converge,
> ilpmax, ilpmin, or shuffle)
> And for the analysis heuristics:
> -misched-cluster,
> -misched-cyclicpath, -misched-regpressure, and -misched-
> fusion
> Are these things mutually exclusive or can they be combined? What
> combination will give the most rigorous analysis and improve scheduling (at
> the cost of longer runtime of llc)
> Phil
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