[llvm-dev] General question about enabling partial inlining

Tue Oct 3 12:46:18 PDT 2017

On Tue, Oct 3, 2017 at 9:45 AM, Graham Yiu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi Jun,
>
> If we were to enable this by default, I think we'd make a push to enable
> it with or without PGO. I'm not sure what's currently preventing the
> partial inlining pass to be enabled by default, actually. David Li may have
> a better sense on this as he's been actively working on it most recently.
>

Longer term, the partial-inliner should really be just a 'function
outlining pass' that serves as an enabler for more aggressive inlining.
That of course can be enabled by default (assuming good cost
model/heuristics) before the regular inliner.

David

>
>
> As for the cost model, right now it's platform independent, so I'm
> assuming you'll need some sort of hook for platform-specific costs/bonuses
> to detect spilling of different types of registers. Also, I'm not quite
> sure how you'll do this type of detection at the IR level. Are you thinking
> some sort of heuristic?
>
> Graham Yiu
> LLVM Compiler Development
> IBM Toronto Software Lab
> Office: (905) 413-4077 C2-707/8200/Markham
> Email: gyiu at ca.ibm.com
>
> [image: Inactive hide details for "Jun Lim" ---10/03/2017 12:21:38 PM---Hi
> Graham,]"Jun Lim" ---10/03/2017 12:21:38 PM---Hi Graham,
>
> From: "Jun Lim" <junbuml at codeaurora.org>
> To: "'Graham Yiu'" <gyiu at ca.ibm.com>
> Cc: <llvm-dev at lists.llvm.org>
> Date: 10/03/2017 12:21 PM
> Subject: RE: [llvm-dev] General question about enabling partial inlining
> ------------------------------
>
>
>
> Hi Graham,
>
> Thanks for sharing this. Are you planning on enabling the pass only on
> PGO? Even in non-PGO, I noticed some performance gains when we are
> aggressive in partially inlining the early return part, especially when the
> callee spill CSRs in the entry block. At a high level, I have two
> questions:
> 1. What is the main obstacle that prevent the pass from being enabled by
> default?
> 2. Would it make sense to give some bonus in the cost model when we
> detect the possibility of spilling CSRs in the entry block?
>
> Thanks,
> Jun
> *From:* Graham Yiu [mailto:gyiu at ca.ibm.com <gyiu at ca.ibm.com>]
> *Sent:* Tuesday, October 3, 2017 11:08 AM
> *To:* junbuml at codeaurora.org
> *Cc:* llvm-dev at lists.llvm.org
> *Subject:* Re: [llvm-dev] General question about enabling partial inlining
>
> Hi Jun,
>
> We're actually looking at enhancing the partial inlining pass right now
> (see *http://lists.llvm.org/pipermail/llvm-dev/2017-August/116515.html*
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_pipermail_llvm-2Ddev_2017-2DAugust_116515.html&d=DwMFAg&c=jf_iaSHvJObTbx-siA1ZOg&r=4ST7e3kMd0GTi3w9ByK5Cw&m=9oYOvB3l33-euX7ag6texitDSABCTLWfauz0YGW7zZ8&s=lZOJDeoavpuEHo29CLd9Kvkn1ibSdgK5125f13O-LYQ&e=>
> )
>
> We'd be interested in turning on the pass by default some time in the
> future, if our enhancements prove beneficial.
>
> Cheers,
>
> Graham Yiu
> LLVM Compiler Development
> IBM Toronto Software Lab
> Office: (905) 413-4077 C2-707/8200/Markham
> Email: *gyiu at ca.ibm.com* <gyiu at ca.ibm.com>
>
> [image: Inactive hide details for via llvm-dev ---09/13/2017 01:12:02
> PM---Hi, I noticed some performance gains in some spec benchmarks]via
> llvm-dev ---09/13/2017 01:12:02 PM---Hi, I noticed some performance gains
> in some spec benchmarks without
>
> From: via llvm-dev <*llvm-dev at lists.llvm.org* <llvm-dev at lists.llvm.org>>
> To: *llvm-dev at lists.llvm.org* <llvm-dev at lists.llvm.org>
> Date: 09/13/2017 01:12 PM
> Subject: [llvm-dev] General question about enabling partial inlining
> Sent by: "llvm-dev" <*llvm-dev-bounces at lists.llvm.org*
> <llvm-dev-bounces at lists.llvm.org>>
> ------------------------------
>
>
>
>
> Hi,
>
> I noticed some performance gains in some spec benchmarks without
> significant code size bloat when aggressively performing partial
> inlining, especially when the original callee spill CSRs in the entry
> block. I guess the partial inlining is not enabled mainly due to the
> code size. Is there any other issue which prevent the pass from being
> enabled? Do we have any plan or any on-going works to enable partial
> inlining ?
> Thanks,
> Jun
>
> --
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