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Re: GCC missing -flto optimizations? SPEC lbm benchmark
- From: "Bin.Cheng" <amker dot cheng at gmail dot com>
- To: Steve Ellcey <sellcey at marvell dot com>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Jun Ma <majun4950646 at gmail dot com>
- Date: Fri, 15 Feb 2019 17:11:54 +0800
- Subject: Re: GCC missing -flto optimizations? SPEC lbm benchmark
- References: <firstname.lastname@example.org>
On Fri, Feb 15, 2019 at 3:30 AM Steve Ellcey <email@example.com> wrote:
> I have a question about SPEC CPU 2017 and what GCC can and cannot do
> with -flto. As part of some SPEC analysis I am doing I found that with
> -Ofast, ICC and GCC were not that far apart (especially spec int rate,
> spec fp rate was a slightly larger difference).
> But when I added -ipo to the ICC command and -flto to the GCC command,
> the difference got larger. In particular the 519.lbm_r was more than
> twice as fast with ICC and -ipo, but -flto did not help GCC at all.
> There are other tests that also show this type of improvement with -ipo
> like 538.imagick_r, 544.nab_r, 525.x264_r, 531.deepsjeng_r, and
> 548.exchange2_r, but none are as dramatic as 519.lbm_r. Anyone have
> any idea on what ICC is doing that GCC is missing? Is GCC just not
> agressive enough with its inlining?
IIRC Jun did some investigation before? CCing.
> Steve Ellcey