[llvm-dev] 7-8% compile time slowdowns in LLVM 10

[Josh Stone via llvm-dev]

On 5/11/20 10:53 PM, Chris Lattner wrote:
>
>
>> On May 8, 2020, at 4:40 PM, Josh Stone via llvm-dev
>> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>
>> On 4/14/20 1:26 AM, Neil Henning via llvm-dev wrote:
>>> Hey list,
>>>
>>> TL;DR - LLVM 10 is around 7-8% slower than LLVM 9 when compiling the
>>> same inputs.
>>>
>>> [...] concerns from the Rust folks about LLVM 10's slowdowns [...]
>>
>> I'm one of those Rust folks, and in the last few days I've been
>> trying to dig into this. I focused on one particular benchmark input
>> -- I've attached that IR generated from Rust 1.43.0 for LLVM 9.0.1. I
>> started running a git bisection to see if anything huge jumped out,
>> but it seems to be gradual. Maybe others can take my input and find
>> some pattern to the decline.
>>
>
> Hi Josh,
>
> On behalf of the “LLVM people”, I’d like to publicly thank you for the
> this work to make sure that LLVM compile time performance stays
> acceptable over time.  I think that the Rust community’s diligence in
> terms of tracking, improving, and publicizing compile time performance
> has been incredibly valuable.  Thank you,

Thank you, Chris, I'll certainly share that feedback with the Rust
community.

If there's anything specific I can do to make such data more actionable,
please let me know. I already learned from my Red Hat peers that I
didn't have a full understanding of llc vs opt etc., so I need to
explore more to frame the test in a way that's closer to what rustc
actually does.


Josh

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