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Re: vcs_to_changelog.py very slow on a particular commit

From: Siddhesh Poyarekar
Subject: Re: vcs_to_changelog.py very slow on a particular commit
Date: Thu, 13 Feb 2020 08:13:03 +0530
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 13/02/20 05:11, Simon Marchi wrote:
> Hi Siddhesh (and others),
> I'd like to propose that we start using this script for the GDB project [1], 
> so I tried
> to run it on the binutils-gdb repository.  It works great until it hits 
> commit:
>     4934a27c8c1d5c8623366f5dbafae8af60b96bc0
>     [binutils][arm] arm support for ARMv8.m Custom Datapath Extension
> When we run the script with -d, we see that it is processing the huge 
> `coprocessor_opcodes`
> array in opcodes/arm-dis.c.  The script progresses, but slower and slower as 
> it goes.  It is
> taking so much time that it would not be practical to use it (I did not run 
> it until completion,
> so I don't know how much time it would take) This seems to show some O(n^2) 
> or worse behavior.
> I'm wondering if that can be improved.
> I haven't looked at the implementation of the script to try to figure out why 
> yet, I thought
> I would start by reporting the problem.

Thanks for reporting it.  I agree there is plenty of scope for
optimisation and this commit is a good motivating use case for me to
look into speeding things up.  I'll look into it this weekend.


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