Re: [Valgrind-users] RFC: proposal to remove user annotation from `cg_annotate`

[Nicholas N. <n.n...@gm...>]

I am planning to also remove the `-I`/`--include` option from cg_annotate,
for much the same reasons that I removed user annotated files: it's an
option that made sense in the very early days of cg_annotate, but is of
little or no use today, and it's getting in the way of some other changes I
want to make.

Nick

On Tue, 4 Apr 2023 at 15:52, Nicholas Nethercote <n.n...@gm...>
wrote:

> There were no objections, and I have now removed user annotations from
> `cg_annotate`.
>
> Nick
>
> On Wed, 29 Mar 2023 at 09:03, Nicholas Nethercote <n.n...@gm...>
> wrote:
>
>> Hi,
>>
>> I recently rewrote `cg_annotate`, `cg_diff`, and `cg_merge` in Python.
>> The old versions were written in Perl, Perl, and C, respectively. The new
>> versions are much nicer and easier to modify, and I have various ideas for
>> improving `cg_annotate`. This email is about one of those ideas.
>>
>> A typical way to invoke `cg_annotate` is like this:
>>
>> > cg_annotate cachegrind.out.12345
>>
>> This implies `--auto=yes`, which requests line-by-line "auto-annotation"
>> of source files. I.e. `cg_annotate` will automatically annotate all files
>> in the profile that meet the significance threshold.
>>
>> It's also possible to do something like this:
>>
>> > cg_annotate --auto=no cachegrind.out.12345 a.c b.c
>>
>> Which instead requests "user annotation" of the files `a.c` and `b.c`.
>>
>> My thesis is that auto-annotation suffices in practice for all reasonable
>> use cases, and that user annotation is unnecessary and can be removed.
>>
>> When I first wrote `cg_annotate` in 2002, only user annotation was
>> implemented. Shortly after, I added the `--auto={yes,no}` option. Since
>> then I've never used user annotation, and I suspect nobody else has either.
>> User annotation is ok when dealing with tiny programs, but as soon as you
>> are profiling a program with more than a handful of source files it becomes
>> impractical.
>>
>> The only possible use cases I can think of for user annotation are as
>> follows.
>>
>>    - If you want to see a particular file(s) annotated but you don't
>>    want to see any others, then you can use user annotation in combination
>>    with `--auto=no`. But it's trivial to search through the output for the
>>    particular file, so this doesn't seem important.
>>    - If the path to a file is somehow really messed up in the debug
>>    info, it might be possible that auto-annotation would fail to find it, but
>>    user annotation could find it, possibly in combination with `-I`. But this
>>    seems unlikely. Some basic testing shows that gcc, clang and rustc all
>>    default to using full paths in debug info. gcc supports
>>    `-fdebug-prefix-map` but that seems to mostly be used for changing full
>>    paths to relative paths, which will still work fine.
>>
>> Removing user annotation would (a) simplify the code and docs, and (b)
>> enable the possibility of moving the merge functionality from `cg_merge`
>> into `cg_annotate`, by allowing the user to specify multiple cachegrind.out
>> files as input.
>>
>> So: is anybody using user annotation? Does anybody see any problems with
>> this proposal?
>>
>> Thanks.
>>
>> Nick
>>
>