[cfe-dev] [RFC] Additional frontend timers in -ftime-report

[Vedant Kumar via cfe-dev]

> On Aug 9, 2017, at 10:28 AM, Brian Gesiak via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> Hello all,
> 
> I'd like to hear your thoughts on expanding the amount of information
> provided by `clang -ftime-report`.
> 
> I noticed that `gcc -ftime-report` provides a breakdown of how much
> time GCC spends doing preprocessing, parsing, template instantiation,
> and more. `clang -ftime-report`, on the other hand, gives an
> incredibly detailed breakdown of how long each LLVM pass takes, but
> does not provide much detail on front-end tasks such as preprocessing
> and template instantiation.
> 
> Here's an example of output from `clang -ftime-report` and `gcc
> -ftime-report`:
> https://gist.github.com/modocache/d74833818107ed50d11387a5a4e3fb72
> 
> As a result, when attempting to diagnose slow compile times with
> Clang, my understanding is that users have two choices:
> 
> 1. Use external profiling tools on a `clang` executable that does not
> have its symbols stripped in order to determine what the bottleneck
> is.
> 2. Compile the same code with `gcc -ftime-report` to determine which
> phase is taking a long time. This workflow suits users who aren't
> interested in improving Clang's performance, and are happy to simply
> rewrite their source code so that it compiles faster.
> 
> I think it would be an improvement if Clang output more front-end
> information in `clang -ftime-report`. For example, I've sent up a diff
> that adds timers related to preprocessing:
> https://reviews.llvm.org/D36492. Would anyone be interested in
> reviewing it?
> 
> In addition, if anyone has thoughts on the general idea of adding more
> timers to `clang -ftime-report`, please let me know. Assuming there's
> interest in better resembling `gcc -ftime-report` behavior, I would be
> happy to add timers for preprocessing, parsing, template
> instantiation, and more.

This sounds like a great idea, thanks for working on it!

vedant

> 
> Thanks!
> 
> - Brian Gesiak
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