PointCloudLibrary/pcl

[cmake] Adding support for PCH and Unity builds (using Cotire/CMake 3.16)

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#649 opened on Apr 19, 2014

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help wantedkind: todomodule: cmakeskill: cmake

Description

Have a look at https://github.com/sakra/cotire, it can speed up the build of a CMake project with low effort (by using precompiled headers).

When compiling an example like the extract_indices tutorial, precompiled headers brought down my compile time from 6s to 1.8.

For this example, with g++ -H I found that it includes over 3900 header files. A precompiled header reduces that to 1.

Note that cotire doesn't seem to be able to share precompiled headers across files so far, so it might not be able to help when doing just a single full build once, but it seems like it can dramatically improve build speeds when developing.

The speedup [doesn't seem to work with clang] right now though.

Contributor guide

Tech stack
cpp
Domain
build systemtooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Basic understanding of CMakeFamiliarity with C++ compilation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
Investigate the cotire tool (https://github.com/sakra/cotire) and how it integrates with CMake. Examine PCL's CMake configuration files (e.g., CMakeLists.txt in each module) to determine where precompiled headers and unity builds can be added. Check the discussion in the issue comments for any proposed approaches or concerns. Test with a simple example like extract indices to measure build time improvement using g++ H. Note that cotire may not work with clang, so consider alternative CMake 3.16+ built in support for PCH.