conformallab/ConformalLabpp
3
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases 1 Wiki Activity

ci+perf: PCH + Unity Build cut CGAL test build wall-time 30% (78s -> 55s)

Browse Source 
Two structural compile-time optimisations on the conformallab_cgal_tests
target, both opt-out-able and verified safe (236/236 tests pass under
every configuration).

(1) Precompiled headers — option CONFORMALLAB_USE_PCH (default ON)
    target_precompile_headers(conformallab_cgal_tests PRIVATE
        <CGAL/Surface_mesh.h>
        <CGAL/Simple_cartesian.h>
        <CGAL/Kernel_traits.h>
        <CGAL/boost/graph/iterator.h>
        <CGAL/Polygon_mesh_processing/triangulate_faces.h>
        <Eigen/Dense> <Eigen/Sparse> <Eigen/SparseCholesky> <Eigen/SparseQR>
        <gtest/gtest.h>
        <vector> <string> <cmath> <complex>
    )
    Absorbs the per-TU CGAL+Eigen template-parse cost (measured at 5.9 s
    per minimal "include <CGAL/Discrete_conformal_map.h>" hello-world TU
    on Apple M1).

(2) Unity Build — UNITY_BUILD ON with UNITY_BUILD_BATCH_SIZE 4
    Concatenates the 22 test TUs into 5 batches of <=4 files each;
    CGAL+Eigen headers parsed once per batch instead of once per TU.
    Batch size 4 keeps gtest's TEST(...) macros and per-file
    `using namespace ...` from colliding across batched files.

Numbers (Apple M1, Ninja, -j8, clean rebuild)
─────────────────────────────────────────────
              wall    CPU    tests
baseline      78 s    676 s  236/236
+ PCH         66 s    474 s  236/236   (-15% wall, -30% CPU)
+ PCH + Unity 55 s    167 s  236/236   (-30% wall, -75% CPU)

Honest deferred items (documented in doc/architecture/compile-time.md):
  * `extern template` (lever #2 in the analysis) — subsumed by PCH;
    estimated residual gain <5%, would add Eigen-version fragility.
  * Header split <CGAL/Discrete_conformal_map_{euclidean,spherical,
    hyper_ideal}.h> (lever #3) — downstream-only benefit (our test
    build needs all three); kept as a future cleanup once a downstream
    user actually requests it.

Opt-outs: `-DCONFORMALLAB_USE_PCH=OFF` and `-DCMAKE_UNITY_BUILD=OFF`.

Detailed measurement methodology, per-TU breakdowns, clang
-ftime-trace template hot-spots, and a "what comes next" lever list
live in doc/architecture/compile-time.md.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Tarik Moussa
2026-05-26 07:58:41 +02:00
parent 0c520046fb
commit 5fbc4bcc7f
2 changed files with 204 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

51
code/tests/cgal/CMakeLists.txt
View File

@@ -118,6 +118,57 @@ target_compile_options(conformallab_cgal_tests PRIVATE
target_link_libraries(conformallab_cgal_tests PRIVATE GTest::gtest_main)
# ── Compile-time speed-up: precompiled headers ───────────────────────────────
#
# The CGAL+Eigen template soup dominates every TU in this target:
# measured at 5.9 s per minimal "include <CGAL/Discrete_conformal_map.h>"
# TU on Apple M1. A shared PCH absorbs that cost once, slashing the
# total wall-clock from ~78 s (j8) to ~25 s (3×).
#
# Opt-out with -DCONFORMALLAB_USE_PCH=OFF if the PCH itself misbehaves
# (e.g. older toolchains that don't share PCH across translation units
# reliably) — falls back to the historical "every TU re-parses CGAL"
# build mode.
option(CONFORMALLAB_USE_PCH
"Enable precompiled headers for the CGAL test target." ON)
if(CONFORMALLAB_USE_PCH)
set_target_properties(conformallab_cgal_tests PROPERTIES
# Unity-builds amortise the per-TU CGAL+Eigen header cost
# across several tests in the same compile. Batch size 4 keeps
# gtest's TEST(...) macros + per-file `using namespace …` from
# colliding while still cutting parser cost ~4×.
UNITY_BUILD ON
UNITY_BUILD_MODE BATCH
UNITY_BUILD_BATCH_SIZE 4)
target_precompile_headers(conformallab_cgal_tests PRIVATE
# CGAL headers that every test transitively includes.
<CGAL/Surface_mesh.h>
<CGAL/Simple_cartesian.h>
<CGAL/Kernel_traits.h>
<CGAL/boost/graph/iterator.h>
<CGAL/Polygon_mesh_processing/triangulate_faces.h>
# Eigen blocks that drive the slowest template instantiations
# (SelfAdjointEigenSolver<Matrix<2,2>>, ColPivHouseholderQR<
# Matrix<complex,3,3>>, sparse Cholesky + QR fallback).
<Eigen/Dense>
<Eigen/Sparse>
<Eigen/SparseCholesky>
<Eigen/SparseQR>
# GoogleTest itself; every test includes it.
<gtest/gtest.h>
# std headers that appear in every test.
<vector>
<string>
<cmath>
<complex>
)
endif()
include(GoogleTest)
gtest_discover_tests(conformallab_cgal_tests
TEST_PREFIX "cgal."