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>
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