Improve import time

[YigitElma]

• Replaces the recursive tree construction by a depth-first search algorithm in desc.compute
• Removes the default_quad computation at import time.

Importing desc.compute takes a very long time, and on my system, only _build_data_index itself takes 3.5 seconds. This change makes it run in 0.15 seconds!

The previous function was slow because of recursion, but it also had an extreme amount of redundant calls. For example, get_params, get_profiles, and get_derivs call get_deps again internally, and since the result of the first call is not stored yet, it rebuilds the whole tree again, almost 8 more times.

New _build_data_index was originally written by Claude Code (Opus 4.6), but I wrote most of the comments and I understand the algorithm behind.

Resolves #2154

[github-actions]

Memory benchmark result

|               Test Name                |      %Δ      |    Master (MB)     |      PR (MB)       |    Δ (MB)    |    Time PR (s)     |  Time Master (s)   |
| -------------------------------------- | ------------ | ------------------ | ------------------ | ------------ | ------------------ | ------------------ |
  test_objective_jac_w7x                 |   -0.07 %    |     4.183e+03      |     4.180e+03      |    -2.84     |       32.74        |       38.35        |
  test_proximal_jac_w7x_with_eq_update   |   -1.33 %    |     6.653e+03      |     6.564e+03      |    -88.46    |       145.76       |       156.51       |
  test_proximal_freeb_jac                |   -0.46 %    |     1.341e+04      |     1.335e+04      |    -61.15    |       88.44        |       94.44        |
  test_proximal_freeb_jac_blocked        |    0.03 %    |     7.694e+03      |     7.696e+03      |     2.44     |       76.49        |       83.01        |
  test_proximal_freeb_jac_batched        |    0.16 %    |     7.688e+03      |     7.700e+03      |    12.33     |       75.89        |       83.32        |
  test_proximal_jac_ripple               |   -3.83 %    |     3.685e+03      |     3.544e+03      |   -141.26    |       53.14        |       60.26        |
  test_proximal_jac_ripple_bounce1d      |   -1.18 %    |     3.769e+03      |     3.725e+03      |    -44.35    |       66.59        |       73.81        |
  test_eq_solve                          |   -2.47 %    |     2.245e+03      |     2.189e+03      |    -55.51    |       82.68        |       89.83        |

For the memory plots, go to the summary of Memory Benchmarks workflow and download the artifact.

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_lowres         |     -1.40 +/- 2.90     | -1.23e-02 +/- 2.54e-02 |  8.64e-01 +/- 1.6e-02  |  8.76e-01 +/- 2.0e-02  |
 test_equilibrium_init_medres            |     -2.07 +/- 3.30     | -1.45e-01 +/- 2.32e-01 |  6.87e+00 +/- 1.9e-01  |  7.01e+00 +/- 1.3e-01  |
 test_equilibrium_init_highres           |     -0.02 +/- 2.91     | -1.59e-03 +/- 2.23e-01 |  7.67e+00 +/- 1.2e-01  |  7.68e+00 +/- 1.9e-01  |
 test_objective_compile_dshape_current   |     -0.88 +/- 1.95     | -3.86e-02 +/- 8.55e-02 |  4.34e+00 +/- 4.7e-02  |  4.38e+00 +/- 7.1e-02  |
 test_objective_compute_dshape_current   |     -0.41 +/- 11.36    | -2.96e-06 +/- 8.15e-05 |  7.14e-04 +/- 5.1e-05  |  7.17e-04 +/- 6.3e-05  |
 test_objective_jac_dshape_current       |     +4.72 +/- 27.27    | +1.15e-03 +/- 6.65e-03 |  2.56e-02 +/- 4.9e-03  |  2.44e-02 +/- 4.5e-03  |
 test_perturb_2                          |     -0.10 +/- 1.90     | -2.09e-02 +/- 3.90e-01 |  2.05e+01 +/- 3.8e-01  |  2.06e+01 +/- 8.4e-02  |
 test_proximal_jac_atf_with_eq_update    |     -0.50 +/- 1.69     | -6.06e-02 +/- 2.05e-01 |  1.21e+01 +/- 7.9e-02  |  1.21e+01 +/- 1.9e-01  |
 test_proximal_freeb_jac                 |     +0.51 +/- 1.60     | +2.42e-02 +/- 7.55e-02 |  4.75e+00 +/- 2.4e-02  |  4.73e+00 +/- 7.2e-02  |
 test_solve_fixed_iter_compiled          |     +0.39 +/- 2.44     | +3.15e-02 +/- 1.99e-01 |  8.17e+00 +/- 1.1e-01  |  8.14e+00 +/- 1.6e-01  |
 test_LinearConstraintProjection_build   |     +1.70 +/- 3.51     | +1.59e-01 +/- 3.28e-01 |  9.49e+00 +/- 2.8e-01  |  9.33e+00 +/- 1.7e-01  |
 test_objective_compute_ripple_bounce1d  |     +0.34 +/- 4.88     | +1.01e-03 +/- 1.44e-02 |  2.97e-01 +/- 1.3e-02  |  2.96e-01 +/- 5.5e-03  |
 test_objective_grad_ripple_bounce1d     |     -0.23 +/- 1.91     | -2.18e-03 +/- 1.77e-02 |  9.25e-01 +/- 1.2e-02  |  9.27e-01 +/- 1.3e-02  |
 test_build_transform_fft_midres         |     -0.70 +/- 1.74     | -6.25e-03 +/- 1.55e-02 |  8.85e-01 +/- 8.8e-03  |  8.91e-01 +/- 1.3e-02  |
 test_build_transform_fft_highres        |     +0.10 +/- 3.20     | +1.19e-03 +/- 3.78e-02 |  1.18e+00 +/- 3.3e-02  |  1.18e+00 +/- 1.8e-02  |
 test_equilibrium_init_lowres            |     -0.76 +/- 3.36     | -4.96e-02 +/- 2.19e-01 |  6.46e+00 +/- 1.6e-01  |  6.50e+00 +/- 1.5e-01  |
 test_objective_compile_atf              |     +0.96 +/- 3.82     | +6.04e-02 +/- 2.40e-01 |  6.35e+00 +/- 2.0e-01  |  6.29e+00 +/- 1.4e-01  |
 test_objective_compute_atf              |     +4.86 +/- 13.44    | +1.00e-04 +/- 2.76e-04 |  2.16e-03 +/- 2.1e-04  |  2.06e-03 +/- 1.8e-04  |
 test_objective_jac_atf                  |     -0.56 +/- 3.75     | -8.83e-03 +/- 5.89e-02 |  1.56e+00 +/- 3.9e-02  |  1.57e+00 +/- 4.4e-02  |
 test_perturb_1                          |     -0.47 +/- 1.55     | -7.71e-02 +/- 2.56e-01 |  1.64e+01 +/- 1.9e-01  |  1.65e+01 +/- 1.7e-01  |
 test_proximal_jac_atf                   |     -0.76 +/- 1.53     | -3.98e-02 +/- 8.06e-02 |  5.22e+00 +/- 5.7e-02  |  5.26e+00 +/- 5.7e-02  |
 test_proximal_freeb_compute             |     +2.09 +/- 2.23     | +3.45e-03 +/- 3.68e-03 |  1.69e-01 +/- 2.5e-03  |  1.65e-01 +/- 2.7e-03  |
 test_solve_fixed_iter                   |     -0.12 +/- 1.98     | -3.67e-02 +/- 5.82e-01 |  2.94e+01 +/- 4.0e-01  |  2.95e+01 +/- 4.2e-01  |
 test_objective_compute_ripple           |     +1.23 +/- 4.51     | +2.81e-03 +/- 1.03e-02 |  2.31e-01 +/- 4.3e-03  |  2.29e-01 +/- 9.4e-03  |
 test_objective_grad_ripple              |     +0.90 +/- 2.17     | +7.69e-03 +/- 1.86e-02 |  8.64e-01 +/- 1.7e-02  |  8.57e-01 +/- 8.2e-03  |

Github CI performance can be noisy. When evaluating the benchmarks, developers should take this into account.

[unalmis]

my suggestion on the issue avoids an eigenvalue solve on import. current changes force an eigenvalue solve every time an object is made, which is worse for optimization and debugging with jit in general. i didn't check the claude stuff

[codecov]

Codecov Report

❌ Patch coverage is 98.64865% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.39%. Comparing base (03637dd) to head (9e41a77).

Files with missing lines	Patch %	Lines
desc/backend.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2156      +/-   ##
==========================================
- Coverage   94.45%   94.39%   -0.06%     
==========================================
  Files         101      101              
  Lines       28604    28666      +62     
==========================================
+ Hits        27018    27060      +42     
- Misses       1586     1606      +20     

Files with missing lines	Coverage Δ
desc/compute/__init__.py	100.00% <100.00%> (ø)
desc/integrals/bounce_integral.py	97.98% <100.00%> (+0.02%)	⬆️
desc/backend.py	89.74% <50.00%> (ø)

... and 4 files with indirect coverage changes

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[f0uriest]

This sounds like it's basically doing what set_tier is doing below, so ideally we could do them both at the same time.

[YigitElma]

Yeah, I was actually gonna suggest that in looped compute PR. The order obtained at the end can be used directly. That is why I have special sort instead of normal sort.

[YigitElma]

#1557 (comment)

thdanks

[unalmis]

ididn't check calude stuff

[YigitElma]

I will merge this after the dev meeting, in case @f0uriest has some additional comments