Replace maybe_parallel_for with TBB APIs

[zfergus]

Description

Remove the maybe_parallel_for wrapper and associated headers. Use tbb::parallel_for and tbb::enumerable_thread_specific directly, and update CMake and config to stop defining IPC_TOOLKIT_WITH_TBB

[Copilot]

Pull request overview

This PR removes the maybe_parallel_for abstraction and the IPC_TOOLKIT_WITH_TBB macro, switching affected call sites to use OneTBB APIs (tbb::parallel_for, tbb::blocked_range, tbb::enumerable_thread_specific) directly.

Changes:

• Deleted maybe_parallel_for headers/implementation and removed them from the utils CMake source list.
• Updated smooth contact and potential implementations to use TBB primitives directly for parallel loops and thread-local storage.
• Removed the IPC_TOOLKIT_WITH_TBB define from the generated config header template.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/ipc/utils/maybe_parallel_for.tpp	Removes the conditional TBB wrapper implementation.
src/ipc/utils/maybe_parallel_for.hpp	Removes the public wrapper API and thread-storage helpers.
src/ipc/utils/matrix_cache.cpp	Drops the now-unused maybe_parallel_for include.
src/ipc/utils/CMakeLists.txt	Stops compiling/adding deleted maybe_parallel_for sources.
src/ipc/smooth_contact/smooth_contact_potential.cpp	Replaces wrapper usage with tbb::parallel_for + enumerable_thread_specific.
src/ipc/smooth_contact/smooth_collisions_builder.hpp	Switches merge signatures to take tbb::enumerable_thread_specific directly.
src/ipc/smooth_contact/smooth_collisions_builder.cpp	Updates merge definitions to match new TBB-based signatures.
src/ipc/smooth_contact/smooth_collisions.cpp	Replaces wrapper parallel loops with direct TBB parallel_for ranges.
src/ipc/potentials/potential.cpp	Replaces wrapper usage with direct TBB parallel_for + enumerable_thread_specific.
src/ipc/config.hpp.in	Removes the IPC_TOOLKIT_WITH_TBB macro definition.

Comments suppressed due to low confidence (2)

src/ipc/smooth_contact/smooth_contact_potential.cpp:7

• #include <tbb/combinable.h> appears unused in this translation unit (no tbb::combinable usage). Consider removing it to avoid unused-include warnings in stricter builds.

#include <tbb/blocked_range.h>
#include <tbb/combinable.h>
#include <tbb/enumerable_thread_specific.h>

src/ipc/smooth_contact/smooth_contact_potential.cpp:187

• tbb::parallel_for(size_t(0), storages.size(), ...) uses a lambda parameter of type int. This can cause signed/unsigned warnings and becomes incorrect if the range ever exceeds INT_MAX. Use size_t (or the same index type as the range) for the lambda parameter and downstream indexing.

        tbb::parallel_for(size_t(0), storages.size(), [&](int i) {
            const SparseMatrixCache& cache =
                dynamic_cast<const SparseMatrixCache&>(*storages[i]->cache);
            int offset = offsets[i];

            std::copy(
                cache.entries().begin(), cache.entries().end(),
                triplets.begin() + offset);
            offset += cache.entries().size();

            if (cache.mat().nonZeros() > 0) {
                int count = 0;
                for (int k = 0; k < cache.mat().outerSize(); ++k) {
                    for (Eigen::SparseMatrix<double>::InnerIterator it(
                             cache.mat(), k);
                         it; ++it) {
                        assert(count < cache.mat().nonZeros());
                        triplets[offset + count++] = Eigen::Triplet<double>(
                            it.row(), it.col(), it.value());
                    }
                }
            }
        });

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[Copilot]

tbb::blocked_range<int>(0, candidates.ev_candidates.size()) converts a size_t size to int, which can overflow for large candidate sets and may trigger signed/unsigned warnings. Prefer tbb::blocked_range<size_t> (and adjust the lambda/range types accordingly).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.95%. Comparing base (6051c39) to head (e80c167).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #214      +/-   ##
==========================================
- Coverage   96.96%   96.95%   -0.01%     
==========================================
  Files         159      158       -1     
  Lines       24666    24659       -7     
  Branches      883      882       -1     
==========================================
- Hits        23917    23908       -9     
- Misses        749      751       +2     

Flag	Coverage Δ
unittests	96.95% <100.00%> (-0.01%)	⬇️

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