population.cu takes ~2h to compile from a cold sccache miss (7-arch nvcc build)

[ramakrishnap-nv]

Observed in #1969, run 35740440549: cpp/src/mip_heuristics/diversity/population.cu alone took 1h52m47s to compile (14:53:28→16:46:15 UTC) once its sccache key was invalidated by an unrelated header-only change in cpu_routing_problem.hpp. The rest of the 474-target build finished in minutes; this one file was the critical path for the whole job.

Compiled for 7 architectures in one nvcc invocation: sm_75, 80, 86, 90a, 100f, 120a, 120, with --expt-extended-lambda --expt-relaxed-constexpr -O3 -lineinfo.

Worth investigating:

• Is this file unusually template-heavy for what it does?
• Could it be split into smaller translation units to compile in parallel instead of one monolithic unit?
• Does it need all 7 archs, or could some be dropped/deferred?

A single unrelated header touch shouldn't be able to add ~2h to CI turnaround via one file.

🤖 Generated with Claude Code

[aliceb-nv]

All TUs in CI are built for these 7 archs. population.cu is not in any way special, and unless this is a consistent reproducer across machines, I'd treat that as noise from an unlucky run.