The two MPI_Allreduce calls (data + weight) were the #1 hotspot at 38.5%
CPU time. Since all ranks traverse the same block list and agree on point
ownership, we replace the global reduction with targeted MPI_Bcast from
each owner rank. This also eliminates the weight array/Allreduce entirely,
removes redundant heap allocations (shellf, weight, DH, llb, uub), and
writes interpolation results directly into the output buffer.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
