Gate the FJMPI patch on Fugaku and trim comments [code:salmon]

The patch chain had a RIKYU branch whose only job was to print that it was
not patching. Only Fugaku compiles the Fujitsu MPI path, so apply the patch
there and drop the special case.

Cut the comments back. The measurement history behind each flag does not
belong in a build script.

No functional change.

Signed-off-by: William Dawson <william.dawson@riken.jp>
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PEzS2ybD8VEnQa9Sq5qYUM

Author: william-dawson

programs/salmon/build.sh

@@ -8,23 +8,8 @@ REPO_DIR="SALMON2"
 VERSION_TAG="v.2.2.2"
 BUILD_DIR="build-benchkit"
 
-# RIKYU pin: v.2.2.2 is over a year stale (2025-06-06) and measured
-# GPU-decomposition numbers on this repo were never actually run against it --
-# they came from a much newer, hand-patched checkout (~100 commits ahead,
-# including PR #1276's OpenACC tuning). Rather than let RIKYU silently build
-# something nobody has benchmarked, pin it to FugakuNEXT-v4 on
-# william-dawson/SALMON2 (also open as SALMON-TDDFT/SALMON2#1276) --
-# develop-2.0.0@9b93a8c4 (2026-08-16) plus four commits, one per concern:
-#   1. PR #1276's stencil/current/pseudo-pt OpenACC tuning (batched cuBLAS
-#      GEMM for pseudo-pt, not the old USE_CUDA hand-written kernels --
-#      see below)
-#   2. the nvhpc-openacc-gemm.cmake platform file that wires it up
-#   3. a fix for the Ewald loop tripcounts: nvfortran >= 26.5 evaluates
-#      an OpenACC tripcount on the device, where the derived-type member
-#      the bound came from is not resident, so the loops ran zero times
-#   4. a fix for a 2+ node hang on nvhpc/26.5: the CUDA context is created
-#      before MPI_Init_thread, so the MPI layer's CUDA-awareness probe does
-#      not cache a transfer protocol that deadlocks on device buffers
+# v.2.2.2 is over a year stale and predates the OpenACC tuning, Ewald
+# tripcount fix and multi-node CUDA-context fix that RIKYU needs.
 if [[ "${system}" == "RIKYU" ]]; then
   REPO_URL="https://github.com/william-dawson/SALMON2"
   VERSION_TAG="FugakuNEXT-v4"
@@ -42,18 +27,14 @@ mkdir -p "${BUILD_LOG_DIR}"
 bk_fetch_source "${REPO_URL}" "${REPO_DIR}" "${VERSION_TAG}"
 
 cd "${REPO_DIR}"
-# RIKYU builds a pinned branch that already carries every fix it needs
-# (see VERSION_TAG above), so it is used as-is -- no patching. The patches
-# below exist for the systems that build stock v.2.2.2.
-if [[ "${system}" == "RIKYU" ]]; then
-  echo "RIKYU: building ${VERSION_TAG} unpatched (all fixes are in the branch)"
-elif git apply --check "${FJMPI_PATCH}"; then
-  git apply "${FJMPI_PATCH}"
-elif git apply --reverse --check "${FJMPI_PATCH}" >/dev/null 2>&1; then
-  echo "SALMON Fujitsu MPI topology patch is already applied"
-else
-  echo "SALMON Fujitsu MPI topology patch does not apply to ${VERSION_TAG}" >&2
-  exit 1
+# Only Fugaku compiles the Fujitsu MPI path.
+if [[ "${system}" == "Fugaku" || "${system}" == "FugakuCN" ]]; then
+  if git apply --check "${FJMPI_PATCH}"; then
+    git apply "${FJMPI_PATCH}"
+  elif ! git apply --reverse --check "${FJMPI_PATCH}" >/dev/null 2>&1; then
+    echo "SALMON Fujitsu MPI topology patch does not apply to ${VERSION_TAG}" >&2
+    exit 1
+  fi
 fi
 
 rm -rf "${BUILD_DIR}"
@@ -208,48 +189,6 @@ case "${system}" in
       -DCMAKE_SYSTEM_PROCESSOR=openacc
       -DCMAKE_Fortran_FLAGS="-O3 -Wall -fstrict-aliasing -acc=strict -gpu=cc100,managed,ptxinfo -cudalib=cublas,cusolver,nccl -cuda -Minfo=accel -DUSE_OPENACC -DUSE_GEMM -DUSE_NCCL"
       -DCMAKE_C_FLAGS="-O3 -Wall -alias=ansi -acc=strict -gpu=cc100,managed,ptxinfo -cudalib=cublas,cusolver,nccl -cuda -Minfo=accel -DUSE_OPENACC -DUSE_GEMM -DUSE_NCCL"
-      # Module is nvhpc-hpcx-cuda13/26.5 (HPC-X 2.50 / OpenMPI 5), not
-      # plain nvhpc/26.5: that is the stack the domain-decomposition and
-      # NCCL numbers were measured on. MPI3 is left at its auto-detected
-      # ON -- no FORTRAN_COMPILER_HAS_MPI_VERSION3 override -- because the
-      # GEMM path skips calc_uVpsi_rdivided entirely, so the HPC-X libnbc
-      # bug that motivated the old 26.3 + MPI3=OFF workaround is
-      # unreachable. Do not reintroduce that workaround.
-      #
-      # FugakuNEXT-v3 also computes the nonlocal current density with a
-      # batched GEMM (it was 82% of calculating-curr): current density
-      # 29.5 -> 3.6 s and rt iterations 44.6 -> 18.7 s at 16 GPUs orbital.
-      #
-      # -DUSE_NCCL routes the pseudo-pt domain-decomposition reduce through
-      # ncclAllReduce instead of MPI_Allreduce. MPI_Allreduce performs the
-      # reduction arithmetic on the host even when handed a device pointer,
-      # so it leaves NVLink: measured 5.6 GB/s vs NCCL's 196-521 GB/s on the
-      # same 222 MB device buffer. In SALMON that is pseudo-pt comm 18.2s ->
-      # 1.7s at 4 GPUs (rt iterations 99.1 -> 80.5), energies bit-exact.
-      # It needs nccl in -cudalib. If the MPI stack ever grows a working
-      # GPU-side allreduce (UCC ships a TL_NCCL that currently never
-      # registers), drop -DUSE_NCCL and this becomes plain MPI again.
-      #
-      # NOT -DUSE_CUDA -- that flag controls a completely different, OLDER
-      # optimization path (src/common/{zpseudo,stencil_current}.cu, hand-
-      # written CUDA kernels) that this pinned source (see VERSION_TAG
-      # above) replaces with PR #1276's tuned pure-OpenACC kernels instead:
-      # a batched cuBLAS GEMM rewrite of pseudo-pt (-DUSE_GEMM, needs
-      # cusolver linked in) and an inlined OpenACC current-density kernel.
-      # That's where the real speedup comes from, not USE_CUDA -- measured
-      # data only ever showed the OLD CUDA kernels net *losing* time
-      # (pseudo-pt 3.1-3.5x slower under USE_CUDA than plain OpenACC; the
-      # 1.4-3x win on current-density wasn't enough to make up for it).
-      # USE_CUDA also has a real, deterministic bug independent of any of
-      # this: stencil_current.cu's host wrapper sizes its device idx/idy/idz
-      # buffers by each rank's LOCAL grid extent but indexes them with the
-      # RAW/global grid coordinate, which only happens to fit when a rank's
-      # is()=1 on that axis (single GPU, or pure orbital decomposition,
-      # where every rank owns the full box). Any real-space (nproc_rgrid>1)
-      # decomposition puts a non-first rank at is()>1 on the split axis and
-      # overruns the buffer -- reproduced as a deterministic Accelerator
-      # Fatal Error / CUDA_ERROR_ILLEGAL_ADDRESS in calc_current
-      # (density_matrix.f90) on every axis and Po x Pg combination tried.
     )
     ;;
   *)