FFTPACK 5.1: suppress default-real promotion for Intel and Flang builds

[andrew-platt]

Ready to merge

Feature or improvement description

Fix a Bus error (core dumped) seen at run time when OpenFAST is built with Intel oneAPI after the FFTPACK 5.1 upgrade (#3412).

fftpack5.1.f declares all of its arrays as bare REAL/COMPLEX, while NWTC_FFTPACK.f90 hands it explicitly kinded REAL(SiKi)/COMPLEX(SiKi) buffers and passes their element counts as LENSAV/LENWRK. The default REAL kind inside fftpack5.1.f must therefore stay 4 bytes even when DOUBLE_PRECISION is ON.

That suppression was applied only in the GNU branch of the CMake build (#3412, refined in #3437) and via RealKIND="realKIND4" in the Visual Studio project. With Intel, DOUBLE_PRECISION adds -real-size 64, which promotes both REAL->REAL(8) and COMPLEX->COMPLEX(8), so FFTPACK wrote twice as many bytes as the wrapper's wSave (heap) and wWork (stack automatic) buffers hold. Flang had the same latent defect via -fdefault-real-8.

Nothing diagnosed this at compile time — these are F77 externals with no explicit interfaces, so Intel never reports the argument mismatch — and the resulting heap/stack corruption surfaced as Bus error (core dumped) at run time, away from the FFT call itself.

Key changes:

• modules/nwtc-library/CMakeLists.txt — apply the real-size suppression for Intel and Flang, not just GNU:
  • Intel: -real-size 32 -double-size 64 (with the pre-19 -real_size spelling and the Windows /real-size:32 /double-size:64 form both handled)
  • Flang: -fno-default-real-8
  • -double-size 64 restores the Intel default so the genuine DOUBLE PRECISION accumulators in fftpack5.1.f (DSUM, TPI, ARGH, ...) stay 8 bytes, matching gfortran's -fno-default-double-8. Intel needs no -fallow-argument-mismatch analogue, since it does not diagnose the F77 type punning in the first place.
• modules/nwtc-library/src/NetLib/fftpack/fftpack_kind.f (new) — FFTPACK_REALKIND() reports the default REAL kind that fftpack5.1.f was actually compiled with. Built with the same per-source flags.
• modules/nwtc-library/src/NetLib/fftpack/NWTC_FFTPACK.f90 — CheckFFTPACKRealKind() aborts with an actionable message if that kind is not SiKi; called from all six Init routines (InitCOST, InitCFFT, InitFFT, InitSINT, InitFFT2D, InitCFFT2D). A build system that forgets the flag now fails loudly instead of corrupting memory.
• modules/nwtc-library/tests/test_NWTC_FFTPACK.F90 — new FFTPACK_real_kind unit test asserting FFTPACK_REALKIND() == SiKi, so CI catches a regression in the build flags on any compiler.
• vs-build/modules/NWTC-Library.vfproj — fftpack_kind.f added with RealKIND="realKIND4" in all eight configurations, matching fftpack5.1.f.

Related issue, if one exists

Follow-on to #3412 (FFTPACK 4.1 -> 5.1 upgrade) and #3437 (GNU Debug build fix). No GitHub Issue.

Impacted areas of the software

• modules/nwtc-library — FFTPACK build flags, wrapper module, unit tests
• Build system only for GNU (no behavior change) and Visual Studio (new file, same realKIND4 setting already used for fftpack5.1.f)
• All modules consuming NWTC_FFTPACK, which were affected by the corruption in Intel/Flang double-precision builds:
  • AeroDyn (AeroAcoustics)
  • HydroDyn (Conv_Radiation, WAMIT, WAMIT2)
  • MoorDyn (MoorDyn_Misc)
  • SeaState (Waves, Waves2, UserWaves)
  • TurbSim (TSsubs)

No numerical behavior changes for any build that was already correct — GNU builds and the Visual Studio build already suppressed the promotion, so their generated code is unchanged.

Additional supporting information

The Visual Studio project added by #3412 already carried the Intel equivalent of this fix (RealKIND="realKIND4" on fftpack5.1.f, all eight configurations); only the Intel branch of the CMake build was missed. That is why the defect reproduced on cluster builds but not in the Windows/VS workflow.

The failure mode is worth noting for triage: because the overrun is a silent 2x write into correctly-allocated buffers, the crash location is unrelated to the FFT call and the signal varies (SIGBUS or SIGSEGV) with heap layout. The CheckFFTPACKRealKind guard added here exists specifically so that this class of build misconfiguration reports itself rather than presenting as a random memory fault.

Generative AI usage

Investigation, patch, and unit test written with Claude Code (Opus 5), including one general-purpose subagent for the unit test. All changes reviewed and verified by the author.

Assisted-by: Anthropic Claude claude@anthropic.com

Test results, if applicable

Verified with gfortran 12.2 (DOUBLE_PRECISION=ON, CMAKE_BUILD_TYPE=Release):

• Full openfast target builds clean, no new warnings.
• nwtc_library_utest passes 13/13 FFTPACK tests, including the new FFTPACK_real_kind.
• Negative test: recompiling fftpack5.1.f and fftpack_kind.f with the promotion left on reproduces the broken configuration, and the new guard reports
  FFTPACK 5.1 was compiled with a default REAL kind of 8, but NWTC_FFTPACK requires 4. instead of corrupting memory.
• The GNU code generation is unchanged by this PR (the GNU flag string is identical); the gfortran results above are a regression check, not a reproduction of the reported failure.

[Copilot]

🟡 Changes recommended

The new init-time calls pass an OPTIONAL dummy argument (ErrStat) unconditionally, which is invalid/undefined when the caller omits ErrStat.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR hardens the FFTPACK 5.1 integration in modules/nwtc-library by ensuring fftpack5.1.f is always compiled with 4-byte default REAL (even when DOUBLE_PRECISION=ON) across GNU, Intel, and Flang builds, preventing silent buffer overruns and runtime crashes.

Changes:

• Extend per-source FFTPACK compile-flag suppression to Intel and Flang in CMake, and add fftpack_kind.f to report FFTPACK’s compiled default REAL kind.
• Add a runtime guard (CheckFFTPACKRealKind) in NWTC_FFTPACK init routines to fail fast with an actionable error if FFTPACK was built with the wrong default REAL kind.
• Add a unit test asserting FFTPACK_REALKIND() == SiKi, and include the new source in the Visual Studio project with RealKIND="realKIND4".

File summaries

File	Description
modules/nwtc-library/CMakeLists.txt	Applies per-source flags to keep FFTPACK default REAL at 4 bytes for GNU/Intel/Flang builds.
modules/nwtc-library/src/NetLib/fftpack/fftpack_kind.f	New helper reporting FFTPACK’s compiled default REAL kind for runtime/test verification.
modules/nwtc-library/src/NetLib/fftpack/NWTC_FFTPACK.f90	Adds runtime kind verification and calls it from all FFT init routines.
modules/nwtc-library/tests/test_NWTC_FFTPACK.F90	Adds a regression unit test to catch build-flag regressions in CI.
vs-build/modules/NWTC-Library.vfproj	Adds fftpack_kind.f with realKIND4 across all VS configurations.

Review details

Suppressed comments (5)

modules/nwtc-library/src/NetLib/fftpack/NWTC_FFTPACK.f90:812

• ErrStat is OPTIONAL in InitCFFT; passing it to CheckFFTPACKRealKind unconditionally is invalid if the caller didn’t provide ErrStat. Wrap this in a PRESENT(ErrStat) check and call CheckFFTPACKRealKind() with no args when absent.

      CALL CheckFFTPACKRealKind( ErrStat )
      IF ( PRESENT(ErrStat) ) THEN
         IF ( ErrStat >= AbortErrLev ) RETURN
      ENDIF

modules/nwtc-library/src/NetLib/fftpack/NWTC_FFTPACK.f90:889

• ErrStat is OPTIONAL in InitFFT; this unconditional CALL CheckFFTPACKRealKind(ErrStat) is invalid when ErrStat is absent. Make the call conditional on PRESENT(ErrStat) and call CheckFFTPACKRealKind() without arguments otherwise.

      CALL CheckFFTPACKRealKind( ErrStat )
      IF ( PRESENT(ErrStat) ) THEN
         IF ( ErrStat >= AbortErrLev ) RETURN
      ENDIF

modules/nwtc-library/src/NetLib/fftpack/NWTC_FFTPACK.f90:967

• ErrStat is OPTIONAL in InitSINT; passing an absent OPTIONAL dummy as an actual argument is invalid/undefined. Guard this call with PRESENT(ErrStat) and call CheckFFTPACKRealKind() with no arguments when ErrStat is not present.

      CALL CheckFFTPACKRealKind( ErrStat )
      IF ( PRESENT(ErrStat) ) THEN
         IF ( ErrStat >= AbortErrLev ) RETURN
      ENDIF

modules/nwtc-library/src/NetLib/fftpack/NWTC_FFTPACK.f90:1067

• ErrStat is OPTIONAL in InitFFT2D; passing it unconditionally to CheckFFTPACKRealKind is invalid if the caller omitted ErrStat. Call CheckFFTPACKRealKind(ErrStat) only when PRESENT(ErrStat), otherwise call CheckFFTPACKRealKind() to keep the abort-on-misbuild behavior.

      CALL CheckFFTPACKRealKind( ErrStat )
      IF ( PRESENT(ErrStat) ) THEN
         IF ( ErrStat >= AbortErrLev ) RETURN
      ENDIF

modules/nwtc-library/src/NetLib/fftpack/NWTC_FFTPACK.f90:1236

• ErrStat is OPTIONAL in InitCFFT2D; passing it as an actual argument here is invalid when absent. Wrap in IF (PRESENT(ErrStat)) and call CheckFFTPACKRealKind() with no arguments otherwise.

      CALL CheckFFTPACKRealKind( ErrStat )
      IF ( PRESENT(ErrStat) ) THEN
         IF ( ErrStat >= AbortErrLev ) RETURN
      ENDIF

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Lite

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