Rework Linker dispatching for cross-major nvJitLink/driver skew#1911
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cpcloud wants to merge 4 commits intoNVIDIA:mainfrom
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Rework Linker dispatching for cross-major nvJitLink/driver skew#1911cpcloud wants to merge 4 commits intoNVIDIA:mainfrom
cpcloud wants to merge 4 commits intoNVIDIA:mainfrom
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Replace the module-level "decide once, use everywhere" nvJitLink-vs-driver choice with a per-Linker-instance decision that considers the CUDA driver major version, nvJitLink's availability and major version, the input code types, and whether link-time optimization is requested. The dispatch is factored into a pure helper `_choose_backend()` that is fully unit-testable without a GPU. Its decision matrix: - no nvJitLink, no LTO -> driver - matching majors -> nvJitLink - cross-major, no LTO -> driver (nvJitLink output may not be loadable) - LTO + no nvJitLink -> RuntimeError - LTO + cross-major -> RuntimeError This resolves the cross-major-driver scenario described in NVIDIA#712, where an nvJitLink 12.x may produce a CUBIN the driver 13.x (or vice versa) cannot load. The previous code committed to nvJitLink unconditionally when it was importable. Tests: - `tests/test_linker_dispatch.py` parametrizes the entire matrix against `_choose_backend()` with mocked versions (no GPU, no driver required). - `tests/test_linker.py::TestLinkerDispatch` drives the same decision through the real `Linker` constructor via monkeypatched version probes. - `tests/test_optional_dependency_imports.py` is updated to exercise the new `_probe_nvjitlink()` helper in place of the removed `_decide_nvjitlink_or_driver()`. - `tests/test_program.py` and `tests/test_linker.py` use a small local helper to compute the effective backend for the current environment. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
driver_version() was called unconditionally during Linker.__init__, which fails in environments where nvJitLink is installed but the CUDA driver is absent (e.g., build containers). Now catches the exception and sets driver_major=None. When driver_major is unknown and nvJitLink is available, optimistically selects the nvJitLink backend. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Test helpers calling driver_version() at module scope would crash in no-driver environments before test collection. Mirror the production lazy-probe pattern: catch exceptions and pass None. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Linker-instance dispatch at__init__time_choose_backend()helper for GPU-free unit testingRuntimeErrorfor LTO when backends are incompatibledriver_version()lazily — environments with nvJitLink but no driver (build containers) still work_probe_nvjitlink()cached, warns at most once when nvJitLink is absentBreaking change:
options.link_time_optimization=Truewith nvJitLink absent now raisesRuntimeErrorinstead of silently passingCU_JIT_LTOto the driver (which was not real LTO linking).Decision matrix
Test plan
test_linker_dispatch.py)Closes #712
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