GH-44372: [C++] Fix unaligned load/store implementation for clang-18 #44468
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…ng-18 CLang 18 complains about undefined behavior when memcpy is called on a T-unaligned `T*` pointer. Workaround by casting to `void*`. This is due to this upstream change: llvm/llvm-project#67766
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cpp/src/arrow/util/ubsan.h
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| @@ -73,7 +73,7 @@ inline std::enable_if_t<std::is_trivially_copyable_v<T> && | |||
| U> | |||
| SafeCopy(T value) { | |||
| std::remove_const_t<U> ret; | |||
| std::memcpy(&ret, &value, sizeof(T)); | |||
| std::memcpy(&ret, reinterpret_cast<const void*>(&value), sizeof(T)); | |||
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This one surprises me. If value is on the stack, then it is already correctly aligned for T
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Hmm, that's possible. I couldn't reproduce the original error...
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@github-actions crossbow submit -g cpp |
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Revision: ab378dd Submitted crossbow builds: ursacomputing/crossbow @ actions-be2686045c
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After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit a5850e1. There were no benchmark performance regressions. 🎉 The full Conbench report has more details. It also includes information about 1 possible false positive for unstable benchmarks that are known to sometimes produce them. |
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Rationale for this change
CLang 18 complains about undefined behavior when memcpy is called on a T-unaligned
T*pointer.This is due to this upstream change: llvm/llvm-project#67766
What changes are included in this PR?
Workaround by casting to
void*.Are these changes tested?
By existing CI tests.
Are there any user-facing changes?
No.
misaligned-pointer-useafter clang-18 upgrade #44372