[FIX] Make object construction exception-safe#650
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GCC 11.4 -O3 unsafe-vs-final A/B keeps the no-throw path at 22/22 executed instructions and a byte-identical 85-byte section, while throwing object and array paths remain 28/28 instructions through their first ret with no added guard branch, disarm store, destructor/free call, or memory operation. The throwing hot sections grow 112 to 130 bytes and 115 to 133 bytes: 6 bytes are accepted register/encoding changes and 12 bytes are an unreachable post-ret EH trampoline. free remains exclusive to the cold landing pads, whose sections grow from 5 to 21 bytes.
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This pull request introduces exception safety to SimpleObjAllocator by implementing an AllocGuard RAII helper. This guard ensures that allocated memory is properly freed if an exception is thrown during the in-place construction of an object. Additionally, a unit test has been added to verify that constructor exceptions are correctly propagated. I have no feedback to provide.
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spectrometerHBH
approved these changes
Jul 4, 2026
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This change makes SimpleObjAllocator strongly exception-safe when placement construction throws.
It adds an allocator-local allocation guard to both ordinary object and variable-sized array creation. The guard frees the matching aligned allocation during exception unwinding and is disarmed after successful construction. A focused object test verifies constructor exceptions propagate through make_object.