Add test for GCC 12+ -Wmaybe-uninitialized false positive #56
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This test doesn't emit any warnings under GCC 12+ in CI. |
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Yes I'm trying to figure out how to reproduce it reliably. It might be the build settings? |
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No, it's the test code. It's hard to trigger the warning; you need just the right amount of complexity and a lot of luck. That's because the warning only fires when the optimizer can see that the |
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It's probably going to be easier to reproduce this by using |
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Add variant_gcc_false_positive.cpp to reproduce GCC 12+ spurious -Wmaybe-uninitialized warnings when copying/moving variant containing non-trivially-copyable types like std::exception_ptr and std::string. Tests use boost::system::result which internally uses variant2, and include coroutine-based tests when C++20 coroutine support is available. The test uses -O3 optimization to trigger the aggressive inlining that exposes the false positive where GCC's dataflow analysis cannot prove the discriminator ensures only initialized alternatives are accessed. See boostorg#33
Add diagnostic pragmas to suppress spurious -Wmaybe-uninitialized warnings in GCC 12+ when copying/moving variant with non-trivially copyable types like std::exception_ptr. GCC 12+'s improved dataflow analysis sees code paths for all alternatives via mp_with_index and warns that members may be uninitialized, even though the variant's discriminator guarantees only the active alternative is accessed. The workaround can be disabled by defining BOOST_VARIANT2_GCC12_WORKAROUND to 0 before including the header. Fixes boostorg#33
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