Value-initialize the result local in generated C++ tagged-enum constructors#1167
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sylvestre wants to merge 1 commit into
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Value-initialize the result local in generated C++ tagged-enum constructors#1167sylvestre wants to merge 1 commit into
sylvestre wants to merge 1 commit into
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…uctors
Emit `T result{};` instead of `T result;` in the generated static variant
constructors so the payload union is zero-initialized rather than left
indeterminate. For no-payload variants only the tag is set, so the
previously-uninitialized union produced false "uninitialized scalar"
reports from static-analysis tools (e.g. Coverity). Payload variants are
unaffected: the union is value-initialized and the payload is then
constructed in place via placement new as before.
Add a regression test (tagged_enum_value_init) covering no-payload and
payload variants, and regenerate the affected C++ expectations.
emilio
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Jul 10, 2026
emilio
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@sylvestre I'm confused, why do we want this?
We're methodically initializing the fields right below... So it seems like at worst we're doing more work, and if we're lucky we're only giving more work to the compiler to optimize it out?
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Emit
T result{};instead ofT result;in the generated static variant constructors so the payload union is zero-initialized rather than left indeterminate. For no-payload variants only the tag is set, so the previously-uninitialized union produced false "uninitialized scalar" reports from static-analysis tools (e.g. Coverity). Payload variants are unaffected: the union is value-initialized and the payload is then constructed in place via placement new as before.Add a regression test (tagged_enum_value_init) covering no-payload and payload variants, and regenerate the affected C++ expectations.
This will remove about 110 CID in coverity for firefox