Commit 4334125be506e0c2c5dde4cfc29b31a7ff2bdec6
2025-03-14T16:12:32
Metal: Make StateCache descriptors hash consistent Various descriptors would compare equality and do hashing based on the underlying storage. The storage contains alignment padding and bitfields. The contents of these are not defined, even when the constructors tried to memset and memcpy. The various hash and compare functions also seemed to be missing some elements, like rasterSampleCount. Missing == on fields and hashing unused memory may lead to inconsistency where a==b is true but hash(a) != hash(b). Fix by: Remove the memset/memcpy and write out the operator== and hash() consistently. Initialize the members to their default values. Use uint32_t : 1 instead of bool if the struct tries to optimize for size, since mixing types stops the packing. Use uint32_t to get the alignment to uint32_t, which is mostly what is expected. Use uint32 someVar : N where N is payload bits + padding bits for the last member. This way the assignment clears the padding bits. The goal os to get the operator== to compare the padding bits, which lets the compiler elide the memberwise compares and use word-wise compares where it makes sense. This is an attempt to fix rare crashes related to map inserts and lookups. std::unordered_map will crash if operator== is not consistent with hash. Bug: angleproject:403372465 Change-Id: I0a3a2ff327ac9f65e7d41bc9585cda54ce93ab86 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6355828 Commit-Queue: Kimmo Kinnunen <kkinnunen@apple.com> Auto-Submit: Kimmo Kinnunen <kkinnunen@apple.com> Reviewed-by: Alexey Knyazev <lexa.knyazev@gmail.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>