> In the case where one of the structs has just been computed, attempting to load it as a single 32-bit load can result in a store forwarding failure that would negate the benefit of merging the loads

Would that failure be significantly worse than separate loading?

Just negating the optimization wouldn't be much reason against doing it. A single load is simpler and in the general case faster.

Usually, yeah, it's noticeably worse than using individual loads and stores as it adds around a dozen cycles of latency. This is usually enough for the load to light up hot in a sampling profile. It's possible for that extra latency to be hidden, but then in that case the extra loads/stores wouldn't be an issue either.

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