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llvm: Fix alloca alignment and type selection in AllocOpt #60699
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This feels loosely unsound, since this is the minimum known alignment, and not the required alignment. The JL_SMALL_BYTE_ALIGNMENT value is the largest value that julia.gc_alloc_obj is permitted to return, so it is sometimes reasonable that we can use this as a hint, but we should be sure to clarify that this overalignment is merely a hint to the layout (although being more than 16 will penalize performance since it requires a more expensive stack adjustment on entry)
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But if the allocation required a larger alignment wouldn't we inherit that, that's why we prefer to inherit and just baseline to gc align
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getRetAlign is not the required alignment, it is the minimum, so if it requires it, this would introduce a bug here
but that said, the function isn't capable of giving more than JL_SMALL_BYTE_ALIGNMENT (16) so having getRetAlign return more than 16 here would be a miscompile, so this always gives the correct answer anyways (and increasing from there is only a runtime performance penalty, not a correctness issue)
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It’s the alignment we emitted no? If it required more it would already be a bug no? Unless you mean a gc alloc aligned that wouldn’t tell LLVM