[IRGen] Always load extra tag bits as full bytes in CVW to avoid elem… #74952
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…ination of masking rdar://129627898 LLVM expects integer types of fractional byte sizes to have been written as those types as well, so it expects all unused bytes to be 0. Since we are using the unused extra tag bits to store tags of outer enums, that assumption does not hold here. In regular witnesses, the outer enum would mask out those bytes before checking the tag of the inner enum. In CVW we can't do that, so we have to apply the mask ourselves. To guarantee the mask does not get optimized out, we have to use full bytes instead of fractionals.
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…ination of masking
rdar://129627898
LLVM expects integer types of fractional byte sizes to have been written as those types as well, so it expects all unused bytes to be 0. Since we are using the unused extra tag bits to store tags of outer enums, that assumption does not hold here. In regular witnesses, the outer enum would mask out those bytes before checking the tag of the inner enum. In CVW we can't do that, so we have to apply the mask ourselves. To guarantee the mask does not get optimized out, we have to use full bytes instead of fractionals.