[PATCH] D85191: [AST] Get field size in chars rather than bits in RecordLayoutBuilder.

[Bevin Hansson via Phabricator via cfe-commits]

ebevhan added a comment.

In D85191#2193645 <https://reviews.llvm.org/D85191#2193645>, @rsmith wrote:

>> This is not ideal, since it makes the calculations char size dependent, and breaks for sizes that are not a multiple of the char size.
>
> How can we have a non-bitfield member whose size is not a multiple of the size of a char?

Downstream, we have fixed-point types that are 24 bits large, but where the char size is 16. The type then takes up 2 chars, where 8 of the bits are padding. The only way in Clang to express that the width of the bit representation of a type should be smaller than the number of chars it takes up in memory -- and consequently, produce an `i24` in IR -- is to return a non-charsize multiple from getTypeInfo.

We did it this way because it was possible. If the intent is for getTypeInfo to always return sizes that are multiples of the char size, then the design should be inverted and getTypeInfo should simply be calling getTypeInfoInChars and multiply that result by the char size. But that isn't how it works.


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https://reviews.llvm.org/D85191