rsmith added a comment.

In D85191#2195923 <>, @ebevhan wrote:

> In 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.

This violates the C and C++ language rules, which require the size of every 
type to be a multiple of the size of char. A type with 24 value bits and 8 
padding bits should report a type size of 32 bits, just like `bool` reports a 
size of `CHAR_BIT` bits despite having only 1 value bit, and x86_64 `long 
double` reports a type size of 128 bits despite having only 80 value bits.

  rG LLVM Github Monorepo


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