[PATCH] D122248: [clang][CodeGen]Fix clang crash and add bitfield support in __builtin_dump_struct

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a comment.

In D122248#3403349 <https://reviews.llvm.org/D122248#3403349>, @erichkeane wrote:

> In D122248#3403343 <https://reviews.llvm.org/D122248#3403343>, @yihanaa wrote:
>
>> In D122248#3403315 <https://reviews.llvm.org/D122248#3403315>, @aaron.ballman wrote:
>>
>>> In D122248#3403143 <https://reviews.llvm.org/D122248#3403143>, @yihanaa wrote:
>>>
>>>> 1. Support zero-width bitfield, named bitfield and unnamed bitfield.
>>>> 2. Add a release notes.
>>>>
>>>> The builtin function __builtin_dump_struct behaves for zero-width bitfield and unnamed bitfield as follows
>>>>
>>>>   int printf(const char *fmt, ...);
>>>>   
>>>>   void foo(void) {
>>>>     struct Bar {
>>>>       unsigned c : 1;
>>>>       unsigned : 3;
>>>>       unsigned : 0;
>>>>       unsigned b;
>>>>     };
>>>>   
>>>>     struct Bar a = {
>>>>       .c = 1,
>>>>       .b = 2022,
>>>>     };
>>>>   
>>>>     __builtin_dump_struct(&a, &printf);
>>>>   }
>>>>   
>>>>   int main() {
>>>>     foo();
>>>>     return 0;
>>>>   }
>>>>
>>>> Output:
>>>>
>>>>   struct Bar {
>>>>   unsigned int c : 1
>>>>   unsigned int  : 0
>>>>   unsigned int b : 2022
>>>>   }
>>>
>>> Thank you for the release note and additional test coverage. I'm wondering why we handle the zero-width bit-field differently from the anonymous one (e.g., why do we not have `unsigned int : 3` before the `unsigned int : 0`? It seems a bit odd to drop that from the output.
>>
>> Thanks, I don't know what the value of this zero-width bitfield should output, can it be a empty value as same as unnamed-bitfield’ she field name?
>>
>> for example:
>>
>>   struct Bar {
>>   unsigned int c : 1
>>   unsigned int  : 0
>>   unsigned int  :
>>   unsigned int b : 2022
>>   }
>
> I would definitely expect this, yes.

Oh wow... I was seeing the `:` in the output and thinking that was showing me the bit width after the colon (given that we show the type information), not the value. I wonder how many other folks are tripped up by that sort of thing? In the meantime, now that I understand the printing format better, I would expect that output as well.


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https://reviews.llvm.org/D122248