Incorrect behavior when promoting bit-field of bit-precise type

[Halalaluyafail3]

Clang promotes to the incorrect type when applying integer promotions to bit-fields of bit-precise type, for example:

#include<stdio.h>
int main(void){
	puts(_Generic(
		+(struct{unsigned _BitInt(7)x:2;}){}.x,
	 	unsigned _BitInt(2):"A",unsigned _BitInt(7):"B",int:"C"
	));
}

This program should output "B", but clang outputs "C".

The value from a bit-field of a bit-precise integer type is converted to the corresponding bit-precise
integer type. If the original type is not a bit-precise integer type (6.2.5): if an int can represent all
values of the original type (as restricted by the width, for a bit-field), the value is converted to an
int; otherwise, it is converted to an unsigned int. These are called the integer promotions. All
other types are unchanged by the integer promotions

(footnote) E.g. unsigned _BitInt(7): 2 is a bit-field that can hold the values 0, 1, 2, 3, and converts to unsigned _BitInt(7).

The promoted type of unsigned _BitInt(7)x:2 isn't int, it should be unsigned _BitInt(7) as the footnote says.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (Halalaluyafail3)

Clang promotes to the incorrect type when applying integer promotions to bit-fields of bit-precise type, for example: ```c #include<stdio.h> int main(void){ puts(_Generic( +(struct{unsigned _BitInt(7)x:2;}){}.x, unsigned _BitInt(2):"A",unsigned _BitInt(7):"B",int:"C" )); } ``` This program should output "B", but clang outputs "C". > The value from a bit-field of a bit-precise integer type is converted to the corresponding bit-precise integer type. If the original type is not a bit-precise integer type (6.2.5): if an int can represent all values of the original type (as restricted by the width, for a bit-field), the value is converted to an int; otherwise, it is converted to an unsigned int. These are called the integer promotions. All other types are unchanged by the integer promotions > > (footnote) E.g. unsigned _BitInt(7): 2 is a bit-field that can hold the values 0, 1, 2, 3, and converts to unsigned _BitInt(7).

The promoted type of unsigned _BitInt(7)x:2 isn't int, it should be unsigned _BitInt(7) as the footnote says.

[Sirraide]

Yeah, not too familiar w/ the intricacies of _Generic but I would have expected B here as well.

CC @AaronBallman

[AaronBallman]

Yeah, I agree, this is an issue.