[PATCH vkd3d] vkd3d: Add a function to mark unreachable code.

[Giovanni Mascellani]

Hi,

Il 08/04/22 19:00, Zebediah Figura ha scritto:
> I don't think there's value in specifying a message for cases like this, 
> and I'd rather not have to do so in new code. This applies to pretty 
> much anywhere we have an assert() in a switch default case.
> 
> (Ideally we should avoid the 'default' keyword where possible, although 
> in some cases this is difficult.)

vkd3d_unreachable() is written in a way such that you can pass it NULL 
to it for precisely this reason. I went adding messages for all present 
uses, but it is not mandatory to have one. Does this address your objection?

>> @@ -1542,12 +1534,10 @@ static void write_sm4_cast(struct hlsl_ctx *ctx,
>>               break;
>>           case HLSL_TYPE_BOOL:
>> -            /* Casts to bool should have already been lowered. */
>> -            assert(0);
>> -            break;
>> +            vkd3d_unreachable("Casts to bool should have already been 
>> lowered");
> 
> This one I think should remain an assert. I can more easily see this 
> getting triggered due to some forgotten implicit agreement. Hence we 
> probably shouldn't tell the compiler this code path is unreachable.
> 
> Using an assert(!"string") or assert(0 && "string") construction (or 
> defining our own macro) seems reasonable to me, though.

 From the point of view of the compiler, assert(0) is not really 
different from vkd3d_unreachable(NULL): nothing tells the compiler that 
control will never ever reach it; if it happens, the compiler will print 
a message and abort(). The advantage of vkd3d_unreachable() is that the 
compiler won't try to tell you "Hey, you didn't write your return 
statement!" in places where it doesn't make any sense (because it's 
marked "noreturn").

Thanks, Giovanni.