[PATCH] c++, libstdc++, v3: Implement C++26 P3726R2 - Adjustments to Union Lifetime Rules [PR125845]

[Jason Merrill]

On 9/9/26 6:08 AM, Jakub Jelinek wrote:
> On Wed, Sep 09, 2026 at 12:06:14PM +0200, Tomasz Kaminski wrote:
>>> +      __builtin_start_lifetime (&b.b);
>>> +      __builtin_start_lifetime (&b.b[1]);
>>> +      __builtin_start_lifetime (&b.b[1].b);
>>> +      __builtin_start_lifetime (&b.b[1].b[0][1]); // { dg-error
>>> "'__builtin_is_within_lifetime' with containing object not within lifetime"
>>> }
>>>
>> Should the error say,  __builtin_start_lifetime with containing object not
>> withing lifetime?
> 
> Sure, I can pass const char *name too.
Well, that particular error is already in cxx_eval_start_lifetime, just 
need to correct the string.  But passing down the name does seem useful 
for the errors that stay in is_within_lifetime.

Jason