Re: [PATCH 2/4] allow poisoning input_location in ranges it should not be used

[Jason Merrill <jason@redhat.com>]

On 7/1/21 6:16 AM, Trevor Saunders wrote:
> On Wed, Jun 30, 2021 at 11:13:23AM -0400, David Malcolm wrote:
>> On Wed, 2021-06-30 at 01:35 -0400, Trevor Saunders wrote:
>>> This makes it possible to assert if input_location is used during the
>>> lifetime
>>> of a scope.  This will allow us to find places that currently use it
>>> within a
>>> function and its callees, or prevent adding uses within the lifetime
>>> of a
>>> function after all existing uses are removed.
>>>
>>> bootstrapped and regtested on x86_64-linux-gnu, ok?
>>>
>>> Trev
>>
>> [...snip...]
>>
>>> diff --git a/gcc/diagnostic.c b/gcc/diagnostic.c
>>> index d58586f2526..3f68d1d79eb 100644
>>> --- a/gcc/diagnostic.c
>>> +++ b/gcc/diagnostic.c
>>> @@ -1835,7 +1835,7 @@ internal_error (const char *gmsgid, ...)
>>>     auto_diagnostic_group d;
>>>     va_list ap;
>>>     va_start (ap, gmsgid);
>>> -  rich_location richloc (line_table, input_location);
>>> +  rich_location richloc (line_table, UNKNOWN_LOCATION);
>>>     diagnostic_impl (&richloc, NULL, -1, gmsgid, &ap, DK_ICE);
>>>     va_end (ap);
>>>   
>>
>> I actually make use of this in the analyzer: the analyzer sets
>> input_location to stmt->location when analyzing a given stmt - that
>> way, if the analyzer ICEs, the ICE is shown at the code construct that
>> crashed the analyzer.
>>
>> This behavior is useful to me, and would be lost with the proposed
>> patch.
> 
> I made this change because otherwise if the compiler ICE's while access
> to input_location is blocked we end up infinitely recursing complaining
> we can't access it while trying to say where the last error was.  I was
> nervous about the change before, and now I agree we need something
> else.

How about allowing a scope (like internal_error) to explicitly un-poison 
the variable?

Separately, all the location_t (input_location) changes are pretty 
clunky, can we make that conversion part of the macro?

Jason