[PATCH] treat -Wxxx-larger-than=HWI_MAX special (PR 86631)

[Martin Sebor]

On 07/25/2018 02:34 AM, Richard Biener wrote:
> On Wed, Jul 25, 2018 at 4:07 AM Martin Sebor <msebor@gmail.com> wrote:
>>
>> The very large option argument enhancement committed last week
>> inadvertently introduced an assumption about the LP64 data model
>> that makes the -Wxxx-larger-than options have a different effect
>> at their default documented setting of PTRDIFF_MAX between ILP32
>> and LP64.  As a result, the options are treated as suppressed in
>> ILP32 while triggering the expected warnings for allocations or
>> sizes in excess of the limit in ILP64.
>>
>> To remove this I considered making it possible to use symbolic
>> constants like PTRDIFF_MAX as the option arguments so that
>> then defaults in the .opt files could be set to that.  Sadly,
>> options in GCC are processed before the values of constants
>> like PTRDIFF_MAX for the target are known, and deferring
>> the handling of just the -Wxxx-larger-than= options until
>> the constants have been computed would be too involved to
>> make it worth the effort.
>>
>> To keep things simple I decided to have the code that handles
>> each of the affected options treat the HOST_WIDE_INT_MAX default
>> as a special request to substitute the value of PTRDIFF_MAX at
>> the time.
>>
>> The attached patch implements this.
>
> I wonder if documenting a special value of -1 would be easier for
> users to use.  Your patch doesn't come with adjustments to
> invoke.texi so I wonder how people could know of this special
> handling?

I don't mean for the special value to be used except internally
for the defaults.  Otherwise, users wanting to override the default
will choose a value other than it.  I'm happy to document it in
the .opt file for internal users though.

-1 has the documented effect of disabling the warnings altogether
(-1 is SIZE_MAX) so while I agree that -1 looks better it doesn't
work.  (It would need more significant changes.)

I don't consider this the most elegant design but it's the best
I could think of short of complicating things even more.

Martin