PING [PATCH] improve warning suppression for inlined functions (PR 98465, 98512)

[Martin Sebor]

Ping: https://gcc.gnu.org/pipermail/gcc-patches/2021-January/564060.html

On 1/21/21 4:46 PM, Martin Sebor wrote:
> The initial patch I posted is missing initialization for a couple
> of locals.  I'd noticed it in testing but forgot to add the fix to
> the patch before posting it.  I have corrected that in the updated
> revision and also added the test case from pr98512, and retested
> the whole thing on x86_64-linux.
> 
> On 1/19/21 11:58 AM, Martin Sebor wrote:
>> std::string tends to trigger a class of false positive out of bounds
>> access warnings for code GCC cannot prove is unreachable because of
>> missing aliasing constrains, and that ends up expanded inline into
>> user code.  Simply inserting the contents of a constant char array
>> does that.  In GCC 10 these false positives are suppressed due to
>> -Wno-system-headers, but in GCC 11, to help detect calls rendered
>> invalid by user code passing in either incorrect or insufficiently
>> constrained arguments, -Wno-system-header no longer has this effect
>> on invalid access warnings.
>>
>> To solve the problem without at least partially reverting the change
>> and going back to the GCC 10 way of things for the affected subset
>> of calls (just memcpy and memmove), the attached patch enhances
>> the #pragma GCC diagnostic machinery to consider not just a single
>> location for inlined code but all locations at which an expression
>> and its callers are inlined all the way up the stack.  This gives
>> each author of a function involved in inlining the ability to
>> control a warning issued for the code, not just the user into whose
>> code all the calls end up inlined.  To resolve PR 98465, it lets us
>> suppress the false positives selectively in std::string rather
>> than across the board in GCC.
>>
>> The solution is to provide a new pair of overloads for warning
>> functions that, instead of taking a single location argument, take
>> a tree node from which the location(s) are determined.  The tree
>> argument is indirect because the diagnostic machinery doesn't (and
>> cannot without more intrusive changes) at the moment depend on
>> the various tree definitions.  A nice feature of these overloads
>> is that they do away with the need for the %K directive (and in
>> the future also %G, with another enhancement to accept a gimple*
>> argument).
>>
>> This patch depends on the fix for PR 98664 (already approved but
>> not yet checked in).  I've tested it on x86_64-linux.
>>
>> To avoid fallout I tried to keep the changes to a minimum, and
>> so the design isn't as robust as I'd like it ultimately to be.
>> I plan to enhance it in stage 1.
>>
>> Martin
>