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

[Martin Sebor]

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

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