[Bug middle-end/82123] New: [7 regression] spurious -Wformat-overflow warning for converted vars

["arnd at linaro dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82123

            Bug ID: 82123
           Summary: [7 regression] spurious -Wformat-overflow warning for
                    converted vars
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arnd at linaro dot org
  Target Milestone: ---

This one seems to be related to pr77721 and pr81483. The first however only
happens with -Wformat-overflow=2, and the second one has no type conversion, so
I'm opening a separate pr for this one. Reproduced with gcc-7.1.1 and gcc-8.0.0
(r251692).

$ x86_64-linux-gcc-8.0.0 -c gpiolib-acpi.c -O2 -Wformat-overflow=1
gpiolib-acpi.c: In function 'acpi_gpiochip_request_interrupt':
gpiolib-acpi.c:7:28: warning: '%02X' directive writing between 2 and 4 bytes
into a region of size 3 [-Wformat-overflow=]
   __builtin_sprintf(name, "%02X", pin);
                            ^~~~
gpiolib-acpi.c:7:27: note: directive argument in the range [0, 65535]
   __builtin_sprintf(name, "%02X", pin);
                           ^~~~~~
gpiolib-acpi.c:7:3: note: '__builtin_sprintf' output between 3 and 5 bytes into
a destination of size 3
   __builtin_sprintf(name, "%02X", pin);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

8<----
void acpi_gpiochip_request_interrupt(unsigned short s)
{
        char name[3];
        unsigned int pin = s;

        if (pin <= 255)
                __builtin_sprintf(name, "%02X", pin);
}