[Bug c/84108] New: incorrect -Wattributes warning for packed/aligned conflict

[arnd at linaro dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84108

            Bug ID: 84108
           Summary: incorrect -Wattributes warning for packed/aligned
                    conflict
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arnd at linaro dot org
  Target Milestone: ---

Marking a struct member as both 'packed' and 'aligned()' triggers a warning in
gcc-8:

struct s {
        char x;
        int y __attribute__((packed, aligned(2)));
        int z __attribute__((aligned(2), packed));
} s;

x86_64-linux-gcc-8.0.1 -c -Wall test.c  -O2 -c
test5.c:3:2: warning: ignoring attribute 'aligned' because it conflicts with
attribute 'packed' [-Wattributes]
  int y __attribute__((packed, aligned(2)));
  ^~~
test5.c:4:2: warning: ignoring attribute 'packed' because it conflicts with
attribute 'aligned' [-Wattributes]
  int z __attribute__((aligned(2), packed));
  ^~~

The warning appears to be a mistake, since neither attribute is in fact ignored
here, and both 'y' and 'z' are aligned to two bytes, which matches the gcc
documentation and the behavior of older versions.