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From: "ju.orth at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/99049] New: _Alignof ignores requested alignment of bit-field
 types in ms_struct struct
Date: Wed, 10 Feb 2021 01:16:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99049

            Bug ID: 99049
           Summary: _Alignof ignores requested alignment of bit-field
                    types in ms_struct struct
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ju.orth at gmail dot com
  Target Milestone: ---

Consider

typedef int Int __attribute__((aligned(128)));

struct __attribute__((ms_struct)) X {
        Int i:1;
};

struct Y {
        char c;
        struct X x;
};

int f(void) {
        return _Alignof(struct X);
}

int g(void) {
        return __builtin_offsetof(struct Y, x);
}

When compiling this on x86_64-unknown-linux-gnu, f returns 16 but g returns
128. I believe that _Alignof and __builtin_offsetof as above should always
return the same value.=