https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82914
--- Comment #1 from Paul Eggert <eggert at gnu dot org> ---
(In reply to Paul Eggert from comment #0)
Sorry, but my example in comment #0 (although it illustrates a bug) doesn't
illustrate the bug that crashed GCC. Here's a better example:
struct t { long mem; };
__attribute__ ((aligned (2))) struct t a;
struct __attribute__ ((aligned (2))) t b;
struct t __attribute__ ((aligned (2))) c;
struct t d __attribute__ ((aligned (2)));
This compiles into:
.comm a,8,2
.comm b,8,8
.comm c,8,2
.comm d,8,2
Here, only 'b' is aligned correctly. The variables a, c, and d have an
alignment of only 2, but they should have an alignment of 8 because
__attribute__ ((aligned (8))) is documented to never decrease the alignment of
a structure, only to increase it. The GCC 7.2 documentation
<https://gcc.gnu.org/onlinedocs/gcc-7.2.0/gcc/Common-Variable-Attributes.html>
says, "When used on a struct, or struct member, the 'aligned' attribute can
only increase the alignment; in order to decrease it, the 'packed' attribute
must be specified as well."
