Source: https://bugs.webkit.org/show_bug.cgi?id=38045
Given the following code:
$ cat test.cpp
struct Foo
{
char __attribute__((aligned(4))) c[sizeof(int)];
};
char junk;
Foo f;
int main()
{
int *i = reinterpret_cast<int *>(&f.c);
*i = 0;
}
When compiled for ARM produces the warning:
$ arm-none-linux-gnueabi-g++ -Wcast-align -O3 -fsyntax-only /tmp/test.cpp
test.cpp:11: warning: cast from 'char (*)[4]' to 'int*' increases required
alignment of target type
Note that we requested that Foo::c be aligned to 4 bytes, which is the required
alignment for int. The assembly dump of the build confirms that the alignment
was honoured:
junk:
.space 1
.space 3
.type f, %object
.size f, 4
f:
.space 4
According to Dirk Müller, the following code is at fault (I have no idea where
it's from):
/* Warn about possible alignment problems. */
if (STRICT_ALIGNMENT && warn_cast_align
&& (complain & tf_warning)
· && !VOID_TYPE_P (type)
· && TREE_CODE (TREE_TYPE (intype)) != FUNCTION_TYPE
· && COMPLETE_TYPE_P (TREE_TYPE (type))
· && COMPLETE_TYPE_P (TREE_TYPE (intype))
· && TYPE_ALIGN (TREE_TYPE (type)) > TYPE_ALIGN (TREE_TYPE (intype)))
· warning (OPT_Wcast_align, "cast from %qT to %qT "
"increases required alignment of target type", intype, type);
As it only verifies the aligment of the type in question (char*), not of the
variable in question (&f.c).
--
Summary: warning about increased alignment during casting printed
even though variable is properly aligned
Product: gcc
Version: 4.4.1
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: thiago at kde dot org
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: arm-none-linux-gnueabi
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43976
