Compile attached testcase using:
$ g++-4.4 -c -O1 -fstrict-aliasing -Wstrict-aliasing foo.i
foo.i: In function ‘bool foo()’:
foo.i:8: warning: dereferencing pointer ‘<anonymous>’ does break
strict-aliasing rules
foo.i:26: note: initialized from here
Line 8 has this:
7: APSInt &operator=(const APSInt &RHS) {
8: APInt::operator=(RHS);
Line 26 has this:
26: AdditionalOffset = Val.getInt();
None of these violate the strict aliasing rules.
The only place that could violate the strict aliasing rules in the testcase is
at line 17:
14: void *Data[sizeof(APSInt)];
15: public:
16: APSInt &getInt() {
17: return *(APSInt*)(void*)Data;
g++ 4.3.3 doesn't give any warning, neither does g++ 4.2.4.
I think this is a bug because:
- the warning is not given at the place that (possibly) violates the strict
aliasing rules, but at the place where the pointer obtained by violating the
rules is dereferenced.
- removing line 26 silences the warning, and no warning given for getInt or
operator= anymore
Also does the construct at line 17 really violate the aliasing rules?
$ g++-4.4 -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.0-1~exp1'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-mpfr --enable-objc-gc
--with-arch-32=i486 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.0 (Debian 4.4.0-1~exp1)
--
Summary: Bogus location given for warning, no warning at real
location: dereferencing pointer ‘<anonymous>’ does break
strict-aliasing rules
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: edwintorok at gmail dot com
GCC build triplet: x86_64-linux-gnu
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39891
