[OpenJDK 2D-Dev] [PATCH FOR REVIEW] Building ExtensionSubtables.cpp should use -fno-strict-aliasing

[Andrew Hughes]

----- Original Message -----
> 
> 
> ----- Original Message -----
> > I suppose the problem that some new version of GCC enables this
> > option
> > by default and
> > we could run into a problem at run time if we don't disable it ?
> > 
> 
> Yes, 4.4 to be precise.  It's not particularly new; it came out on
> April 21st, 2009.
> 

FYI, http://gcc.gnu.org/gcc-4.4/porting_to.html

> > But this patch would appear to disable it for the whole ICU library
> > ..
> > and any other C++ code in the .so
> > which I would have to suppose impacts the compiler's ability to
> > optimise
> > the code, in order to
> > eliminate a single warning.
> > 
> > Can you devise a more targeted fix ?
> > 
> 
> Yes, I thought the same.  But I don't see how you can direct flags to
> one specific file in the Makefiles.  Any ideas?
> 
> Alternatively, is this READ_LONG macro even necessary?  I'm not
> surprised
> gcc balks at it to be honest.
> 
> > -phil.
> > 
> > On 5/23/2012 5:59 AM, Andrew Hughes wrote:
> > > At present, the building of ExtensionSubtables.cpp produces a
> > > warning:
> > >
> > > ../../../src/share/native/sun/font/layout/ExtensionSubtables.cpp:57:31:
> > > warning: dereferencing type-punned pointer will break
> > > strict-aliasing rules [-Wstrict-aliasing]
> > >
> > > due to this code:
> > >
> > > // read a 32-bit value that might only be 16-bit-aligned in
> > > memory
> > > #define READ_LONG(code) (le_uint32)((SWAPW(*(le_uint16*)&code)<<
> > >  16) + SWAPW(*(((le_uint16*)&code) + 1)))
> > >
> > > where code is a le_uint32.
> > >
> > > This can be avoided by setting -fno-strict-aliasing, as done in
> > > this webrev:
> > >
> > > http://cr.openjdk.java.net/~andrew/no-strict-aliasing/
> > >
> > > making the code safer in the process.
> > >
> > > Ok for jdk8?  If so, can I have a bug ID for this please?
> > >
> > > Thanks,
> > 
> > 
> 
> --
> Andrew :)
> 
> Free Java Software Engineer
> Red Hat, Inc. (http://www.redhat.com)
> 
> PGP Key: 248BDC07 (https://keys.indymedia.org/)
> Fingerprint = EC5A 1F5E C0AD 1D15 8F1F  8F91 3B96 A578 248B DC07
> 
> 

-- 
Andrew :)

Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

PGP Key: 248BDC07 (https://keys.indymedia.org/)
Fingerprint = EC5A 1F5E C0AD 1D15 8F1F  8F91 3B96 A578 248B DC07