On Thu, Jan 08, 2009 at 03:35:29PM -0800, Ian Lance Taylor wrote: > "H.J. Lu" <hjl.to...@gmail.com> writes: > > > For 4.4, we can apply my patch: > > > > http://gcc.gnu.org/ml/gcc-patches/2009-01/msg00367.html > > > > and update document with > > > > As in the preceding examples, you can explicitly specify the alignment > > (in bytes) that you wish the compiler to use for a given variable or > > structure field. Alternatively, you can leave out the alignment factor > > and just ask the compiler to align a variable or field to the maximum > > useful alignment for the target ABI you are compiling for. For > > example, you could write: > > > > @smallexample > > short array[3] __attribute__ ((aligned)); > > @end smallexample > > > > Whenever you leave out the alignment factor in an @code{aligned} attribute > > specification, the compiler automatically sets the alignment for the > > declared > > variable or field to the largest alignment for the target ABI you are > > compiling for. Doing this can often make copy operations more efficient, > > because the compiler can use whatever instructions copy the biggest > > chunks of memory when performing copies to or from the variables or > > fields that you have aligned this way. > > Shouldn't the docs say something about memory allocation? As in, > malloc should return memory aligned to that boundary? > > For that matter, don't we have a problem on x86 GNU/Linux, where > malloc returns an 8-byte alignment but attribute((aligned)) is a 16 > byte alignment?
In that case, malloc should be changed to return items that are 16-byte aligned if any type needs 16-byte alignment for any possible ISA. -- Michael Meissner, IBM 4 Technology Place Drive, MS 2203A, Westford, MA, 01886, USA meiss...@linux.vnet.ibm.com
