http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49413
Gabriel M. Beddingfield <gabriel at teuton dot org> changed:
What |Removed |Added
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CC| |gabriel at teuton dot org
--- Comment #8 from Gabriel M. Beddingfield <gabriel at teuton dot org>
2011-08-04 03:59:01 UTC ---
I ran into the same problem (gcc 4.5.2, Ubuntu 11.04, x86 Core Duo).
Unfortunately, it looks like Mr. Pinski is right.
I don't have a copy of the C99 spec, but I do have the C++ 2003 spec. It says
that alignment requirements are implementation-defined. In 3.9.2 it says
"Pointers to cv-qualified and cv-unqualified versions (3.9.3) of
layout-compatible types shall have the same value representation and alignment
requirements(3.9)." I'm sure C99 has a similar requirement.
I.e. since a `double` is required to be 8-byte aligned, so is a valid
`double*`. Unfortunately, this means that:
double *ra = malloc(512*sizeof(double));
...can return an invalid (unaligned) array.
However, on most archs I'm pretty sure the optimizer already checks alignment
in order to do things like SIMD instructions. So this is probably a valid
FEATURE REQUEST... that the optimizer supports (but not necc. optimize)
pointers with arbitrary alignment.
