Currently in GCC, you can access an element of a vector by using an union or by accessing the element via a pointer. Code like, (ignore the fact vector is not defined to __attribute__((vector_size(16))) ):
float f(vector float t)
{
return *(float*)&t;
}Would store the whole vector to memory and then load back into a floating point register. This is not a good thing as some targets (x86_64) actually has returns scalar values in the vector register. On other targets it can cause other issues. The correct way to solve this issue is by having GCC produce a BIT_FIELD_REF for the INDIRECT_REF. After doing that, this function for an example on the SPU target (which is not in the FSF GCC yet), we just get a branch for the return and no other code. On PPC (with altivec), we get a stevx instead of a full stvx which should save on cycles and it also saves on stack size in larger functions which does the above more.
Patch was posted at: http://gcc.gnu.org/ml/gcc-patches/2006-11/msg01464.html