Three attributes currently are defined for PowerPC configurations:
altivec, ms_struct and gcc_struct.
For full documentation of the ms_struct and gcc_struct
attributes please see the documentation in x86 Type Attributes.
The altivec attribute allows one to declare AltiVec vector data
types supported by the AltiVec Programming Interface Manual. The
attribute requires an argument to specify one of three vector types:
vector__, pixel__ (always followed by unsigned short),
and bool__ (always followed by unsigned).
__attribute__((altivec(vector__))) __attribute__((altivec(pixel__))) unsigned short __attribute__((altivec(bool__))) unsigned
These attributes mainly are intended to support the __vector,
__pixel, and __bool AltiVec keywords.