Happy days.. That wasn't obvious to me. I'll check out the details later.
Thanks. Colm
The PowerPC (look in config/rs6000) has no stack. All GCC needs is that you define a register to be the stack pointer (STACK_POINTER_REGNUM) and this register doesn't have to be a base register (see "Addressing modes" in the GCC Internals manual). Even a pushm1 pattern (see "Standard Pattern Names for Generation") is not necessary if you are happy with the code that GCC itself comes up with.
