regSpill :: Instruction instr=> Platform-> [LiveCmmDecl statics instr]the code
-> UniqSet Intavailable stack slots
-> Intcurrent number of spill slots.
-> UniqSet VirtualRegthe regs to spill
-> UniqSM ([LiveCmmDecl statics instr], UniqSet Int, Int, SpillStats)
Spill all these virtual regs to stack slots.
Bumps the number of required stack slots if required.
TODO: See if we can split some of the live ranges instead of just globally spilling the virtual reg. This might make the spill cleaner's job easier.
TODO: On CISCy x86 and x86_64 we don't necessarily have to add a mov instruction when making spills. If an instr is using a spilled virtual we may be able to address the spill slot directly.