[LLVMdev] Register allocation in two passes

[Jakob Stoklund Olesen]

On Nov 30, 2011, at 12:17 PM, Borja Ferrer wrote:

> Thanks for all the hints Jakob, I've added the following piece of code after the spill code handling inside selectOrSplit() (ignoring some control logic):
> 
>   for (LiveIntervals::const_iterator I = LIS->begin(), E = LIS->end(); I != E;
>        ++I)
>   {
>     unsigned VirtReg = I->first;
>     if ((TargetRegisterInfo::isVirtualRegister(VirtReg))
>         && (VRM->getPhys(VirtReg) == REG_Y))
>     {
>       LiveInterval &LI = LIS->getInterval(VirtReg);
>       unassign(LI, REG_Y);
>       enqueue(&LI);
>     }
>   }
> RegClassInfo.runOnMachineFunction(VRM->getMachineFunction()); // update reserve reglist
> 
> So similar to what's done in LRE_WillShrinkVirtReg(), it searches for live intervals where REG_Y is allocated and evicts them for reallocation. I don't know if there's a faster way of doing this but it's working :)

Looks good.

It is probably faster to scan the LiveIntervalUnion for REG_Y for assigned virtual registers, but the above code will work just fine.

Technically, you should also check REG_Y's aliases, but there probably aren't any.

> About your first question: the register has to be reserved throughout the whole function.
> 
> Thanks for the help

Glad to help.

/jakob