Fix RegScavenger::unprocess

[greened]

Summary

RegScavenger::unprocess walks backward, so it should undo the effects of defs before undoing effects of kills. Previously it did things in the opposite order, leaving a register apparently unused (dead) in the case where an instruction both used (killed) and defined a register.

[MatzeB]

LGTM.

That said the medium to short term plan is to get rid of kill flags, which means RegisterScavenger::forward() and RegisterScavenger::unprocess() will no longer work (or at least give you conservative results which aren't very useful). I'd recommend to switch your code to LiveRegUnits/LivePhysRegs (in case you don't need emergency spilling) or RegisterScavenger::backward() instead!

[greened]

Thanks for the heads-up. I will start using backward().

[greened]

Did this ever land? If not how do I get it committed?

[MatzeB]

I assume you don't have commit access?
Usually it's the author of the patch that commits it unless he doesn't have commit access yet in which case it's upon the reviewers.

[greened]

I had commit access at one time but I don't know if I still do. If I do, I guess I can commit via svn but how do I get all the nice metadata in the commit log like "Differential Revision?" Do people just add it manually?

[kparzysz]

I add it by hand. I think arcanist will do that for you automatically, but I've never used it.

llvm/trunk/lib/CodeGen/RegisterScavenging.cpp

 void RegScavenger::unprocess() {
   assert(Tracking && "Cannot unprocess because we're not tracking");
 
   MachineInstr &MI = *MBBI;
   if (!MI.isDebugInstr()) {
     determineKillsAndDefs();
 
     // Commit the changes.
-    setUsed(KillRegUnits);
     setUnused(DefRegUnits);
+    setUsed(KillRegUnits);
   }
 
   if (MBBI == MBB->begin()) {
     MBBI = MachineBasicBlock::iterator(nullptr);
     Tracking = false;
   } else
     --MBBI;
 }