Fix global live range splitting regmask accuracy.

Pretend that regmask interference ends at the 'dead' slot, even when
there is other interference ending at the 'reg' slot of the same
instruction.

llvm-svn: 150531

Author: stoklund

llvm/lib/CodeGen/InterferenceCache.cpp

@@ -185,7 +185,8 @@ void InterferenceCache::Entry::update(unsigned MBBNum) {
 
   // Also check for register mask interference.
   SlotIndex Limit = BI->Last.isValid() ? BI->Last : Start;
-  for (unsigned i = RegMaskSlots.size(); i && RegMaskSlots[i-1] > Limit; --i)
+  for (unsigned i = RegMaskSlots.size();
+       i && RegMaskSlots[i-1].getDeadSlot() > Limit; --i)
     if (MachineOperand::clobbersPhysReg(RegMaskBits[i-1], PhysReg)) {
       // Register mask i-1 clobbers PhysReg after the LIU interference.
       // Model the regmask clobber as a dead def.