[AMDGCN] Fix overly optimistic GCNUpwardRPTracker

[rampitec]

Summary

1. Remove defs when moving past the defining instruction, not right on it. If an instruction defines and uses a register its pressure is actually 2, not 0.
2. Do not remove tied defs. If def is a tied operand it is not really a new def, just a redefinition.

[rampitec]

Widthraw the revision in favor of D33289.

lib/Target/AMDGPU/GCNIterativeScheduler.cpp

GCNIterativeScheduler::getRegionPressure(MachineBasicBlock::iterator Begin,
   } else {
     assert(UPTracker.isValid());
   }
 
   for (auto I = BottomMI; I != Begin; --I)
     UPTracker.recede(*I);
 
   UPTracker.recede(*Begin);
+  // Second recede to the same instruction to commit all defs.
+  // Current pressure will be updated, but max will stay higher.
+  UPTracker.recede(*Begin);
 
   assert(UPTracker.isValid() ||
          (dbgs() << "Tracked region ",
           printRegion(dbgs(), Begin, End, LIS), false));
   return UPTracker.moveMaxPressure();
 }
 
 // returns max pressure for a tentative schedule

lib/Target/AMDGPU/GCNRegPressure.cpp

LaneBitmask GCNUpwardRPTracker::getUsedRegMask(const MachineOperand &MO) const {
   // dominate uses anyway.
   auto SI = LIS.getInstructionIndex(*MO.getParent()).getBaseIndex();
   return getLiveLaneMask(MO.getReg(), SI, LIS, *MRI);
 }
 
 void GCNUpwardRPTracker::recede(const MachineInstr &MI) {
   assert(MRI && "call reset first");
 
-  LastTrackedMI = &MI;
-
-  if (MI.isDebugValue())
-    return;
-
   // process all defs first to ensure early clobbers are handled correctly
   // iterating over operands() to catch implicit defs
-  for (const auto &MO : MI.operands()) {
-    if (!MO.isReg() || !MO.isDef() ||
+  if (LastTrackedMI && !LastTrackedMI->isDebugValue()) {
+    for (const auto &MO : LastTrackedMI->operands()) {
+      if (!MO.isReg() || !MO.isDef() || MO.isTied() ||
           !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
         continue;
 
       auto Reg = MO.getReg();
       auto &LiveMask = LiveRegs[Reg];
       auto PrevMask = LiveMask;
       LiveMask &= ~getDefRegMask(MO);
       CurPressure.inc(Reg, PrevMask, LiveMask, *MRI);
     }
+  }
+
+  LastTrackedMI = &MI;
+
+  if (MI.isDebugValue())
+    return;
 
   // then all uses
   for (const auto &MO : MI.uses()) {
     if (!MO.isReg() || !MO.readsReg() ||
         !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
       continue;
 
     auto Reg = MO.getReg();
     auto &LiveMask = LiveRegs[Reg];
     auto PrevMask = LiveMask;
     LiveMask |= getUsedRegMask(MO);
     CurPressure.inc(Reg, PrevMask, LiveMask, *MRI);
   }