AMDGPU/InsertWaitcnt: Remove unused WaitAtBeginning

[msearles]

LGTM

lib/Target/AMDGPU/SIInsertWaitcnts.cpp

RegInterval getRegInterval(const MachineInstr *MI, const SIInstrInfo *TII,
                              const MachineRegisterInfo *MRI,
                              const SIRegisterInfo *TRI, unsigned OpNo,
                              bool Def) const;
 
   void setExpScore(const MachineInstr *MI, const SIInstrInfo *TII,
                    const SIRegisterInfo *TRI, const MachineRegisterInfo *MRI,
                    unsigned OpNo, int32_t Val);
 
-  void setWaitAtBeginning() { WaitAtBeginning = true; }
-  void clearWaitAtBeginning() { WaitAtBeginning = false; }
-  bool getWaitAtBeginning() const { return WaitAtBeginning; }
   int32_t getMaxVGPR() const { return VgprUB; }
   int32_t getMaxSGPR() const { return SgprUB; }
 
   bool counterOutOfOrder(InstCounterType T) const;
   bool simplifyWaitcnt(AMDGPU::Waitcnt &Wait) const;
   bool simplifyWaitcnt(InstCounterType T, unsigned &Count) const;
   void determineWait(InstCounterType T, int ScoreToWait,
                      AMDGPU::Waitcnt &Wait) const;
public:
   void setPostOrder(int32_t PostOrderIn) { PostOrder = PostOrderIn; }
   int32_t getPostOrder() const { return PostOrder; }
 
   void print(raw_ostream &);
   void dump() { print(dbgs()); }
 
 private:
   const GCNSubtarget *ST = nullptr;
-  bool WaitAtBeginning = false;
   bool RevisitLoop = false;
   int32_t PostOrder = 0;
   int32_t ScoreLBs[NUM_INST_CNTS] = {0};
   int32_t ScoreUBs[NUM_INST_CNTS] = {0};
   uint32_t PendingEvents = 0;
   bool MixedPendingEvents[NUM_INST_CNTS] = {false};
   // Remember the last flat memory operation.
   int32_t LastFlat[NUM_INST_CNTS] = {0};
void SIInsertWaitcnts::generateWaitcntInstBefore(
   setForceEmitWaitcnt();
   bool IsForceEmitWaitcnt = isForceEmitWaitcnt();
 
   if (MI.isDebugInstr())
     return;
 
   AMDGPU::Waitcnt Wait;
 
-  // See if an s_waitcnt is forced at block entry, or is needed at
-  // program end.
-  if (ScoreBrackets->getWaitAtBeginning()) {
-    // Note that we have already cleared the state, so we don't need to update
-    // it.
-    ScoreBrackets->clearWaitAtBeginning();
-    Wait = AMDGPU::Waitcnt::allZero();
-  }
-
   // See if this instruction has a forced S_WAITCNT VM.
   // TODO: Handle other cases of NeedsWaitcntVmBefore()
-  else if (MI.getOpcode() == AMDGPU::BUFFER_WBINVL1 ||
+  if (MI.getOpcode() == AMDGPU::BUFFER_WBINVL1 ||
            MI.getOpcode() == AMDGPU::BUFFER_WBINVL1_SC ||
            MI.getOpcode() == AMDGPU::BUFFER_WBINVL1_VOL) {
     Wait.VmCnt = 0;
   }
 
   // All waits must be resolved at call return.
   // NOTE: this could be improved with knowledge of all call sites or
   //   with knowledge of the called routines.
void SIInsertWaitcnts::mergeInputScoreBrackets(MachineBasicBlock &Block) {
   ScoreBrackets->clear();
 
   // See if there are any uninitialized predecessors. If so, emit an
   // s_waitcnt 0 at the beginning of the block.
   for (MachineBasicBlock *Pred : Block.predecessors()) {
     BlockWaitcntBrackets *PredScoreBrackets =
         BlockWaitcntBracketsMap[Pred].get();
     bool Visited = BlockVisitedSet.count(Pred);
-    if (!Visited || PredScoreBrackets->getWaitAtBeginning()) {
+    if (!Visited)
       continue;
-    }
     for (auto T : inst_counter_types()) {
       int span =
           PredScoreBrackets->getScoreUB(T) - PredScoreBrackets->getScoreLB(T);
       MaxPending[T] = std::max(MaxPending[T], span);
       span =
           PredScoreBrackets->pendingFlat(T) - PredScoreBrackets->getScoreLB(T);
       MaxFlat[T] = std::max(MaxFlat[T], span);
     }
   }
 
-#if 0
-  // LC does not (unlike) add a waitcnt at beginning. Leaving it as marker.
-  // TODO: how does LC distinguish between function entry and main entry?
-  // If this is the entry to a function, force a wait.
-  MachineBasicBlock &Entry = Block.getParent()->front();
-  if (Entry.getNumber() == Block.getNumber()) {
-    ScoreBrackets->setWaitAtBeginning();
-    return;
-  }
-#endif
-
   // Now set the current Block's brackets to the largest ending bracket.
   for (auto T : inst_counter_types()) {
     ScoreBrackets->setScoreUB(T, MaxPending[T]);
     ScoreBrackets->setScoreLB(T, 0);
     ScoreBrackets->setLastFlat(T, MaxFlat[T]);
   }
 
   // Set the register scoreboard.