[CodeGen] Introduce MachineBasicBlock::replacePhiUsesOfBlockWith helper and use it. NFC

[bjope]

Summary

Found a couple of places in the code where all the PHI nodes
of a MBB is updated, replacing references to one MBB by
reference to another MBB instead.

This patch simply refactors the code to use a common helper
(MachineBasicBlock::replacePhiUsesOfBlockWith) for such PHI
node updates.

[arsenm]

llvm/include/llvm/CodeGen/MachineBasicBlock.h

496–497

I don't think updatePHIs is a good name for a public version of this. replacePhiPredecessorWith maybe?

[bjope]

llvm/include/llvm/CodeGen/MachineBasicBlock.h

496–497

True that. replacePhiPredecessorWith sounds good to me.

[bjope]

Update: Renamed updatePHIs as replacePhiUsesOfBlockWith. Name choosen to "match" the already existing ReplaceUsesOfBlockWith which basically does the same thing but for all instructions in the block.

llvm/include/llvm/CodeGen/MachineBasicBlock.h

#endif
   void copySuccessor(MachineBasicBlock *Orig, succ_iterator I);
 
   /// Split the old successor into old plus new and updates the probability
   /// info.
   void splitSuccessor(MachineBasicBlock *Old, MachineBasicBlock *New,
                       bool NormalizeSuccProbs = false);
 
   /// Transfers all the successors from MBB to this machine basic block (i.e.,
   /// copies all the successors FromMBB and remove all the successors from
   /// FromMBB).
   void transferSuccessors(MachineBasicBlock *FromMBB);
 
   /// Transfers all the successors, as in transferSuccessors, and update PHI
   /// operands in the successor blocks which refer to FromMBB to refer to this.
   void transferSuccessorsAndUpdatePHIs(MachineBasicBlock *FromMBB);
 
   /// Return true if any of the successors have probabilities attached to them.
   bool hasSuccessorProbabilities() const { return !Probs.empty(); }
#endif
 
   /// This method unlinks 'this' from the containing function and deletes it.
   void eraseFromParent();
 
   /// Given a machine basic block that branched to 'Old', change the code and
   /// CFG so that it branches to 'New' instead.
   void ReplaceUsesOfBlockWith(MachineBasicBlock *Old, MachineBasicBlock *New);
 
+  /// Update PHI nodes in this MBB to refer to ToMBB instead of FromMBB.
+  void replacePhiUsesOfBlockWith(MachineBasicBlock *FromMBB,
+                                 MachineBasicBlock *ToMBB);
+
   /// Various pieces of code can cause excess edges in the CFG to be inserted.
   /// If we have proven that MBB can only branch to DestA and DestB, remove any
   /// other MBB successors from the CFG. DestA and DestB can be null. Besides
   /// DestA and DestB, retain other edges leading to LandingPads (currently
   /// there can be only one; we don't check or require that here). Note it is
   /// possible that DestA and/or DestB are LandingPads.
   bool CorrectExtraCFGEdges(MachineBasicBlock *DestA,
                             MachineBasicBlock *DestB,

llvm/lib/CodeGen/MachineBasicBlock.cpp

 
 void MachineBasicBlock::transferSuccessors(MachineBasicBlock *FromMBB) {
   if (this == FromMBB)
     return;
 
   while (!FromMBB->succ_empty()) {
     MachineBasicBlock *Succ = *FromMBB->succ_begin();
 
-    // If probability list is empty it means we don't use it (disabled optimization).
+    // If probability list is empty it means we don't use it (disabled
+    // optimization).
     if (!FromMBB->Probs.empty()) {
       auto Prob = *FromMBB->Probs.begin();
       addSuccessor(Succ, Prob);
     } else
       addSuccessorWithoutProb(Succ);
 
     FromMBB->removeSuccessor(Succ);
   }
while (!FromMBB->succ_empty()) {
     if (!FromMBB->Probs.empty()) {
       auto Prob = *FromMBB->Probs.begin();
       addSuccessor(Succ, Prob);
     } else
       addSuccessorWithoutProb(Succ);
     FromMBB->removeSuccessor(Succ);
 
     // Fix up any PHI nodes in the successor.
-    for (MachineBasicBlock::instr_iterator MI = Succ->instr_begin(),
-           ME = Succ->instr_end(); MI != ME && MI->isPHI(); ++MI)
-      for (unsigned i = 2, e = MI->getNumOperands()+1; i != e; i += 2) {
-        MachineOperand &MO = MI->getOperand(i);
-        if (MO.getMBB() == FromMBB)
-          MO.setMBB(this);
-      }
+    Succ->replacePhiUsesOfBlockWith(FromMBB, this);
   }
   normalizeSuccProbs();
 }
 
 bool MachineBasicBlock::isPredecessor(const MachineBasicBlock *MBB) const {
   return is_contained(predecessors(), MBB);
 }
 
if (Indexes) {
         // so we first remove any instruction that already has an index.
         if (Indexes->hasIndex(MI))
           Indexes->removeMachineInstrFromMaps(MI);
         Indexes->insertMachineInstrInMaps(MI);
       }
     }
   }
 
-  // Fix PHI nodes in Succ so they refer to NMBB instead of this
-  for (MachineBasicBlock::instr_iterator
-         i = Succ->instr_begin(),e = Succ->instr_end();
-       i != e && i->isPHI(); ++i)
-    for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
-      if (i->getOperand(ni+1).getMBB() == this)
-        i->getOperand(ni+1).setMBB(NMBB);
+  // Fix PHI nodes in Succ so they refer to NMBB instead of this.
+  Succ->replacePhiUsesOfBlockWith(this, NMBB);
 
   // Inherit live-ins from the successor
   for (const auto &LI : Succ->liveins())
     NMBB->addLiveIn(LI);
 
   // Update LiveVariables.
   const TargetRegisterInfo *TRI = MF->getSubtarget().getRegisterInfo();
   if (LV) {
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
           I->getOperand(i).getMBB() == Old)
         I->getOperand(i).setMBB(New);
   }
 
   // Update the successor information.
   replaceSuccessor(Old, New);
 }
 
+void MachineBasicBlock::replacePhiUsesOfBlockWith(MachineBasicBlock *FromMBB,
+                                                  MachineBasicBlock *ToMBB) {
+  for (MachineInstr &MI : phis())
+    for (unsigned i = 2, e = MI.getNumOperands() + 1; i != e; i += 2) {
+      MachineOperand &MO = MI.getOperand(i);
+      if (MO.getMBB() == FromMBB)
+        MO.setMBB(ToMBB);
+    }
+}
+
 /// Various pieces of code can cause excess edges in the CFG to be inserted.  If
 /// we have proven that MBB can only branch to DestA and DestB, remove any other
 /// MBB successors from the CFG.  DestA and DestB can be null.
 ///
 /// Besides DestA and DestB, retain other edges leading to LandingPads
 /// (currently there can be only one; we don't check or require that here).
 /// Note it is possible that DestA and/or DestB are LandingPads.
 bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,

llvm/lib/CodeGen/MachinePipeliner.cpp

for (unsigned i = LastStage; i >= 1; --i, ++EpilogStage) {
 
     LLVM_DEBUG({
       dbgs() << "epilog:\n";
       NewBB->dump();
     });
   }
 
   // Fix any Phi nodes in the loop exit block.
-  for (MachineInstr &MI : *LoopExitBB) {
-    if (!MI.isPHI())
-      break;
-    for (unsigned i = 2, e = MI.getNumOperands() + 1; i != e; i += 2) {
-      MachineOperand &MO = MI.getOperand(i);
-      if (MO.getMBB() == BB)
-        MO.setMBB(PredBB);
-    }
-  }
+  LoopExitBB->replacePhiUsesOfBlockWith(BB, PredBB);
 
   // Create a branch to the new epilog from the kernel.
   // Remove the original branch and add a new branch to the epilog.
   TII->removeBranch(*KernelBB);
   TII->insertBranch(*KernelBB, KernelBB, EpilogStart, Cond, DebugLoc());
   // Add a branch to the loop exit.
   if (EpilogBBs.size() > 0) {
     MachineBasicBlock *LastEpilogBB = EpilogBBs.back();