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

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::replacePhiUsesWith) for such PHI node
updates.

Reviewers: t.p.northover, arsenm, uabelho

Subscribers: wdng, hiraditya, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66750

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@370463 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineBasicBlock.h

@@ -735,6 +735,10 @@ public:
   /// CFG so that it branches to 'New' instead.
   void ReplaceUsesOfBlockWith(MachineBasicBlock *Old, MachineBasicBlock *New);
 
+  /// Update all phi nodes in this basic block to refer to basic block \p New
+  /// instead of basic block \p Old.
+  void replacePhiUsesWith(MachineBasicBlock *Old, MachineBasicBlock *New);
+
   /// 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

lib/CodeGen/MachineBasicBlock.cpp

@@ -778,7 +778,8 @@ void MachineBasicBlock::transferSuccessors(MachineBasicBlock *FromMBB) {
   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);
@@ -804,13 +805,7 @@ MachineBasicBlock::transferSuccessorsAndUpdatePHIs(MachineBasicBlock *FromMBB) {
     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->replacePhiUsesWith(FromMBB, this);
   }
   normalizeSuccProbs();
 }
@@ -985,13 +980,8 @@ MachineBasicBlock *MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ,
     }
   }
 
-  // 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->replacePhiUsesWith(this, NMBB);
 
   // Inherit live-ins from the successor
   for (const auto &LI : Succ->liveins())
@@ -1223,6 +1213,16 @@ void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
   replaceSuccessor(Old, New);
 }
 
+void MachineBasicBlock::replacePhiUsesWith(MachineBasicBlock *Old,
+                                           MachineBasicBlock *New) {
+  for (MachineInstr &MI : phis())
+    for (unsigned i = 2, e = MI.getNumOperands() + 1; i != e; i += 2) {
+      MachineOperand &MO = MI.getOperand(i);
+      if (MO.getMBB() == Old)
+        MO.setMBB(New);
+    }
+}
+
 /// 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.

lib/CodeGen/MachinePipeliner.cpp

@@ -2234,15 +2234,7 @@ void SwingSchedulerDAG::generateEpilog(SMSchedule &Schedule, unsigned LastStage,
   }
 
   // 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->replacePhiUsesWith(BB, PredBB);
 
   // Create a branch to the new epilog from the kernel.
   // Remove the original branch and add a new branch to the epilog.