[JumpThreading] Factor out common code to update the SSA form (NFC)

[kazu]

Summary

This patch factors out common code to update the SSA form in
JumpThreading.cpp -- partly for readability and partly to facilitate
an coming patch of my own.

[wmi]

LGTM.

llvm/include/llvm/Transforms/Scalar/JumpThreading.h

public:
 
   void releaseMemory() {
     BFI.reset();
     BPI.reset();
   }
 
   void FindLoopHeaders(Function &F);
   bool ProcessBlock(BasicBlock *BB);
+  void UpdateSSA(BasicBlock *BB, BasicBlock *NewBB,
+                 DenseMap<Instruction *, Value *> &ValueMapping);
   bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs,
                   BasicBlock *SuccBB);
   bool DuplicateCondBranchOnPHIIntoPred(
       BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs);
 
   bool ComputeValueKnownInPredecessorsImpl(
       Value *V, BasicBlock *BB, jumpthreading::PredValueInfo &Result,
       jumpthreading::ConstantPreference Preference,

llvm/lib/Transforms/Scalar/JumpThreading.cpp

if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
       if (I != ValueMap.end())
         IV = I->second;
     }
 
     PN.addIncoming(IV, NewPred);
   }
 }
 
+/// Update the SSA form.  NewBB contains instructions that are copied from BB.
+/// ValueMapping maps old values in BB to new ones in NewBB.
+void JumpThreadingPass::UpdateSSA(
+    BasicBlock *BB, BasicBlock *NewBB,
+    DenseMap<Instruction *, Value *> &ValueMapping) {
+  // If there were values defined in BB that are used outside the block, then we
+  // now have to update all uses of the value to use either the original value,
+  // the cloned value, or some PHI derived value.  This can require arbitrary
+  // PHI insertion, of which we are prepared to do, clean these up now.
+  SSAUpdater SSAUpdate;
+  SmallVector<Use *, 16> UsesToRename;
+
+  for (Instruction &I : *BB) {
+    // Scan all uses of this instruction to see if it is used outside of its
+    // block, and if so, record them in UsesToRename.
+    for (Use &U : I.uses()) {
+      Instruction *User = cast<Instruction>(U.getUser());
+      if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
+        if (UserPN->getIncomingBlock(U) == BB)
+          continue;
+      } else if (User->getParent() == BB)
+        continue;
+
+      UsesToRename.push_back(&U);
+    }
+
+    // If there are no uses outside the block, we're done with this instruction.
+    if (UsesToRename.empty())
+      continue;
+    LLVM_DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
+
+    // We found a use of I outside of BB.  Rename all uses of I that are outside
+    // its block to be uses of the appropriate PHI node etc.  See ValuesInBlocks
+    // with the two values we know.
+    SSAUpdate.Initialize(I.getType(), I.getName());
+    SSAUpdate.AddAvailableValue(BB, &I);
+    SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]);
+
+    while (!UsesToRename.empty())
+      SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
+    LLVM_DEBUG(dbgs() << "\n");
+  }
+}
+
 /// ThreadEdge - We have decided that it is safe and profitable to factor the
 /// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB
 /// across BB.  Transform the IR to reflect this change.
 bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
                                    const SmallVectorImpl<BasicBlock *> &PredBBs,
                                    BasicBlock *SuccBB) {
   // If threading to the same block as we come from, we would infinite loop.
   if (SuccBB == BB) {
if (PredTerm->getSuccessor(i) == BB) {
       PredTerm->setSuccessor(i, NewBB);
     }
 
   // Enqueue required DT updates.
   DTU->applyUpdatesPermissive({{DominatorTree::Insert, NewBB, SuccBB},
                                {DominatorTree::Insert, PredBB, NewBB},
                                {DominatorTree::Delete, PredBB, BB}});
 
-  // If there were values defined in BB that are used outside the block, then we
-  // now have to update all uses of the value to use either the original value,
-  // the cloned value, or some PHI derived value.  This can require arbitrary
-  // PHI insertion, of which we are prepared to do, clean these up now.
-  SSAUpdater SSAUpdate;
-  SmallVector<Use*, 16> UsesToRename;
-
-  for (Instruction &I : *BB) {
-    // Scan all uses of this instruction to see if their uses are no longer
-    // dominated by the previous def and if so, record them in UsesToRename.
-    // Also, skip phi operands from PredBB - we'll remove them anyway.
-    for (Use &U : I.uses()) {
-      Instruction *User = cast<Instruction>(U.getUser());
-      if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
-        if (UserPN->getIncomingBlock(U) == BB)
-          continue;
-      } else if (User->getParent() == BB)
-        continue;
-
-      UsesToRename.push_back(&U);
-    }
-
-    // If there are no uses outside the block, we're done with this instruction.
-    if (UsesToRename.empty())
-      continue;
-    LLVM_DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
-
-    // We found a use of I outside of BB.  Rename all uses of I that are outside
-    // its block to be uses of the appropriate PHI node etc.  See ValuesInBlocks
-    // with the two values we know.
-    SSAUpdate.Initialize(I.getType(), I.getName());
-    SSAUpdate.AddAvailableValue(BB, &I);
-    SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]);
-
-    while (!UsesToRename.empty())
-      SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
-    LLVM_DEBUG(dbgs() << "\n");
-  }
+  UpdateSSA(BB, NewBB, ValueMapping);
 
   // At this point, the IR is fully up to date and consistent.  Do a quick scan
   // over the new instructions and zap any that are constants or dead.  This
   // frequently happens because of phi translation.
   SimplifyInstructionsInBlock(NewBB, TLI);
 
   // Update the edge weight from BB to SuccBB, which should be less than before.
   UpdateBlockFreqAndEdgeWeight(PredBB, BB, NewBB, SuccBB);
bool JumpThreadingPass::DuplicateCondBranchOnPHIIntoPred(
   // Check to see if the targets of the branch had PHI nodes. If so, we need to
   // add entries to the PHI nodes for branch from PredBB now.
   BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
   AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
                                   ValueMapping);
   AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
                                   ValueMapping);
 
-  // If there were values defined in BB that are used outside the block, then we
-  // now have to update all uses of the value to use either the original value,
-  // the cloned value, or some PHI derived value.  This can require arbitrary
-  // PHI insertion, of which we are prepared to do, clean these up now.
-  SSAUpdater SSAUpdate;
-  SmallVector<Use*, 16> UsesToRename;
-  for (Instruction &I : *BB) {
-    // Scan all uses of this instruction to see if it is used outside of its
-    // block, and if so, record them in UsesToRename.
-    for (Use &U : I.uses()) {
-      Instruction *User = cast<Instruction>(U.getUser());
-      if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
-        if (UserPN->getIncomingBlock(U) == BB)
-          continue;
-      } else if (User->getParent() == BB)
-        continue;
-
-      UsesToRename.push_back(&U);
-    }
-
-    // If there are no uses outside the block, we're done with this instruction.
-    if (UsesToRename.empty())
-      continue;
-
-    LLVM_DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
-
-    // We found a use of I outside of BB.  Rename all uses of I that are outside
-    // its block to be uses of the appropriate PHI node etc.  See ValuesInBlocks
-    // with the two values we know.
-    SSAUpdate.Initialize(I.getType(), I.getName());
-    SSAUpdate.AddAvailableValue(BB, &I);
-    SSAUpdate.AddAvailableValue(PredBB, ValueMapping[&I]);
-
-    while (!UsesToRename.empty())
-      SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
-    LLVM_DEBUG(dbgs() << "\n");
-  }
+  UpdateSSA(BB, PredBB, ValueMapping);
 
   // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
   // that we nuked.
   BB->removePredecessor(PredBB, true);
 
   // Remove the unconditional branch at the end of the PredBB block.
   OldPredBranch->eraseFromParent();
   DTU->applyUpdatesPermissive(Updates);