Commit 0016c1f4 authored by Kazu Hirata's avatar Kazu Hirata
Browse files

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

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.

Reviewers: wmi

Subscribers: hiraditya, jfb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69811
parent 77debf51

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

+2 −0
Original line number Diff line number Diff line
@@ -109,6 +109,8 @@ public: 


  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(

llvm/lib/Transforms/Scalar/JumpThreading.cpp

+46 −75
Original line number Diff line number Diff line
@@ -1920,6 +1920,50 @@ static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB, 
  }

}



/// 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.
@@ -2045,44 +2089,7 @@ bool JumpThreadingPass::ThreadEdge(BasicBlock *BB, 
                               {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
@@ -2366,43 +2373,7 @@ bool JumpThreadingPass::DuplicateCondBranchOnPHIIntoPred( 
  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.