path: root/lib/Transforms/Utils/Local.cpp

//===-- Local.cpp - Functions to perform local transformations ------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This family of functions perform various local transformations to the
// program.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/ProfileInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Constants.h"
#include "llvm/DIBuilder.h"
#include "llvm/DataLayout.h"
#include "llvm/DebugInfo.h"
#include "llvm/DerivedTypes.h"
#include "llvm/GlobalAlias.h"
#include "llvm/GlobalVariable.h"
#include "llvm/IRBuilder.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Intrinsics.h"
#include "llvm/MDBuilder.h"
#include "llvm/Metadata.h"
#include "llvm/Operator.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;

//===----------------------------------------------------------------------===//
//  Local constant propagation.
//

/// ConstantFoldTerminator - If a terminator instruction is predicated on a
/// constant value, convert it into an unconditional branch to the constant
/// destination.  This is a nontrivial operation because the successors of this
/// basic block must have their PHI nodes updated.
/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
/// conditions and indirectbr addresses this might make dead if
/// DeleteDeadConditions is true.
bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
                                  const TargetLibraryInfo *TLI) {
  TerminatorInst *T = BB->getTerminator();
  IRBuilder<> Builder(T);

  // Branch - See if we are conditional jumping on constant
  if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
    if (BI->isUnconditional()) return false;  // Can't optimize uncond branch
    BasicBlock *Dest1 = BI->getSuccessor(0);
    BasicBlock *Dest2 = BI->getSuccessor(1);

    if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
      // Are we branching on constant?
      // YES.  Change to unconditional branch...
      BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
      BasicBlock *OldDest     = Cond->getZExtValue() ? Dest2 : Dest1;

      //cerr << "Function: " << T->getParent()->getParent()
      //     << "\nRemoving branch from " << T->getParent()
      //     << "\n\nTo: " << OldDest << endl;

      // Let the basic block know that we are letting go of it.  Based on this,
      // it will adjust it's PHI nodes.
      OldDest->removePredecessor(BB);

      // Replace the conditional branch with an unconditional one.
      Builder.CreateBr(Destination);
      BI->eraseFromParent();
      return true;
    }
    
    if (Dest2 == Dest1) {       // Conditional branch to same location?
      // This branch matches something like this:
      //     br bool %cond, label %Dest, label %Dest
      // and changes it into:  br label %Dest

      // Let the basic block know that we are letting go of one copy of it.
      assert(BI->getParent() && "Terminator not inserted in block!");
      Dest1->removePredecessor(BI->getParent());

      // Replace the conditional branch with an unconditional one.
      Builder.CreateBr(Dest1);
      Value *Cond = BI->getCondition();
      BI->eraseFromParent();
      if (DeleteDeadConditions)
        RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
      return true;
    }
    return false;
  }
  
  if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
    // If we are switching on a constant, we can convert the switch into a
    // single branch instruction!
    ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
    BasicBlock *TheOnlyDest = SI->getDefaultDest();
    BasicBlock *DefaultDest = TheOnlyDest;

    // Figure out which case it goes to.
    for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
         i != e; ++i) {
      // Found case matching a constant operand?
      if (i.getCaseValue() == CI) {
        TheOnlyDest = i.getCaseSuccessor();
        break;
      }

      // Check to see if this branch is going to the same place as the default
      // dest.  If so, eliminate it as an explicit compare.
      if (i.getCaseSuccessor() == DefaultDest) {
        MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
        // MD should have 2 + NumCases operands.
        if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) {
          // Collect branch weights into a vector.
          SmallVector<uint32_t, 8> Weights;
          for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e