+/// GetIfCondition - Given a basic block (BB) with two predecessors (and
+/// presumably PHI nodes in it), check to see if the merge at this block is due
+/// to an "if condition". If so, return the boolean condition that determines
+/// which entry into BB will be taken. Also, return by references the block
+/// that will be entered from if the condition is true, and the block that will
+/// be entered if the condition is false.
+///
+///
+static Value *GetIfCondition(BasicBlock *BB,
+ BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
+ assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
+ "Function can only handle blocks with 2 predecessors!");
+ BasicBlock *Pred1 = *pred_begin(BB);
+ BasicBlock *Pred2 = *++pred_begin(BB);
+
+ // We can only handle branches. Other control flow will be lowered to
+ // branches if possible anyway.
+ if (!isa<BranchInst>(Pred1->getTerminator()) ||
+ !isa<BranchInst>(Pred2->getTerminator()))
+ return 0;
+ BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
+ BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
+
+ // Eliminate code duplication by ensuring that Pred1Br is conditional if
+ // either are.
+ if (Pred2Br->isConditional()) {
+ // If both branches are conditional, we don't have an "if statement". In
+ // reality, we could transform this case, but since the condition will be
+ // required anyway, we stand no chance of eliminating it, so the xform is
+ // probably not profitable.
+ if (Pred1Br->isConditional())
+ return 0;
+
+ std::swap(Pred1, Pred2);
+ std::swap(Pred1Br, Pred2Br);
+ }
+
+ if (Pred1Br->isConditional()) {
+ // If we found a conditional branch predecessor, make sure that it branches
+ // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
+ if (Pred1Br->getSuccessor(0) == BB &&
+ Pred1Br->getSuccessor(1) == Pred2) {
+ IfTrue = Pred1;
+ IfFalse = Pred2;
+ } else if (Pred1Br->getSuccessor(0) == Pred2 &&
+ Pred1Br->getSuccessor(1) == BB) {
+ IfTrue = Pred2;
+ IfFalse = Pred1;
+ } else {
+ // We know that one arm of the conditional goes to BB, so the other must
+ // go somewhere unrelated, and this must not be an "if statement".
+ return 0;
+ }
+
+ // The only thing we have to watch out for here is to make sure that Pred2
+ // doesn't have incoming edges from other blocks. If it does, the condition
+ // doesn't dominate BB.
+ if (++pred_begin(Pred2) != pred_end(Pred2))
+ return 0;
+
+ return Pred1Br->getCondition();
+ }
+
+ // Ok, if we got here, both predecessors end with an unconditional branch to
+ // BB. Don't panic! If both blocks only have a single (identical)
+ // predecessor, and THAT is a conditional branch, then we're all ok!
+ if (pred_begin(Pred1) == pred_end(Pred1) ||
+ ++pred_begin(Pred1) != pred_end(Pred1) ||
+ pred_begin(Pred2) == pred_end(Pred2) ||
+ ++pred_begin(Pred2) != pred_end(Pred2) ||
+ *pred_begin(Pred1) != *pred_begin(Pred2))
+ return 0;
+
+ // Otherwise, if this is a conditional branch, then we can use it!
+ BasicBlock *CommonPred = *pred_begin(Pred1);
+ if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
+ assert(BI->isConditional() && "Two successors but not conditional?");
+ if (BI->getSuccessor(0) == Pred1) {
+ IfTrue = Pred1;
+ IfFalse = Pred2;
+ } else {
+ IfTrue = Pred2;
+ IfFalse = Pred1;
+ }
+ return BI->getCondition();
+ }
+ return 0;
+}
+
+
+// If we have a merge point of an "if condition" as accepted above, return true
+// if the specified value dominates the block. We don't handle the true
+// generality of domination here, just a special case which works well enough
+// for us.
+static bool DominatesMergePoint(Value *V, BasicBlock *BB, bool AllowAggressive){
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (!I) return true; // Non-instructions all dominate instructions.
+ BasicBlock *PBB = I->getParent();
+
+ // We don't want to allow wierd loops that might have the "if condition" in
+ // the bottom of this block.
+ if (PBB == BB) return false;
+
+ // If this instruction is defined in a block that contains an unconditional
+ // branch to BB, then it must be in the 'conditional' part of the "if
+ // statement".
+ if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
+ if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
+ if (!AllowAggressive) return false;
+ // Okay, it looks like the instruction IS in the "condition". Check to
+ // see if its a cheap instruction to unconditionally compute, and if it
+ // only uses stuff defined outside of the condition. If so, hoist it out.
+ switch (I->getOpcode()) {
+ default: return false; // Cannot hoist this out safely.
+ case Instruction::Load:
+ // We can hoist loads that are non-volatile and obviously cannot trap.
+ if (cast<LoadInst>(I)->isVolatile())
+ return false;
+ if (!isa<AllocaInst>(I->getOperand(0)) &&
+ !isa<Constant>(I->getOperand(0)))
+ return false;
+
+ // Finally, we have to check to make sure there are no instructions
+ // before the load in its basic block, as we are going to hoist the loop
+ // out to its predecessor.
+ if (PBB->begin() != BasicBlock::iterator(I))
+ return false;
+ break;
+ case Instruction::Add:
+ case Instruction::Sub:
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor:
+ case Instruction::Shl:
+ case Instruction::Shr:
+ break; // These are all cheap and non-trapping instructions.
+ }
+
+ // Okay, we can only really hoist these out if their operands are not
+ // defined in the conditional region.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (!DominatesMergePoint(I->getOperand(i), BB, false))
+ return false;
+ // Okay, it's safe to do this!
+ }
+
+ return true;
+}
+
+// GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq
+// instructions that compare a value against a constant, return the value being
+// compared, and stick the constant into the Values vector.
+static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
+ if (Instruction *Inst = dyn_cast<Instruction>(V))
+ if (Inst->getOpcode() == Instruction::SetEQ) {
+ if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
+ Values.push_back(C);
+ return Inst->getOperand(0);
+ } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
+ Values.push_back(C);
+ return Inst->getOperand(1);
+ }
+ } else if (Inst->getOpcode() == Instruction::Or) {
+ if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
+ if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
+ if (LHS == RHS)
+ return LHS;
+ }
+ return 0;
+}
+
+// GatherConstantSetNEs - Given a potentially 'and'd together collection of
+// setne instructions that compare a value against a constant, return the value
+// being compared, and stick the constant into the Values vector.
+static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
+ if (Instruction *Inst = dyn_cast<Instruction>(V))
+ if (Inst->getOpcode() == Instruction::SetNE) {
+ if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
+ Values.push_back(C);
+ return Inst->getOperand(0);
+ } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
+ Values.push_back(C);
+ return Inst->getOperand(1);
+ }
+ } else if (Inst->getOpcode() == Instruction::Cast) {
+ // Cast of X to bool is really a comparison against zero.
+ assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!");
+ Values.push_back(ConstantInt::get(Inst->getOperand(0)->getType(), 0));
+ return Inst->getOperand(0);
+ } else if (Inst->getOpcode() == Instruction::And) {
+ if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
+ if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
+ if (LHS == RHS)
+ return LHS;
+ }
+ return 0;
+}
+
+
+
+/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
+/// bunch of comparisons of one value against constants, return the value and
+/// the constants being compared.
+static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
+ std::vector<ConstantInt*> &Values) {
+ if (Cond->getOpcode() == Instruction::Or) {
+ CompVal = GatherConstantSetEQs(Cond, Values);
+
+ // Return true to indicate that the condition is true if the CompVal is
+ // equal to one of the constants.
+ return true;
+ } else if (Cond->getOpcode() == Instruction::And) {
+ CompVal = GatherConstantSetNEs(Cond, Values);
+
+ // Return false to indicate that the condition is false if the CompVal is
+ // equal to one of the constants.
+ return false;
+ }
+ return false;
+}
+
+/// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
+/// has no side effects, nuke it. If it uses any instructions that become dead
+/// because the instruction is now gone, nuke them too.
+static void ErasePossiblyDeadInstructionTree(Instruction *I) {
+ if (isInstructionTriviallyDead(I)) {
+ std::vector<Value*> Operands(I->op_begin(), I->op_end());
+ I->getParent()->getInstList().erase(I);
+ for (unsigned i = 0, e = Operands.size(); i != e; ++i)
+ if (Instruction *OpI = dyn_cast<Instruction>(Operands[i]))
+ ErasePossiblyDeadInstructionTree(OpI);
+ }
+}
+
+/// SafeToMergeTerminators - Return true if it is safe to merge these two
+/// terminator instructions together.
+///
+static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
+ if (SI1 == SI2) return false; // Can't merge with self!
+
+ // It is not safe to merge these two switch instructions if they have a common
+ // successor, and if that successor has a PHI node, and if *that* PHI node has
+ // conflicting incoming values from the two switch blocks.
+ BasicBlock *SI1BB = SI1->getParent();
+ BasicBlock *SI2BB = SI2->getParent();
+ std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
+
+ for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
+ if (SI1Succs.count(*I))
+ for (BasicBlock::iterator BBI = (*I)->begin();
+ PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI)
+ if (PN->getIncomingValueForBlock(SI1BB) !=
+ PN->getIncomingValueForBlock(SI2BB))
+ return false;
+
+ return true;
+}
+
+/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
+/// now be entries in it from the 'NewPred' block. The values that will be
+/// flowing into the PHI nodes will be the same as those coming in from
+/// ExistPred, an existing predecessor of Succ.
+static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
+ BasicBlock *ExistPred) {
+ assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
+ succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
+ if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
+
+ for (BasicBlock::iterator I = Succ->begin();
+ PHINode *PN = dyn_cast<PHINode>(I); ++I) {
+ Value *V = PN->getIncomingValueForBlock(ExistPred);
+ PN->addIncoming(V, NewPred);
+ }
+}
+
+// isValueEqualityComparison - Return true if the specified terminator checks to
+// see if a value is equal to constant integer value.
+static Value *isValueEqualityComparison(TerminatorInst *TI) {
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ // Do not permit merging of large switch instructions into their
+ // predecessors unless there is only one predecessor.
+ if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
+ pred_end(SI->getParent())) > 128)
+ return 0;
+
+ return SI->getCondition();
+ }
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI))
+ if (BI->isConditional() && BI->getCondition()->hasOneUse())
+ if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
+ if ((SCI->getOpcode() == Instruction::SetEQ ||
+ SCI->getOpcode() == Instruction::SetNE) &&
+ isa<ConstantInt>(SCI->getOperand(1)))
+ return SCI->getOperand(0);
+ return 0;
+}
+
+// Given a value comparison instruction, decode all of the 'cases' that it
+// represents and return the 'default' block.
+static BasicBlock *
+GetValueEqualityComparisonCases(TerminatorInst *TI,
+ std::vector<std::pair<ConstantInt*,
+ BasicBlock*> > &Cases) {
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ Cases.reserve(SI->getNumCases());
+ for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
+ Cases.push_back(std::make_pair(cast<ConstantInt>(SI->getCaseValue(i)),
+ SI->getSuccessor(i)));
+ return SI->getDefaultDest();
+ }
+
+ BranchInst *BI = cast<BranchInst>(TI);
+ SetCondInst *SCI = cast<SetCondInst>(BI->getCondition());
+ Cases.push_back(std::make_pair(cast<ConstantInt>(SCI->getOperand(1)),
+ BI->getSuccessor(SCI->getOpcode() ==
+ Instruction::SetNE)));
+ return BI->getSuccessor(SCI->getOpcode() == Instruction::SetEQ);
+}
+
+
+// FoldValueComparisonIntoPredecessors - The specified terminator is a value
+// equality comparison instruction (either a switch or a branch on "X == c").
+// See if any of the predecessors of the terminator block are value comparisons
+// on the same value. If so, and if safe to do so, fold them together.
+static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
+ BasicBlock *BB = TI->getParent();
+ Value *CV = isValueEqualityComparison(TI); // CondVal
+ assert(CV && "Not a comparison?");
+ bool Changed = false;
+
+ std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
+ while (!Preds.empty()) {
+ BasicBlock *Pred = Preds.back();
+ Preds.pop_back();
+
+ // See if the predecessor is a comparison with the same value.
+ TerminatorInst *PTI = Pred->getTerminator();
+ Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
+
+ if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
+ // Figure out which 'cases' to copy from SI to PSI.
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
+ BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
+
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
+ BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
+
+ // Based on whether the default edge from PTI goes to BB or not, fill in
+ // PredCases and PredDefault with the new switch cases we would like to
+ // build.
+ std::vector<BasicBlock*> NewSuccessors;
+
+ if (PredDefault == BB) {
+ // If this is the default destination from PTI, only the edges in TI
+ // that don't occur in PTI, or that branch to BB will be activated.
+ std::set<ConstantInt*> PTIHandled;
+ for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
+ if (PredCases[i].second != BB)
+ PTIHandled.insert(PredCases[i].first);
+ else {
+ // The default destination is BB, we don't need explicit targets.
+ std::swap(PredCases[i], PredCases.back());
+ PredCases.pop_back();
+ --i; --e;
+ }
+
+ // Reconstruct the new switch statement we will be building.
+ if (PredDefault != BBDefault) {
+ PredDefault->removePredecessor(Pred);
+ PredDefault = BBDefault;
+ NewSuccessors.push_back(BBDefault);
+ }
+ for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
+ if (!PTIHandled.count(BBCases[i].first) &&
+ BBCases[i].second != BBDefault) {
+ PredCases.push_back(BBCases[i]);
+ NewSuccessors.push_back(BBCases[i].second);
+ }
+
+ } else {
+ // If this is not the default destination from PSI, only the edges
+ // in SI that occur in PSI with a destination of BB will be
+ // activated.
+ std::set<ConstantInt*> PTIHandled;
+ for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
+ if (PredCases[i].second == BB) {
+ PTIHandled.insert(PredCases[i].first);
+ std::swap(PredCases[i], PredCases.back());
+ PredCases.pop_back();
+ --i; --e;
+ }
+
+ // Okay, now we know which constants were sent to BB from the
+ // predecessor. Figure out where they will all go now.
+ for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
+ if (PTIHandled.count(BBCases[i].first)) {
+ // If this is one we are capable of getting...
+ PredCases.push_back(BBCases[i]);
+ NewSuccessors.push_back(BBCases[i].second);
+ PTIHandled.erase(BBCases[i].first);// This constant is taken care of
+ }
+
+ // If there are any constants vectored to BB that TI doesn't handle,
+ // they must go to the default destination of TI.
+ for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
+ E = PTIHandled.end(); I != E; ++I) {
+ PredCases.push_back(std::make_pair(*I, BBDefault));
+ NewSuccessors.push_back(BBDefault);
+ }
+ }
+
+ // Okay, at this point, we know which new successor Pred will get. Make
+ // sure we update the number of entries in the PHI nodes for these
+ // successors.
+ for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
+ AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
+
+ // Now that the successors are updated, create the new Switch instruction.
+ SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PTI);
+ for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
+ NewSI->addCase(PredCases[i].first, PredCases[i].second);
+ Pred->getInstList().erase(PTI);
+
+ // Okay, last check. If BB is still a successor of PSI, then we must
+ // have an infinite loop case. If so, add an infinitely looping block
+ // to handle the case to preserve the behavior of the code.
+ BasicBlock *InfLoopBlock = 0;
+ for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
+ if (NewSI->getSuccessor(i) == BB) {
+ if (InfLoopBlock == 0) {
+ // Insert it at the end of the loop, because it's either code,
+ // or it won't matter if it's hot. :)
+ InfLoopBlock = new BasicBlock("infloop", BB->getParent());
+ new BranchInst(InfLoopBlock, InfLoopBlock);
+ }
+ NewSI->setSuccessor(i, InfLoopBlock);
+ }
+
+ Changed = true;
+ }
+ }
+ return Changed;
+}
+
+namespace {
+ /// ConstantIntOrdering - This class implements a stable ordering of constant
+ /// integers that does not depend on their address. This is important for
+ /// applications that sort ConstantInt's to ensure uniqueness.
+ struct ConstantIntOrdering {
+ bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
+ return LHS->getRawValue() < RHS->getRawValue();
+ }
+ };
+}
+