bool ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, BasicBlock *SuccBB);
bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
BasicBlock *PredBB);
-
- typedef SmallVectorImpl<std::pair<ConstantInt*,
- BasicBlock*> > PredValueInfo;
-
- bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
- PredValueInfo &Result);
- bool ProcessThreadableEdges(Instruction *CondInst, BasicBlock *BB);
-
-
+
+ BasicBlock *FactorCommonPHIPreds(PHINode *PN, Value *Val);
bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
bool ProcessJumpOnPHI(PHINode *PN);
+ bool ProcessBranchOnLogical(Value *V, BasicBlock *BB, bool isAnd);
+ bool ProcessBranchOnCompare(CmpInst *Cmp, BasicBlock *BB);
bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
};
LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
}
-/// GetResultOfComparison - Given an icmp/fcmp predicate and the left and right
-/// hand sides of the compare instruction, try to determine the result. If the
-/// result can not be determined, a null pointer is returned.
-static Constant *GetResultOfComparison(CmpInst::Predicate pred,
- Value *LHS, Value *RHS) {
- if (Constant *CLHS = dyn_cast<Constant>(LHS))
- if (Constant *CRHS = dyn_cast<Constant>(RHS))
- return ConstantExpr::getCompare(pred, CLHS, CRHS);
-
- if (LHS == RHS)
- if (isa<IntegerType>(LHS->getType()) || isa<PointerType>(LHS->getType())) {
- if (ICmpInst::isTrueWhenEqual(pred))
- return ConstantInt::getTrue(LHS->getContext());
- else
- return ConstantInt::getFalse(LHS->getContext());
- }
- return 0;
-}
-
-
-/// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see
-/// if we can infer that the value is a known ConstantInt in any of our
-/// predecessors. If so, return the known the list of value and pred BB in the
-/// result vector. If a value is known to be undef, it is returned as null.
-///
-/// The BB basic block is known to start with a PHI node.
-///
-/// This returns true if there were any known values.
+/// FactorCommonPHIPreds - If there are multiple preds with the same incoming
+/// value for the PHI, factor them together so we get one block to thread for
+/// the whole group.
+/// This is important for things like "phi i1 [true, true, false, true, x]"
+/// where we only need to clone the block for the true blocks once.
///
-///
-/// TODO: Per PR2563, we could infer value range information about a predecessor
-/// based on its terminator.
-bool JumpThreading::
-ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
- PHINode *TheFirstPHI = cast<PHINode>(BB->begin());
-
- // If V is a constantint, then it is known in all predecessors.
- if (isa<ConstantInt>(V) || isa<UndefValue>(V)) {
- ConstantInt *CI = dyn_cast<ConstantInt>(V);
- Result.resize(TheFirstPHI->getNumIncomingValues());
- for (unsigned i = 0, e = Result.size(); i != e; ++i)
- Result[i] = std::make_pair(CI, TheFirstPHI->getIncomingBlock(i));
- return true;
- }
-
- // If V is a non-instruction value, or an instruction in a different block,
- // then it can't be derived from a PHI.
- Instruction *I = dyn_cast<Instruction>(V);
- if (I == 0 || I->getParent() != BB)
- return false;
-
- /// If I is a PHI node, then we know the incoming values for any constants.
- if (PHINode *PN = dyn_cast<PHINode>(I)) {
- for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
- Value *InVal = PN->getIncomingValue(i);
- if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) {
- ConstantInt *CI = dyn_cast<ConstantInt>(InVal);
- Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i)));
- }
- }
- return !Result.empty();
- }
-
- SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals;
-
- // Handle some boolean conditions.
- if (I->getType()->getPrimitiveSizeInBits() == 1) {
- // X | true -> true
- // X & false -> false
- if (I->getOpcode() == Instruction::Or ||
- I->getOpcode() == Instruction::And) {
- ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals);
- ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals);
-
- if (LHSVals.empty() && RHSVals.empty())
- return false;
-
- ConstantInt *InterestingVal;
- if (I->getOpcode() == Instruction::Or)
- InterestingVal = ConstantInt::getTrue(I->getContext());
- else
- InterestingVal = ConstantInt::getFalse(I->getContext());
-
- // Scan for the sentinel.
- for (unsigned i = 0, e = LHSVals.size(); i != e; ++i)
- if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0)
- Result.push_back(LHSVals[i]);
- for (unsigned i = 0, e = RHSVals.size(); i != e; ++i)
- if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0)
- Result.push_back(RHSVals[i]);
- return !Result.empty();
- }
-
- // TODO: Should handle the NOT form of XOR.
+BasicBlock *JumpThreading::FactorCommonPHIPreds(PHINode *PN, Value *Val) {
+ SmallVector<BasicBlock*, 16> CommonPreds;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingValue(i) == Val)
+ CommonPreds.push_back(PN->getIncomingBlock(i));
+
+ if (CommonPreds.size() == 1)
+ return CommonPreds[0];
- }
-
- // Handle compare with phi operand, where the PHI is defined in this block.
- if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
- PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0));
- if (PN && PN->getParent() == BB) {
- // We can do this simplification if any comparisons fold to true or false.
- // See if any do.
- for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
- BasicBlock *PredBB = PN->getIncomingBlock(i);
- Value *LHS = PN->getIncomingValue(i);
- Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
-
- Constant *Res = GetResultOfComparison(Cmp->getPredicate(), LHS, RHS);
- if (Res == 0) continue;
-
- if (isa<UndefValue>(Res))
- Result.push_back(std::make_pair((ConstantInt*)0, PredBB));
- else if (ConstantInt *CI = dyn_cast<ConstantInt>(Res))
- Result.push_back(std::make_pair(CI, PredBB));
- }
-
- return !Result.empty();
- }
-
- // TODO: We could also recurse to see if we can determine constants another
- // way.
- }
- return false;
+ DEBUG(errs() << " Factoring out " << CommonPreds.size()
+ << " common predecessors.\n");
+ return SplitBlockPredecessors(PN->getParent(),
+ &CommonPreds[0], CommonPreds.size(),
+ ".thr_comm", this);
}
-
-
+
/// GetBestDestForBranchOnUndef - If we determine that the specified block ends
/// in an undefined jump, decide which block is best to revector to.
// successor, merge the blocks. This encourages recursive jump threading
// because now the condition in this block can be threaded through
// predecessors of our predecessor block.
- if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
+ if (BasicBlock *SinglePred = BB->getSinglePredecessor())
if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
SinglePred != BB) {
// If SinglePred was a loop header, BB becomes one.
BB->moveBefore(&BB->getParent()->getEntryBlock());
return true;
}
- }
-
- // Look to see if the terminator is a branch of switch, if not we can't thread
- // it.
+
+ // See if this block ends with a branch or switch. If so, see if the
+ // condition is a phi node. If so, and if an entry of the phi node is a
+ // constant, we can thread the block.
Value *Condition;
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
// Can't thread an unconditional jump.
if (PN->getParent() == BB)
return ProcessJumpOnPHI(PN);
+ // If this is a conditional branch whose condition is and/or of a phi, try to
+ // simplify it.
+ if ((CondInst->getOpcode() == Instruction::And ||
+ CondInst->getOpcode() == Instruction::Or) &&
+ isa<BranchInst>(BB->getTerminator()) &&
+ ProcessBranchOnLogical(CondInst, BB,
+ CondInst->getOpcode() == Instruction::And))
+ return true;
+
if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
- if (!isa<PHINode>(CondCmp->getOperand(0)) ||
- cast<PHINode>(CondCmp->getOperand(0))->getParent() != BB) {
- // If we have a comparison, loop over the predecessors to see if there is
- // a condition with a lexically identical value.
- pred_iterator PI = pred_begin(BB), E = pred_end(BB);
- for (; PI != E; ++PI)
- if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
- if (PBI->isConditional() && *PI != BB) {
- if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
- if (CI->getOperand(0) == CondCmp->getOperand(0) &&
- CI->getOperand(1) == CondCmp->getOperand(1) &&
- CI->getPredicate() == CondCmp->getPredicate()) {
- // TODO: Could handle things like (x != 4) --> (x == 17)
- if (ProcessBranchOnDuplicateCond(*PI, BB))
- return true;
- }
+ if (isa<PHINode>(CondCmp->getOperand(0))) {
+ // If we have "br (phi != 42)" and the phi node has any constant values
+ // as operands, we can thread through this block.
+ //
+ // If we have "br (cmp phi, x)" and the phi node contains x such that the
+ // comparison uniquely identifies the branch target, we can thread
+ // through this block.
+
+ if (ProcessBranchOnCompare(CondCmp, BB))
+ return true;
+ }
+
+ // If we have a comparison, loop over the predecessors to see if there is
+ // a condition with the same value.
+ pred_iterator PI = pred_begin(BB), E = pred_end(BB);
+ for (; PI != E; ++PI)
+ if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
+ if (PBI->isConditional() && *PI != BB) {
+ if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
+ if (CI->getOperand(0) == CondCmp->getOperand(0) &&
+ CI->getOperand(1) == CondCmp->getOperand(1) &&
+ CI->getPredicate() == CondCmp->getPredicate()) {
+ // TODO: Could handle things like (x != 4) --> (x == 17)
+ if (ProcessBranchOnDuplicateCond(*PI, BB))
+ return true;
}
}
- }
+ }
}
// Check for some cases that are worth simplifying. Right now we want to look
if (SimplifyPartiallyRedundantLoad(LI))
return true;
-
- // Handle a variety of cases where we are branching on something derived from
- // a PHI node in the current block. If we can prove that any predecessors
- // compute a predictable value based on a PHI node, thread those predecessors.
- //
- // We only bother doing this if the current block has a PHI node and if the
- // conditional instruction lives in the current block. If either condition
- // fail, this won't be a computable value anyway.
- if (CondInst->getParent() == BB && isa<PHINode>(BB->front()))
- if (ProcessThreadableEdges(CondInst, BB))
- return true;
-
-
// TODO: If we have: "br (X > 0)" and we have a predecessor where we know
// "(X == 4)" thread through this block.
return true;
}
-/// FindMostPopularDest - The specified list contains multiple possible
-/// threadable destinations. Pick the one that occurs the most frequently in
-/// the list.
-static BasicBlock *
-FindMostPopularDest(BasicBlock *BB,
- const SmallVectorImpl<std::pair<BasicBlock*,
- BasicBlock*> > &PredToDestList) {
- assert(!PredToDestList.empty());
-
- // Determine popularity. If there are multiple possible destinations, we
- // explicitly choose to ignore 'undef' destinations. We prefer to thread
- // blocks with known and real destinations to threading undef. We'll handle
- // them later if interesting.
- DenseMap<BasicBlock*, unsigned> DestPopularity;
- for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
- if (PredToDestList[i].second)
- DestPopularity[PredToDestList[i].second]++;
-
- // Find the most popular dest.
- DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
- BasicBlock *MostPopularDest = DPI->first;
- unsigned Popularity = DPI->second;
- SmallVector<BasicBlock*, 4> SamePopularity;
-
- for (++DPI; DPI != DestPopularity.end(); ++DPI) {
- // If the popularity of this entry isn't higher than the popularity we've
- // seen so far, ignore it.
- if (DPI->second < Popularity)
- ; // ignore.
- else if (DPI->second == Popularity) {
- // If it is the same as what we've seen so far, keep track of it.
- SamePopularity.push_back(DPI->first);
- } else {
- // If it is more popular, remember it.
- SamePopularity.clear();
- MostPopularDest = DPI->first;
- Popularity = DPI->second;
- }
- }
-
- // Okay, now we know the most popular destination. If there is more than
- // destination, we need to determine one. This is arbitrary, but we need
- // to make a deterministic decision. Pick the first one that appears in the
- // successor list.
- if (!SamePopularity.empty()) {
- SamePopularity.push_back(MostPopularDest);
- TerminatorInst *TI = BB->getTerminator();
- for (unsigned i = 0; ; ++i) {
- assert(i != TI->getNumSuccessors() && "Didn't find any successor!");
-
- if (std::find(SamePopularity.begin(), SamePopularity.end(),
- TI->getSuccessor(i)) == SamePopularity.end())
- continue;
-
- MostPopularDest = TI->getSuccessor(i);
- break;
- }
- }
-
- // Okay, we have finally picked the most popular destination.
- return MostPopularDest;
-}
-bool JumpThreading::ProcessThreadableEdges(Instruction *CondInst,
- BasicBlock *BB) {
- // If threading this would thread across a loop header, don't even try to
- // thread the edge.
- if (LoopHeaders.count(BB))
- return false;
-
-
+/// ProcessJumpOnPHI - We have a conditional branch or switch on a PHI node in
+/// the current block. See if there are any simplifications we can do based on
+/// inputs to the phi node.
+///
+bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) {
+ BasicBlock *BB = PN->getParent();
- SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> PredValues;
- if (!ComputeValueKnownInPredecessors(CondInst, BB, PredValues))
- return false;
- assert(!PredValues.empty() &&
- "ComputeValueKnownInPredecessors returned true with no values");
-
- DEBUG(errs() << "IN BB: " << *BB;
- for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
- errs() << " BB '" << BB->getName() << "': FOUND condition = ";
- if (PredValues[i].first)
- errs() << *PredValues[i].first;
- else
- errs() << "UNDEF";
- errs() << " for pred '" << PredValues[i].second->getName()
- << "'.\n";
- });
-
- // Decide what we want to thread through. Convert our list of known values to
- // a list of known destinations for each pred. This also discards duplicate
- // predecessors and keeps track of the undefined inputs (which are represented
- // as a null dest in the PredToDestList.
- SmallPtrSet<BasicBlock*, 16> SeenPreds;
- SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList;
-
- BasicBlock *OnlyDest = 0;
- BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
-
- for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
- BasicBlock *Pred = PredValues[i].second;
- if (!SeenPreds.insert(Pred))
- continue; // Duplicate predecessor entry.
-
- // If the predecessor ends with an indirect goto, we can't change its
- // destination.
- if (isa<IndirectBrInst>(Pred->getTerminator()))
- continue;
-
- ConstantInt *Val = PredValues[i].first;
+ // See if the phi node has any constant integer or undef values. If so, we
+ // can determine where the corresponding predecessor will branch.
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ Value *PredVal = PN->getIncomingValue(i);
- BasicBlock *DestBB;
- if (Val == 0) // Undef.
- DestBB = 0;
- else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
- DestBB = BI->getSuccessor(Val->isZero());
- else {
- SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
- DestBB = SI->getSuccessor(SI->findCaseValue(Val));
+ // Check to see if this input is a constant integer. If so, the direction
+ // of the branch is predictable.
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(PredVal)) {
+ // Merge any common predecessors that will act the same.
+ BasicBlock *PredBB = FactorCommonPHIPreds(PN, CI);
+
+ BasicBlock *SuccBB;
+ if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
+ SuccBB = BI->getSuccessor(CI->isZero());
+ else {
+ SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
+ SuccBB = SI->getSuccessor(SI->findCaseValue(CI));
+ }
+
+ // Ok, try to thread it!
+ return ThreadEdge(BB, PredBB, SuccBB);
}
-
- // If we have exactly one destination, remember it for efficiency below.
- if (i == 0)
- OnlyDest = DestBB;
- else if (OnlyDest != DestBB)
- OnlyDest = MultipleDestSentinel;
- PredToDestList.push_back(std::make_pair(Pred, DestBB));
- }
-
- // If all edges were unthreadable, we fail.
- if (PredToDestList.empty())
- return false;
-
- // Determine which is the most common successor. If we have many inputs and
- // this block is a switch, we want to start by threading the batch that goes
- // to the most popular destination first. If we only know about one
- // threadable destination (the common case) we can avoid this.
- BasicBlock *MostPopularDest = OnlyDest;
-
- if (MostPopularDest == MultipleDestSentinel)
- MostPopularDest = FindMostPopularDest(BB, PredToDestList);
-
- // Now that we know what the most popular destination is, factor all
- // predecessors that will jump to it into a single predecessor.
- SmallVector<BasicBlock*, 16> PredsToFactor;
- for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
- if (PredToDestList[i].second == MostPopularDest) {
- BasicBlock *Pred = PredToDestList[i].first;
+ // If the input is an undef, then it doesn't matter which way it will go.
+ // Pick an arbitrary dest and thread the edge.
+ if (UndefValue *UV = dyn_cast<UndefValue>(PredVal)) {
+ // Merge any common predecessors that will act the same.
+ BasicBlock *PredBB = FactorCommonPHIPreds(PN, UV);
+ BasicBlock *SuccBB =
+ BB->getTerminator()->getSuccessor(GetBestDestForJumpOnUndef(BB));
- // This predecessor may be a switch or something else that has multiple
- // edges to the block. Factor each of these edges by listing them
- // according to # occurrences in PredsToFactor.
- TerminatorInst *PredTI = Pred->getTerminator();
- for (unsigned i = 0, e = PredTI->getNumSuccessors(); i != e; ++i)
- if (PredTI->getSuccessor(i) == BB)
- PredsToFactor.push_back(Pred);
+ // Ok, try to thread it!
+ return ThreadEdge(BB, PredBB, SuccBB);
}
-
- BasicBlock *PredToThread;
- if (PredsToFactor.size() == 1)
- PredToThread = PredsToFactor[0];
- else {
- DEBUG(errs() << " Factoring out " << PredsToFactor.size()
- << " common predecessors.\n");
- PredToThread = SplitBlockPredecessors(BB, &PredsToFactor[0],
- PredsToFactor.size(),
- ".thr_comm", this);
}
- // If the threadable edges are branching on an undefined value, we get to pick
- // the destination that these predecessors should get to.
- if (MostPopularDest == 0)
- MostPopularDest = BB->getTerminator()->
- getSuccessor(GetBestDestForJumpOnUndef(BB));
-
- // Ok, try to thread it!
- return ThreadEdge(BB, PredToThread, MostPopularDest);
-}
-
-/// ProcessJumpOnPHI - We have a conditional branch or switch on a PHI node in
-/// the current block. See if there are any simplifications we can do based on
-/// inputs to the phi node.
-///
-bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) {
- BasicBlock *BB = PN->getParent();
-
- // If any of the predecessor blocks end in an unconditional branch, we can
- // *duplicate* the jump into that block in order to further encourage jump
- // threading and to eliminate cases where we have branch on a phi of an icmp
- // (branch on icmp is much better).
+ // If the incoming values are all variables, we don't know the destination of
+ // any predecessors. However, if any of the predecessor blocks end in an
+ // unconditional branch, we can *duplicate* the jump into that block in order
+ // to further encourage jump threading and to eliminate cases where we have
+ // branch on a phi of an icmp (branch on icmp is much better).
// We don't want to do this tranformation for switches, because we don't
// really want to duplicate a switch.
}
+/// ProcessJumpOnLogicalPHI - PN's basic block contains a conditional branch
+/// whose condition is an AND/OR where one side is PN. If PN has constant
+/// operands that permit us to evaluate the condition for some operand, thread
+/// through the block. For example with:
+/// br (and X, phi(Y, Z, false))
+/// the predecessor corresponding to the 'false' will always jump to the false
+/// destination of the branch.
+///
+bool JumpThreading::ProcessBranchOnLogical(Value *V, BasicBlock *BB,
+ bool isAnd) {
+ // If this is a binary operator tree of the same AND/OR opcode, check the
+ // LHS/RHS.
+ if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
+ if ((isAnd && BO->getOpcode() == Instruction::And) ||
+ (!isAnd && BO->getOpcode() == Instruction::Or)) {
+ if (ProcessBranchOnLogical(BO->getOperand(0), BB, isAnd))
+ return true;
+ if (ProcessBranchOnLogical(BO->getOperand(1), BB, isAnd))
+ return true;
+ }
+
+ // If this isn't a PHI node, we can't handle it.
+ PHINode *PN = dyn_cast<PHINode>(V);
+ if (!PN || PN->getParent() != BB) return false;
+
+ // We can only do the simplification for phi nodes of 'false' with AND or
+ // 'true' with OR. See if we have any entries in the phi for this.
+ unsigned PredNo = ~0U;
+ ConstantInt *PredCst = ConstantInt::get(Type::getInt1Ty(BB->getContext()),
+ !isAnd);
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ if (PN->getIncomingValue(i) == PredCst) {
+ PredNo = i;
+ break;
+ }
+ }
+
+ // If no match, bail out.
+ if (PredNo == ~0U)
+ return false;
+
+ // If so, we can actually do this threading. Merge any common predecessors
+ // that will act the same.
+ BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredCst);
+
+ // Next, figure out which successor we are threading to. If this was an AND,
+ // the constant must be FALSE, and we must be targeting the 'false' block.
+ // If this is an OR, the constant must be TRUE, and we must be targeting the
+ // 'true' block.
+ BasicBlock *SuccBB = BB->getTerminator()->getSuccessor(isAnd);
+
+ // Ok, try to thread it!
+ return ThreadEdge(BB, PredBB, SuccBB);
+}
+
+/// GetResultOfComparison - Given an icmp/fcmp predicate and the left and right
+/// hand sides of the compare instruction, try to determine the result. If the
+/// result can not be determined, a null pointer is returned.
+static Constant *GetResultOfComparison(CmpInst::Predicate pred,
+ Value *LHS, Value *RHS,
+ LLVMContext &Context) {
+ if (Constant *CLHS = dyn_cast<Constant>(LHS))
+ if (Constant *CRHS = dyn_cast<Constant>(RHS))
+ return ConstantExpr::getCompare(pred, CLHS, CRHS);
+
+ if (LHS == RHS)
+ if (isa<IntegerType>(LHS->getType()) || isa<PointerType>(LHS->getType()))
+ return ICmpInst::isTrueWhenEqual(pred) ?
+ ConstantInt::getTrue(Context) : ConstantInt::getFalse(Context);
+
+ return 0;
+}
+
+/// ProcessBranchOnCompare - We found a branch on a comparison between a phi
+/// node and a value. If we can identify when the comparison is true between
+/// the phi inputs and the value, we can fold the compare for that edge and
+/// thread through it.
+bool JumpThreading::ProcessBranchOnCompare(CmpInst *Cmp, BasicBlock *BB) {
+ PHINode *PN = cast<PHINode>(Cmp->getOperand(0));
+ Value *RHS = Cmp->getOperand(1);
+
+ // If the phi isn't in the current block, an incoming edge to this block
+ // doesn't control the destination.
+ if (PN->getParent() != BB)
+ return false;
+
+ // We can do this simplification if any comparisons fold to true or false.
+ // See if any do.
+ Value *PredVal = 0;
+ bool TrueDirection = false;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ PredVal = PN->getIncomingValue(i);
+
+ Constant *Res = GetResultOfComparison(Cmp->getPredicate(), PredVal,
+ RHS, Cmp->getContext());
+ if (!Res) {
+ PredVal = 0;
+ continue;
+ }
+
+ // If this folded to a constant expr, we can't do anything.
+ if (ConstantInt *ResC = dyn_cast<ConstantInt>(Res)) {
+ TrueDirection = ResC->getZExtValue();
+ break;
+ }
+ // If this folded to undef, just go the false way.
+ if (isa<UndefValue>(Res)) {
+ TrueDirection = false;
+ break;
+ }
+
+ // Otherwise, we can't fold this input.
+ PredVal = 0;
+ }
+
+ // If no match, bail out.
+ if (PredVal == 0)
+ return false;
+
+ // If so, we can actually do this threading. Merge any common predecessors
+ // that will act the same.
+ BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredVal);
+
+ // Next, get our successor.
+ BasicBlock *SuccBB = BB->getTerminator()->getSuccessor(!TrueDirection);
+
+ // Ok, try to thread it!
+ return ThreadEdge(BB, PredBB, SuccBB);
+}
+
+
/// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
/// predecessor to the PHIBB block. If it has PHI nodes, add entries for
/// NewPred using the entries from OldPred (suitably mapped).
projects / oota-llvm.git / commitdiff