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-rw-r--r--llvm/lib/Transforms/Scalar/JumpThreading.cpp606
1 files changed, 363 insertions, 243 deletions
diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index e623f917662..c0fd45da1f5 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -72,17 +72,23 @@ namespace {
void FindLoopHeaders(Function &F);
bool ProcessBlock(BasicBlock *BB);
- bool ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, BasicBlock *SuccBB);
+ bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock*> &PredBBs,
+ BasicBlock *SuccBB);
bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
BasicBlock *PredBB);
-
- BasicBlock *FactorCommonPHIPreds(PHINode *PN, Value *Val);
+
+ typedef SmallVectorImpl<std::pair<ConstantInt*,
+ BasicBlock*> > PredValueInfo;
+
+ bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
+ PredValueInfo &Result);
+ bool ProcessThreadableEdges(Instruction *CondInst, BasicBlock *BB);
+
+
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);
};
@@ -198,28 +204,133 @@ void JumpThreading::FindLoopHeaders(Function &F) {
LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
}
-/// 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.
+/// 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.
///
-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];
+///
+/// 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();
+ }
- DEBUG(errs() << " Factoring out " << CommonPreds.size()
- << " common predecessors.\n");
- return SplitBlockPredecessors(PN->getParent(),
- &CommonPreds[0], CommonPreds.size(),
- ".thr_comm", this);
-}
+ // TODO: Should handle the NOT form of XOR.
+
+ }
+ // 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;
+}
+
+
/// GetBestDestForBranchOnUndef - If we determine that the specified block ends
/// in an undefined jump, decide which block is best to revector to.
@@ -250,7 +361,7 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
// 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.
@@ -266,10 +377,10 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
BB->moveBefore(&BB->getParent()->getEntryBlock());
return true;
}
-
- // 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.
+ }
+
+ // Look to see if the terminator is a branch of switch, if not we can't thread
+ // it.
Value *Condition;
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
// Can't thread an unconditional jump.
@@ -345,44 +456,26 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
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))) {
- // 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;
+ 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;
+ }
}
}
- }
+ }
}
// Check for some cases that are worth simplifying. Right now we want to look
@@ -401,6 +494,19 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
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.
@@ -458,8 +564,11 @@ bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB,
// Next, figure out which successor we are threading to.
BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir);
+ SmallVector<BasicBlock*, 2> Preds;
+ Preds.push_back(PredBB);
+
// Ok, try to thread it!
- return ThreadEdge(BB, PredBB, SuccBB);
+ return ThreadEdge(BB, Preds, SuccBB);
}
/// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that
@@ -689,55 +798,186 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
return true;
}
-
-/// 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();
+/// 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;
+ }
+ }
- // 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);
-
- // 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);
+ // 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!");
- 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));
- }
+ if (std::find(SamePopularity.begin(), SamePopularity.end(),
+ TI->getSuccessor(i)) == SamePopularity.end())
+ continue;
- // Ok, try to thread it!
- return ThreadEdge(BB, PredBB, SuccBB);
+ 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;
+
+
+
+ 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;
+
+ 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));
}
+
+ // If we have exactly one destination, remember it for efficiency below.
+ if (i == 0)
+ OnlyDest = DestBB;
+ else if (OnlyDest != DestBB)
+ OnlyDest = MultipleDestSentinel;
- // 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));
+ 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;
- // Ok, try to thread it!
- return ThreadEdge(BB, PredBB, SuccBB);
+ // 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);
}
- }
+
+ // 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, PredsToFactor, 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 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).
+ // 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.
@@ -758,137 +998,6 @@ bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) {
}
-/// 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).
@@ -913,10 +1022,11 @@ static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
}
}
-/// ThreadEdge - We have decided that it is safe and profitable to thread an
-/// edge from PredBB to SuccBB across BB. Transform the IR to reflect this
-/// change.
-bool JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB,
+/// 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 JumpThreading::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) {
@@ -928,8 +1038,7 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB,
// If threading this would thread across a loop header, don't thread the edge.
// See the comments above FindLoopHeaders for justifications and caveats.
if (LoopHeaders.count(BB)) {
- DEBUG(errs() << " Not threading from '" << PredBB->getName()
- << "' across loop header BB '" << BB->getName()
+ DEBUG(errs() << " Not threading across loop header BB '" << BB->getName()
<< "' to dest BB '" << SuccBB->getName()
<< "' - it might create an irreducible loop!\n");
return false;
@@ -942,6 +1051,17 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB,
return false;
}
+ // And finally, do it! Start by factoring the predecessors is needed.
+ BasicBlock *PredBB;
+ if (PredBBs.size() == 1)
+ PredBB = PredBBs[0];
+ else {
+ DEBUG(errs() << " Factoring out " << PredBBs.size()
+ << " common predecessors.\n");
+ PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(),
+ ".thr_comm", this);
+ }
+
// And finally, do it!
DEBUG(errs() << " Threading edge from '" << PredBB->getName() << "' to '"
<< SuccBB->getName() << "' with cost: " << JumpThreadCost
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