From 5729d38c81bc2e3b21a2bb7a80a8cde384fc7b7b Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Sat, 7 Nov 2009 08:05:03 +0000 Subject: [PATCH] reapply 86289, 86278, 86270, 86267, 86266 & 86264 plus a fix (making pred factoring only happen if threading is guaranteed to be successful). This now survives an X86-64 bootstrap of llvm-gcc. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86355 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/JumpThreading.cpp | 606 ++++++++++++++---------- test/Transforms/JumpThreading/basic.ll | 31 ++ test/Transforms/JumpThreading/crash.ll | 22 + 3 files changed, 416 insertions(+), 243 deletions(-) diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp index e623f917662..c0fd45da1f5 100644 --- a/lib/Transforms/Scalar/JumpThreading.cpp +++ b/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 &PredBBs, + BasicBlock *SuccBB); bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, BasicBlock *PredBB); - - BasicBlock *FactorCommonPHIPreds(PHINode *PN, Value *Val); + + typedef SmallVectorImpl > 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(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(LHS)) + if (Constant *CRHS = dyn_cast(RHS)) + return ConstantExpr::getCompare(pred, CLHS, CRHS); + + if (LHS == RHS) + if (isa(LHS->getType()) || isa(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 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(BB->begin()); + + // If V is a constantint, then it is known in all predecessors. + if (isa(V) || isa(V)) { + ConstantInt *CI = dyn_cast(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(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(I)) { + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + Value *InVal = PN->getIncomingValue(i); + if (isa(InVal) || isa(InVal)) { + ConstantInt *CI = dyn_cast(InVal); + Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i))); + } + } + return !Result.empty(); + } + + SmallVector, 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(I)) { + PHINode *PN = dyn_cast(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(Res)) + Result.push_back(std::make_pair((ConstantInt*)0, PredBB)); + else if (ConstantInt *CI = dyn_cast(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(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(BB->getTerminator()) && - ProcessBranchOnLogical(CondInst, BB, - CondInst->getOpcode() == Instruction::And)) - return true; - if (CmpInst *CondCmp = dyn_cast(CondInst)) { - if (isa(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((*PI)->getTerminator())) - if (PBI->isConditional() && *PI != BB) { - if (CmpInst *CI = dyn_cast(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(CondCmp->getOperand(0)) || + cast(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((*PI)->getTerminator())) + if (PBI->isConditional() && *PI != BB) { + if (CmpInst *CI = dyn_cast(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(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 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 > &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 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::iterator DPI = DestPopularity.begin(); + BasicBlock *MostPopularDest = DPI->first; + unsigned Popularity = DPI->second; + SmallVector 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(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(BB->getTerminator())) - SuccBB = BI->getSuccessor(CI->isZero()); - else { - SwitchInst *SI = cast(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, 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 SeenPreds; + SmallVector, 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(Pred->getTerminator())) + continue; + + ConstantInt *Val = PredValues[i].first; + + BasicBlock *DestBB; + if (Val == 0) // Undef. + DestBB = 0; + else if (BranchInst *BI = dyn_cast(BB->getTerminator())) + DestBB = BI->getSuccessor(Val->isZero()); + else { + SwitchInst *SI = cast(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(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 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(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(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(LHS)) - if (Constant *CRHS = dyn_cast(RHS)) - return ConstantExpr::getCompare(pred, CLHS, CRHS); - - if (LHS == RHS) - if (isa(LHS->getType()) || isa(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(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(Res)) { - TrueDirection = ResC->getZExtValue(); - break; - } - // If this folded to undef, just go the false way. - if (isa(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 &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 diff --git a/test/Transforms/JumpThreading/basic.ll b/test/Transforms/JumpThreading/basic.ll index 3d936b8f30f..7b444ad0a91 100644 --- a/test/Transforms/JumpThreading/basic.ll +++ b/test/Transforms/JumpThreading/basic.ll @@ -170,5 +170,36 @@ BB4: } +;; This tests that the branch in 'merge' can be cloned up into T1. +;; rdar://7367025 +define i32 @test7(i1 %cond, i1 %cond2) { +Entry: +; CHECK: @test7 + %v1 = call i32 @f1() + br i1 %cond, label %Merge, label %F1 + +F1: + %v2 = call i32 @f2() + br label %Merge + +Merge: + %B = phi i32 [%v1, %Entry], [%v2, %F1] + %M = icmp ne i32 %B, %v1 + %N = icmp eq i32 %B, 47 + %O = and i1 %M, %N + br i1 %O, label %T2, label %F2 +; CHECK: Merge: +; CHECK-NOT: phi +; CHECK-NEXT: %v2 = call i32 @f2() + +T2: + call void @f3() + ret i32 %B + +F2: + ret i32 %B +; CHECK: F2: +; CHECK-NEXT: phi i32 +} diff --git a/test/Transforms/JumpThreading/crash.ll b/test/Transforms/JumpThreading/crash.ll index 862b40378bc..7e2a2a047d1 100644 --- a/test/Transforms/JumpThreading/crash.ll +++ b/test/Transforms/JumpThreading/crash.ll @@ -170,3 +170,25 @@ bb32.i: ret i32 1 } + +define fastcc void @test5(i1 %tmp, i32 %tmp1) nounwind ssp { +entry: + br i1 %tmp, label %bb12, label %bb13 + + +bb12: + br label %bb13 + +bb13: + %.lcssa31 = phi i32 [ undef, %bb12 ], [ %tmp1, %entry ] + %A = and i1 undef, undef + br i1 %A, label %bb15, label %bb61 + +bb15: + ret void + + +bb61: + ret void +} + -- 2.34.1