#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/GlobalVariable.h"
+#include "llvm/IRBuilder.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
+#include "llvm/MDBuilder.h"
#include "llvm/Metadata.h"
#include "llvm/Operator.h"
#include "llvm/Type.h"
-#include "llvm/Analysis/InstructionSimplify.h"
-#include "llvm/Analysis/ValueTracking.h"
-#include "llvm/Target/TargetData.h"
-#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/Debug.h"
-#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/NoFolder.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <algorithm>
#include <set>
#include <map>
STATISTIC(NumSpeculations, "Number of speculative executed instructions");
namespace {
+ /// ValueEqualityComparisonCase - Represents a case of a switch.
+ struct ValueEqualityComparisonCase {
+ ConstantInt *Value;
+ BasicBlock *Dest;
+
+ ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
+ : Value(Value), Dest(Dest) {}
+
+ bool operator<(ValueEqualityComparisonCase RHS) const {
+ // Comparing pointers is ok as we only rely on the order for uniquing.
+ return Value < RHS.Value;
+ }
+ };
+
class SimplifyCFGOpt {
const TargetData *const TD;
Value *isValueEqualityComparison(TerminatorInst *TI);
BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
- std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
+ std::vector<ValueEqualityComparisonCase> &Cases);
bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
BasicBlock *Pred,
IRBuilder<> &Builder);
return true;
}
+/// isProfitableToFoldUnconditional - Return true if it is safe and profitable
+/// to merge these two terminator instructions together, where SI1 is an
+/// unconditional branch. PhiNodes will store all PHI nodes in common
+/// successors.
+///
+static bool isProfitableToFoldUnconditional(BranchInst *SI1,
+ BranchInst *SI2,
+ Instruction *Cond,
+ SmallVectorImpl<PHINode*> &PhiNodes) {
+ if (SI1 == SI2) return false; // Can't merge with self!
+ assert(SI1->isUnconditional() && SI2->isConditional());
+
+ // We fold the unconditional branch if we can easily update all PHI nodes in
+ // common successors:
+ // 1> We have a constant incoming value for the conditional branch;
+ // 2> We have "Cond" as the incoming value for the unconditional branch;
+ // 3> SI2->getCondition() and Cond have same operands.
+ CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
+ if (!Ci2) return false;
+ if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
+ Cond->getOperand(1) == Ci2->getOperand(1)) &&
+ !(Cond->getOperand(0) == Ci2->getOperand(1) &&
+ Cond->getOperand(1) == Ci2->getOperand(0)))
+ return false;
+
+ BasicBlock *SI1BB = SI1->getParent();
+ BasicBlock *SI2BB = SI2->getParent();
+ SmallPtrSet<BasicBlock*, 16> 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();
+ isa<PHINode>(BBI); ++BBI) {
+ PHINode *PN = cast<PHINode>(BBI);
+ if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
+ !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB)))
+ return false;
+ PhiNodes.push_back(PN);
+ }
+ 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
/// decode all of the 'cases' that it represents and return the 'default' block.
BasicBlock *SimplifyCFGOpt::
GetValueEqualityComparisonCases(TerminatorInst *TI,
- std::vector<std::pair<ConstantInt*,
- BasicBlock*> > &Cases) {
+ std::vector<ValueEqualityComparisonCase>
+ &Cases) {
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
Cases.reserve(SI->getNumCases());
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
- Cases.push_back(std::make_pair(i.getCaseValue(),
- i.getCaseSuccessor()));
+ Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(),
+ i.getCaseSuccessor()));
return SI->getDefaultDest();
}
BranchInst *BI = cast<BranchInst>(TI);
ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
- Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
- BI->getSuccessor(ICI->getPredicate() ==
- ICmpInst::ICMP_NE)));
+ BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
+ Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1),
+ TD),
+ Succ));
return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
}
/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
/// in the list that match the specified block.
static void EliminateBlockCases(BasicBlock *BB,
- std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
+ std::vector<ValueEqualityComparisonCase> &Cases) {
for (unsigned i = 0, e = Cases.size(); i != e; ++i)
- if (Cases[i].second == BB) {
+ if (Cases[i].Dest == BB) {
Cases.erase(Cases.begin()+i);
--i; --e;
}
/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
/// well.
static bool
-ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
- std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
- std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
+ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
+ std::vector<ValueEqualityComparisonCase > &C2) {
+ std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
// Make V1 be smaller than V2.
if (V1->size() > V2->size())
if (V1->size() == 0) return false;
if (V1->size() == 1) {
// Just scan V2.
- ConstantInt *TheVal = (*V1)[0].first;
+ ConstantInt *TheVal = (*V1)[0].Value;
for (unsigned i = 0, e = V2->size(); i != e; ++i)
- if (TheVal == (*V2)[i].first)
+ if (TheVal == (*V2)[i].Value)
return true;
}
array_pod_sort(V2->begin(), V2->end());
unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
while (i1 != e1 && i2 != e2) {
- if ((*V1)[i1].first == (*V2)[i2].first)
+ if ((*V1)[i1].Value == (*V2)[i2].Value)
return true;
- if ((*V1)[i1].first < (*V2)[i2].first)
+ if ((*V1)[i1].Value < (*V2)[i2].Value)
++i1;
else
++i2;
if (ThisVal != PredVal) return false; // Different predicates.
// Find out information about when control will move from Pred to TI's block.
- std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
+ std::vector<ValueEqualityComparisonCase> PredCases;
BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
PredCases);
EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
// Find information about how control leaves this block.
- std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
+ std::vector<ValueEqualityComparisonCase> ThisCases;
BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
(void) NI;
// Remove PHI node entries for the dead edge.
- ThisCases[0].second->removePredecessor(TI->getParent());
+ ThisCases[0].Dest->removePredecessor(TI->getParent());
DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
<< "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
// Okay, TI has cases that are statically dead, prune them away.
SmallPtrSet<Constant*, 16> DeadCases;
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
- DeadCases.insert(PredCases[i].first);
+ DeadCases.insert(PredCases[i].Value);
DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
<< "Through successor TI: " << *TI);
ConstantInt *TIV = 0;
BasicBlock *TIBB = TI->getParent();
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
- if (PredCases[i].second == TIBB) {
+ if (PredCases[i].Dest == TIBB) {
if (TIV != 0)
return false; // Cannot handle multiple values coming to this block.
- TIV = PredCases[i].first;
+ TIV = PredCases[i].Value;
}
assert(TIV && "No edge from pred to succ?");
// BB. Find out which successor will unconditionally be branched to.
BasicBlock *TheRealDest = 0;
for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
- if (ThisCases[i].first == TIV) {
- TheRealDest = ThisCases[i].second;
+ if (ThisCases[i].Value == TIV) {
+ TheRealDest = ThisCases[i].Dest;
break;
}
if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
// Figure out which 'cases' to copy from SI to PSI.
- std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
+ std::vector<ValueEqualityComparisonCase> BBCases;
BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
- std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
+ std::vector<ValueEqualityComparisonCase> PredCases;
BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
// Based on whether the default edge from PTI goes to BB or not, fill in
// that don't occur in PTI, or that branch to BB will be activated.
std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
- if (PredCases[i].second != BB)
- PTIHandled.insert(PredCases[i].first);
+ if (PredCases[i].Dest != BB)
+ PTIHandled.insert(PredCases[i].Value);
else {
// The default destination is BB, we don't need explicit targets.
std::swap(PredCases[i], PredCases.back());
NewSuccessors.push_back(BBDefault);
}
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
- if (!PTIHandled.count(BBCases[i].first) &&
- BBCases[i].second != BBDefault) {
+ if (!PTIHandled.count(BBCases[i].Value) &&
+ BBCases[i].Dest != BBDefault) {
PredCases.push_back(BBCases[i]);
- NewSuccessors.push_back(BBCases[i].second);
+ NewSuccessors.push_back(BBCases[i].Dest);
}
} else {
// activated.
std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
- if (PredCases[i].second == BB) {
- PTIHandled.insert(PredCases[i].first);
+ if (PredCases[i].Dest == BB) {
+ PTIHandled.insert(PredCases[i].Value);
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 (PTIHandled.count(BBCases[i].Value)) {
// 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
+ NewSuccessors.push_back(BBCases[i].Dest);
+ PTIHandled.erase(BBCases[i].Value);// This constant is taken care of
}
// If there are any constants vectored to BB that TI doesn't handle,
for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
PTIHandled.begin(),
E = PTIHandled.end(); I != E; ++I) {
- PredCases.push_back(std::make_pair(*I, BBDefault));
+ PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault));
NewSuccessors.push_back(BBDefault);
}
}
PredCases.size());
NewSI->setDebugLoc(PTI->getDebugLoc());
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
- NewSI->addCase(PredCases[i].first, PredCases[i].second);
+ NewSI->addCase(PredCases[i].Value, PredCases[i].Dest);
EraseTerminatorInstAndDCECond(PTI);
return Result;
}
+/// checkCSEInPredecessor - Return true if the given instruction is available
+/// in its predecessor block. If yes, the instruction will be removed.
+///
+static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
+ if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
+ return false;
+ for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
+ Instruction *PBI = &*I;
+ // Check whether Inst and PBI generate the same value.
+ if (Inst->isIdenticalTo(PBI)) {
+ Inst->replaceAllUsesWith(PBI);
+ Inst->eraseFromParent();
+ return true;
+ }
+ }
+ return false;
+}
/// FoldBranchToCommonDest - If this basic block is simple enough, and if a
/// predecessor branches to us and one of our successors, fold the block into
bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
BasicBlock *BB = BI->getParent();
- Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
+ Instruction *Cond = 0;
+ if (BI->isConditional())
+ Cond = dyn_cast<Instruction>(BI->getCondition());
+ else {
+ // For unconditional branch, check for a simple CFG pattern, where
+ // BB has a single predecessor and BB's successor is also its predecessor's
+ // successor. If such pattern exisits, check for CSE between BB and its
+ // predecessor.
+ if (BasicBlock *PB = BB->getSinglePredecessor())
+ if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
+ if (PBI->isConditional() &&
+ (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
+ BI->getSuccessor(0) == PBI->getSuccessor(1))) {
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end();
+ I != E; ) {
+ Instruction *Curr = I++;
+ if (isa<CmpInst>(Curr)) {
+ Cond = Curr;
+ break;
+ }
+ // Quit if we can't remove this instruction.
+ if (!checkCSEInPredecessor(Curr, PB))
+ return false;
+ }
+ }
+
+ if (Cond == 0)
+ return false;
+ }
+
if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
Cond->getParent() != BB || !Cond->hasOneUse())
return false;
// Finally, don't infinitely unroll conditional loops.
BasicBlock *TrueDest = BI->getSuccessor(0);
- BasicBlock *FalseDest = BI->getSuccessor(1);
+ BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0;
if (TrueDest == BB || FalseDest == BB)
return false;
// Check that we have two conditional branches. If there is a PHI node in
// the common successor, verify that the same value flows in from both
// blocks.
- if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
+ SmallVector<PHINode*, 4> PHIs;
+ if (PBI == 0 || PBI->isUnconditional() ||
+ (BI->isConditional() &&
+ !SafeToMergeTerminators(BI, PBI)) ||
+ (!BI->isConditional() &&
+ !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
continue;
// Determine if the two branches share a common destination.
Instruction::BinaryOps Opc;
bool InvertPredCond = false;
- if (PBI->getSuccessor(0) == TrueDest)
- Opc = Instruction::Or;
- else if (PBI->getSuccessor(1) == FalseDest)
- Opc = Instruction::And;
- else if (PBI->getSuccessor(0) == FalseDest)
- Opc = Instruction::And, InvertPredCond = true;
- else if (PBI->getSuccessor(1) == TrueDest)
- Opc = Instruction::Or, InvertPredCond = true;
- else
- continue;
+ if (BI->isConditional()) {
+ if (PBI->getSuccessor(0) == TrueDest)
+ Opc = Instruction::Or;
+ else if (PBI->getSuccessor(1) == FalseDest)
+ Opc = Instruction::And;
+ else if (PBI->getSuccessor(0) == FalseDest)
+ Opc = Instruction::And, InvertPredCond = true;
+ else if (PBI->getSuccessor(1) == TrueDest)
+ Opc = Instruction::Or, InvertPredCond = true;
+ else
+ continue;
+ } else {
+ if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
+ continue;
+ }
// Ensure that any values used in the bonus instruction are also used
// by the terminator of the predecessor. This means that those values
New->takeName(Cond);
Cond->setName(New->getName()+".old");
- Instruction *NewCond =
- cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
+ if (BI->isConditional()) {
+ Instruction *NewCond =
+ cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
New, "or.cond"));
- PBI->setCondition(NewCond);
- if (PBI->getSuccessor(0) == BB) {
- AddPredecessorToBlock(TrueDest, PredBlock, BB);
- PBI->setSuccessor(0, TrueDest);
- }
- if (PBI->getSuccessor(1) == BB) {
- AddPredecessorToBlock(FalseDest, PredBlock, BB);
- PBI->setSuccessor(1, FalseDest);
+ PBI->setCondition(NewCond);
+
+ if (PBI->getSuccessor(0) == BB) {
+ AddPredecessorToBlock(TrueDest, PredBlock, BB);
+ PBI->setSuccessor(0, TrueDest);
+ }
+ if (PBI->getSuccessor(1) == BB) {
+ AddPredecessorToBlock(FalseDest, PredBlock, BB);
+ PBI->setSuccessor(1, FalseDest);
+ }
+ } else {
+ // Update PHI nodes in the common successors.
+ for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
+ ConstantInt *PBI_C = cast<ConstantInt>(
+ PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
+ assert(PBI_C->getType()->isIntegerTy(1));
+ Instruction *MergedCond = 0;
+ if (PBI->getSuccessor(0) == TrueDest) {
+ // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
+ // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
+ // is false: !PBI_Cond and BI_Value
+ Instruction *NotCond =
+ cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
+ "not.cond"));
+ MergedCond =
+ cast<Instruction>(Builder.CreateBinOp(Instruction::And,
+ NotCond, New,
+ "and.cond"));
+ if (PBI_C->isOne())
+ MergedCond =
+ cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
+ PBI->getCondition(), MergedCond,
+ "or.cond"));
+ } else {
+ // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
+ // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
+ // is false: PBI_Cond and BI_Value
+ MergedCond =
+ cast<Instruction>(Builder.CreateBinOp(Instruction::And,
+ PBI->getCondition(), New,
+ "and.cond"));
+ if (PBI_C->isOne()) {
+ Instruction *NotCond =
+ cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
+ "not.cond"));
+ MergedCond =
+ cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
+ NotCond, MergedCond,
+ "or.cond"));
+ }
+ }
+ // Update PHI Node.
+ PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
+ MergedCond);
+ }
+ // Change PBI from Conditional to Unconditional.
+ BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
+ EraseTerminatorInstAndDCECond(PBI);
+ PBI = New_PBI;
}
// TODO: If BB is reachable from all paths through PredBlock, then we
// Merge probability data into PredBlock's branch.
APInt A, B, C, D;
- if (ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
+ if (PBI->isConditional() && BI->isConditional() &&
+ ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
// Given IR which does:
// bbA:
// br i1 %x, label %bbB, label %bbC
ProbTrue = ProbTrue.udiv(GCD);
ProbFalse = ProbFalse.udiv(GCD);
- LLVMContext &Context = BI->getContext();
- Value *Ops[3];
- Ops[0] = BI->getMetadata(LLVMContext::MD_prof)->getOperand(0);
- Ops[1] = ConstantInt::get(Context, ProbTrue);
- Ops[2] = ConstantInt::get(Context, ProbFalse);
- PBI->setMetadata(LLVMContext::MD_prof, MDNode::get(Context, Ops));
+ MDBuilder MDB(BI->getContext());
+ MDNode *N = MDB.createBranchWeights(ProbTrue.getZExtValue(),
+ ProbFalse.getZExtValue());
+ PBI->setMetadata(LLVMContext::MD_prof, N);
} else {
PBI->setMetadata(LLVMContext::MD_prof, NULL);
}
return true;
}
+ // If this basic block is ONLY a compare and a branch, and if a predecessor
+ // branches to us and our successor, fold the comparison into the
+ // predecessor and use logical operations to update the incoming value
+ // for PHI nodes in common successor.
+ if (FoldBranchToCommonDest(BI))
+ return SimplifyCFG(BB) | true;
return false;
}
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