//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "jump-threading"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Pass.h"
-#include "llvm/Analysis/InstructionSimplify.h"
-#include "llvm/Analysis/LazyValueInfo.h"
-#include "llvm/Transforms/Utils/BasicBlockUtils.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Transforms/Utils/SSAUpdater.h"
-#include "llvm/Target/TargetData.h"
#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/LazyValueInfo.h"
+#include "llvm/Analysis/Loads.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
-#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetLibraryInfo.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/SSAUpdater.h"
using namespace llvm;
+#define DEBUG_TYPE "jump-threading"
+
STATISTIC(NumThreads, "Number of jumps threaded");
STATISTIC(NumFolds, "Number of terminators folded");
STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi");
static cl::opt<unsigned>
-Threshold("jump-threading-threshold",
+BBDuplicateThreshold("jump-threading-threshold",
cl::desc("Max block size to duplicate for jump threading"),
cl::init(6), cl::Hidden);
-// Turn on use of LazyValueInfo.
-static cl::opt<bool>
-EnableLVI("enable-jump-threading-lvi", cl::ReallyHidden);
-
+namespace {
+ // These are at global scope so static functions can use them too.
+ typedef SmallVectorImpl<std::pair<Constant*, BasicBlock*> > PredValueInfo;
+ typedef SmallVector<std::pair<Constant*, BasicBlock*>, 8> PredValueInfoTy;
+ // This is used to keep track of what kind of constant we're currently hoping
+ // to find.
+ enum ConstantPreference {
+ WantInteger,
+ WantBlockAddress
+ };
-namespace {
/// This pass performs 'jump threading', which looks at blocks that have
/// multiple predecessors and multiple successors. If one or more of the
/// predecessors of the block can be proven to always jump to one of the
/// revectored to the false side of the second if.
///
class JumpThreading : public FunctionPass {
- TargetData *TD;
+ const DataLayout *DL;
+ TargetLibraryInfo *TLI;
LazyValueInfo *LVI;
#ifdef NDEBUG
SmallPtrSet<BasicBlock*, 16> LoopHeaders;
#else
SmallSet<AssertingVH<BasicBlock>, 16> LoopHeaders;
#endif
+ DenseSet<std::pair<Value*, BasicBlock*> > RecursionSet;
+
+ unsigned BBDupThreshold;
+
+ // RAII helper for updating the recursion stack.
+ struct RecursionSetRemover {
+ DenseSet<std::pair<Value*, BasicBlock*> > &TheSet;
+ std::pair<Value*, BasicBlock*> ThePair;
+
+ RecursionSetRemover(DenseSet<std::pair<Value*, BasicBlock*> > &S,
+ std::pair<Value*, BasicBlock*> P)
+ : TheSet(S), ThePair(P) { }
+
+ ~RecursionSetRemover() {
+ TheSet.erase(ThePair);
+ }
+ };
public:
static char ID; // Pass identification
- JumpThreading() : FunctionPass(&ID) {}
+ JumpThreading(int T = -1) : FunctionPass(ID) {
+ BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
+ initializeJumpThreadingPass(*PassRegistry::getPassRegistry());
+ }
- bool runOnFunction(Function &F);
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- if (EnableLVI)
- AU.addRequired<LazyValueInfo>();
+ bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<LazyValueInfo>();
+ AU.addPreserved<LazyValueInfo>();
+ AU.addRequired<TargetLibraryInfo>();
}
-
+
void FindLoopHeaders(Function &F);
bool ProcessBlock(BasicBlock *BB);
bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock*> &PredBBs,
BasicBlock *SuccBB);
bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
const SmallVectorImpl<BasicBlock *> &PredBBs);
-
- typedef SmallVectorImpl<std::pair<ConstantInt*,
- BasicBlock*> > PredValueInfo;
-
+
bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
- PredValueInfo &Result);
- bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB);
-
-
- bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
- bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
+ PredValueInfo &Result,
+ ConstantPreference Preference,
+ Instruction *CxtI = nullptr);
+ bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
+ ConstantPreference Preference,
+ Instruction *CxtI = nullptr);
bool ProcessBranchOnPHI(PHINode *PN);
bool ProcessBranchOnXOR(BinaryOperator *BO);
-
+
bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
+ bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
};
}
char JumpThreading::ID = 0;
-static RegisterPass<JumpThreading>
-X("jump-threading", "Jump Threading");
+INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading",
+ "Jump Threading", false, false)
+INITIALIZE_PASS_DEPENDENCY(LazyValueInfo)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
+INITIALIZE_PASS_END(JumpThreading, "jump-threading",
+ "Jump Threading", false, false)
// Public interface to the Jump Threading pass
-FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); }
+FunctionPass *llvm::createJumpThreadingPass(int Threshold) { return new JumpThreading(Threshold); }
/// runOnFunction - Top level algorithm.
///
bool JumpThreading::runOnFunction(Function &F) {
+ if (skipOptnoneFunction(F))
+ return false;
+
DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n");
- TD = getAnalysisIfAvailable<TargetData>();
- LVI = EnableLVI ? &getAnalysis<LazyValueInfo>() : 0;
-
+ DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
+ DL = DLP ? &DLP->getDataLayout() : nullptr;
+ TLI = &getAnalysis<TargetLibraryInfo>();
+ LVI = &getAnalysis<LazyValueInfo>();
+
+ // Remove unreachable blocks from function as they may result in infinite
+ // loop. We do threading if we found something profitable. Jump threading a
+ // branch can create other opportunities. If these opportunities form a cycle
+ // i.e. if any jump treading is undoing previous threading in the path, then
+ // we will loop forever. We take care of this issue by not jump threading for
+ // back edges. This works for normal cases but not for unreachable blocks as
+ // they may have cycle with no back edge.
+ removeUnreachableBlocks(F);
+
FindLoopHeaders(F);
-
+
bool Changed, EverChanged = false;
do {
Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
BasicBlock *BB = I;
- // Thread all of the branches we can over this block.
+ // Thread all of the branches we can over this block.
while (ProcessBlock(BB))
Changed = true;
-
+
++I;
-
+
// If the block is trivially dead, zap it. This eliminates the successor
// edges which simplifies the CFG.
if (pred_begin(BB) == pred_end(BB) &&
DEBUG(dbgs() << " JT: Deleting dead block '" << BB->getName()
<< "' with terminator: " << *BB->getTerminator() << '\n');
LoopHeaders.erase(BB);
+ LVI->eraseBlock(BB);
DeleteDeadBlock(BB);
Changed = true;
- } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
- // Can't thread an unconditional jump, but if the block is "almost
- // empty", we can replace uses of it with uses of the successor and make
- // this dead.
- if (BI->isUnconditional() &&
- BB != &BB->getParent()->getEntryBlock()) {
- BasicBlock::iterator BBI = BB->getFirstNonPHI();
- // Ignore dbg intrinsics.
- while (isa<DbgInfoIntrinsic>(BBI))
- ++BBI;
+ continue;
+ }
+
+ BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
+
+ // Can't thread an unconditional jump, but if the block is "almost
+ // empty", we can replace uses of it with uses of the successor and make
+ // this dead.
+ if (BI && BI->isUnconditional() &&
+ BB != &BB->getParent()->getEntryBlock() &&
// If the terminator is the only non-phi instruction, try to nuke it.
- if (BBI->isTerminator()) {
- // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the
- // block, we have to make sure it isn't in the LoopHeaders set. We
- // reinsert afterward if needed.
- bool ErasedFromLoopHeaders = LoopHeaders.erase(BB);
- BasicBlock *Succ = BI->getSuccessor(0);
-
- if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) {
- Changed = true;
- // If we deleted BB and BB was the header of a loop, then the
- // successor is now the header of the loop.
- BB = Succ;
- }
-
- if (ErasedFromLoopHeaders)
- LoopHeaders.insert(BB);
- }
+ BB->getFirstNonPHIOrDbg()->isTerminator()) {
+ // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the
+ // block, we have to make sure it isn't in the LoopHeaders set. We
+ // reinsert afterward if needed.
+ bool ErasedFromLoopHeaders = LoopHeaders.erase(BB);
+ BasicBlock *Succ = BI->getSuccessor(0);
+
+ // FIXME: It is always conservatively correct to drop the info
+ // for a block even if it doesn't get erased. This isn't totally
+ // awesome, but it allows us to use AssertingVH to prevent nasty
+ // dangling pointer issues within LazyValueInfo.
+ LVI->eraseBlock(BB);
+ if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) {
+ Changed = true;
+ // If we deleted BB and BB was the header of a loop, then the
+ // successor is now the header of the loop.
+ BB = Succ;
}
+
+ if (ErasedFromLoopHeaders)
+ LoopHeaders.insert(BB);
}
}
EverChanged |= Changed;
} while (Changed);
-
+
LoopHeaders.clear();
return EverChanged;
}
/// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
-/// thread across it.
-static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
+/// thread across it. Stop scanning the block when passing the threshold.
+static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
+ unsigned Threshold) {
/// Ignore PHI nodes, these will be flattened when duplication happens.
BasicBlock::const_iterator I = BB->getFirstNonPHI();
-
+
// FIXME: THREADING will delete values that are just used to compute the
// branch, so they shouldn't count against the duplication cost.
-
-
+
// Sum up the cost of each instruction until we get to the terminator. Don't
// include the terminator because the copy won't include it.
unsigned Size = 0;
for (; !isa<TerminatorInst>(I); ++I) {
+
+ // Stop scanning the block if we've reached the threshold.
+ if (Size > Threshold)
+ return Size;
+
// Debugger intrinsics don't incur code size.
if (isa<DbgInfoIntrinsic>(I)) continue;
-
+
// If this is a pointer->pointer bitcast, it is free.
- if (isa<BitCastInst>(I) && isa<PointerType>(I->getType()))
+ if (isa<BitCastInst>(I) && I->getType()->isPointerTy())
continue;
-
+
// All other instructions count for at least one unit.
++Size;
-
+
// Calls are more expensive. If they are non-intrinsic calls, we model them
// as having cost of 4. If they are a non-vector intrinsic, we model them
// as having cost of 2 total, and if they are a vector intrinsic, we model
// them as having cost 1.
if (const CallInst *CI = dyn_cast<CallInst>(I)) {
- if (!isa<IntrinsicInst>(CI))
+ if (CI->cannotDuplicate())
+ // Blocks with NoDuplicate are modelled as having infinite cost, so they
+ // are never duplicated.
+ return ~0U;
+ else if (!isa<IntrinsicInst>(CI))
Size += 3;
- else if (!isa<VectorType>(CI->getType()))
+ else if (!CI->getType()->isVectorTy())
Size += 1;
}
}
-
+
// Threading through a switch statement is particularly profitable. If this
// block ends in a switch, decrease its cost to make it more likely to happen.
if (isa<SwitchInst>(I))
Size = Size > 6 ? Size-6 : 0;
-
+
+ // The same holds for indirect branches, but slightly more so.
+ if (isa<IndirectBrInst>(I))
+ Size = Size > 8 ? Size-8 : 0;
+
return Size;
}
void JumpThreading::FindLoopHeaders(Function &F) {
SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
FindFunctionBackedges(F, Edges);
-
+
for (unsigned i = 0, e = Edges.size(); i != e; ++i)
LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
}
+/// getKnownConstant - Helper method to determine if we can thread over a
+/// terminator with the given value as its condition, and if so what value to
+/// use for that. What kind of value this is depends on whether we want an
+/// integer or a block address, but an undef is always accepted.
+/// Returns null if Val is null or not an appropriate constant.
+static Constant *getKnownConstant(Value *Val, ConstantPreference Preference) {
+ if (!Val)
+ return nullptr;
+
+ // Undef is "known" enough.
+ if (UndefValue *U = dyn_cast<UndefValue>(Val))
+ return U;
+
+ if (Preference == WantBlockAddress)
+ return dyn_cast<BlockAddress>(Val->stripPointerCasts());
+
+ return dyn_cast<ConstantInt>(Val);
+}
+
/// 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 list of value and pred BB in the
-/// result vector. If a value is known to be undef, it is returned as null.
+/// if we can infer that the value is a known ConstantInt/BlockAddress or undef
+/// in any of our predecessors. If so, return the known list of value and pred
+/// BB in the result vector.
///
/// This returns true if there were any known values.
///
bool JumpThreading::
-ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
- // 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);
-
+ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, PredValueInfo &Result,
+ ConstantPreference Preference,
+ Instruction *CxtI) {
+ // This method walks up use-def chains recursively. Because of this, we could
+ // get into an infinite loop going around loops in the use-def chain. To
+ // prevent this, keep track of what (value, block) pairs we've already visited
+ // and terminate the search if we loop back to them
+ if (!RecursionSet.insert(std::make_pair(V, BB)).second)
+ return false;
+
+ // An RAII help to remove this pair from the recursion set once the recursion
+ // stack pops back out again.
+ RecursionSetRemover remover(RecursionSet, std::make_pair(V, BB));
+
+ // If V is a constant, then it is known in all predecessors.
+ if (Constant *KC = getKnownConstant(V, Preference)) {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
- Result.push_back(std::make_pair(CI, *PI));
+ Result.push_back(std::make_pair(KC, *PI));
+
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) {
-
+ if (!I || I->getParent() != BB) {
+
// Okay, if this is a live-in value, see if it has a known value at the end
// of any of our predecessors.
//
/// TODO: Per PR2563, we could infer value range information about a
/// predecessor based on its terminator.
//
- if (LVI) {
- // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if
- // "I" is a non-local compare-with-a-constant instruction. This would be
- // able to handle value inequalities better, for example if the compare is
- // "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
- // Perhaps getConstantOnEdge should be smart enough to do this?
-
- for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
- // If the value is known by LazyValueInfo to be a constant in a
- // predecessor, use that information to try to thread this block.
- Constant *PredCst = LVI->getConstantOnEdge(V, *PI, BB);
- if (PredCst == 0 ||
- (!isa<ConstantInt>(PredCst) && !isa<UndefValue>(PredCst)))
- continue;
-
- Result.push_back(std::make_pair(dyn_cast<ConstantInt>(PredCst), *PI));
- }
-
- return !Result.empty();
+ // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if
+ // "I" is a non-local compare-with-a-constant instruction. This would be
+ // able to handle value inequalities better, for example if the compare is
+ // "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
+ // Perhaps getConstantOnEdge should be smart enough to do this?
+
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *P = *PI;
+ // If the value is known by LazyValueInfo to be a constant in a
+ // predecessor, use that information to try to thread this block.
+ Constant *PredCst = LVI->getConstantOnEdge(V, P, BB, CxtI);
+ if (Constant *KC = getKnownConstant(PredCst, Preference))
+ Result.push_back(std::make_pair(KC, P));
}
-
- return false;
+
+ return !Result.empty();
}
-
+
/// 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)));
+ if (Constant *KC = getKnownConstant(InVal, Preference)) {
+ Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
+ } else {
+ Constant *CI = LVI->getConstantOnEdge(InVal,
+ PN->getIncomingBlock(i),
+ BB, CxtI);
+ if (Constant *KC = getKnownConstant(CI, Preference))
+ Result.push_back(std::make_pair(KC, PN->getIncomingBlock(i)));
}
}
+
return !Result.empty();
}
-
- SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals;
+
+ PredValueInfoTy LHSVals, RHSVals;
// Handle some boolean conditions.
- if (I->getType()->getPrimitiveSizeInBits() == 1) {
+ if (I->getType()->getPrimitiveSizeInBits() == 1) {
+ assert(Preference == WantInteger && "One-bit non-integer type?");
// 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);
-
+ ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
+ WantInteger, CxtI);
+ ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals,
+ WantInteger, CxtI);
+
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.
+
+ SmallPtrSet<BasicBlock*, 4> LHSKnownBBs;
+
+ // Scan for the sentinel. If we find an undef, force it to the
+ // interesting value: x|undef -> true and x&undef -> false.
for (unsigned i = 0, e = LHSVals.size(); i != e; ++i)
- if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0)
+ if (LHSVals[i].first == InterestingVal ||
+ isa<UndefValue>(LHSVals[i].first)) {
Result.push_back(LHSVals[i]);
+ Result.back().first = InterestingVal;
+ LHSKnownBBs.insert(LHSVals[i].second);
+ }
for (unsigned i = 0, e = RHSVals.size(); i != e; ++i)
- if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0)
- Result.push_back(RHSVals[i]);
+ if (RHSVals[i].first == InterestingVal ||
+ isa<UndefValue>(RHSVals[i].first)) {
+ // If we already inferred a value for this block on the LHS, don't
+ // re-add it.
+ if (!LHSKnownBBs.count(RHSVals[i].second)) {
+ Result.push_back(RHSVals[i]);
+ Result.back().first = InterestingVal;
+ }
+ }
+
return !Result.empty();
}
-
+
// Handle the NOT form of XOR.
if (I->getOpcode() == Instruction::Xor &&
isa<ConstantInt>(I->getOperand(1)) &&
cast<ConstantInt>(I->getOperand(1))->isOne()) {
- ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result);
+ ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result,
+ WantInteger, CxtI);
if (Result.empty())
return false;
// Invert the known values.
for (unsigned i = 0, e = Result.size(); i != e; ++i)
- if (Result[i].first)
- Result[i].first =
- cast<ConstantInt>(ConstantExpr::getNot(Result[i].first));
+ Result[i].first = ConstantExpr::getNot(Result[i].first);
+
return true;
}
+
+ // Try to simplify some other binary operator values.
+ } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
+ assert(Preference != WantBlockAddress
+ && "A binary operator creating a block address?");
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
+ PredValueInfoTy LHSVals;
+ ComputeValueKnownInPredecessors(BO->getOperand(0), BB, LHSVals,
+ WantInteger, CxtI);
+
+ // Try to use constant folding to simplify the binary operator.
+ for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) {
+ Constant *V = LHSVals[i].first;
+ Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI);
+
+ if (Constant *KC = getKnownConstant(Folded, WantInteger))
+ Result.push_back(std::make_pair(KC, LHSVals[i].second));
+ }
+ }
+
+ return !Result.empty();
}
-
+
// Handle compare with phi operand, where the PHI is defined in this block.
if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
+ assert(Preference == WantInteger && "Compares only produce integers");
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.
BasicBlock *PredBB = PN->getIncomingBlock(i);
Value *LHS = PN->getIncomingValue(i);
Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
-
- Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, TD);
- if (Res == 0) {
- if (!LVI || !isa<Constant>(RHS))
+
+ Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, DL);
+ if (!Res) {
+ if (!isa<Constant>(RHS))
continue;
-
- LazyValueInfo::Tristate
+
+ LazyValueInfo::Tristate
ResT = LVI->getPredicateOnEdge(Cmp->getPredicate(), LHS,
- cast<Constant>(RHS), PredBB, BB);
+ cast<Constant>(RHS), PredBB, BB,
+ CxtI ? CxtI : Cmp);
if (ResT == LazyValueInfo::Unknown)
continue;
Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT);
}
-
- 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));
+
+ if (Constant *KC = getKnownConstant(Res, WantInteger))
+ Result.push_back(std::make_pair(KC, PredBB));
}
-
+
return !Result.empty();
}
-
-
+
// If comparing a live-in value against a constant, see if we know the
// live-in value on any predecessors.
- if (LVI && isa<Constant>(Cmp->getOperand(1)) &&
- Cmp->getType()->isInteger() && // Not vector compare.
- (!isa<Instruction>(Cmp->getOperand(0)) ||
- cast<Instruction>(Cmp->getOperand(0))->getParent() != BB)) {
- Constant *RHSCst = cast<Constant>(Cmp->getOperand(1));
-
- for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
- // If the value is known by LazyValueInfo to be a constant in a
- // predecessor, use that information to try to thread this block.
- LazyValueInfo::Tristate
- Res = LVI->getPredicateOnEdge(Cmp->getPredicate(), Cmp->getOperand(0),
- RHSCst, *PI, BB);
- if (Res == LazyValueInfo::Unknown)
- continue;
+ if (isa<Constant>(Cmp->getOperand(1)) && Cmp->getType()->isIntegerTy()) {
+ if (!isa<Instruction>(Cmp->getOperand(0)) ||
+ cast<Instruction>(Cmp->getOperand(0))->getParent() != BB) {
+ Constant *RHSCst = cast<Constant>(Cmp->getOperand(1));
+
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB);PI != E; ++PI){
+ BasicBlock *P = *PI;
+ // If the value is known by LazyValueInfo to be a constant in a
+ // predecessor, use that information to try to thread this block.
+ LazyValueInfo::Tristate Res =
+ LVI->getPredicateOnEdge(Cmp->getPredicate(), Cmp->getOperand(0),
+ RHSCst, P, BB, CxtI ? CxtI : Cmp);
+ if (Res == LazyValueInfo::Unknown)
+ continue;
- Constant *ResC = ConstantInt::get(Cmp->getType(), Res);
- Result.push_back(std::make_pair(cast<ConstantInt>(ResC), *PI));
+ Constant *ResC = ConstantInt::get(Cmp->getType(), Res);
+ Result.push_back(std::make_pair(ResC, P));
+ }
+
+ return !Result.empty();
+ }
+
+ // Try to find a constant value for the LHS of a comparison,
+ // and evaluate it statically if we can.
+ if (Constant *CmpConst = dyn_cast<Constant>(Cmp->getOperand(1))) {
+ PredValueInfoTy LHSVals;
+ ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
+ WantInteger, CxtI);
+
+ for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) {
+ Constant *V = LHSVals[i].first;
+ Constant *Folded = ConstantExpr::getCompare(Cmp->getPredicate(),
+ V, CmpConst);
+ if (Constant *KC = getKnownConstant(Folded, WantInteger))
+ Result.push_back(std::make_pair(KC, LHSVals[i].second));
+ }
+
+ return !Result.empty();
+ }
+ }
+ }
+
+ if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
+ // Handle select instructions where at least one operand is a known constant
+ // and we can figure out the condition value for any predecessor block.
+ Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference);
+ Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference);
+ PredValueInfoTy Conds;
+ if ((TrueVal || FalseVal) &&
+ ComputeValueKnownInPredecessors(SI->getCondition(), BB, Conds,
+ WantInteger, CxtI)) {
+ for (unsigned i = 0, e = Conds.size(); i != e; ++i) {
+ Constant *Cond = Conds[i].first;
+
+ // Figure out what value to use for the condition.
+ bool KnownCond;
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(Cond)) {
+ // A known boolean.
+ KnownCond = CI->isOne();
+ } else {
+ assert(isa<UndefValue>(Cond) && "Unexpected condition value");
+ // Either operand will do, so be sure to pick the one that's a known
+ // constant.
+ // FIXME: Do this more cleverly if both values are known constants?
+ KnownCond = (TrueVal != nullptr);
+ }
+
+ // See if the select has a known constant value for this predecessor.
+ if (Constant *Val = KnownCond ? TrueVal : FalseVal)
+ Result.push_back(std::make_pair(Val, Conds[i].second));
}
-
+
return !Result.empty();
}
}
- return false;
+
+ // If all else fails, see if LVI can figure out a constant value for us.
+ Constant *CI = LVI->getConstant(V, BB, CxtI);
+ if (Constant *KC = getKnownConstant(CI, Preference)) {
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
+ Result.push_back(std::make_pair(KC, *PI));
+ }
+
+ return !Result.empty();
}
for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
TestBB = BBTerm->getSuccessor(i);
unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
- if (NumPreds < MinNumPreds)
+ if (NumPreds < MinNumPreds) {
MinSucc = i;
+ MinNumPreds = NumPreds;
+ }
}
-
+
return MinSucc;
}
+static bool hasAddressTakenAndUsed(BasicBlock *BB) {
+ if (!BB->hasAddressTaken()) return false;
+
+ // If the block has its address taken, it may be a tree of dead constants
+ // hanging off of it. These shouldn't keep the block alive.
+ BlockAddress *BA = BlockAddress::get(BB);
+ BA->removeDeadConstantUsers();
+ return !BA->use_empty();
+}
+
/// ProcessBlock - If there are any predecessors whose control can be threaded
/// through to a successor, transform them now.
bool JumpThreading::ProcessBlock(BasicBlock *BB) {
if (pred_begin(BB) == pred_end(BB) &&
BB != &BB->getParent()->getEntryBlock())
return false;
-
+
// If this block has a single predecessor, and if that pred has a single
// 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 (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
- SinglePred != BB) {
+ SinglePred != BB && !hasAddressTakenAndUsed(BB)) {
// If SinglePred was a loop header, BB becomes one.
if (LoopHeaders.erase(SinglePred))
LoopHeaders.insert(BB);
-
- // Remember if SinglePred was the entry block of the function. If so, we
- // will need to move BB back to the entry position.
- bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
+
+ LVI->eraseBlock(SinglePred);
MergeBasicBlockIntoOnlyPred(BB);
-
- if (isEntry && BB != &BB->getParent()->getEntryBlock())
- 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.
+ // What kind of constant we're looking for.
+ ConstantPreference Preference = WantInteger;
+
+ // Look to see if the terminator is a conditional branch, switch or indirect
+ // branch, if not we can't thread it.
Value *Condition;
- if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
+ Instruction *Terminator = BB->getTerminator();
+ if (BranchInst *BI = dyn_cast<BranchInst>(Terminator)) {
// Can't thread an unconditional jump.
if (BI->isUnconditional()) return false;
Condition = BI->getCondition();
- } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(Terminator)) {
Condition = SI->getCondition();
- else
+ } else if (IndirectBrInst *IB = dyn_cast<IndirectBrInst>(Terminator)) {
+ // Can't thread indirect branch with no successors.
+ if (IB->getNumSuccessors() == 0) return false;
+ Condition = IB->getAddress()->stripPointerCasts();
+ Preference = WantBlockAddress;
+ } else {
return false; // Must be an invoke.
-
- // If the terminator of this block is branching on a constant, simplify the
- // terminator to an unconditional branch. This can occur due to threading in
- // other blocks.
- if (isa<ConstantInt>(Condition)) {
- DEBUG(dbgs() << " In block '" << BB->getName()
- << "' folding terminator: " << *BB->getTerminator() << '\n');
- ++NumFolds;
- ConstantFoldTerminator(BB);
- return true;
}
-
+
+ // Run constant folding to see if we can reduce the condition to a simple
+ // constant.
+ if (Instruction *I = dyn_cast<Instruction>(Condition)) {
+ Value *SimpleVal = ConstantFoldInstruction(I, DL, TLI);
+ if (SimpleVal) {
+ I->replaceAllUsesWith(SimpleVal);
+ I->eraseFromParent();
+ Condition = SimpleVal;
+ }
+ }
+
// If the terminator is branching on an undef, we can pick any of the
// successors to branch to. Let GetBestDestForJumpOnUndef decide.
if (isa<UndefValue>(Condition)) {
unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
-
+
// Fold the branch/switch.
TerminatorInst *BBTerm = BB->getTerminator();
for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
if (i == BestSucc) continue;
- RemovePredecessorAndSimplify(BBTerm->getSuccessor(i), BB, TD);
+ BBTerm->getSuccessor(i)->removePredecessor(BB, true);
}
-
+
DEBUG(dbgs() << " In block '" << BB->getName()
<< "' folding undef terminator: " << *BBTerm << '\n');
BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
BBTerm->eraseFromParent();
return true;
}
-
- Instruction *CondInst = dyn_cast<Instruction>(Condition);
- // If the condition is an instruction defined in another block, see if a
- // predecessor has the same condition:
- // br COND, BBX, BBY
- // BBX:
- // br COND, BBZ, BBW
- if (!LVI &&
- !Condition->hasOneUse() && // Multiple uses.
- (CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition.
- pred_iterator PI = pred_begin(BB), E = pred_end(BB);
- if (isa<BranchInst>(BB->getTerminator())) {
- for (; PI != E; ++PI)
- if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
- if (PBI->isConditional() && PBI->getCondition() == Condition &&
- ProcessBranchOnDuplicateCond(*PI, BB))
- return true;
- } else {
- assert(isa<SwitchInst>(BB->getTerminator()) && "Unknown jump terminator");
- for (; PI != E; ++PI)
- if (SwitchInst *PSI = dyn_cast<SwitchInst>((*PI)->getTerminator()))
- if (PSI->getCondition() == Condition &&
- ProcessSwitchOnDuplicateCond(*PI, BB))
- return true;
- }
+ // If the terminator of this block is branching on a constant, simplify the
+ // terminator to an unconditional branch. This can occur due to threading in
+ // other blocks.
+ if (getKnownConstant(Condition, Preference)) {
+ DEBUG(dbgs() << " In block '" << BB->getName()
+ << "' folding terminator: " << *BB->getTerminator() << '\n');
+ ++NumFolds;
+ ConstantFoldTerminator(BB, true);
+ return true;
}
+ Instruction *CondInst = dyn_cast<Instruction>(Condition);
+
// All the rest of our checks depend on the condition being an instruction.
- if (CondInst == 0) {
+ if (!CondInst) {
// FIXME: Unify this with code below.
- if (LVI && ProcessThreadableEdges(Condition, BB))
+ if (ProcessThreadableEdges(Condition, BB, Preference, Terminator))
return true;
return false;
- }
-
-
+ }
+
+
if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
- if (!LVI &&
- (!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;
- }
- }
- }
+ // For a comparison where the LHS is outside this block, it's possible
+ // that we've branched on it before. Used LVI to see if we can simplify
+ // the branch based on that.
+ BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
+ Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
+ pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
+ if (CondBr && CondConst && CondBr->isConditional() && PI != PE &&
+ (!isa<Instruction>(CondCmp->getOperand(0)) ||
+ cast<Instruction>(CondCmp->getOperand(0))->getParent() != BB)) {
+ // For predecessor edge, determine if the comparison is true or false
+ // on that edge. If they're all true or all false, we can simplify the
+ // branch.
+ // FIXME: We could handle mixed true/false by duplicating code.
+ LazyValueInfo::Tristate Baseline =
+ LVI->getPredicateOnEdge(CondCmp->getPredicate(), CondCmp->getOperand(0),
+ CondConst, *PI, BB, CondCmp);
+ if (Baseline != LazyValueInfo::Unknown) {
+ // Check that all remaining incoming values match the first one.
+ while (++PI != PE) {
+ LazyValueInfo::Tristate Ret =
+ LVI->getPredicateOnEdge(CondCmp->getPredicate(),
+ CondCmp->getOperand(0), CondConst, *PI, BB,
+ CondCmp);
+ if (Ret != Baseline) break;
+ }
+
+ // If we terminated early, then one of the values didn't match.
+ if (PI == PE) {
+ unsigned ToRemove = Baseline == LazyValueInfo::True ? 1 : 0;
+ unsigned ToKeep = Baseline == LazyValueInfo::True ? 0 : 1;
+ CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
+ BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
+ CondBr->eraseFromParent();
+ return true;
+ }
+ }
+
+ } else if (CondBr && CondConst && CondBr->isConditional()) {
+ // There might be an invairant in the same block with the conditional
+ // that can determine the predicate.
+
+ LazyValueInfo::Tristate Ret =
+ LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
+ CondConst, CondCmp);
+ if (Ret != LazyValueInfo::Unknown) {
+ unsigned ToRemove = Ret == LazyValueInfo::True ? 1 : 0;
+ unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1;
+ CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
+ BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
+ CondBr->eraseFromParent();
+ return true;
+ }
}
+
+ if (CondBr && CondConst && TryToUnfoldSelect(CondCmp, BB))
+ return true;
}
// Check for some cases that are worth simplifying. Right now we want to look
if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
if (isa<Constant>(CondCmp->getOperand(1)))
SimplifyValue = CondCmp->getOperand(0);
-
+
// TODO: There are other places where load PRE would be profitable, such as
// more complex comparisons.
if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
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.
//
- if (ProcessThreadableEdges(CondInst, BB))
+ if (ProcessThreadableEdges(CondInst, BB, Preference, Terminator))
return true;
-
+
// If this is an otherwise-unfoldable branch on a phi node in the current
// block, see if we can simplify.
if (PHINode *PN = dyn_cast<PHINode>(CondInst))
if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
return ProcessBranchOnPHI(PN);
-
-
+
+
// If this is an otherwise-unfoldable branch on a XOR, see if we can simplify.
if (CondInst->getOpcode() == Instruction::Xor &&
CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
return ProcessBranchOnXOR(cast<BinaryOperator>(CondInst));
-
-
- // TODO: If we have: "br (X > 0)" and we have a predecessor where we know
- // "(X == 4)", thread through this block.
-
- return false;
-}
-
-/// ProcessBranchOnDuplicateCond - We found a block and a predecessor of that
-/// block that jump on exactly the same condition. This means that we almost
-/// always know the direction of the edge in the DESTBB:
-/// PREDBB:
-/// br COND, DESTBB, BBY
-/// DESTBB:
-/// br COND, BBZ, BBW
-///
-/// If DESTBB has multiple predecessors, we can't just constant fold the branch
-/// in DESTBB, we have to thread over it.
-bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB,
- BasicBlock *BB) {
- BranchInst *PredBI = cast<BranchInst>(PredBB->getTerminator());
-
- // If both successors of PredBB go to DESTBB, we don't know anything. We can
- // fold the branch to an unconditional one, which allows other recursive
- // simplifications.
- bool BranchDir;
- if (PredBI->getSuccessor(1) != BB)
- BranchDir = true;
- else if (PredBI->getSuccessor(0) != BB)
- BranchDir = false;
- else {
- DEBUG(dbgs() << " In block '" << PredBB->getName()
- << "' folding terminator: " << *PredBB->getTerminator() << '\n');
- ++NumFolds;
- ConstantFoldTerminator(PredBB);
- return true;
- }
-
- BranchInst *DestBI = cast<BranchInst>(BB->getTerminator());
- // If the dest block has one predecessor, just fix the branch condition to a
- // constant and fold it.
- if (BB->getSinglePredecessor()) {
- DEBUG(dbgs() << " In block '" << BB->getName()
- << "' folding condition to '" << BranchDir << "': "
- << *BB->getTerminator() << '\n');
- ++NumFolds;
- Value *OldCond = DestBI->getCondition();
- DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
- BranchDir));
- ConstantFoldTerminator(BB);
- RecursivelyDeleteTriviallyDeadInstructions(OldCond);
- return true;
- }
-
-
- // 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, Preds, SuccBB);
-}
-/// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that
-/// block that switch on exactly the same condition. This means that we almost
-/// always know the direction of the edge in the DESTBB:
-/// PREDBB:
-/// switch COND [... DESTBB, BBY ... ]
-/// DESTBB:
-/// switch COND [... BBZ, BBW ]
-///
-/// Optimizing switches like this is very important, because simplifycfg builds
-/// switches out of repeated 'if' conditions.
-bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB,
- BasicBlock *DestBB) {
- // Can't thread edge to self.
- if (PredBB == DestBB)
- return false;
-
- SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator());
- SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator());
-
- // There are a variety of optimizations that we can potentially do on these
- // blocks: we order them from most to least preferable.
-
- // If DESTBB *just* contains the switch, then we can forward edges from PREDBB
- // directly to their destination. This does not introduce *any* code size
- // growth. Skip debug info first.
- BasicBlock::iterator BBI = DestBB->begin();
- while (isa<DbgInfoIntrinsic>(BBI))
- BBI++;
-
- // FIXME: Thread if it just contains a PHI.
- if (isa<SwitchInst>(BBI)) {
- bool MadeChange = false;
- // Ignore the default edge for now.
- for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) {
- ConstantInt *DestVal = DestSI->getCaseValue(i);
- BasicBlock *DestSucc = DestSI->getSuccessor(i);
-
- // Okay, DestSI has a case for 'DestVal' that goes to 'DestSucc'. See if
- // PredSI has an explicit case for it. If so, forward. If it is covered
- // by the default case, we can't update PredSI.
- unsigned PredCase = PredSI->findCaseValue(DestVal);
- if (PredCase == 0) continue;
-
- // If PredSI doesn't go to DestBB on this value, then it won't reach the
- // case on this condition.
- if (PredSI->getSuccessor(PredCase) != DestBB &&
- DestSI->getSuccessor(i) != DestBB)
- continue;
-
- // Do not forward this if it already goes to this destination, this would
- // be an infinite loop.
- if (PredSI->getSuccessor(PredCase) == DestSucc)
- continue;
-
- // Otherwise, we're safe to make the change. Make sure that the edge from
- // DestSI to DestSucc is not critical and has no PHI nodes.
- DEBUG(dbgs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI);
- DEBUG(dbgs() << "THROUGH: " << *DestSI);
+ // TODO: If we have: "br (X > 0)" and we have a predecessor where we know
+ // "(X == 4)", thread through this block.
- // If the destination has PHI nodes, just split the edge for updating
- // simplicity.
- if (isa<PHINode>(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){
- SplitCriticalEdge(DestSI, i, this);
- DestSucc = DestSI->getSuccessor(i);
- }
- FoldSingleEntryPHINodes(DestSucc);
- PredSI->setSuccessor(PredCase, DestSucc);
- MadeChange = true;
- }
-
- if (MadeChange)
- return true;
- }
-
return false;
}
-
/// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
/// load instruction, eliminate it by replacing it with a PHI node. This is an
/// important optimization that encourages jump threading, and needs to be run
/// interlaced with other jump threading tasks.
bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
- // Don't hack volatile loads.
- if (LI->isVolatile()) return false;
-
+ // Don't hack volatile/atomic loads.
+ if (!LI->isSimple()) return false;
+
// If the load is defined in a block with exactly one predecessor, it can't be
// partially redundant.
BasicBlock *LoadBB = LI->getParent();
if (LoadBB->getSinglePredecessor())
return false;
-
+
+ // If the load is defined in a landing pad, it can't be partially redundant,
+ // because the edges between the invoke and the landing pad cannot have other
+ // instructions between them.
+ if (LoadBB->isLandingPad())
+ return false;
+
Value *LoadedPtr = LI->getOperand(0);
// If the loaded operand is defined in the LoadBB, it can't be available.
if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
if (PtrOp->getParent() == LoadBB)
return false;
-
+
// Scan a few instructions up from the load, to see if it is obviously live at
// the entry to its block.
BasicBlock::iterator BBIt = LI;
- if (Value *AvailableVal =
+ if (Value *AvailableVal =
FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt, 6)) {
// If the value if the load is locally available within the block, just use
// it. This frequently occurs for reg2mem'd allocas.
//cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
-
+
// If the returned value is the load itself, replace with an undef. This can
// only happen in dead loops.
if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
+ if (AvailableVal->getType() != LI->getType())
+ AvailableVal =
+ CastInst::CreateBitOrPointerCast(AvailableVal, LI->getType(), "", LI);
LI->replaceAllUsesWith(AvailableVal);
LI->eraseFromParent();
return true;
// might clobber its value.
if (BBIt != LoadBB->begin())
return false;
-
-
+
+ // If all of the loads and stores that feed the value have the same AA tags,
+ // then we can propagate them onto any newly inserted loads.
+ AAMDNodes AATags;
+ LI->getAAMetadata(AATags);
+
SmallPtrSet<BasicBlock*, 8> PredsScanned;
typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
AvailablePredsTy AvailablePreds;
- BasicBlock *OneUnavailablePred = 0;
-
+ BasicBlock *OneUnavailablePred = nullptr;
+
// If we got here, the loaded value is transparent through to the start of the
// block. Check to see if it is available in any of the predecessor blocks.
for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
BasicBlock *PredBB = *PI;
// If we already scanned this predecessor, skip it.
- if (!PredsScanned.insert(PredBB))
+ if (!PredsScanned.insert(PredBB).second)
continue;
// Scan the predecessor to see if the value is available in the pred.
BBIt = PredBB->end();
- Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
+ AAMDNodes ThisAATags;
+ Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6,
+ nullptr, &ThisAATags);
if (!PredAvailable) {
OneUnavailablePred = PredBB;
continue;
}
-
+
+ // If AA tags disagree or are not present, forget about them.
+ if (AATags != ThisAATags) AATags = AAMDNodes();
+
// If so, this load is partially redundant. Remember this info so that we
// can create a PHI node.
AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
}
-
+
// If the loaded value isn't available in any predecessor, it isn't partially
// redundant.
if (AvailablePreds.empty()) return false;
-
+
// Okay, the loaded value is available in at least one (and maybe all!)
// predecessors. If the value is unavailable in more than one unique
// predecessor, we want to insert a merge block for those common predecessors.
// This ensures that we only have to insert one reload, thus not increasing
// code size.
- BasicBlock *UnavailablePred = 0;
-
+ BasicBlock *UnavailablePred = nullptr;
+
// If there is exactly one predecessor where the value is unavailable, the
// already computed 'OneUnavailablePred' block is it. If it ends in an
// unconditional branch, we know that it isn't a critical edge.
// Add all the unavailable predecessors to the PredsToSplit list.
for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
- PI != PE; ++PI)
- if (!AvailablePredSet.count(*PI))
- PredsToSplit.push_back(*PI);
-
+ PI != PE; ++PI) {
+ BasicBlock *P = *PI;
+ // If the predecessor is an indirect goto, we can't split the edge.
+ if (isa<IndirectBrInst>(P->getTerminator()))
+ return false;
+
+ if (!AvailablePredSet.count(P))
+ PredsToSplit.push_back(P);
+ }
+
// Split them out to their own block.
UnavailablePred =
- SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(),
- "thread-pre-split", this);
+ SplitBlockPredecessors(LoadBB, PredsToSplit, "thread-pre-split", this);
}
-
+
// If the value isn't available in all predecessors, then there will be
// exactly one where it isn't available. Insert a load on that edge and add
// it to the AvailablePreds list.
if (UnavailablePred) {
assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
"Can't handle critical edge here!");
- Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr", false,
+ LoadInst *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr", false,
LI->getAlignment(),
UnavailablePred->getTerminator());
+ NewVal->setDebugLoc(LI->getDebugLoc());
+ if (AATags)
+ NewVal->setAAMetadata(AATags);
+
AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
}
-
+
// Now we know that each predecessor of this block has a value in
// AvailablePreds, sort them for efficient access as we're walking the preds.
array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
-
+
// Create a PHI node at the start of the block for the PRE'd load value.
- PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin());
+ pred_iterator PB = pred_begin(LoadBB), PE = pred_end(LoadBB);
+ PHINode *PN = PHINode::Create(LI->getType(), std::distance(PB, PE), "",
+ LoadBB->begin());
PN->takeName(LI);
-
+ PN->setDebugLoc(LI->getDebugLoc());
+
// Insert new entries into the PHI for each predecessor. A single block may
// have multiple entries here.
- for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E;
- ++PI) {
- AvailablePredsTy::iterator I =
+ for (pred_iterator PI = PB; PI != PE; ++PI) {
+ BasicBlock *P = *PI;
+ AvailablePredsTy::iterator I =
std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
- std::make_pair(*PI, (Value*)0));
-
- assert(I != AvailablePreds.end() && I->first == *PI &&
+ std::make_pair(P, (Value*)nullptr));
+
+ assert(I != AvailablePreds.end() && I->first == P &&
"Didn't find entry for predecessor!");
-
- PN->addIncoming(I->second, I->first);
+
+ // If we have an available predecessor but it requires casting, insert the
+ // cast in the predecessor and use the cast. Note that we have to update the
+ // AvailablePreds vector as we go so that all of the PHI entries for this
+ // predecessor use the same bitcast.
+ Value *&PredV = I->second;
+ if (PredV->getType() != LI->getType())
+ PredV = CastInst::CreateBitOrPointerCast(PredV, LI->getType(), "",
+ P->getTerminator());
+
+ PN->addIncoming(PredV, I->first);
}
-
+
//cerr << "PRE: " << *LI << *PN << "\n";
-
+
LI->replaceAllUsesWith(PN);
LI->eraseFromParent();
-
+
return true;
}
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
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.
SamePopularity.clear();
MostPopularDest = DPI->first;
Popularity = DPI->second;
- }
+ }
}
-
- // Okay, now we know the most popular destination. If there is more than
+
+ // Okay, now we know the most popular destination. If there is more than one
// 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.
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(Value *Cond, BasicBlock *BB) {
+bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
+ ConstantPreference Preference,
+ Instruction *CxtI) {
// 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(Cond, BB, PredValues))
+
+ PredValueInfoTy PredValues;
+ if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues, Preference, CxtI))
return false;
+
assert(!PredValues.empty() &&
"ComputeValueKnownInPredecessors returned true with no values");
DEBUG(dbgs() << "IN BB: " << *BB;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
- dbgs() << " BB '" << BB->getName() << "': FOUND condition = ";
- if (PredValues[i].first)
- dbgs() << *PredValues[i].first;
- else
- dbgs() << "UNDEF";
- dbgs() << " for pred '" << PredValues[i].second->getName()
- << "'.\n";
+ dbgs() << " BB '" << BB->getName() << "': FOUND condition = "
+ << *PredValues[i].first
+ << " 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 *OnlyDest = nullptr;
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))
+ if (!SeenPreds.insert(Pred).second)
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;
-
+
+ Constant *Val = PredValues[i].first;
+
BasicBlock *DestBB;
- if (Val == 0) // Undef.
- DestBB = 0;
+ if (isa<UndefValue>(Val))
+ DestBB = nullptr;
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));
+ DestBB = BI->getSuccessor(cast<ConstantInt>(Val)->isZero());
+ else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
+ DestBB = SI->findCaseValue(cast<ConstantInt>(Val)).getCaseSuccessor();
+ } else {
+ assert(isa<IndirectBrInst>(BB->getTerminator())
+ && "Unexpected terminator");
+ DestBB = cast<BlockAddress>(Val)->getBasicBlock();
}
// If we have exactly one destination, remember it for efficiency below.
- if (i == 0)
+ if (PredToDestList.empty())
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;
-
+
// 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.
// 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)
+ if (!MostPopularDest)
MostPopularDest = BB->getTerminator()->
getSuccessor(GetBestDestForJumpOnUndef(BB));
-
+
// Ok, try to thread it!
return ThreadEdge(BB, PredsToFactor, MostPopularDest);
}
/// ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch 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::ProcessBranchOnPHI(PHINode *PN) {
BasicBlock *BB = PN->getParent();
-
+
// TODO: We could make use of this to do it once for blocks with common PHI
// values.
SmallVector<BasicBlock*, 1> PredBBs;
PredBBs.resize(1);
-
+
// If any of the predecessor blocks end in an unconditional branch, we can
// *duplicate* the conditional branch into that block in order to further
// encourage jump threading and to eliminate cases where we have branch on a
/// ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on
/// a xor instruction in the current block. See if there are any
/// simplifications we can do based on inputs to the xor.
-///
+///
bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
BasicBlock *BB = BO->getParent();
-
+
// If either the LHS or RHS of the xor is a constant, don't do this
// optimization.
if (isa<ConstantInt>(BO->getOperand(0)) ||
isa<ConstantInt>(BO->getOperand(1)))
return false;
-
+
// If the first instruction in BB isn't a phi, we won't be able to infer
// anything special about any particular predecessor.
if (!isa<PHINode>(BB->front()))
return false;
-
+
// If we have a xor as the branch input to this block, and we know that the
// LHS or RHS of the xor in any predecessor is true/false, then we can clone
// the condition into the predecessor and fix that value to true, saving some
// %Y = icmp ne i32 %A, %B
// br i1 %Z, ...
- SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> XorOpValues;
+ PredValueInfoTy XorOpValues;
bool isLHS = true;
- if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues)) {
+ if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues,
+ WantInteger, BO)) {
assert(XorOpValues.empty());
- if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues))
+ if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues,
+ WantInteger, BO))
return false;
isLHS = false;
}
-
+
assert(!XorOpValues.empty() &&
"ComputeValueKnownInPredecessors returned true with no values");
// predecessors can be of the set true, false, or undef.
unsigned NumTrue = 0, NumFalse = 0;
for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) {
- if (!XorOpValues[i].first) continue; // Ignore undefs for the count.
- if (XorOpValues[i].first->isZero())
+ if (isa<UndefValue>(XorOpValues[i].first))
+ // Ignore undefs for the count.
+ continue;
+ if (cast<ConstantInt>(XorOpValues[i].first)->isZero())
++NumFalse;
else
++NumTrue;
}
-
+
// Determine which value to split on, true, false, or undef if neither.
- ConstantInt *SplitVal = 0;
+ ConstantInt *SplitVal = nullptr;
if (NumTrue > NumFalse)
SplitVal = ConstantInt::getTrue(BB->getContext());
else if (NumTrue != 0 || NumFalse != 0)
SplitVal = ConstantInt::getFalse(BB->getContext());
-
+
// Collect all of the blocks that this can be folded into so that we can
// factor this once and clone it once.
SmallVector<BasicBlock*, 8> BlocksToFoldInto;
for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) {
- if (XorOpValues[i].first != SplitVal && XorOpValues[i].first != 0) continue;
+ if (XorOpValues[i].first != SplitVal &&
+ !isa<UndefValue>(XorOpValues[i].first))
+ continue;
BlocksToFoldInto.push_back(XorOpValues[i].second);
}
-
+
// If we inferred a value for all of the predecessors, then duplication won't
// help us. However, we can just replace the LHS or RHS with the constant.
if (BlocksToFoldInto.size() ==
cast<PHINode>(BB->front()).getNumIncomingValues()) {
- if (SplitVal == 0) {
+ if (!SplitVal) {
// If all preds provide undef, just nuke the xor, because it is undef too.
BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
BO->eraseFromParent();
// If all preds provide 1, set the computed value to 1.
BO->setOperand(!isLHS, SplitVal);
}
-
+
return true;
}
-
+
// Try to duplicate BB into PredBB.
return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
}
// Ok, we have a PHI node. Figure out what the incoming value was for the
// DestBlock.
Value *IV = PN->getIncomingValueForBlock(OldPred);
-
+
// Remap the value if necessary.
if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst);
if (I != ValueMap.end())
IV = I->second;
}
-
+
PN->addIncoming(IV, NewPred);
}
}
/// 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,
+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) {
<< "' - would thread to self!\n");
return false;
}
-
+
// 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)) {
return false;
}
- unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
- if (JumpThreadCost > Threshold) {
+ unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB, BBDupThreshold);
+ if (JumpThreadCost > BBDupThreshold) {
DEBUG(dbgs() << " Not threading BB '" << BB->getName()
<< "' - Cost is too high: " << JumpThreadCost << "\n");
return false;
}
-
+
// And finally, do it! Start by factoring the predecessors is needed.
BasicBlock *PredBB;
if (PredBBs.size() == 1)
else {
DEBUG(dbgs() << " Factoring out " << PredBBs.size()
<< " common predecessors.\n");
- PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(),
- ".thr_comm", this);
+ PredBB = SplitBlockPredecessors(BB, PredBBs, ".thr_comm", this);
}
-
+
// And finally, do it!
DEBUG(dbgs() << " Threading edge from '" << PredBB->getName() << "' to '"
<< SuccBB->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n "
<< *BB << "\n");
-
+
+ LVI->threadEdge(PredBB, BB, SuccBB);
+
// We are going to have to map operands from the original BB block to the new
// copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
// account for entry from PredBB.
DenseMap<Instruction*, Value*> ValueMapping;
-
- BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
- BB->getName()+".thread",
+
+ BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
+ BB->getName()+".thread",
BB->getParent(), BB);
NewBB->moveAfter(PredBB);
-
+
BasicBlock::iterator BI = BB->begin();
for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
-
+
// Clone the non-phi instructions of BB into NewBB, keeping track of the
// mapping and using it to remap operands in the cloned instructions.
for (; !isa<TerminatorInst>(BI); ++BI) {
New->setName(BI->getName());
NewBB->getInstList().push_back(New);
ValueMapping[BI] = New;
-
+
// Remap operands to patch up intra-block references.
for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
New->setOperand(i, I->second);
}
}
-
+
// We didn't copy the terminator from BB over to NewBB, because there is now
// an unconditional jump to SuccBB. Insert the unconditional jump.
- BranchInst::Create(SuccBB, NewBB);
-
+ BranchInst *NewBI =BranchInst::Create(SuccBB, NewBB);
+ NewBI->setDebugLoc(BB->getTerminator()->getDebugLoc());
+
// Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
// PHI nodes for NewBB now.
AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
-
+
// If there were values defined in BB that are used outside the block, then we
// now have to update all uses of the value to use either the original value,
// the cloned value, or some PHI derived value. This can require arbitrary
for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
// Scan all uses of this instruction to see if it is used outside of its
// block, and if so, record them in UsesToRename.
- for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
- ++UI) {
- Instruction *User = cast<Instruction>(*UI);
+ for (Use &U : I->uses()) {
+ Instruction *User = cast<Instruction>(U.getUser());
if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
- if (UserPN->getIncomingBlock(UI) == BB)
+ if (UserPN->getIncomingBlock(U) == BB)
continue;
} else if (User->getParent() == BB)
continue;
-
- UsesToRename.push_back(&UI.getUse());
+
+ UsesToRename.push_back(&U);
}
-
+
// If there are no uses outside the block, we're done with this instruction.
if (UsesToRename.empty())
continue;
-
+
DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n");
// We found a use of I outside of BB. Rename all uses of I that are outside
// its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
// with the two values we know.
- SSAUpdate.Initialize(I);
+ SSAUpdate.Initialize(I->getType(), I->getName());
SSAUpdate.AddAvailableValue(BB, I);
SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]);
-
+
while (!UsesToRename.empty())
SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
DEBUG(dbgs() << "\n");
}
-
-
+
+
// Ok, NewBB is good to go. Update the terminator of PredBB to jump to
// NewBB instead of BB. This eliminates predecessors from BB, which requires
// us to simplify any PHI nodes in BB.
TerminatorInst *PredTerm = PredBB->getTerminator();
for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
if (PredTerm->getSuccessor(i) == BB) {
- RemovePredecessorAndSimplify(BB, PredBB, TD);
+ BB->removePredecessor(PredBB, true);
PredTerm->setSuccessor(i, NewBB);
}
-
+
// At this point, the IR is fully up to date and consistent. Do a quick scan
// over the new instructions and zap any that are constants or dead. This
// frequently happens because of phi translation.
- SimplifyInstructionsInBlock(NewBB, TD);
-
+ SimplifyInstructionsInBlock(NewBB, DL, TLI);
+
// Threaded an edge!
++NumThreads;
return true;
<< "' - it might create an irreducible loop!\n");
return false;
}
-
- unsigned DuplicationCost = getJumpThreadDuplicationCost(BB);
- if (DuplicationCost > Threshold) {
+
+ unsigned DuplicationCost = getJumpThreadDuplicationCost(BB, BBDupThreshold);
+ if (DuplicationCost > BBDupThreshold) {
DEBUG(dbgs() << " Not duplicating BB '" << BB->getName()
<< "' - Cost is too high: " << DuplicationCost << "\n");
return false;
}
-
+
// And finally, do it! Start by factoring the predecessors is needed.
BasicBlock *PredBB;
if (PredBBs.size() == 1)
else {
DEBUG(dbgs() << " Factoring out " << PredBBs.size()
<< " common predecessors.\n");
- PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(),
- ".thr_comm", this);
+ PredBB = SplitBlockPredecessors(BB, PredBBs, ".thr_comm", this);
}
-
+
// Okay, we decided to do this! Clone all the instructions in BB onto the end
// of PredBB.
DEBUG(dbgs() << " Duplicating block '" << BB->getName() << "' into end of '"
<< PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB << "\n");
-
+
// Unless PredBB ends with an unconditional branch, split the edge so that we
// can just clone the bits from BB into the end of the new PredBB.
- BranchInst *OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
-
- if (!OldPredBranch->isUnconditional()) {
+ BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator());
+
+ if (!OldPredBranch || !OldPredBranch->isUnconditional()) {
PredBB = SplitEdge(PredBB, BB, this);
OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
}
-
+
// We are going to have to map operands from the original BB block into the
// PredBB block. Evaluate PHI nodes in BB.
DenseMap<Instruction*, Value*> ValueMapping;
-
+
BasicBlock::iterator BI = BB->begin();
for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
-
+
// Clone the non-phi instructions of BB into PredBB, keeping track of the
// mapping and using it to remap operands in the cloned instructions.
for (; BI != BB->end(); ++BI) {
Instruction *New = BI->clone();
-
+
// Remap operands to patch up intra-block references.
for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
// If this instruction can be simplified after the operands are updated,
// just use the simplified value instead. This frequently happens due to
// phi translation.
- if (Value *IV = SimplifyInstruction(New, TD)) {
+ if (Value *IV = SimplifyInstruction(New, DL)) {
delete New;
ValueMapping[BI] = IV;
} else {
ValueMapping[BI] = New;
}
}
-
+
// Check to see if the targets of the branch had PHI nodes. If so, we need to
// add entries to the PHI nodes for branch from PredBB now.
BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
ValueMapping);
AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
ValueMapping);
-
+
// If there were values defined in BB that are used outside the block, then we
// now have to update all uses of the value to use either the original value,
// the cloned value, or some PHI derived value. This can require arbitrary
for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
// Scan all uses of this instruction to see if it is used outside of its
// block, and if so, record them in UsesToRename.
- for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
- ++UI) {
- Instruction *User = cast<Instruction>(*UI);
+ for (Use &U : I->uses()) {
+ Instruction *User = cast<Instruction>(U.getUser());
if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
- if (UserPN->getIncomingBlock(UI) == BB)
+ if (UserPN->getIncomingBlock(U) == BB)
continue;
} else if (User->getParent() == BB)
continue;
-
- UsesToRename.push_back(&UI.getUse());
+
+ UsesToRename.push_back(&U);
}
-
+
// If there are no uses outside the block, we're done with this instruction.
if (UsesToRename.empty())
continue;
-
+
DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n");
-
+
// We found a use of I outside of BB. Rename all uses of I that are outside
// its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
// with the two values we know.
- SSAUpdate.Initialize(I);
+ SSAUpdate.Initialize(I->getType(), I->getName());
SSAUpdate.AddAvailableValue(BB, I);
SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]);
-
+
while (!UsesToRename.empty())
SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
DEBUG(dbgs() << "\n");
}
-
+
// PredBB no longer jumps to BB, remove entries in the PHI node for the edge
// that we nuked.
- RemovePredecessorAndSimplify(BB, PredBB, TD);
-
+ BB->removePredecessor(PredBB, true);
+
// Remove the unconditional branch at the end of the PredBB block.
OldPredBranch->eraseFromParent();
-
+
++NumDupes;
return true;
}
+/// TryToUnfoldSelect - Look for blocks of the form
+/// bb1:
+/// %a = select
+/// br bb
+///
+/// bb2:
+/// %p = phi [%a, %bb] ...
+/// %c = icmp %p
+/// br i1 %c
+///
+/// And expand the select into a branch structure if one of its arms allows %c
+/// to be folded. This later enables threading from bb1 over bb2.
+bool JumpThreading::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) {
+ BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
+ PHINode *CondLHS = dyn_cast<PHINode>(CondCmp->getOperand(0));
+ Constant *CondRHS = cast<Constant>(CondCmp->getOperand(1));
+
+ if (!CondBr || !CondBr->isConditional() || !CondLHS ||
+ CondLHS->getParent() != BB)
+ return false;
+
+ for (unsigned I = 0, E = CondLHS->getNumIncomingValues(); I != E; ++I) {
+ BasicBlock *Pred = CondLHS->getIncomingBlock(I);
+ SelectInst *SI = dyn_cast<SelectInst>(CondLHS->getIncomingValue(I));
+ // Look if one of the incoming values is a select in the corresponding
+ // predecessor.
+ if (!SI || SI->getParent() != Pred || !SI->hasOneUse())
+ continue;
+
+ BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator());
+ if (!PredTerm || !PredTerm->isUnconditional())
+ continue;
+
+ // Now check if one of the select values would allow us to constant fold the
+ // terminator in BB. We don't do the transform if both sides fold, those
+ // cases will be threaded in any case.
+ LazyValueInfo::Tristate LHSFolds =
+ LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1),
+ CondRHS, Pred, BB, CondCmp);
+ LazyValueInfo::Tristate RHSFolds =
+ LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2),
+ CondRHS, Pred, BB, CondCmp);
+ if ((LHSFolds != LazyValueInfo::Unknown ||
+ RHSFolds != LazyValueInfo::Unknown) &&
+ LHSFolds != RHSFolds) {
+ // Expand the select.
+ //
+ // Pred --
+ // | v
+ // | NewBB
+ // | |
+ // |-----
+ // v
+ // BB
+ BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold",
+ BB->getParent(), BB);
+ // Move the unconditional branch to NewBB.
+ PredTerm->removeFromParent();
+ NewBB->getInstList().insert(NewBB->end(), PredTerm);
+ // Create a conditional branch and update PHI nodes.
+ BranchInst::Create(NewBB, BB, SI->getCondition(), Pred);
+ CondLHS->setIncomingValue(I, SI->getFalseValue());
+ CondLHS->addIncoming(SI->getTrueValue(), NewBB);
+ // The select is now dead.
+ SI->eraseFromParent();
+
+ // Update any other PHI nodes in BB.
+ for (BasicBlock::iterator BI = BB->begin();
+ PHINode *Phi = dyn_cast<PHINode>(BI); ++BI)
+ if (Phi != CondLHS)
+ Phi->addIncoming(Phi->getIncomingValueForBlock(Pred), NewBB);
+ return true;
+ }
+ }
+ return false;
+}
projects / oota-llvm.git / blobdiff