//
//===----------------------------------------------------------------------===//
-#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/ConstantFolding.h"
-#include "llvm/Analysis/InstructionSimplify.h"
-#include "llvm/Analysis/LazyValueInfo.h"
-#include "llvm/Analysis/Loads.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/Target/TargetLibraryInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
-#include "llvm/ADT/Statistic.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/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");
/// revectored to the false side of the second if.
///
class JumpThreading : public FunctionPass {
- TargetData *TD;
+ const DataLayout *DL;
TargetLibraryInfo *TLI;
LazyValueInfo *LVI;
#ifdef NDEBUG
initializeJumpThreadingPass(*PassRegistry::getPassRegistry());
}
- bool runOnFunction(Function &F);
+ bool runOnFunction(Function &F) override;
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LazyValueInfo>();
AU.addPreserved<LazyValueInfo>();
AU.addRequired<TargetLibraryInfo>();
bool ProcessBranchOnXOR(BinaryOperator *BO);
bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
+ bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
};
}
/// 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>();
+ DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
+ DL = DLP ? &DLP->getDataLayout() : nullptr;
TLI = &getAnalysis<TargetLibraryInfo>();
LVI = &getAnalysis<LazyValueInfo>();
}
/// 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;
// 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 (!CI->getType()->isVectorTy())
Size += 1;
/// Returns null if Val is null or not an appropriate constant.
static Constant *getKnownConstant(Value *Val, ConstantPreference Preference) {
if (!Val)
- return 0;
+ return nullptr;
// Undef is "known" enough.
if (UndefValue *U = dyn_cast<UndefValue>(Val))
// 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.
Value *LHS = PN->getIncomingValue(i);
Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
- Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, TD);
- if (Res == 0) {
+ Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, DL);
+ if (!Res) {
if (!isa<Constant>(RHS))
continue;
// 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 != 0);
+ KnownCond = (TrueVal != nullptr);
}
// See if the select has a known constant value for this predecessor.
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(Terminator)) {
Condition = SI->getCondition();
} 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 {
// 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, TD, TLI);
+ Value *SimpleVal = ConstantFoldInstruction(I, DL, TLI);
if (SimpleVal) {
I->replaceAllUsesWith(SimpleVal);
I->eraseFromParent();
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 (ProcessThreadableEdges(Condition, BB, Preference))
return true;
return true;
}
}
+
}
+
+ if (CondBr && CondConst && TryToUnfoldSelect(CondCmp, BB))
+ return true;
}
// Check for some cases that are worth simplifying. Right now we want to look
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
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 (BBIt != LoadBB->begin())
return false;
+ // If all of the loads and stores that feed the value have the same TBAA tag,
+ // then we can propagate it onto any newly inserted loads.
+ MDNode *TBAATag = LI->getMetadata(LLVMContext::MD_tbaa);
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.
// Scan the predecessor to see if the value is available in the pred.
BBIt = PredBB->end();
- Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
+ MDNode *ThisTBAATag = nullptr;
+ Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6,
+ nullptr, &ThisTBAATag);
if (!PredAvailable) {
OneUnavailablePred = PredBB;
continue;
}
+ // If tbaa tags disagree or are not present, forget about them.
+ if (TBAATag != ThisTBAATag) TBAATag = nullptr;
+
// 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));
// 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
LI->getAlignment(),
UnavailablePred->getTerminator());
NewVal->setDebugLoc(LI->getDebugLoc());
+ if (TBAATag)
+ NewVal->setMetadata(LLVMContext::MD_tbaa, TBAATag);
+
AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
}
BasicBlock *P = *PI;
AvailablePredsTy::iterator I =
std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
- std::make_pair(P, (Value*)0));
+ std::make_pair(P, (Value*)nullptr));
assert(I != AvailablePreds.end() && I->first == P &&
"Didn't find entry for predecessor!");
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 *DestBB;
if (isa<UndefValue>(Val))
- DestBB = 0;
+ DestBB = nullptr;
else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
DestBB = BI->getSuccessor(cast<ConstantInt>(Val)->isZero());
- else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
- DestBB = SI->getSuccessor(SI->findCaseValue(cast<ConstantInt>(Val)));
- else {
+ 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 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));
}
// 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)
// 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();
return false;
}
- unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
+ unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB, Threshold);
if (JumpThreadCost > Threshold) {
DEBUG(dbgs() << " Not threading BB '" << BB->getName()
<< "' - Cost is too high: " << JumpThreadCost << "\n");
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.
// 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 false;
}
- unsigned DuplicationCost = getJumpThreadDuplicationCost(BB);
+ unsigned DuplicationCost = getJumpThreadDuplicationCost(BB, Threshold);
if (DuplicationCost > Threshold) {
DEBUG(dbgs() << " Not duplicating BB '" << BB->getName()
<< "' - Cost is too high: " << DuplicationCost << "\n");
// can just clone the bits from BB into the end of the new PredBB.
BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator());
- if (OldPredBranch == 0 || !OldPredBranch->isUnconditional()) {
+ if (!OldPredBranch || !OldPredBranch->isUnconditional()) {
PredBB = SplitEdge(PredBB, BB, this);
OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
}
// 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 {
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.
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);
+ LazyValueInfo::Tristate RHSFolds =
+ LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2),
+ CondRHS, Pred, BB);
+ 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;
+}