195 changes: 82 additions & 113 deletions llvm/lib/Transforms/Scalar/JumpThreading.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -11,31 +11,25 @@
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Scalar/JumpThreading.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/DenseMap.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/GlobalsModRef.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/MDBuilder.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"
Expand All @@ -46,6 +40,7 @@
#include <algorithm>
#include <memory>
using namespace llvm;
using namespace jumpthreading;

#define DEBUG_TYPE "jump-threading"

Expand All @@ -66,17 +61,6 @@ ImplicationSearchThreshold(
cl::init(3), cl::Hidden);

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
};

/// 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
Expand All @@ -94,37 +78,11 @@ namespace {
/// revectored to the false side of the second if.
///
class JumpThreading : public FunctionPass {
TargetLibraryInfo *TLI;
LazyValueInfo *LVI;
std::unique_ptr<BlockFrequencyInfo> BFI;
std::unique_ptr<BranchProbabilityInfo> BPI;
bool HasProfileData;
#ifdef NDEBUG
SmallPtrSet<const BasicBlock *, 16> LoopHeaders;
#else
SmallSet<AssertingVH<const 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);
}
};
JumpThreadingPass Impl;

public:
static char ID; // Pass identification
JumpThreading(int T = -1) : FunctionPass(ID) {
BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
JumpThreading(int T = -1) : FunctionPass(ID), Impl(T) {
initializeJumpThreadingPass(*PassRegistry::getPassRegistry());
}

Expand All @@ -137,39 +95,7 @@ namespace {
AU.addRequired<TargetLibraryInfoWrapperPass>();
}

void releaseMemory() override {
BFI.reset();
BPI.reset();
}

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);

bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
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 ProcessImpliedCondition(BasicBlock *BB);

bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
bool TryToUnfoldSelectInCurrBB(BasicBlock *BB);

private:
BasicBlock *SplitBlockPreds(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
const char *Suffix);
void UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB, BasicBlock *BB,
BasicBlock *NewBB, BasicBlock *SuccBB);
void releaseMemory() override { Impl.releaseMemory(); }
};
}

Expand All @@ -184,24 +110,68 @@ INITIALIZE_PASS_END(JumpThreading, "jump-threading",
// Public interface to the Jump Threading pass
FunctionPass *llvm::createJumpThreadingPass(int Threshold) { return new JumpThreading(Threshold); }

JumpThreadingPass::JumpThreadingPass(int T) {
BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
}

/// runOnFunction - Top level algorithm.
///
bool JumpThreading::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
auto TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
auto LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
std::unique_ptr<BlockFrequencyInfo> BFI;
std::unique_ptr<BranchProbabilityInfo> BPI;
bool HasProfileData = F.getEntryCount().hasValue();
if (HasProfileData) {
LoopInfo LI{DominatorTree(F)};
BPI.reset(new BranchProbabilityInfo(F, LI));
BFI.reset(new BlockFrequencyInfo(F, *BPI, LI));
}
return Impl.runImpl(F, TLI, LVI, HasProfileData, std::move(BFI),
std::move(BPI));
}

PreservedAnalyses JumpThreadingPass::run(Function &F,
AnalysisManager<Function> &AM) {

auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &LVI = AM.getResult<LazyValueAnalysis>(F);
std::unique_ptr<BlockFrequencyInfo> BFI;
std::unique_ptr<BranchProbabilityInfo> BPI;
bool HasProfileData = F.getEntryCount().hasValue();
if (HasProfileData) {
LoopInfo LI{DominatorTree(F)};
BPI.reset(new BranchProbabilityInfo(F, LI));
BFI.reset(new BlockFrequencyInfo(F, *BPI, LI));
}
bool Changed =
runImpl(F, &TLI, &LVI, HasProfileData, std::move(BFI), std::move(BPI));
if (!Changed)
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<LazyValueAnalysis>();
PA.preserve<GlobalsAA>();
return PreservedAnalyses::none();
}

bool JumpThreadingPass::runImpl(Function &F, TargetLibraryInfo *TLI_,
LazyValueInfo *LVI_, bool HasProfileData_,
std::unique_ptr<BlockFrequencyInfo> BFI_,
std::unique_ptr<BranchProbabilityInfo> BPI_) {

DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n");
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
TLI = TLI_;
LVI = LVI_;
BFI.reset();
BPI.reset();
// When profile data is available, we need to update edge weights after
// successful jump threading, which requires both BPI and BFI being available.
HasProfileData = F.getEntryCount().hasValue();
HasProfileData = HasProfileData_;
if (HasProfileData) {
LoopInfo LI{DominatorTree(F)};
BPI.reset(new BranchProbabilityInfo(F, LI));
BFI.reset(new BlockFrequencyInfo(F, *BPI, LI));
BPI = std::move(BPI_);
BFI = std::move(BFI_);
}

// Remove unreachable blocks from function as they may result in infinite
Expand Down Expand Up @@ -364,7 +334,7 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
/// enough to track all of these properties and keep it up-to-date as the CFG
/// mutates, so we don't allow any of these transformations.
///
void JumpThreading::FindLoopHeaders(Function &F) {
void JumpThreadingPass::FindLoopHeaders(Function &F) {
SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
FindFunctionBackedges(F, Edges);

Expand Down Expand Up @@ -398,10 +368,9 @@ static Constant *getKnownConstant(Value *Val, ConstantPreference Preference) {
///
/// This returns true if there were any known values.
///
bool JumpThreading::
ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, PredValueInfo &Result,
ConstantPreference Preference,
Instruction *CxtI) {
bool JumpThreadingPass::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
Expand Down Expand Up @@ -727,7 +696,7 @@ static bool hasAddressTakenAndUsed(BasicBlock *BB) {

/// ProcessBlock - If there are any predecessors whose control can be threaded
/// through to a successor, transform them now.
bool JumpThreading::ProcessBlock(BasicBlock *BB) {
bool JumpThreadingPass::ProcessBlock(BasicBlock *BB) {
// If the block is trivially dead, just return and let the caller nuke it.
// This simplifies other transformations.
if (pred_empty(BB) &&
Expand Down Expand Up @@ -911,7 +880,7 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
return false;
}

bool JumpThreading::ProcessImpliedCondition(BasicBlock *BB) {
bool JumpThreadingPass::ProcessImpliedCondition(BasicBlock *BB) {
auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BI || !BI->isConditional())
return false;
Expand Down Expand Up @@ -950,7 +919,7 @@ bool JumpThreading::ProcessImpliedCondition(BasicBlock *BB) {
/// 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) {
bool JumpThreadingPass::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
// Don't hack volatile/atomic loads.
if (!LI->isSimple()) return false;

Expand Down Expand Up @@ -1198,9 +1167,9 @@ FindMostPopularDest(BasicBlock *BB,
return MostPopularDest;
}

bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
ConstantPreference Preference,
Instruction *CxtI) {
bool JumpThreadingPass::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))
Expand Down Expand Up @@ -1306,7 +1275,7 @@ bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
/// 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) {
bool JumpThreadingPass::ProcessBranchOnPHI(PHINode *PN) {
BasicBlock *BB = PN->getParent();

// TODO: We could make use of this to do it once for blocks with common PHI
Expand Down Expand Up @@ -1336,7 +1305,7 @@ bool JumpThreading::ProcessBranchOnPHI(PHINode *PN) {
/// 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) {
bool JumpThreadingPass::ProcessBranchOnXOR(BinaryOperator *BO) {
BasicBlock *BB = BO->getParent();

// If either the LHS or RHS of the xor is a constant, don't do this
Expand Down Expand Up @@ -1464,9 +1433,9 @@ static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
/// ThreadEdge - We have decided that it is safe and profitable to factor the
/// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB
/// across BB. Transform the IR to reflect this change.
bool JumpThreading::ThreadEdge(BasicBlock *BB,
const SmallVectorImpl<BasicBlock*> &PredBBs,
BasicBlock *SuccBB) {
bool JumpThreadingPass::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) {
DEBUG(dbgs() << " Not threading across BB '" << BB->getName()
Expand Down Expand Up @@ -1620,9 +1589,9 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB,
/// Create a new basic block that will be the predecessor of BB and successor of
/// all blocks in Preds. When profile data is availble, update the frequency of
/// this new block.
BasicBlock *JumpThreading::SplitBlockPreds(BasicBlock *BB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix) {
BasicBlock *JumpThreadingPass::SplitBlockPreds(BasicBlock *BB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix) {
// Collect the frequencies of all predecessors of BB, which will be used to
// update the edge weight on BB->SuccBB.
BlockFrequency PredBBFreq(0);
Expand All @@ -1642,10 +1611,10 @@ BasicBlock *JumpThreading::SplitBlockPreds(BasicBlock *BB,
/// Update the block frequency of BB and branch weight and the metadata on the
/// edge BB->SuccBB. This is done by scaling the weight of BB->SuccBB by 1 -
/// Freq(PredBB->BB) / Freq(BB->SuccBB).
void JumpThreading::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
BasicBlock *BB,
BasicBlock *NewBB,
BasicBlock *SuccBB) {
void JumpThreadingPass::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
BasicBlock *BB,
BasicBlock *NewBB,
BasicBlock *SuccBB) {
if (!HasProfileData)
return;

Expand Down Expand Up @@ -1706,8 +1675,8 @@ void JumpThreading::UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
/// If we can duplicate the contents of BB up into PredBB do so now, this
/// improves the odds that the branch will be on an analyzable instruction like
/// a compare.
bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
const SmallVectorImpl<BasicBlock *> &PredBBs) {
bool JumpThreadingPass::DuplicateCondBranchOnPHIIntoPred(
BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs) {
assert(!PredBBs.empty() && "Can't handle an empty set");

// If BB is a loop header, then duplicating this block outside the loop would
Expand Down Expand Up @@ -1856,7 +1825,7 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
///
/// 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) {
bool JumpThreadingPass::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));
Expand Down Expand Up @@ -1934,7 +1903,7 @@ bool JumpThreading::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) {
/// select if the associated PHI has at least one constant. If the unfolded
/// select is not jump-threaded, it will be folded again in the later
/// optimizations.
bool JumpThreading::TryToUnfoldSelectInCurrBB(BasicBlock *BB) {
bool JumpThreadingPass::TryToUnfoldSelectInCurrBB(BasicBlock *BB) {
// 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))
Expand Down
1 change: 1 addition & 0 deletions llvm/test/Transforms/JumpThreading/thread-loads.ll
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
; RUN: opt < %s -jump-threading -S | FileCheck %s
; RUN: opt < %s -passes=jump-threading -S | FileCheck %s

target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i386-apple-darwin7"
Expand Down