JumpThreading.cpp File Reference

#include "llvm/Transforms/Scalar/JumpThreading.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/GuardUtils.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/ProfDataUtils.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/BlockFrequency.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <cassert>
#include <cstdint>
#include <iterator>
#include <memory>
#include <utility>

Go to the source code of this file.

Macros
#define	DEBUG_TYPE   "jump-threading"

Functions
	STATISTIC (NumThreads, "Number of jumps threaded")
	STATISTIC (NumFolds, "Number of terminators folded")
	STATISTIC (NumDupes, "Number of branch blocks duplicated to eliminate phi")
static void	updatePredecessorProfileMetadata (PHINode *PN, BasicBlock *BB)
static bool	replaceFoldableUses (Instruction *Cond, Value *ToVal, BasicBlock *KnownAtEndOfBB)
static unsigned	getJumpThreadDuplicationCost (const TargetTransformInfo *TTI, BasicBlock *BB, Instruction *StopAt, unsigned Threshold)
	Return the cost of duplicating a piece of this block from first non-phi and before StopAt instruction to thread across it.
static Constant *	getKnownConstant (Value *Val, ConstantPreference Preference)
	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.
static unsigned	getBestDestForJumpOnUndef (BasicBlock *BB)
	GetBestDestForBranchOnUndef - If we determine that the specified block ends in an undefined jump, decide which block is best to revector to.
static bool	hasAddressTakenAndUsed (BasicBlock *BB)
static bool	isOpDefinedInBlock (Value *Op, BasicBlock *BB)
	Return true if Op is an instruction defined in the given block.
static BasicBlock *	findMostPopularDest (BasicBlock *BB, const SmallVectorImpl< std::pair< BasicBlock *, BasicBlock * > > &PredToDestList)
	findMostPopularDest - The specified list contains multiple possible threadable destinations.
static void	addPHINodeEntriesForMappedBlock (BasicBlock *PHIBB, BasicBlock *OldPred, BasicBlock *NewPred, ValueToValueMapTy &ValueMap)
	addPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new predecessor to the PHIBB block.

Variables
static cl::opt< unsigned >	BBDuplicateThreshold ("jump-threading-threshold", cl::desc("Max block size to duplicate for jump threading"), cl::init(6), cl::Hidden)
static cl::opt< unsigned >	ImplicationSearchThreshold ("jump-threading-implication-search-threshold", cl::desc("The number of predecessors to search for a stronger " "condition to use to thread over a weaker condition"), cl::init(3), cl::Hidden)
static cl::opt< unsigned >	PhiDuplicateThreshold ("jump-threading-phi-threshold", cl::desc("Max PHIs in BB to duplicate for jump threading"), cl::init(76), cl::Hidden)
static cl::opt< bool >	ThreadAcrossLoopHeaders ("jump-threading-across-loop-headers", cl::desc("Allow JumpThreading to thread across loop headers, for testing"), cl::init(false), cl::Hidden)

Macro Definition Documentation

DEBUG_TYPE

#define DEBUG_TYPE   "jump-threading"

Definition at line 80 of file JumpThreading.cpp.

Function Documentation

addPHINodeEntriesForMappedBlock()

static void addPHINodeEntriesForMappedBlock ( BasicBlock *  PHIBB, BasicBlock *  OldPred, BasicBlock *  NewPred, ValueToValueMapTy &  ValueMap  )

static

addPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new predecessor to the PHIBB block.

If it has PHI nodes, add entries for NewPred using the entries from OldPred (suitably mapped).

Definition at line 1866 of file JumpThreading.cpp.

References llvm::ValueMap< KeyT, ValueT, Config >::end(), llvm::ValueMap< KeyT, ValueT, Config >::find(), I, IV, and llvm::BasicBlock::phis().

Referenced by llvm::JumpThreadingPass::duplicateCondBranchOnPHIIntoPred(), llvm::JumpThreadingPass::threadEdge(), and llvm::JumpThreadingPass::threadThroughTwoBasicBlocks().

findMostPopularDest()

static BasicBlock * findMostPopularDest ( BasicBlock *  BB, const SmallVectorImpl< std::pair< BasicBlock *, BasicBlock * > > &  PredToDestList  )

static

findMostPopularDest - The specified list contains multiple possible threadable destinations.

Pick the one that occurs the most frequently in the list.

Definition at line 1465 of file JumpThreading.cpp.

References assert(), llvm::max_element(), and llvm::successors().

Referenced by llvm::JumpThreadingPass::processThreadableEdges().

getBestDestForJumpOnUndef()

static unsigned getBestDestForJumpOnUndef ( BasicBlock *  BB )

static

GetBestDestForBranchOnUndef - If we determine that the specified block ends in an undefined jump, decide which block is best to revector to.

Since we can pick an arbitrary destination, we pick the successor with the fewest predecessors. This should reduce the in-degree of the others.

Definition at line 917 of file JumpThreading.cpp.

References llvm::Instruction::getNumSuccessors(), llvm::Instruction::getSuccessor(), llvm::BasicBlock::getTerminator(), and llvm::pred_size().

Referenced by llvm::JumpThreadingPass::processBlock(), and llvm::JumpThreadingPass::processThreadableEdges().

getJumpThreadDuplicationCost()

static unsigned getJumpThreadDuplicationCost ( const TargetTransformInfo *  TTI, BasicBlock *  BB, Instruction *  StopAt, unsigned  Threshold  )

static

Return the cost of duplicating a piece of this block from first non-phi and before StopAt instruction to thread across it.

Stop scanning the block when exceeding the threshold. If duplication is impossible, returns ~0U.

Ignore PHI nodes, these will be flattened when duplication happens.

Definition at line 425 of file JumpThreading.cpp.

References assert(), llvm::TargetTransformInfo::getInstructionCost(), llvm::ilist_detail::node_parent_access< NodeTy, ParentTy >::getParent(), llvm::BasicBlock::getTerminator(), I, PhiDuplicateThreshold, Size, llvm::TargetTransformInfo::TCC_Free, and llvm::TargetTransformInfo::TCK_SizeAndLatency.

Referenced by llvm::JumpThreadingPass::duplicateCondBranchOnPHIIntoPred(), llvm::JumpThreadingPass::maybethreadThroughTwoBasicBlocks(), llvm::JumpThreadingPass::threadGuard(), and llvm::JumpThreadingPass::tryThreadEdge().

getKnownConstant()

static Constant * getKnownConstant ( Value *  Val, ConstantPreference  Preference  )

static

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.

Definition at line 537 of file JumpThreading.cpp.

References llvm::Value::stripPointerCasts(), and llvm::jumpthreading::WantBlockAddress.

Referenced by llvm::JumpThreadingPass::computeValueKnownInPredecessorsImpl(), and llvm::JumpThreadingPass::processBlock().

hasAddressTakenAndUsed()

static bool hasAddressTakenAndUsed ( BasicBlock *  BB )

static

Definition at line 935 of file JumpThreading.cpp.

References llvm::BlockAddress::get(), llvm::BasicBlock::hasAddressTaken(), llvm::Constant::removeDeadConstantUsers(), and llvm::Value::use_empty().

Referenced by llvm::JumpThreadingPass::maybeMergeBasicBlockIntoOnlyPred().

isOpDefinedInBlock()

static bool isOpDefinedInBlock ( Value *  Op, BasicBlock *  BB  )

static

Return true if Op is an instruction defined in the given block.

Definition at line 1210 of file JumpThreading.cpp.

Referenced by llvm::JumpThreadingPass::simplifyPartiallyRedundantLoad().

replaceFoldableUses()

static bool replaceFoldableUses ( Instruction *  Cond, Value *  ToVal, BasicBlock *  KnownAtEndOfBB  )

static

Definition at line 391 of file JumpThreading.cpp.

References assert(), Cond, llvm::filterDbgVars(), llvm::Value::getType(), I, llvm::isGuaranteedToTransferExecutionToSuccessor(), llvm::replaceNonLocalUsesWith(), and llvm::reverse().

Referenced by llvm::JumpThreadingPass::processBlock(), and llvm::JumpThreadingPass::processThreadableEdges().

STATISTIC() [1/3]

STATISTIC	(	NumDupes	,
		"Number of branch blocks duplicated to eliminate phi"
	)

STATISTIC() [2/3]

STATISTIC	(	NumFolds	,
		"Number of terminators folded"
	)

STATISTIC() [3/3]

STATISTIC	(	NumThreads	,
		"Number of jumps threaded"
	)

updatePredecessorProfileMetadata()

static void updatePredecessorProfileMetadata ( PHINode *  PN, BasicBlock *  BB  )

static

Definition at line 147 of file JumpThreading.cpp.

References llvm::SmallPtrSetImpl< PtrType >::count(), llvm::extractBranchWeights(), llvm::BranchProbability::getBranchProbability(), llvm::BranchProbability::getCompl(), llvm::PHINode::getIncomingBlock(), llvm::PHINode::getIncomingValue(), llvm::BranchProbability::getNumerator(), llvm::PHINode::getNumIncomingValues(), llvm::BranchInst::getSuccessor(), llvm::BasicBlock::getTerminator(), llvm::Value::getType(), llvm::hasBranchWeightOrigin(), llvm::SmallPtrSetImpl< PtrType >::insert(), llvm::BranchInst::isConditional(), llvm::Type::isIntegerTy(), llvm::ConstantInt::isOne(), and llvm::setBranchWeights().

Referenced by llvm::JumpThreadingPass::processBlock().

Variable Documentation

BBDuplicateThreshold

cl::opt< unsigned > BBDuplicateThreshold("jump-threading-threshold", cl::desc("Max block size to duplicate for jump threading"), cl::init(6), cl::Hidden) ( "jump-threading-threshold"  , cl::desc("Max block size to duplicate for jump threading")  , cl::init(6)  , cl::Hidden    )

static

Referenced by llvm::JumpThreadingPass::JumpThreadingPass(), and llvm::JumpThreadingPass::runImpl().

ImplicationSearchThreshold

cl::opt< unsigned > ImplicationSearchThreshold("jump-threading-implication-search-threshold", cl::desc("The number of predecessors to search for a stronger " "condition to use to thread over a weaker condition"), cl::init(3), cl::Hidden) ( "jump-threading-implication-search-threshold"  , cl::desc("The number of predecessors to search for a stronger " "condition to use to thread over a weaker condition")  , cl::init(3)  , cl::Hidden    )

static

Referenced by llvm::JumpThreadingPass::processImpliedCondition().

PhiDuplicateThreshold

cl::opt< unsigned > PhiDuplicateThreshold("jump-threading-phi-threshold", cl::desc("Max PHIs in BB to duplicate for jump threading"), cl::init(76), cl::Hidden) ( "jump-threading-phi-threshold"  , cl::desc("Max PHIs in BB to duplicate for jump threading")  , cl::init(76)  , cl::Hidden    )

static

Referenced by getJumpThreadDuplicationCost().

ThreadAcrossLoopHeaders

cl::opt< bool > ThreadAcrossLoopHeaders("jump-threading-across-loop-headers", cl::desc("Allow JumpThreading to thread across loop headers, for testing"), cl::init(false), cl::Hidden) ( "jump-threading-across-loop-headers"  , cl::desc("Allow JumpThreading to thread across loop headers, for testing")  , cl::init(false)  , cl::Hidden    )

static

Referenced by llvm::JumpThreadingPass::runImpl().