LLVM  4.0.0
Macros | Functions | Variables
JumpThreading.cpp File Reference
#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/Statistic.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/LoopInfo.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/Pass.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/Local.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include <algorithm>
#include <memory>
Include dependency graph for JumpThreading.cpp:

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")
 
 INITIALIZE_PASS_BEGIN (JumpThreading,"jump-threading","Jump Threading", false, false) INITIALIZE_PASS_END(JumpThreading
 
static unsigned getJumpThreadDuplicationCost (const BasicBlock *BB, unsigned Threshold)
 getJumpThreadDuplicationCost - Return the cost of duplicating this block to thread across it. More...
 
static ConstantgetKnownConstant (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. More...
 
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. More...
 
static bool hasAddressTakenAndUsed (BasicBlock *BB)
 
static BasicBlockFindMostPopularDest (BasicBlock *BB, const SmallVectorImpl< std::pair< BasicBlock *, BasicBlock * > > &PredToDestList)
 FindMostPopularDest - The specified list contains multiple possible threadable destinations. More...
 
static void AddPHINodeEntriesForMappedBlock (BasicBlock *PHIBB, BasicBlock *OldPred, BasicBlock *NewPred, DenseMap< Instruction *, Value * > &ValueMap)
 AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new predecessor to the PHIBB block. More...
 

Variables

static cl::opt< unsignedBBDuplicateThreshold ("jump-threading-threshold", cl::desc("Max block size to duplicate for jump threading"), cl::init(6), cl::Hidden)
 
static cl::opt< unsignedImplicationSearchThreshold ("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
 
jump Jump Threading
 
jump Jump false
 

Macro Definition Documentation

#define DEBUG_TYPE   "jump-threading"

Definition at line 45 of file JumpThreading.cpp.

Function Documentation

static void AddPHINodeEntriesForMappedBlock ( BasicBlock PHIBB,
BasicBlock OldPred,
BasicBlock NewPred,
DenseMap< Instruction *, Value * > &  ValueMap 
)
static
static BasicBlock* FindMostPopularDest ( BasicBlock BB,
const SmallVectorImpl< std::pair< BasicBlock *, BasicBlock * > > &  PredToDestList 
)
static
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 673 of file JumpThreading.cpp.

References llvm::TerminatorInst::getNumSuccessors(), llvm::TerminatorInst::getSuccessor(), llvm::BasicBlock::getTerminator(), i, llvm::pred_begin(), and llvm::pred_end().

Referenced by llvm::JumpThreadingPass::ProcessBlock(), and llvm::JumpThreadingPass::ProcessThreadableEdges().

static unsigned getJumpThreadDuplicationCost ( const BasicBlock BB,
unsigned  Threshold 
)
static

getJumpThreadDuplicationCost - Return the cost of duplicating this block to thread across it.

Stop scanning the block when passing the threshold.

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

Definition at line 260 of file JumpThreading.cpp.

References llvm::BasicBlock::getFirstNonPHI(), llvm::BasicBlock::getTerminator(), and I.

Referenced by llvm::JumpThreadingPass::DuplicateCondBranchOnPHIIntoPred(), and llvm::JumpThreadingPass::ThreadEdge().

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 354 of file JumpThreading.cpp.

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

Referenced by llvm::JumpThreadingPass::ComputeValueKnownInPredecessors(), and llvm::JumpThreadingPass::ProcessBlock().

static bool hasAddressTakenAndUsed ( BasicBlock BB)
static
INITIALIZE_PASS_BEGIN ( JumpThreading  ,
"jump-threading ,
"Jump Threading ,
false  ,
false   
)
STATISTIC ( NumThreads  ,
"Number of jumps threaded"   
)
STATISTIC ( NumFolds  ,
"Number of terminators folded"   
)
STATISTIC ( NumDupes  ,
"Number of branch blocks duplicated to eliminate phi"   
)

Variable Documentation

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

Definition at line 107 of file JumpThreading.cpp.

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
jump threading

Definition at line 107 of file JumpThreading.cpp.

jump Jump Threading

Definition at line 107 of file JumpThreading.cpp.