LLVM  14.0.0git
Macros | Functions | Variables
BranchFolding.cpp File Reference
#include "BranchFolding.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineJumpTableInfo.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/MachineSizeOpts.h"
#include "llvm/CodeGen/MBFIWrapper.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/InitializePasses.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/BlockFrequency.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include <cassert>
#include <cstddef>
#include <iterator>
#include <numeric>
Include dependency graph for BranchFolding.cpp:

Go to the source code of this file.

Macros

#define DEBUG_TYPE   "branch-folder"
 

Functions

 STATISTIC (NumDeadBlocks, "Number of dead blocks removed")
 
 STATISTIC (NumBranchOpts, "Number of branches optimized")
 
 STATISTIC (NumTailMerge, "Number of block tails merged")
 
 STATISTIC (NumHoist, "Number of times common instructions are hoisted")
 
 STATISTIC (NumTailCalls, "Number of tail calls optimized")
 
 INITIALIZE_PASS (BranchFolderPass, DEBUG_TYPE, "Control Flow Optimizer", false, false) bool BranchFolderPass
 
static unsigned HashMachineInstr (const MachineInstr &MI)
 HashMachineInstr - Compute a hash value for MI and its operands. More...
 
static unsigned HashEndOfMBB (const MachineBasicBlock &MBB)
 HashEndOfMBB - Hash the last instruction in the MBB. More...
 
static bool countsAsInstruction (const MachineInstr &MI)
 Whether MI should be counted as an instruction when calculating common tail. More...
 
static MachineBasicBlock::iterator skipBackwardPastNonInstructions (MachineBasicBlock::iterator I, MachineBasicBlock *MBB)
 Iterate backwards from the given iterator I, towards the beginning of the block. More...
 
static unsigned ComputeCommonTailLength (MachineBasicBlock *MBB1, MachineBasicBlock *MBB2, MachineBasicBlock::iterator &I1, MachineBasicBlock::iterator &I2)
 Given two machine basic blocks, return the number of instructions they actually have in common together at their end. More...
 
static unsigned EstimateRuntime (MachineBasicBlock::iterator I, MachineBasicBlock::iterator E)
 EstimateRuntime - Make a rough estimate for how long it will take to run the specified code. More...
 
static void FixTail (MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB, const TargetInstrInfo *TII)
 
static unsigned CountTerminators (MachineBasicBlock *MBB, MachineBasicBlock::iterator &I)
 CountTerminators - Count the number of terminators in the given block and set I to the position of the first non-terminator, if there is one, or MBB->end() otherwise. More...
 
static bool blockEndsInUnreachable (const MachineBasicBlock *MBB)
 A no successor, non-return block probably ends in unreachable and is cold. More...
 
static bool ProfitableToMerge (MachineBasicBlock *MBB1, MachineBasicBlock *MBB2, unsigned MinCommonTailLength, unsigned &CommonTailLen, MachineBasicBlock::iterator &I1, MachineBasicBlock::iterator &I2, MachineBasicBlock *SuccBB, MachineBasicBlock *PredBB, DenseMap< const MachineBasicBlock *, int > &EHScopeMembership, bool AfterPlacement, MBFIWrapper &MBBFreqInfo, ProfileSummaryInfo *PSI)
 ProfitableToMerge - Check if two machine basic blocks have a common tail and decide if it would be profitable to merge those tails. More...
 
static void mergeOperations (MachineBasicBlock::iterator MBBIStartPos, MachineBasicBlock &MBBCommon)
 
static bool IsEmptyBlock (MachineBasicBlock *MBB)
 
static bool IsBranchOnlyBlock (MachineBasicBlock *MBB)
 
static bool IsBetterFallthrough (MachineBasicBlock *MBB1, MachineBasicBlock *MBB2)
 IsBetterFallthrough - Return true if it would be clearly better to fall-through to MBB1 than to fall through into MBB2. More...
 
static DebugLoc getBranchDebugLoc (MachineBasicBlock &MBB)
 getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch instructions on the block. More...
 
static void copyDebugInfoToPredecessor (const TargetInstrInfo *TII, MachineBasicBlock &MBB, MachineBasicBlock &PredMBB)
 
static void copyDebugInfoToSuccessor (const TargetInstrInfo *TII, MachineBasicBlock &MBB, MachineBasicBlock &SuccMBB)
 
static void salvageDebugInfoFromEmptyBlock (const TargetInstrInfo *TII, MachineBasicBlock &MBB)
 
static MachineBasicBlockfindFalseBlock (MachineBasicBlock *BB, MachineBasicBlock *TrueBB)
 findFalseBlock - BB has a fallthrough. More...
 
template<class Container >
static void addRegAndItsAliases (Register Reg, const TargetRegisterInfo *TRI, Container &Set)
 
static MachineBasicBlock::iterator findHoistingInsertPosAndDeps (MachineBasicBlock *MBB, const TargetInstrInfo *TII, const TargetRegisterInfo *TRI, SmallSet< Register, 4 > &Uses, SmallSet< Register, 4 > &Defs)
 findHoistingInsertPosAndDeps - Find the location to move common instructions in successors to. More...
 

Variables

static cl::opt< cl::boolOrDefaultFlagEnableTailMerge ("enable-tail-merge", cl::init(cl::BOU_UNSET), cl::Hidden)
 
static cl::opt< unsigned > TailMergeThreshold ("tail-merge-threshold", cl::desc("Max number of predecessors to consider tail merging"), cl::init(150), cl::Hidden)
 
static cl::opt< unsigned > TailMergeSize ("tail-merge-size", cl::desc("Min number of instructions to consider tail merging"), cl::init(3), cl::Hidden)
 

Macro Definition Documentation

◆ DEBUG_TYPE

#define DEBUG_TYPE   "branch-folder"

Definition at line 66 of file BranchFolding.cpp.

Function Documentation

◆ addRegAndItsAliases()

template<class Container >
static void addRegAndItsAliases ( Register  Reg,
const TargetRegisterInfo TRI,
Container &  Set 
)
static

Definition at line 1775 of file BranchFolding.cpp.

References llvm::MCRegAliasIterator::isValid(), Reg, and TRI.

Referenced by findHoistingInsertPosAndDeps().

◆ blockEndsInUnreachable()

static bool blockEndsInUnreachable ( const MachineBasicBlock MBB)
static

A no successor, non-return block probably ends in unreachable and is cold.

Also consider a block that ends in an indirect branch to be a return block, since many targets use plain indirect branches to return.

Definition at line 515 of file BranchFolding.cpp.

References llvm::MachineBasicBlock::back(), llvm::MachineBasicBlock::empty(), llvm::MachineInstr::isIndirectBranch(), llvm::MachineInstr::isReturn(), MBB, and llvm::MachineBasicBlock::succ_empty().

Referenced by ProfitableToMerge().

◆ ComputeCommonTailLength()

static unsigned ComputeCommonTailLength ( MachineBasicBlock MBB1,
MachineBasicBlock MBB2,
MachineBasicBlock::iterator I1,
MachineBasicBlock::iterator I2 
)
static

Given two machine basic blocks, return the number of instructions they actually have in common together at their end.

If a common tail is found (at least by one instruction), then iterators for the first shared instruction in each block are returned as well.

Non-instructions according to countsAsInstruction are ignored.

Definition at line 321 of file BranchFolding.cpp.

References llvm::MachineBasicBlock::end(), llvm::MachineInstr::NoMerge, and skipBackwardPastNonInstructions().

Referenced by ProfitableToMerge().

◆ copyDebugInfoToPredecessor()

static void copyDebugInfoToPredecessor ( const TargetInstrInfo TII,
MachineBasicBlock MBB,
MachineBasicBlock PredMBB 
)
static

◆ copyDebugInfoToSuccessor()

static void copyDebugInfoToSuccessor ( const TargetInstrInfo TII,
MachineBasicBlock MBB,
MachineBasicBlock SuccMBB 
)
static

◆ countsAsInstruction()

static bool countsAsInstruction ( const MachineInstr MI)
static

Whether MI should be counted as an instruction when calculating common tail.

Definition at line 297 of file BranchFolding.cpp.

References MI.

Referenced by EstimateRuntime(), mergeOperations(), and skipBackwardPastNonInstructions().

◆ CountTerminators()

static unsigned CountTerminators ( MachineBasicBlock MBB,
MachineBasicBlock::iterator I 
)
static

CountTerminators - Count the number of terminators in the given block and set I to the position of the first non-terminator, if there is one, or MBB->end() otherwise.

Definition at line 496 of file BranchFolding.cpp.

References llvm::MachineBasicBlock::begin(), llvm::MachineBasicBlock::end(), I, and MBB.

Referenced by ProfitableToMerge().

◆ EstimateRuntime()

static unsigned EstimateRuntime ( MachineBasicBlock::iterator  I,
MachineBasicBlock::iterator  E 
)
static

EstimateRuntime - Make a rough estimate for how long it will take to run the specified code.

Definition at line 433 of file BranchFolding.cpp.

References countsAsInstruction(), E, and I.

◆ findFalseBlock()

static MachineBasicBlock* findFalseBlock ( MachineBasicBlock BB,
MachineBasicBlock TrueBB 
)
static

findFalseBlock - BB has a fallthrough.

Find its 'false' successor given its 'true' successor.

Definition at line 1766 of file BranchFolding.cpp.

References BB.

◆ findHoistingInsertPosAndDeps()

static MachineBasicBlock::iterator findHoistingInsertPosAndDeps ( MachineBasicBlock MBB,
const TargetInstrInfo TII,
const TargetRegisterInfo TRI,
SmallSet< Register, 4 > &  Uses,
SmallSet< Register, 4 > &  Defs 
)
static

findHoistingInsertPosAndDeps - Find the location to move common instructions in successors to.

The location is usually just before the terminator, however if the terminator is a conditional branch and its previous instruction is the flag setting instruction, the previous instruction is the preferred location. This function also gathers uses and defs of the instructions from the insertion point to the end of the block. The data is used by HoistCommonCodeInSuccs to ensure safety.

Definition at line 1793 of file BranchFolding.cpp.

References addRegAndItsAliases(), llvm::MachineBasicBlock::begin(), llvm::MachineBasicBlock::end(), llvm::MachineBasicBlock::getFirstTerminator(), llvm::Register::isPhysicalRegister(), llvm::HexagonInstrInfo::isPredicated(), llvm::MCRegisterInfo::DiffListIterator::isValid(), MBB, llvm::prev_nodbg(), Reg, TII, TRI, and Uses.

◆ FixTail()

static void FixTail ( MachineBasicBlock CurMBB,
MachineBasicBlock SuccBB,
const TargetInstrInfo TII 
)
static

◆ getBranchDebugLoc()

static DebugLoc getBranchDebugLoc ( MachineBasicBlock MBB)
static

getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch instructions on the block.

Definition at line 1258 of file BranchFolding.cpp.

References llvm::MachineBasicBlock::end(), llvm::MachineBasicBlock::getLastNonDebugInstr(), I, and MBB.

◆ HashEndOfMBB()

static unsigned HashEndOfMBB ( const MachineBasicBlock MBB)
static

HashEndOfMBB - Hash the last instruction in the MBB.

Definition at line 288 of file BranchFolding.cpp.

References llvm::MachineBasicBlock::end(), llvm::MachineBasicBlock::getLastNonDebugInstr(), HashMachineInstr(), I, and MBB.

◆ HashMachineInstr()

static unsigned HashMachineInstr ( const MachineInstr MI)
static

◆ INITIALIZE_PASS()

INITIALIZE_PASS ( BranchFolderPass  ,
DEBUG_TYPE  ,
"Control Flow Optimizer ,
false  ,
false   
)

◆ IsBetterFallthrough()

static bool IsBetterFallthrough ( MachineBasicBlock MBB1,
MachineBasicBlock MBB2 
)
static

IsBetterFallthrough - Return true if it would be clearly better to fall-through to MBB1 than to fall through into MBB2.

This has to return a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will result in infinite loops.

Definition at line 1235 of file BranchFolding.cpp.

References assert(), llvm::MachineBasicBlock::end(), llvm::MachineBasicBlock::getLastNonDebugInstr(), and llvm::MachineBasicBlock::isSuccessor().

◆ IsBranchOnlyBlock()

static bool IsBranchOnlyBlock ( MachineBasicBlock MBB)
static

◆ IsEmptyBlock()

static bool IsEmptyBlock ( MachineBasicBlock MBB)
static

◆ mergeOperations()

static void mergeOperations ( MachineBasicBlock::iterator  MBBIStartPos,
MachineBasicBlock MBBCommon 
)
static

◆ ProfitableToMerge()

static bool ProfitableToMerge ( MachineBasicBlock MBB1,
MachineBasicBlock MBB2,
unsigned  MinCommonTailLength,
unsigned &  CommonTailLen,
MachineBasicBlock::iterator I1,
MachineBasicBlock::iterator I2,
MachineBasicBlock SuccBB,
MachineBasicBlock PredBB,
DenseMap< const MachineBasicBlock *, int > &  EHScopeMembership,
bool  AfterPlacement,
MBFIWrapper MBBFreqInfo,
ProfileSummaryInfo PSI 
)
static

ProfitableToMerge - Check if two machine basic blocks have a common tail and decide if it would be profitable to merge those tails.

Return the length of the common tail and iterators to the first common instruction in each block. MBB1, MBB2 The blocks to check MinCommonTailLength Minimum size of tail block to be merged. CommonTailLen Out parameter to record the size of the shared tail between MBB1 and MBB2 I1, I2 Iterator references that will be changed to point to the first instruction in the common tail shared by MBB1,MBB2 SuccBB A common successor of MBB1, MBB2 which are in a canonical form relative to SuccBB PredBB The layout predecessor of SuccBB, if any. EHScopeMembership map from block to EH scope #. AfterPlacement True if we are merging blocks after layout. Stricter thresholds apply to prevent undoing tail-duplication.

Definition at line 540 of file BranchFolding.cpp.

References assert(), llvm::MachineBasicBlock::back(), llvm::MachineBasicBlock::begin(), llvm::MachineFunction::begin(), blockEndsInUnreachable(), llvm::MachineBasicBlock::canFallThrough(), ComputeCommonTailLength(), CountTerminators(), llvm::dbgs(), llvm::DenseMapBase< DenseMap< KeyT, ValueT, DenseMapInfo< KeyT >, llvm::detail::DenseMapPair< KeyT, ValueT > >, KeyT, ValueT, DenseMapInfo< KeyT >, llvm::detail::DenseMapPair< KeyT, ValueT > >::empty(), llvm::DenseMapBase< DenseMap< KeyT, ValueT, DenseMapInfo< KeyT >, llvm::detail::DenseMapPair< KeyT, ValueT > >, KeyT, ValueT, DenseMapInfo< KeyT >, llvm::detail::DenseMapPair< KeyT, ValueT > >::end(), llvm::MachineBasicBlock::end(), llvm::DenseMapBase< DenseMap< KeyT, ValueT, DenseMapInfo< KeyT >, llvm::detail::DenseMapPair< KeyT, ValueT > >, KeyT, ValueT, DenseMapInfo< KeyT >, llvm::detail::DenseMapPair< KeyT, ValueT > >::find(), llvm::MachineFunction::getFunction(), llvm::MachineBasicBlock::getParent(), llvm::Function::hasOptSize(), I, llvm::MachineInstr::isBarrier(), llvm::MachineBasicBlock::isLayoutSuccessor(), LLVM_DEBUG, MBB, llvm::printMBBReference(), llvm::shouldOptimizeForSize(), llvm::skipDebugInstructionsForward(), llvm::MachineBasicBlock::succ_empty(), and llvm::MachineBasicBlock::succ_size().

◆ salvageDebugInfoFromEmptyBlock()

static void salvageDebugInfoFromEmptyBlock ( const TargetInstrInfo TII,
MachineBasicBlock MBB 
)
static

◆ skipBackwardPastNonInstructions()

static MachineBasicBlock::iterator skipBackwardPastNonInstructions ( MachineBasicBlock::iterator  I,
MachineBasicBlock MBB 
)
static

Iterate backwards from the given iterator I, towards the beginning of the block.

If a MI satisfying 'countsAsInstruction' is found, return an iterator pointing to that MI. If no such MI is found, return the end iterator.

Definition at line 305 of file BranchFolding.cpp.

References llvm::MachineBasicBlock::begin(), countsAsInstruction(), llvm::MachineBasicBlock::end(), I, and MBB.

Referenced by ComputeCommonTailLength().

◆ STATISTIC() [1/5]

STATISTIC ( NumBranchOpts  ,
"Number of branches optimized"   
)

◆ STATISTIC() [2/5]

STATISTIC ( NumDeadBlocks  ,
"Number of dead blocks removed  
)

◆ STATISTIC() [3/5]

STATISTIC ( NumHoist  ,
"Number of times common instructions are hoisted"   
)

◆ STATISTIC() [4/5]

STATISTIC ( NumTailCalls  ,
"Number of tail calls optimized"   
)

◆ STATISTIC() [5/5]

STATISTIC ( NumTailMerge  ,
"Number of block tails merged"   
)

Variable Documentation

◆ FlagEnableTailMerge

cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge", cl::init(cl::BOU_UNSET), cl::Hidden)
static

◆ TailMergeSize

cl::opt<unsigned> TailMergeSize("tail-merge-size", cl::desc("Min number of instructions to consider tail merging"), cl::init(3), cl::Hidden)
static

◆ TailMergeThreshold

cl::opt<unsigned> TailMergeThreshold("tail-merge-threshold", cl::desc("Max number of predecessors to consider tail merging"), cl::init(150), cl::Hidden)
static