LoopPeel.cpp File Reference

#include "llvm/Transforms/Utils/LoopPeel.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/BasicBlock.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/LLVMContext.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/ProfDataUtils.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/LoopSimplify.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <optional>

Include dependency graph for LoopPeel.cpp:

Go to the source code of this file.

Classes
struct	WeightInfo

Macros
#define	DEBUG_TYPE   "loop-peel"

Functions
	STATISTIC (NumPeeled, "Number of loops peeled")
static unsigned	peelToTurnInvariantLoadsDerefencebale (Loop &L, DominatorTree &DT, AssumptionCache *AC)
static unsigned	countToEliminateCompares (Loop &L, unsigned MaxPeelCount, ScalarEvolution &SE)
static bool	violatesLegacyMultiExitLoopCheck (Loop *L)
	This "heuristic" exactly matches implicit behavior which used to exist inside getLoopEstimatedTripCount.
static void	updateBranchWeights (Instruction *Term, WeightInfo &Info)
	Update the branch weights of an exiting block of a peeled-off loop iteration.
static void	initBranchWeights (DenseMap< Instruction *, WeightInfo > &WeightInfos, Loop *L)
	Initialize the weights for all exiting blocks.
static void	fixupBranchWeights (Instruction *Term, const WeightInfo &Info)
	Update the weights of original exiting block after peeling off all iterations.
static void	cloneLoopBlocks (Loop *L, unsigned IterNumber, BasicBlock *InsertTop, BasicBlock *InsertBot, SmallVectorImpl< std::pair< BasicBlock *, BasicBlock * > > &ExitEdges, SmallVectorImpl< BasicBlock * > &NewBlocks, LoopBlocksDFS &LoopBlocks, ValueToValueMapTy &VMap, ValueToValueMapTy &LVMap, DominatorTree *DT, LoopInfo *LI, ArrayRef< MDNode * > LoopLocalNoAliasDeclScopes, ScalarEvolution &SE)
	Clones the body of the loop L, putting it between InsertTop and InsertBot.

Variables
static cl::opt< unsigned >	UnrollPeelCount ("unroll-peel-count", cl::Hidden, cl::desc("Set the unroll peeling count, for testing purposes"))
static cl::opt< bool >	UnrollAllowPeeling ("unroll-allow-peeling", cl::init(true), cl::Hidden, cl::desc("Allows loops to be peeled when the dynamic " "trip count is known to be low."))
static cl::opt< bool >	UnrollAllowLoopNestsPeeling ("unroll-allow-loop-nests-peeling", cl::init(false), cl::Hidden, cl::desc("Allows loop nests to be peeled."))
static cl::opt< unsigned >	UnrollPeelMaxCount ("unroll-peel-max-count", cl::init(7), cl::Hidden, cl::desc("Max average trip count which will cause loop peeling."))
static cl::opt< unsigned >	UnrollForcePeelCount ("unroll-force-peel-count", cl::init(0), cl::Hidden, cl::desc("Force a peel count regardless of profiling information."))
static cl::opt< bool >	DisableAdvancedPeeling ("disable-advanced-peeling", cl::init(false), cl::Hidden, cl::desc("Disable advance peeling. Issues for convergent targets (D134803)."))
static const char *	PeeledCountMetaData = "llvm.loop.peeled.count"

Macro Definition Documentation

DEBUG_TYPE

#define DEBUG_TYPE   "loop-peel"

Definition at line 49 of file LoopPeel.cpp.

Function Documentation

cloneLoopBlocks()

static void cloneLoopBlocks ( Loop *  L, unsigned  IterNumber, BasicBlock *  InsertTop, BasicBlock *  InsertBot, SmallVectorImpl< std::pair< BasicBlock *, BasicBlock * > > &  ExitEdges, SmallVectorImpl< BasicBlock * > &  NewBlocks, LoopBlocksDFS &  LoopBlocks, ValueToValueMapTy &  VMap, ValueToValueMapTy &  LVMap, DominatorTree *  DT, LoopInfo *  LI, ArrayRef< MDNode * >  LoopLocalNoAliasDeclScopes, ScalarEvolution &  SE  )

static

Clones the body of the loop L, putting it between InsertTop and InsertBot.

Parameters

	IterNumber	The serial number of the iteration currently being peeled off.
	ExitEdges	The exit edges of the original loop.
[out]	NewBlocks	A list of the blocks in the newly created clone
[out]	VMap	The value map between the loop and the new clone.
	LoopBlocks	A helper for DFS-traversal of the loop.
	LVMap	A value-map that maps instructions from the original loop to instructions in the last peeled-off iteration.

Definition at line 689 of file LoopPeel.cpp.

References llvm::LoopBase< BlockT, LoopT >::addBasicBlockToLoop(), llvm::DominatorTreeBase< NodeT, IsPostDom >::addNewBlock(), llvm::LoopBlocksDFS::beginRPO(), llvm::DominatorTreeBase< NodeT, IsPostDom >::changeImmediateDominator(), llvm::cloneAndAdaptNoAliasScopes(), llvm::CloneBasicBlock(), llvm::cloneLoop(), llvm::LoopBlocksDFS::endRPO(), llvm::Instruction::eraseFromParent(), F, llvm::ScalarEvolution::forgetValue(), llvm::DomTreeNodeBase< NodeT >::getBlock(), llvm::DomTreeNodeBase< NodeT >::getIDom(), llvm::PHINode::getIncomingValueForBlock(), llvm::LoopInfoBase< BlockT, LoopT >::getLoopFor(), llvm::DominatorTreeBase< NodeT, IsPostDom >::getNode(), llvm::BasicBlock::getTerminator(), I, PHI, llvm::SmallVectorTemplateBase< T, bool >::push_back(), and llvm::Instruction::setSuccessor().

Referenced by llvm::peelLoop().

countToEliminateCompares()

static unsigned countToEliminateCompares ( Loop &  L, unsigned  MaxPeelCount, ScalarEvolution &  SE  )

static

Definition at line 343 of file LoopPeel.cpp.

References assert(), llvm::SCEVAddRecExpr::evaluateAtIteration(), llvm::ScalarEvolution::evaluatePredicate(), llvm::ScalarEvolution::getAddExpr(), llvm::ScalarEvolution::getConstant(), llvm::SCEVAddRecExpr::getLoop(), llvm::ScalarEvolution::getMonotonicPredicateType(), llvm::ScalarEvolution::getSCEV(), llvm::SCEVAddRecExpr::getStepRecurrence(), llvm::SCEV::getType(), llvm::SCEVNAryExpr::hasNoSelfWrap(), llvm::SCEVAddRecExpr::isAffine(), llvm::ICmpInst::isEquality(), llvm::ScalarEvolution::isKnownPredicate(), llvm::PatternMatch::m_ICmp(), llvm::PatternMatch::m_Value(), llvm::PatternMatch::match(), and std::swap().

Referenced by llvm::computePeelCount().

fixupBranchWeights()

static void fixupBranchWeights ( Instruction *  Term, const WeightInfo &  Info  )

static

Update the weights of original exiting block after peeling off all iterations.

Definition at line 673 of file LoopPeel.cpp.

References llvm::MDBuilder::createBranchWeights(), and Info.

Referenced by llvm::peelLoop().

initBranchWeights()

static void initBranchWeights ( DenseMap< Instruction *, WeightInfo > &  WeightInfos, Loop *  L  )

static

Initialize the weights for all exiting blocks.

Definition at line 628 of file LoopPeel.cpp.

References llvm::extractBranchWeights(), llvm::DenseMapBase< DerivedT, KeyT, ValueT, KeyInfoT, BucketT >::insert(), llvm::SmallVectorTemplateBase< T, bool >::push_back(), llvm::successors(), and llvm::zip().

Referenced by llvm::peelLoop().

peelToTurnInvariantLoadsDerefencebale()

static unsigned peelToTurnInvariantLoadsDerefencebale ( Loop &  L, DominatorTree &  DT, AssumptionCache *  AC  )

static

Definition at line 276 of file LoopPeel.cpp.

References llvm::any_of(), llvm::SmallPtrSetImpl< PtrType >::contains(), DL, llvm::DominatorTree::dominates(), llvm::SmallPtrSetImpl< PtrType >::end(), llvm::SmallPtrSetImpl< PtrType >::find(), llvm::BasicBlock::getTerminator(), I, llvm::SmallPtrSetImpl< PtrType >::insert(), llvm::isDereferenceablePointer(), and Ptr.

Referenced by llvm::computePeelCount().

STATISTIC()

STATISTIC	(	NumPeeled	,
		"Number of loops peeled"
	)

updateBranchWeights()

static void updateBranchWeights ( Instruction *  Term, WeightInfo &  Info  )

static

Update the branch weights of an exiting block of a peeled-off loop iteration.

Let F is a weight of the edge to continue (fallthrough) into the loop. Let E is a weight of the edge to an exit. F/(F+E) is a probability to go to loop and E/(F+E) is a probability to go to exit. Then, Estimated ExitCount = F / E. For I-th (counting from 0) peeled off iteration we set the the weights for the peeled exit as (EC - I, 1). It gives us reasonable distribution, The probability to go to exit 1/(EC-I) increases. At the same time the estimated exit count in the remainder loop reduces by I. To avoid dealing with division rounding we can just multiple both part of weights to E and use weight as (F - I * E, E).

Definition at line 616 of file LoopPeel.cpp.

References llvm::MDBuilder::createBranchWeights(), llvm::enumerate(), Idx, and Info.

Referenced by llvm::peelLoop().

violatesLegacyMultiExitLoopCheck()

static bool violatesLegacyMultiExitLoopCheck ( Loop *  L )

static

This "heuristic" exactly matches implicit behavior which used to exist inside getLoopEstimatedTripCount.

It was added here to keep an improvement inside that API from causing peeling to become more aggressive. This should probably be removed.

Definition at line 450 of file LoopPeel.cpp.

References llvm::any_of(), assert(), llvm::BranchInst::getNumSuccessors(), llvm::BranchInst::getSuccessor(), llvm::BasicBlock::getTerminatingDeoptimizeCall(), and llvm::BasicBlock::getTerminator().

Referenced by llvm::computePeelCount().

Variable Documentation

DisableAdvancedPeeling

cl::opt< bool > DisableAdvancedPeeling("disable-advanced-peeling", cl::init(false), cl::Hidden, cl::desc( "Disable advance peeling. Issues for convergent targets (D134803).")) ( "disable-advanced-peeling"  , cl::init(false)  , cl::Hidden  , cl::desc( "Disable advance peeling. Issues for convergent targets (D134803).")    )

static

Referenced by llvm::canPeel().

PeeledCountMetaData

const char* PeeledCountMetaData = "llvm.loop.peeled.count"

static

Definition at line 80 of file LoopPeel.cpp.

Referenced by llvm::computePeelCount(), and llvm::peelLoop().

UnrollAllowLoopNestsPeeling

cl::opt< bool > UnrollAllowLoopNestsPeeling("unroll-allow-loop-nests-peeling", cl::init(false), cl::Hidden, cl::desc("Allows loop nests to be peeled.")) ( "unroll-allow-loop-nests-peeling"  , cl::init(false)  , cl::Hidden  , cl::desc("Allows loop nests to be peeled.")    )

static

Referenced by llvm::gatherPeelingPreferences().

UnrollAllowPeeling

cl::opt< bool > UnrollAllowPeeling("unroll-allow-peeling", cl::init(true), cl::Hidden, cl::desc("Allows loops to be peeled when the dynamic " "trip count is known to be low.")) ( "unroll-allow-peeling"  , cl::init(true)  , cl::Hidden  , cl::desc("Allows loops to be peeled when the dynamic " "trip count is known to be low.")    )

static

Referenced by llvm::gatherPeelingPreferences().

UnrollForcePeelCount

cl::opt< unsigned > UnrollForcePeelCount("unroll-force-peel-count", cl::init(0), cl::Hidden, cl::desc("Force a peel count regardless of profiling information.")) ( "unroll-force-peel-count"  , cl::init(0)  , cl::Hidden  , cl::desc("Force a peel count regardless of profiling information.")    )

static

Referenced by llvm::computePeelCount().

UnrollPeelCount

cl::opt< unsigned > UnrollPeelCount("unroll-peel-count", cl::Hidden, cl::desc("Set the unroll peeling count, for testing purposes")) ( "unroll-peel-count"  , cl::Hidden  , cl::desc("Set the unroll peeling count, for testing purposes")    )

static

Referenced by llvm::gatherPeelingPreferences().

UnrollPeelMaxCount

cl::opt< unsigned > UnrollPeelMaxCount("unroll-peel-max-count", cl::init(7), cl::Hidden, cl::desc("Max average trip count which will cause loop peeling.")) ( "unroll-peel-max-count"  , cl::init(7)  , cl::Hidden  , cl::desc("Max average trip count which will cause loop peeling.")    )

static

Referenced by llvm::computePeelCount().