#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/ScalarEvolutionPatternMatch.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/ScalarEvolutionExpander.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <optional>

Classes
struct	WeightInfo

Macros
#define	DEBUG_TYPE "loop-peel"

Functions
	STATISTIC (NumPeeled, "Number of loops peeled")

	STATISTIC (NumPeeledEnd, "Number of loops peeled from end")

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

static bool	shouldPeelLastIteration (Loop &L, CmpPredicate Pred, const SCEVAddRecExpr LeftAR, const SCEV RightSCEV, ScalarEvolution &SE, const TargetTransformInfo &TTI)
	Returns true if the last iteration can be peeled off and the condition (Pred LeftAR, RightSCEV) is known at the last iteration and the inverse condition is known at the second-to-last.

static std::pair< unsigned, unsigned >	countToEliminateCompares (Loop &L, unsigned MaxPeelCount, ScalarEvolution &SE, const TargetTransformInfo &TTI)

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	cloneLoopBlocks (Loop L, unsigned IterNumber, bool PeelLast, BasicBlock InsertTop, BasicBlock InsertBot, BasicBlock OrigPreHeader, 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 cl::opt< bool >	EnablePeelingForIV ("enable-peeling-for-iv", cl::init(false), cl::Hidden, cl::desc("Enable peeling to convert Phi nodes into IVs"))

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

Macro Definition Documentation

◆ DEBUG_TYPE

#define DEBUG_TYPE "loop-peel"

Definition at line 52 of file LoopPeel.cpp.

Function Documentation

◆ cloneLoopBlocks()

static void cloneLoopBlocks	(	Loop *	L,
		unsigned	IterNumber,
		bool	PeelLast,
		BasicBlock *	InsertTop,
		BasicBlock *	InsertBot,
		BasicBlock *	OrigPreHeader,
		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.
	PeelLast	Peel off the last iterations from `L`.
	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 975 of file LoopPeel.cpp.

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

Referenced by llvm::peelLoop().

◆ countToEliminateCompares()

static std::pair< unsigned, unsigned > countToEliminateCompares	(	Loop &	L,
		unsigned	MaxPeelCount,
		ScalarEvolution &	SE,
		const TargetTransformInfo &	TTI
	)

static

Definition at line 541 of file LoopPeel.cpp.

References assert(), llvm::Depth, llvm::SCEVAddRecExpr::evaluateAtIteration(), llvm::ScalarEvolution::evaluatePredicate(), llvm::ScalarEvolution::getAddExpr(), llvm::ScalarEvolution::getConstant(), llvm::ScalarEvolution::getConstantMaxBackedgeTakenCount(), llvm::SCEVAddRecExpr::getLoop(), llvm::ScalarEvolution::getMonotonicPredicateType(), llvm::ScalarEvolution::getSCEV(), llvm::SCEVAddRecExpr::getStepRecurrence(), llvm::SCEV::getType(), llvm::Value::getType(), llvm::SCEVNAryExpr::hasNoSelfWrap(), I, llvm::SCEVAddRecExpr::isAffine(), llvm::ICmpInst::isEquality(), llvm::Type::isIntegerTy(), llvm::ScalarEvolution::isKnownNegative(), llvm::ScalarEvolution::isKnownPositive(), llvm::ScalarEvolution::isKnownPredicate(), LHS, llvm::PatternMatch::m_And(), llvm::PatternMatch::m_ICmp(), llvm::PatternMatch::m_Or(), llvm::PatternMatch::m_Value(), llvm::SCEVPatternMatch::match(), RHS, shouldPeelLastIteration(), and std::swap().

Referenced by llvm::computePeelCount().

◆ initBranchWeights()

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

static

Initialize the weights for all exiting blocks.

Definition at line 921 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 418 of file LoopPeel.cpp.

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

Referenced by llvm::computePeelCount().

◆ shouldPeelLastIteration()

static bool shouldPeelLastIteration	(	Loop &	L,
		CmpPredicate	Pred,
		const SCEVAddRecExpr *	LeftAR,
		const SCEV *	RightSCEV,
		ScalarEvolution &	SE,
		const TargetTransformInfo &	TTI
	)

static

Returns true if the last iteration can be peeled off and the condition (Pred LeftAR, RightSCEV) is known at the last iteration and the inverse condition is known at the second-to-last.

Definition at line 503 of file LoopPeel.cpp.

References llvm::ScalarEvolution::applyLoopGuards(), llvm::canPeelLastIteration(), llvm::ScalarEvolution::LoopGuards::collect(), llvm::SCEVAddRecExpr::evaluateAtIteration(), llvm::ScalarEvolution::getBackedgeTakenCount(), llvm::ScalarEvolution::getMinusSCEV(), llvm::ScalarEvolution::getOne(), llvm::SCEV::getType(), llvm::SCEVExpander::isHighCostExpansion(), llvm::ScalarEvolution::isKnownNonZero(), llvm::ScalarEvolution::isKnownPredicate(), and llvm::SCEVCheapExpansionBudget.

Referenced by countToEliminateCompares().

◆ STATISTIC() [1/2]

STATISTIC	(	NumPeeled	,
		"Number of loops peeled"
	)

◆ STATISTIC() [2/2]

STATISTIC	(	NumPeeledEnd	,
		"Number of loops peeled from end"
	)

◆ 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 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 906 of file LoopPeel.cpp.

References llvm::enumerate(), Idx, Info, and llvm::setBranchWeights().

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 722 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().

◆ EnablePeelingForIV

cl::opt< bool > EnablePeelingForIV("enable-peeling-for-iv", cl::init(false), cl::Hidden, cl::desc("Enable peeling to convert Phi nodes into IVs"))	(	"enable-peeling-for-iv"	,
		cl::init(false)	,
		cl::Hidden	,
		cl::desc("Enable peeling to convert Phi nodes into IVs")
	)

static

Referenced by llvm::computePeelCount().

◆ PeeledCountMetaData

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

static

Definition at line 88 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().

Classes

Macros

Functions

Variables

Macro Definition Documentation

◆ DEBUG_TYPE

Function Documentation

◆ cloneLoopBlocks()

◆ countToEliminateCompares()

◆ initBranchWeights()

◆ peelToTurnInvariantLoadsDerefencebale()

◆ shouldPeelLastIteration()

◆ STATISTIC() [1/2]

◆ STATISTIC() [2/2]

◆ updateBranchWeights()

◆ violatesLegacyMultiExitLoopCheck()

Variable Documentation

◆ DisableAdvancedPeeling

◆ EnablePeelingForIV

◆ PeeledCountMetaData

◆ UnrollAllowLoopNestsPeeling

◆ UnrollAllowPeeling

◆ UnrollForcePeelCount

◆ UnrollPeelCount

◆ UnrollPeelMaxCount