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llvm-6502/include/llvm/Analysis/ScalarEvolution.h
Dan Gohman 2c364ad4a6 Make GetMinTrailingZeros a member function of ScalarEvolution, 
so that it can access the TargetData member (when available) and
use ValueTracking.h information to compute information for
SCEVUnknown Values.

Also add GetMinLeadingZeros and GetMinSignBits functions,
with minimal implementations.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73794 91177308-0d34-0410-b5e6-96231b3b80d8
2009-06-19 23:29:04 +00:00

600 lines
24 KiB
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//===- llvm/Analysis/ScalarEvolution.h - Scalar Evolution -------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The ScalarEvolution class is an LLVM pass which can be used to analyze and
// catagorize scalar expressions in loops. It specializes in recognizing
// general induction variables, representing them with the abstract and opaque
// SCEV class. Given this analysis, trip counts of loops and other important
// properties can be obtained.
//
// This analysis is primarily useful for induction variable substitution and
// strength reduction.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_SCALAREVOLUTION_H
#define LLVM_ANALYSIS_SCALAREVOLUTION_H
#include "llvm/Pass.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/ADT/DenseMap.h"
#include <iosfwd>
namespace llvm {
class APInt;
class ConstantInt;
class Type;
class SCEVHandle;
class ScalarEvolution;
class TargetData;
template<> struct DenseMapInfo<SCEVHandle>;
/// SCEV - This class represents an analyzed expression in the program. These
/// are reference-counted opaque objects that the client is not allowed to
/// do much with directly.
///
class SCEV {
const unsigned SCEVType; // The SCEV baseclass this node corresponds to
mutable unsigned RefCount;
friend class SCEVHandle;
friend class DenseMapInfo<SCEVHandle>;
void addRef() const { ++RefCount; }
void dropRef() const {
if (--RefCount == 0)
delete this;
}
const ScalarEvolution* parent;
SCEV(const SCEV &); // DO NOT IMPLEMENT
void operator=(const SCEV &); // DO NOT IMPLEMENT
protected:
virtual ~SCEV();
public:
explicit SCEV(unsigned SCEVTy, const ScalarEvolution* p) :
SCEVType(SCEVTy), RefCount(0), parent(p) {}
unsigned getSCEVType() const { return SCEVType; }
/// isLoopInvariant - Return true if the value of this SCEV is unchanging in
/// the specified loop.
virtual bool isLoopInvariant(const Loop *L) const = 0;
/// hasComputableLoopEvolution - Return true if this SCEV changes value in a
/// known way in the specified loop. This property being true implies that
/// the value is variant in the loop AND that we can emit an expression to
/// compute the value of the expression at any particular loop iteration.
virtual bool hasComputableLoopEvolution(const Loop *L) const = 0;
/// getType - Return the LLVM type of this SCEV expression.
///
virtual const Type *getType() const = 0;
/// isZero - Return true if the expression is a constant zero.
///
bool isZero() const;
/// isOne - Return true if the expression is a constant one.
///
bool isOne() const;
/// replaceSymbolicValuesWithConcrete - If this SCEV internally references
/// the symbolic value "Sym", construct and return a new SCEV that produces
/// the same value, but which uses the concrete value Conc instead of the
/// symbolic value. If this SCEV does not use the symbolic value, it
/// returns itself.
virtual SCEVHandle
replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
const SCEVHandle &Conc,
ScalarEvolution &SE) const = 0;
/// dominates - Return true if elements that makes up this SCEV dominates
/// the specified basic block.
virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const = 0;
/// print - Print out the internal representation of this scalar to the
/// specified stream. This should really only be used for debugging
/// purposes.
virtual void print(raw_ostream &OS) const = 0;
void print(std::ostream &OS) const;
void print(std::ostream *OS) const { if (OS) print(*OS); }
/// dump - This method is used for debugging.
///
void dump() const;
};
inline raw_ostream &operator<<(raw_ostream &OS, const SCEV &S) {
S.print(OS);
return OS;
}
inline std::ostream &operator<<(std::ostream &OS, const SCEV &S) {
S.print(OS);
return OS;
}
/// SCEVCouldNotCompute - An object of this class is returned by queries that
/// could not be answered. For example, if you ask for the number of
/// iterations of a linked-list traversal loop, you will get one of these.
/// None of the standard SCEV operations are valid on this class, it is just a
/// marker.
struct SCEVCouldNotCompute : public SCEV {
SCEVCouldNotCompute(const ScalarEvolution* p);
~SCEVCouldNotCompute();
// None of these methods are valid for this object.
virtual bool isLoopInvariant(const Loop *L) const;
virtual const Type *getType() const;
virtual bool hasComputableLoopEvolution(const Loop *L) const;
virtual void print(raw_ostream &OS) const;
virtual SCEVHandle
replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
const SCEVHandle &Conc,
ScalarEvolution &SE) const;
virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const {
return true;
}
/// Methods for support type inquiry through isa, cast, and dyn_cast:
static inline bool classof(const SCEVCouldNotCompute *S) { return true; }
static bool classof(const SCEV *S);
};
/// SCEVHandle - This class is used to maintain the SCEV object's refcounts,
/// freeing the objects when the last reference is dropped.
class SCEVHandle {
const SCEV *S;
SCEVHandle(); // DO NOT IMPLEMENT
public:
SCEVHandle(const SCEV *s) : S(s) {
assert(S && "Cannot create a handle to a null SCEV!");
S->addRef();
}
SCEVHandle(const SCEVHandle &RHS) : S(RHS.S) {
S->addRef();
}
~SCEVHandle() { S->dropRef(); }
operator const SCEV*() const { return S; }
const SCEV &operator*() const { return *S; }
const SCEV *operator->() const { return S; }
bool operator==(const SCEV *RHS) const { return S == RHS; }
bool operator!=(const SCEV *RHS) const { return S != RHS; }
const SCEVHandle &operator=(SCEV *RHS) {
if (S != RHS) {
S->dropRef();
S = RHS;
S->addRef();
}
return *this;
}
const SCEVHandle &operator=(const SCEVHandle &RHS) {
if (S != RHS.S) {
S->dropRef();
S = RHS.S;
S->addRef();
}
return *this;
}
};
template<typename From> struct simplify_type;
template<> struct simplify_type<const SCEVHandle> {
typedef const SCEV* SimpleType;
static SimpleType getSimplifiedValue(const SCEVHandle &Node) {
return Node;
}
};
template<> struct simplify_type<SCEVHandle>
: public simplify_type<const SCEVHandle> {};
// Specialize DenseMapInfo for SCEVHandle so that SCEVHandle may be used
// as a key in DenseMaps.
template<>
struct DenseMapInfo<SCEVHandle> {
static inline SCEVHandle getEmptyKey() {
static SCEVCouldNotCompute Empty(0);
if (Empty.RefCount == 0)
Empty.addRef();
return &Empty;
}
static inline SCEVHandle getTombstoneKey() {
static SCEVCouldNotCompute Tombstone(0);
if (Tombstone.RefCount == 0)
Tombstone.addRef();
return &Tombstone;
}
static unsigned getHashValue(const SCEVHandle &Val) {
return DenseMapInfo<const SCEV *>::getHashValue(Val);
}
static bool isEqual(const SCEVHandle &LHS, const SCEVHandle &RHS) {
return LHS == RHS;
}
static bool isPod() { return false; }
};
/// ScalarEvolution - This class is the main scalar evolution driver. Because
/// client code (intentionally) can't do much with the SCEV objects directly,
/// they must ask this class for services.
///
class ScalarEvolution : public FunctionPass {
/// SCEVCallbackVH - A CallbackVH to arrange for ScalarEvolution to be
/// notified whenever a Value is deleted.
class SCEVCallbackVH : public CallbackVH {
ScalarEvolution *SE;
virtual void deleted();
virtual void allUsesReplacedWith(Value *New);
public:
SCEVCallbackVH(Value *V, ScalarEvolution *SE = 0);
};
friend class SCEVCallbackVH;
friend class SCEVExpander;
/// F - The function we are analyzing.
///
Function *F;
/// LI - The loop information for the function we are currently analyzing.
///
LoopInfo *LI;
/// TD - The target data information for the target we are targetting.
///
TargetData *TD;
/// CouldNotCompute - This SCEV is used to represent unknown trip
/// counts and things.
SCEVHandle CouldNotCompute;
/// Scalars - This is a cache of the scalars we have analyzed so far.
///
std::map<SCEVCallbackVH, SCEVHandle> Scalars;
/// BackedgeTakenInfo - Information about the backedge-taken count
/// of a loop. This currently inclues an exact count and a maximum count.
///
struct BackedgeTakenInfo {
/// Exact - An expression indicating the exact backedge-taken count of
/// the loop if it is known, or a SCEVCouldNotCompute otherwise.
SCEVHandle Exact;
/// Exact - An expression indicating the least maximum backedge-taken
/// count of the loop that is known, or a SCEVCouldNotCompute.
SCEVHandle Max;
/*implicit*/ BackedgeTakenInfo(SCEVHandle exact) :
Exact(exact), Max(exact) {}
/*implicit*/ BackedgeTakenInfo(const SCEV *exact) :
Exact(exact), Max(exact) {}
BackedgeTakenInfo(SCEVHandle exact, SCEVHandle max) :
Exact(exact), Max(max) {}
/// hasAnyInfo - Test whether this BackedgeTakenInfo contains any
/// computed information, or whether it's all SCEVCouldNotCompute
/// values.
bool hasAnyInfo() const {
return !isa<SCEVCouldNotCompute>(Exact) ||
!isa<SCEVCouldNotCompute>(Max);
}
};
/// BackedgeTakenCounts - Cache the backedge-taken count of the loops for
/// this function as they are computed.
std::map<const Loop*, BackedgeTakenInfo> BackedgeTakenCounts;
/// ConstantEvolutionLoopExitValue - This map contains entries for all of
/// the PHI instructions that we attempt to compute constant evolutions for.
/// This allows us to avoid potentially expensive recomputation of these
/// properties. An instruction maps to null if we are unable to compute its
/// exit value.
std::map<PHINode*, Constant*> ConstantEvolutionLoopExitValue;
/// ValuesAtScopes - This map contains entries for all the instructions
/// that we attempt to compute getSCEVAtScope information for without
/// using SCEV techniques, which can be expensive.
std::map<Instruction *, std::map<const Loop *, Constant *> > ValuesAtScopes;
/// createSCEV - We know that there is no SCEV for the specified value.
/// Analyze the expression.
SCEVHandle createSCEV(Value *V);
/// createNodeForPHI - Provide the special handling we need to analyze PHI
/// SCEVs.
SCEVHandle createNodeForPHI(PHINode *PN);
/// createNodeForGEP - Provide the special handling we need to analyze GEP
/// SCEVs.
SCEVHandle createNodeForGEP(User *GEP);
/// ReplaceSymbolicValueWithConcrete - This looks up the computed SCEV value
/// for the specified instruction and replaces any references to the
/// symbolic value SymName with the specified value. This is used during
/// PHI resolution.
void ReplaceSymbolicValueWithConcrete(Instruction *I,
const SCEVHandle &SymName,
const SCEVHandle &NewVal);
/// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given
/// loop, lazily computing new values if the loop hasn't been analyzed
/// yet.
const BackedgeTakenInfo &getBackedgeTakenInfo(const Loop *L);
/// ComputeBackedgeTakenCount - Compute the number of times the specified
/// loop will iterate.
BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L);
/// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition
/// of 'icmp op load X, cst', try to see if we can compute the trip count.
SCEVHandle
ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI,
Constant *RHS,
const Loop *L,
ICmpInst::Predicate p);
/// ComputeBackedgeTakenCountExhaustively - If the trip is known to execute
/// a constant number of times (the condition evolves only from constants),
/// try to evaluate a few iterations of the loop until we get the exit
/// condition gets a value of ExitWhen (true or false). If we cannot
/// evaluate the trip count of the loop, return CouldNotCompute.
SCEVHandle ComputeBackedgeTakenCountExhaustively(const Loop *L, Value *Cond,
bool ExitWhen);
/// HowFarToZero - Return the number of times a backedge comparing the
/// specified value to zero will execute. If not computable, return
/// CouldNotCompute.
SCEVHandle HowFarToZero(const SCEV *V, const Loop *L);
/// HowFarToNonZero - Return the number of times a backedge checking the
/// specified value for nonzero will execute. If not computable, return
/// CouldNotCompute.
SCEVHandle HowFarToNonZero(const SCEV *V, const Loop *L);
/// HowManyLessThans - Return the number of times a backedge containing the
/// specified less-than comparison will execute. If not computable, return
/// CouldNotCompute. isSigned specifies whether the less-than is signed.
BackedgeTakenInfo HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
const Loop *L, bool isSigned);
/// getLoopPredecessor - If the given loop's header has exactly one unique
/// predecessor outside the loop, return it. Otherwise return null.
BasicBlock *getLoopPredecessor(const Loop *L);
/// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB
/// (which may not be an immediate predecessor) which has exactly one
/// successor from which BB is reachable, or null if no such block is
/// found.
BasicBlock* getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB);
/// getConstantEvolutionLoopExitValue - If we know that the specified Phi is
/// in the header of its containing loop, we know the loop executes a
/// constant number of times, and the PHI node is just a recurrence
/// involving constants, fold it.
Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs,
const Loop *L);
/// forgetLoopPHIs - Delete the memoized SCEVs associated with the
/// PHI nodes in the given loop. This is used when the trip count of
/// the loop may have changed.
void forgetLoopPHIs(const Loop *L);
public:
static char ID; // Pass identification, replacement for typeid
ScalarEvolution();
/// isSCEVable - Test if values of the given type are analyzable within
/// the SCEV framework. This primarily includes integer types, and it
/// can optionally include pointer types if the ScalarEvolution class
/// has access to target-specific information.
bool isSCEVable(const Type *Ty) const;
/// getTypeSizeInBits - Return the size in bits of the specified type,
/// for which isSCEVable must return true.
uint64_t getTypeSizeInBits(const Type *Ty) const;
/// getEffectiveSCEVType - Return a type with the same bitwidth as
/// the given type and which represents how SCEV will treat the given
/// type, for which isSCEVable must return true. For pointer types,
/// this is the pointer-sized integer type.
const Type *getEffectiveSCEVType(const Type *Ty) const;
/// getSCEV - Return a SCEV expression handle for the full generality of the
/// specified expression.
SCEVHandle getSCEV(Value *V);
SCEVHandle getConstant(ConstantInt *V);
SCEVHandle getConstant(const APInt& Val);
SCEVHandle getConstant(const Type *Ty, uint64_t V, bool isSigned = false);
SCEVHandle getTruncateExpr(const SCEVHandle &Op, const Type *Ty);
SCEVHandle getZeroExtendExpr(const SCEVHandle &Op, const Type *Ty);
SCEVHandle getSignExtendExpr(const SCEVHandle &Op, const Type *Ty);
SCEVHandle getAnyExtendExpr(const SCEVHandle &Op, const Type *Ty);
SCEVHandle getAddExpr(SmallVectorImpl<SCEVHandle> &Ops);
SCEVHandle getAddExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) {
SmallVector<SCEVHandle, 2> Ops;
Ops.push_back(LHS);
Ops.push_back(RHS);
return getAddExpr(Ops);
}
SCEVHandle getAddExpr(const SCEVHandle &Op0, const SCEVHandle &Op1,
const SCEVHandle &Op2) {
SmallVector<SCEVHandle, 3> Ops;
Ops.push_back(Op0);
Ops.push_back(Op1);
Ops.push_back(Op2);
return getAddExpr(Ops);
}
SCEVHandle getMulExpr(SmallVectorImpl<SCEVHandle> &Ops);
SCEVHandle getMulExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) {
SmallVector<SCEVHandle, 2> Ops;
Ops.push_back(LHS);
Ops.push_back(RHS);
return getMulExpr(Ops);
}
SCEVHandle getUDivExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
SCEVHandle getAddRecExpr(const SCEVHandle &Start, const SCEVHandle &Step,
const Loop *L);
SCEVHandle getAddRecExpr(SmallVectorImpl<SCEVHandle> &Operands,
const Loop *L);
SCEVHandle getAddRecExpr(const SmallVectorImpl<SCEVHandle> &Operands,
const Loop *L) {
SmallVector<SCEVHandle, 4> NewOp(Operands.begin(), Operands.end());
return getAddRecExpr(NewOp, L);
}
SCEVHandle getSMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
SCEVHandle getSMaxExpr(SmallVectorImpl<SCEVHandle> &Operands);
SCEVHandle getUMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
SCEVHandle getUMaxExpr(SmallVectorImpl<SCEVHandle> &Operands);
SCEVHandle getUnknown(Value *V);
SCEVHandle getCouldNotCompute();
/// getNegativeSCEV - Return the SCEV object corresponding to -V.
///
SCEVHandle getNegativeSCEV(const SCEVHandle &V);
/// getNotSCEV - Return the SCEV object corresponding to ~V.
///
SCEVHandle getNotSCEV(const SCEVHandle &V);
/// getMinusSCEV - Return LHS-RHS.
///
SCEVHandle getMinusSCEV(const SCEVHandle &LHS,
const SCEVHandle &RHS);
/// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion
/// of the input value to the specified type. If the type must be
/// extended, it is zero extended.
SCEVHandle getTruncateOrZeroExtend(const SCEVHandle &V, const Type *Ty);
/// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion
/// of the input value to the specified type. If the type must be
/// extended, it is sign extended.
SCEVHandle getTruncateOrSignExtend(const SCEVHandle &V, const Type *Ty);
/// getNoopOrZeroExtend - Return a SCEV corresponding to a conversion of
/// the input value to the specified type. If the type must be extended,
/// it is zero extended. The conversion must not be narrowing.
SCEVHandle getNoopOrZeroExtend(const SCEVHandle &V, const Type *Ty);
/// getNoopOrSignExtend - Return a SCEV corresponding to a conversion of
/// the input value to the specified type. If the type must be extended,
/// it is sign extended. The conversion must not be narrowing.
SCEVHandle getNoopOrSignExtend(const SCEVHandle &V, const Type *Ty);
/// getNoopOrAnyExtend - Return a SCEV corresponding to a conversion of
/// the input value to the specified type. If the type must be extended,
/// it is extended with unspecified bits. The conversion must not be
/// narrowing.
SCEVHandle getNoopOrAnyExtend(const SCEVHandle &V, const Type *Ty);
/// getTruncateOrNoop - Return a SCEV corresponding to a conversion of the
/// input value to the specified type. The conversion must not be
/// widening.
SCEVHandle getTruncateOrNoop(const SCEVHandle &V, const Type *Ty);
/// getIntegerSCEV - Given an integer or FP type, create a constant for the
/// specified signed integer value and return a SCEV for the constant.
SCEVHandle getIntegerSCEV(int Val, const Type *Ty);
/// hasSCEV - Return true if the SCEV for this value has already been
/// computed.
bool hasSCEV(Value *V) const;
/// setSCEV - Insert the specified SCEV into the map of current SCEVs for
/// the specified value.
void setSCEV(Value *V, const SCEVHandle &H);
/// getSCEVAtScope - Return a SCEV expression handle for the specified value
/// at the specified scope in the program. The L value specifies a loop
/// nest to evaluate the expression at, where null is the top-level or a
/// specified loop is immediately inside of the loop.
///
/// This method can be used to compute the exit value for a variable defined
/// in a loop by querying what the value will hold in the parent loop.
///
/// In the case that a relevant loop exit value cannot be computed, the
/// original value V is returned.
SCEVHandle getSCEVAtScope(const SCEV *S, const Loop *L);
/// getSCEVAtScope - This is a convenience function which does
/// getSCEVAtScope(getSCEV(V), L).
SCEVHandle getSCEVAtScope(Value *V, const Loop *L);
/// isLoopGuardedByCond - Test whether entry to the loop is protected by
/// a conditional between LHS and RHS. This is used to help avoid max
/// expressions in loop trip counts.
bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
const SCEV *LHS, const SCEV *RHS);
/// getBackedgeTakenCount - If the specified loop has a predictable
/// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute
/// object. The backedge-taken count is the number of times the loop header
/// will be branched to from within the loop. This is one less than the
/// trip count of the loop, since it doesn't count the first iteration,
/// when the header is branched to from outside the loop.
///
/// Note that it is not valid to call this method on a loop without a
/// loop-invariant backedge-taken count (see
/// hasLoopInvariantBackedgeTakenCount).
///
SCEVHandle getBackedgeTakenCount(const Loop *L);
/// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except
/// return the least SCEV value that is known never to be less than the
/// actual backedge taken count.
SCEVHandle getMaxBackedgeTakenCount(const Loop *L);
/// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop
/// has an analyzable loop-invariant backedge-taken count.
bool hasLoopInvariantBackedgeTakenCount(const Loop *L);
/// forgetLoopBackedgeTakenCount - This method should be called by the
/// client when it has changed a loop in a way that may effect
/// ScalarEvolution's ability to compute a trip count, or if the loop
/// is deleted.
void forgetLoopBackedgeTakenCount(const Loop *L);
/// GetMinTrailingZeros - Determine the minimum number of zero bits that S is
/// guaranteed to end in (at every loop iteration). It is, at the same time,
/// the minimum number of times S is divisible by 2. For example, given {4,+,8}
/// it returns 2. If S is guaranteed to be 0, it returns the bitwidth of S.
uint32_t GetMinTrailingZeros(const SCEVHandle &S);
/// GetMinLeadingZeros - Determine the minimum number of zero bits that S is
/// guaranteed to begin with (at every loop iteration).
uint32_t GetMinLeadingZeros(const SCEVHandle &S);
/// GetMinSignBits - Determine the minimum number of sign bits that S is
/// guaranteed to begin with.
uint32_t GetMinSignBits(const SCEVHandle &S);
virtual bool runOnFunction(Function &F);
virtual void releaseMemory();
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
void print(raw_ostream &OS, const Module* = 0) const;
virtual void print(std::ostream &OS, const Module* = 0) const;
void print(std::ostream *OS, const Module* M = 0) const {
if (OS) print(*OS, M);
}
};
}
#endif
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