llvm-6502/include/llvm/Analysis/ScalarEvolution.h
Dan Gohman f8a8be86e3 De-pImpl-ify ScalarEvolution. The pImpl pattern doesn't provide much
practical benefit in the case of ScalarEvolution, and it's otherwise
a nuisance.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@69749 91177308-0d34-0410-b5e6-96231b3b80d8
2009-04-21 23:15:49 +00:00

461 lines
18 KiB
C++

//===- 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 <iosfwd>
namespace llvm {
class APInt;
class ConstantInt;
class Type;
class SCEVHandle;
class ScalarEvolution;
class TargetData;
/// SCEV - This class represent 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;
void addRef() const { ++RefCount; }
void dropRef() const {
if (--RefCount == 0)
delete this;
}
SCEV(const SCEV &); // DO NOT IMPLEMENT
void operator=(const SCEV &); // DO NOT IMPLEMENT
protected:
virtual ~SCEV();
public:
explicit SCEV(unsigned SCEVTy) : SCEVType(SCEVTy), RefCount(0) {}
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;
/// 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();
~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 {
SCEV *S;
SCEVHandle(); // DO NOT IMPLEMENT
public:
SCEVHandle(const SCEV *s) : S(const_cast<SCEV*>(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 SCEV*() const { return S; }
SCEV &operator*() const { return *S; }
SCEV *operator->() const { return S; }
bool operator==(SCEV *RHS) const { return S == RHS; }
bool operator!=(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 SCEV* SimpleType;
static SimpleType getSimplifiedValue(const SCEVHandle &Node) {
return Node;
}
};
template<> struct simplify_type<SCEVHandle>
: public simplify_type<const SCEVHandle> {};
/// 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 {
/// 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;
/// UnknownValue - This SCEV is used to represent unknown trip counts and
/// things.
SCEVHandle UnknownValue;
/// Scalars - This is a cache of the scalars we have analyzed so far.
///
std::map<Value*, SCEVHandle> Scalars;
/// BackedgeTakenCounts - Cache the backedge-taken count of the loops for
/// this function as they are computed.
std::map<const Loop*, SCEVHandle> 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;
/// 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);
/// 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);
/// ComputeBackedgeTakenCount - Compute the number of times the specified
/// loop will iterate.
SCEVHandle 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 UnknownValue.
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
/// UnknownValue.
SCEVHandle HowFarToZero(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
/// UnknownValue.
SCEVHandle HowFarToNonZero(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
/// UnknownValue. isSigned specifies whether the less-than is signed.
SCEVHandle HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
bool isSigned);
/// 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);
/// getSCEVAtScope - Compute the value of the specified expression within
/// the indicated loop (which may be null to indicate in no loop). If the
/// expression cannot be evaluated, return UnknownValue itself.
SCEVHandle getSCEVAtScope(SCEV *S, 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 getTruncateExpr(const SCEVHandle &Op, const Type *Ty);
SCEVHandle getZeroExtendExpr(const SCEVHandle &Op, const Type *Ty);
SCEVHandle getSignExtendExpr(const SCEVHandle &Op, const Type *Ty);
SCEVHandle getAddExpr(std::vector<SCEVHandle> &Ops);
SCEVHandle getAddExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) {
std::vector<SCEVHandle> Ops;
Ops.push_back(LHS);
Ops.push_back(RHS);
return getAddExpr(Ops);
}
SCEVHandle getAddExpr(const SCEVHandle &Op0, const SCEVHandle &Op1,
const SCEVHandle &Op2) {
std::vector<SCEVHandle> Ops;
Ops.push_back(Op0);
Ops.push_back(Op1);
Ops.push_back(Op2);
return getAddExpr(Ops);
}
SCEVHandle getMulExpr(std::vector<SCEVHandle> &Ops);
SCEVHandle getMulExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) {
std::vector<SCEVHandle> 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(std::vector<SCEVHandle> &Operands,
const Loop *L);
SCEVHandle getAddRecExpr(const std::vector<SCEVHandle> &Operands,
const Loop *L) {
std::vector<SCEVHandle> NewOp(Operands);
return getAddRecExpr(NewOp, L);
}
SCEVHandle getSMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
SCEVHandle getSMaxExpr(std::vector<SCEVHandle> Operands);
SCEVHandle getUMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
SCEVHandle getUMaxExpr(std::vector<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);
/// 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.
///
/// If this value is not computable at this scope, a SCEVCouldNotCompute
/// object is returned.
SCEVHandle getSCEVAtScope(Value *V, const Loop *L);
/// isLoopGuardedByCond - Test whether entry to the loop is protected by
/// a conditional between LHS and RHS.
bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
SCEV *LHS, 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);
/// 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);
/// deleteValueFromRecords - This method should be called by the
/// client before it removes a Value from the program, to make sure
/// that no dangling references are left around.
void deleteValueFromRecords(Value *V);
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