Add a new analysis

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12619 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2004-04-02 20:23:17 +00:00
parent 7aa773bc07
commit 53e677abad
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//===- llvm/Analysis/ScalarEvolution.h - Scalar Evolution -------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and 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 <set>
namespace llvm {
class Instruction;
class Type;
class ConstantRange;
class Loop;
class LoopInfo;
class SCEVHandle;
class ScalarEvolutionRewriter;
/// 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
unsigned RefCount;
friend class SCEVHandle;
void addRef() { ++RefCount; }
void dropRef() {
if (--RefCount == 0) {
#if 0
std::cerr << "DELETING: " << this << ": ";
print(std::cerr);
std::cerr << "\n";
#endif
delete this;
}
}
SCEV(const SCEV &); // DO NOT IMPLEMENT
void operator=(const SCEV &); // DO NOT IMPLEMENT
protected:
virtual ~SCEV();
public:
SCEV(unsigned SCEVTy) : SCEVType(SCEVTy), RefCount(0) {}
unsigned getSCEVType() const { return SCEVType; }
/// getValueRange - Return the tightest constant bounds that this value is
/// known to have. This method is only valid on integer SCEV objects.
virtual ConstantRange getValueRange() const;
/// 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;
/// expandCodeFor - Given a rewriter object, expand this SCEV into a closed
/// form expression and return a Value corresponding to the expression in
/// question.
virtual Value *expandCodeFor(ScalarEvolutionRewriter &SER,
Instruction *InsertPt) = 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(std::ostream &OS) const = 0;
/// dump - This method is used for debugging.
///
void dump() const;
};
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();
// 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 Value *expandCodeFor(ScalarEvolutionRewriter &, Instruction *);
virtual void print(std::ostream &OS) const;
/// 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(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 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 {
void *Impl; // ScalarEvolution uses the pimpl pattern
public:
ScalarEvolution() : Impl(0) {}
/// getSCEV - Return a SCEV expression handle for the full generality of the
/// specified expression.
SCEVHandle getSCEV(Value *V) const;
/// 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) const;
/// getIterationCount - If the specified loop has a predictable iteration
/// count, return it, otherwise return a SCEVCouldNotCompute object.
SCEVHandle getIterationCount(const Loop *L) const;
/// hasLoopInvariantIterationCount - Return true if the specified loop has
/// an analyzable loop-invariant iteration count.
bool hasLoopInvariantIterationCount(const Loop *L) const;
/// deleteInstructionFromRecords - This method should be called by the
/// client before it removes an instruction from the program, to make sure
/// that no dangling references are left around.
void deleteInstructionFromRecords(Instruction *I) const;
/// shouldSubstituteIndVar - Return true if we should perform induction
/// variable substitution for this variable. This is a hack because we
/// don't have a strength reduction pass yet. When we do we will promote
/// all vars, because we can strength reduce them later as desired.
bool shouldSubstituteIndVar(const SCEV *S) const;
virtual bool runOnFunction(Function &F);
virtual void releaseMemory();
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual void print(std::ostream &OS) const;
};
/// ScalarEvolutionRewriter - This class uses information about analyze
/// scalars to rewrite expressions in canonical form. This can be used for
/// induction variable substitution, strength reduction, or loop exit value
/// replacement.
///
/// Clients should create an instance of this class when rewriting is needed,
/// and destroying it when finished to allow the release of the associated
/// memory.
class ScalarEvolutionRewriter {
ScalarEvolution &SE;
LoopInfo &LI;
std::map<SCEVHandle, Value*> InsertedExpressions;
std::set<Instruction*> InsertedInstructions;
public:
ScalarEvolutionRewriter(ScalarEvolution &se, LoopInfo &li)
: SE(se), LI(li) {}
/// isInsertedInstruction - Return true if the specified instruction was
/// inserted by the code rewriter. If so, the client should not modify the
/// instruction.
bool isInsertedInstruction(Instruction *I) const {
return InsertedInstructions.count(I);
}
/// GetOrInsertCanonicalInductionVariable - This method returns the
/// canonical induction variable of the specified type for the specified
/// loop (inserts one if there is none). A canonical induction variable
/// starts at zero and steps by one on each iteration.
Value *GetOrInsertCanonicalInductionVariable(const Loop *L, const Type *Ty);
/// ExpandCodeFor - Insert code to directly compute the specified SCEV
/// expression into the program. The inserted code is inserted into the
/// specified block.
///
/// If a particular value sign is required, a type may be specified for the
/// result.
Value *ExpandCodeFor(SCEVHandle SH, Instruction *InsertPt,
const Type *Ty = 0);
};
}
#endif

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