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llvm-mirror/lib/VMCore/ConstantFolding.cpp
Chris Lattner 226ea8166e Add a missing break, which caused a crash in an obscure situation 
llvm-svn: 12825
2004-04-11 01:29:30 +00:00

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//===- ConstantFolding.cpp - LLVM constant folder -------------------------===//
//
// 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.
//
//===----------------------------------------------------------------------===//
//
// This file implements folding of constants for LLVM. This implements the
// (internal) ConstantFolding.h interface, which is used by the
// ConstantExpr::get* methods to automatically fold constants when possible.
//
// The current constant folding implementation is implemented in two pieces: the
// template-based folder for simple primitive constants like ConstantInt, and
// the special case hackery that we use to symbolically evaluate expressions
// that use ConstantExprs.
//
//===----------------------------------------------------------------------===//
#include "ConstantFolding.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include <cmath>
using namespace llvm;
namespace {
struct ConstRules {
ConstRules() {}
// Binary Operators...
virtual Constant *add(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *sub(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *mul(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *div(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *rem(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *op_and(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *op_or (const Constant *V1, const Constant *V2) const = 0;
virtual Constant *op_xor(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *shl(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *shr(const Constant *V1, const Constant *V2) const = 0;
virtual Constant *lessthan(const Constant *V1, const Constant *V2) const =0;
virtual Constant *equalto(const Constant *V1, const Constant *V2) const = 0;
// Casting operators.
virtual Constant *castToBool (const Constant *V) const = 0;
virtual Constant *castToSByte (const Constant *V) const = 0;
virtual Constant *castToUByte (const Constant *V) const = 0;
virtual Constant *castToShort (const Constant *V) const = 0;
virtual Constant *castToUShort(const Constant *V) const = 0;
virtual Constant *castToInt (const Constant *V) const = 0;
virtual Constant *castToUInt (const Constant *V) const = 0;
virtual Constant *castToLong (const Constant *V) const = 0;
virtual Constant *castToULong (const Constant *V) const = 0;
virtual Constant *castToFloat (const Constant *V) const = 0;
virtual Constant *castToDouble(const Constant *V) const = 0;
virtual Constant *castToPointer(const Constant *V,
const PointerType *Ty) const = 0;
// ConstRules::get - Return an instance of ConstRules for the specified
// constant operands.
//
static ConstRules &get(const Constant *V1, const Constant *V2);
private:
ConstRules(const ConstRules &); // Do not implement
ConstRules &operator=(const ConstRules &); // Do not implement
};
}
//===----------------------------------------------------------------------===//
// TemplateRules Class
//===----------------------------------------------------------------------===//
//
// TemplateRules - Implement a subclass of ConstRules that provides all
// operations as noops. All other rules classes inherit from this class so
// that if functionality is needed in the future, it can simply be added here
// and to ConstRules without changing anything else...
//
// This class also provides subclasses with typesafe implementations of methods
// so that don't have to do type casting.
//
template<class ArgType, class SubClassName>
class TemplateRules : public ConstRules {
//===--------------------------------------------------------------------===//
// Redirecting functions that cast to the appropriate types
//===--------------------------------------------------------------------===//
virtual Constant *add(const Constant *V1, const Constant *V2) const {
return SubClassName::Add((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *sub(const Constant *V1, const Constant *V2) const {
return SubClassName::Sub((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *mul(const Constant *V1, const Constant *V2) const {
return SubClassName::Mul((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *div(const Constant *V1, const Constant *V2) const {
return SubClassName::Div((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *rem(const Constant *V1, const Constant *V2) const {
return SubClassName::Rem((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *op_and(const Constant *V1, const Constant *V2) const {
return SubClassName::And((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *op_or(const Constant *V1, const Constant *V2) const {
return SubClassName::Or((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *op_xor(const Constant *V1, const Constant *V2) const {
return SubClassName::Xor((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *shl(const Constant *V1, const Constant *V2) const {
return SubClassName::Shl((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *shr(const Constant *V1, const Constant *V2) const {
return SubClassName::Shr((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *lessthan(const Constant *V1, const Constant *V2) const {
return SubClassName::LessThan((const ArgType *)V1, (const ArgType *)V2);
}
virtual Constant *equalto(const Constant *V1, const Constant *V2) const {
return SubClassName::EqualTo((const ArgType *)V1, (const ArgType *)V2);
}
// Casting operators. ick
virtual Constant *castToBool(const Constant *V) const {
return SubClassName::CastToBool((const ArgType*)V);
}
virtual Constant *castToSByte(const Constant *V) const {
return SubClassName::CastToSByte((const ArgType*)V);
}
virtual Constant *castToUByte(const Constant *V) const {
return SubClassName::CastToUByte((const ArgType*)V);
}
virtual Constant *castToShort(const Constant *V) const {
return SubClassName::CastToShort((const ArgType*)V);
}
virtual Constant *castToUShort(const Constant *V) const {
return SubClassName::CastToUShort((const ArgType*)V);
}
virtual Constant *castToInt(const Constant *V) const {
return SubClassName::CastToInt((const ArgType*)V);
}
virtual Constant *castToUInt(const Constant *V) const {
return SubClassName::CastToUInt((const ArgType*)V);
}
virtual Constant *castToLong(const Constant *V) const {
return SubClassName::CastToLong((const ArgType*)V);
}
virtual Constant *castToULong(const Constant *V) const {
return SubClassName::CastToULong((const ArgType*)V);
}
virtual Constant *castToFloat(const Constant *V) const {
return SubClassName::CastToFloat((const ArgType*)V);
}
virtual Constant *castToDouble(const Constant *V) const {
return SubClassName::CastToDouble((const ArgType*)V);
}
virtual Constant *castToPointer(const Constant *V,
const PointerType *Ty) const {
return SubClassName::CastToPointer((const ArgType*)V, Ty);
}
//===--------------------------------------------------------------------===//
// Default "noop" implementations
//===--------------------------------------------------------------------===//
static Constant *Add(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *Sub(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *Mul(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *Div(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *Rem(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *And(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *Or (const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *Xor(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *Shl(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *Shr(const ArgType *V1, const ArgType *V2) { return 0; }
static Constant *LessThan(const ArgType *V1, const ArgType *V2) {
return 0;
}
static Constant *EqualTo(const ArgType *V1, const ArgType *V2) {
return 0;
}
// Casting operators. ick
static Constant *CastToBool (const Constant *V) { return 0; }
static Constant *CastToSByte (const Constant *V) { return 0; }
static Constant *CastToUByte (const Constant *V) { return 0; }
static Constant *CastToShort (const Constant *V) { return 0; }
static Constant *CastToUShort(const Constant *V) { return 0; }
static Constant *CastToInt (const Constant *V) { return 0; }
static Constant *CastToUInt (const Constant *V) { return 0; }
static Constant *CastToLong (const Constant *V) { return 0; }
static Constant *CastToULong (const Constant *V) { return 0; }
static Constant *CastToFloat (const Constant *V) { return 0; }
static Constant *CastToDouble(const Constant *V) { return 0; }
static Constant *CastToPointer(const Constant *,
const PointerType *) {return 0;}
};
//===----------------------------------------------------------------------===//
// EmptyRules Class
//===----------------------------------------------------------------------===//
//
// EmptyRules provides a concrete base class of ConstRules that does nothing
//
struct EmptyRules : public TemplateRules<Constant, EmptyRules> {
static Constant *EqualTo(const Constant *V1, const Constant *V2) {
if (V1 == V2) return ConstantBool::True;
return 0;
}
};
//===----------------------------------------------------------------------===//
// BoolRules Class
//===----------------------------------------------------------------------===//
//
// BoolRules provides a concrete base class of ConstRules for the 'bool' type.
//
struct BoolRules : public TemplateRules<ConstantBool, BoolRules> {
static Constant *LessThan(const ConstantBool *V1, const ConstantBool *V2){
return ConstantBool::get(V1->getValue() < V2->getValue());
}
static Constant *EqualTo(const Constant *V1, const Constant *V2) {
return ConstantBool::get(V1 == V2);
}
static Constant *And(const ConstantBool *V1, const ConstantBool *V2) {
return ConstantBool::get(V1->getValue() & V2->getValue());
}
static Constant *Or(const ConstantBool *V1, const ConstantBool *V2) {
return ConstantBool::get(V1->getValue() | V2->getValue());
}
static Constant *Xor(const ConstantBool *V1, const ConstantBool *V2) {
return ConstantBool::get(V1->getValue() ^ V2->getValue());
}
// Casting operators. ick
#define DEF_CAST(TYPE, CLASS, CTYPE) \
static Constant *CastTo##TYPE (const ConstantBool *V) { \
return CLASS::get(Type::TYPE##Ty, (CTYPE)(bool)V->getValue()); \
}
DEF_CAST(Bool , ConstantBool, bool)
DEF_CAST(SByte , ConstantSInt, signed char)
DEF_CAST(UByte , ConstantUInt, unsigned char)
DEF_CAST(Short , ConstantSInt, signed short)
DEF_CAST(UShort, ConstantUInt, unsigned short)
DEF_CAST(Int , ConstantSInt, signed int)
DEF_CAST(UInt , ConstantUInt, unsigned int)
DEF_CAST(Long , ConstantSInt, int64_t)
DEF_CAST(ULong , ConstantUInt, uint64_t)
DEF_CAST(Float , ConstantFP , float)
DEF_CAST(Double, ConstantFP , double)
#undef DEF_CAST
};
//===----------------------------------------------------------------------===//
// NullPointerRules Class
//===----------------------------------------------------------------------===//
//
// NullPointerRules provides a concrete base class of ConstRules for null
// pointers.
//
struct NullPointerRules : public TemplateRules<ConstantPointerNull,
NullPointerRules> {
static Constant *EqualTo(const Constant *V1, const Constant *V2) {
return ConstantBool::True; // Null pointers are always equal
}
static Constant *CastToBool(const Constant *V) {
return ConstantBool::False;
}
static Constant *CastToSByte (const Constant *V) {
return ConstantSInt::get(Type::SByteTy, 0);
}
static Constant *CastToUByte (const Constant *V) {
return ConstantUInt::get(Type::UByteTy, 0);
}
static Constant *CastToShort (const Constant *V) {
return ConstantSInt::get(Type::ShortTy, 0);
}
static Constant *CastToUShort(const Constant *V) {
return ConstantUInt::get(Type::UShortTy, 0);
}
static Constant *CastToInt (const Constant *V) {
return ConstantSInt::get(Type::IntTy, 0);
}
static Constant *CastToUInt (const Constant *V) {
return ConstantUInt::get(Type::UIntTy, 0);
}
static Constant *CastToLong (const Constant *V) {
return ConstantSInt::get(Type::LongTy, 0);
}
static Constant *CastToULong (const Constant *V) {
return ConstantUInt::get(Type::ULongTy, 0);
}
static Constant *CastToFloat (const Constant *V) {
return ConstantFP::get(Type::FloatTy, 0);
}
static Constant *CastToDouble(const Constant *V) {
return ConstantFP::get(Type::DoubleTy, 0);
}
static Constant *CastToPointer(const ConstantPointerNull *V,
const PointerType *PTy) {
return ConstantPointerNull::get(PTy);
}
};
//===----------------------------------------------------------------------===//
// DirectRules Class
//===----------------------------------------------------------------------===//
//
// DirectRules provides a concrete base classes of ConstRules for a variety of
// different types. This allows the C++ compiler to automatically generate our
// constant handling operations in a typesafe and accurate manner.
//
template<class ConstantClass, class BuiltinType, Type **Ty, class SuperClass>
struct DirectRules : public TemplateRules<ConstantClass, SuperClass> {
static Constant *Add(const ConstantClass *V1, const ConstantClass *V2) {
BuiltinType R = (BuiltinType)V1->getValue() + (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *Sub(const ConstantClass *V1, const ConstantClass *V2) {
BuiltinType R = (BuiltinType)V1->getValue() - (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *Mul(const ConstantClass *V1, const ConstantClass *V2) {
BuiltinType R = (BuiltinType)V1->getValue() * (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *Div(const ConstantClass *V1, const ConstantClass *V2) {
if (V2->isNullValue()) return 0;
BuiltinType R = (BuiltinType)V1->getValue() / (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *LessThan(const ConstantClass *V1, const ConstantClass *V2) {
bool R = (BuiltinType)V1->getValue() < (BuiltinType)V2->getValue();
return ConstantBool::get(R);
}
static Constant *EqualTo(const ConstantClass *V1, const ConstantClass *V2) {
bool R = (BuiltinType)V1->getValue() == (BuiltinType)V2->getValue();
return ConstantBool::get(R);
}
static Constant *CastToPointer(const ConstantClass *V,
const PointerType *PTy) {
if (V->isNullValue()) // Is it a FP or Integral null value?
return ConstantPointerNull::get(PTy);
return 0; // Can't const prop other types of pointers
}
// Casting operators. ick
#define DEF_CAST(TYPE, CLASS, CTYPE) \
static Constant *CastTo##TYPE (const ConstantClass *V) { \
return CLASS::get(Type::TYPE##Ty, (CTYPE)(BuiltinType)V->getValue()); \
}
DEF_CAST(Bool , ConstantBool, bool)
DEF_CAST(SByte , ConstantSInt, signed char)
DEF_CAST(UByte , ConstantUInt, unsigned char)
DEF_CAST(Short , ConstantSInt, signed short)
DEF_CAST(UShort, ConstantUInt, unsigned short)
DEF_CAST(Int , ConstantSInt, signed int)
DEF_CAST(UInt , ConstantUInt, unsigned int)
DEF_CAST(Long , ConstantSInt, int64_t)
DEF_CAST(ULong , ConstantUInt, uint64_t)
DEF_CAST(Float , ConstantFP , float)
DEF_CAST(Double, ConstantFP , double)
#undef DEF_CAST
};
//===----------------------------------------------------------------------===//
// DirectIntRules Class
//===----------------------------------------------------------------------===//
//
// DirectIntRules provides implementations of functions that are valid on
// integer types, but not all types in general.
//
template <class ConstantClass, class BuiltinType, Type **Ty>
struct DirectIntRules
: public DirectRules<ConstantClass, BuiltinType, Ty,
DirectIntRules<ConstantClass, BuiltinType, Ty> > {
static Constant *Div(const ConstantClass *V1, const ConstantClass *V2) {
if (V2->isNullValue()) return 0;
if (V2->isAllOnesValue() && // MIN_INT / -1
(BuiltinType)V1->getValue() == -(BuiltinType)V1->getValue())
return 0;
BuiltinType R = (BuiltinType)V1->getValue() / (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *Rem(const ConstantClass *V1,
const ConstantClass *V2) {
if (V2->isNullValue()) return 0; // X / 0
if (V2->isAllOnesValue() && // MIN_INT / -1
(BuiltinType)V1->getValue() == -(BuiltinType)V1->getValue())
return 0;
BuiltinType R = (BuiltinType)V1->getValue() % (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *And(const ConstantClass *V1, const ConstantClass *V2) {
BuiltinType R = (BuiltinType)V1->getValue() & (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *Or(const ConstantClass *V1, const ConstantClass *V2) {
BuiltinType R = (BuiltinType)V1->getValue() | (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *Xor(const ConstantClass *V1, const ConstantClass *V2) {
BuiltinType R = (BuiltinType)V1->getValue() ^ (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *Shl(const ConstantClass *V1, const ConstantClass *V2) {
BuiltinType R = (BuiltinType)V1->getValue() << (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
static Constant *Shr(const ConstantClass *V1, const ConstantClass *V2) {
BuiltinType R = (BuiltinType)V1->getValue() >> (BuiltinType)V2->getValue();
return ConstantClass::get(*Ty, R);
}
};
//===----------------------------------------------------------------------===//
// DirectFPRules Class
//===----------------------------------------------------------------------===//
//
/// DirectFPRules provides implementations of functions that are valid on
/// floating point types, but not all types in general.
///
template <class ConstantClass, class BuiltinType, Type **Ty>
struct DirectFPRules
: public DirectRules<ConstantClass, BuiltinType, Ty,
DirectFPRules<ConstantClass, BuiltinType, Ty> > {
static Constant *Rem(const ConstantClass *V1, const ConstantClass *V2) {
if (V2->isNullValue()) return 0;
BuiltinType Result = std::fmod((BuiltinType)V1->getValue(),
(BuiltinType)V2->getValue());
return ConstantClass::get(*Ty, Result);
}
};
/// ConstRules::get - This method returns the constant rules implementation that
/// implements the semantics of the two specified constants.
ConstRules &ConstRules::get(const Constant *V1, const Constant *V2) {
static EmptyRules EmptyR;
static BoolRules BoolR;
static NullPointerRules NullPointerR;
static DirectIntRules<ConstantSInt, signed char , &Type::SByteTy> SByteR;
static DirectIntRules<ConstantUInt, unsigned char , &Type::UByteTy> UByteR;
static DirectIntRules<ConstantSInt, signed short, &Type::ShortTy> ShortR;
static DirectIntRules<ConstantUInt, unsigned short, &Type::UShortTy> UShortR;
static DirectIntRules<ConstantSInt, signed int , &Type::IntTy> IntR;
static DirectIntRules<ConstantUInt, unsigned int , &Type::UIntTy> UIntR;
static DirectIntRules<ConstantSInt, int64_t , &Type::LongTy> LongR;
static DirectIntRules<ConstantUInt, uint64_t , &Type::ULongTy> ULongR;
static DirectFPRules <ConstantFP , float , &Type::FloatTy> FloatR;
static DirectFPRules <ConstantFP , double , &Type::DoubleTy> DoubleR;
if (isa<ConstantExpr>(V1) || isa<ConstantExpr>(V2) ||
isa<ConstantPointerRef>(V1) || isa<ConstantPointerRef>(V2))
return EmptyR;
switch (V1->getType()->getPrimitiveID()) {
default: assert(0 && "Unknown value type for constant folding!");
case Type::BoolTyID: return BoolR;
case Type::PointerTyID: return NullPointerR;
case Type::SByteTyID: return SByteR;
case Type::UByteTyID: return UByteR;
case Type::ShortTyID: return ShortR;
case Type::UShortTyID: return UShortR;
case Type::IntTyID: return IntR;
case Type::UIntTyID: return UIntR;
case Type::LongTyID: return LongR;
case Type::ULongTyID: return ULongR;
case Type::FloatTyID: return FloatR;
case Type::DoubleTyID: return DoubleR;
}
}
//===----------------------------------------------------------------------===//
// ConstantFold*Instruction Implementations
//===----------------------------------------------------------------------===//
//
// These methods contain the special case hackery required to symbolically
// evaluate some constant expression cases, and use the ConstantRules class to
// evaluate normal constants.
//
static unsigned getSize(const Type *Ty) {
unsigned S = Ty->getPrimitiveSize();
return S ? S : 8; // Treat pointers at 8 bytes
}
Constant *llvm::ConstantFoldCastInstruction(const Constant *V,
const Type *DestTy) {
if (V->getType() == DestTy) return (Constant*)V;
// Cast of a global address to boolean is always true.
if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
if (DestTy == Type::BoolTy)
// FIXME: When we support 'external weak' references, we have to prevent
// this transformation from happening. In the meantime we avoid folding
// any cast of an external symbol.
if (!CPR->getValue()->isExternal())
return ConstantBool::True;
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
if (CE->getOpcode() == Instruction::Cast) {
Constant *Op = const_cast<Constant*>(CE->getOperand(0));
// Try to not produce a cast of a cast, which is almost always redundant.
if (!Op->getType()->isFloatingPoint() &&
!CE->getType()->isFloatingPoint() &&
!DestTy->getType()->isFloatingPoint()) {
unsigned S1 = getSize(Op->getType()), S2 = getSize(CE->getType());
unsigned S3 = getSize(DestTy);
if (Op->getType() == DestTy && S3 >= S2)
return Op;
if (S1 >= S2 && S2 >= S3)
return ConstantExpr::getCast(Op, DestTy);
if (S1 <= S2 && S2 >= S3 && S1 <= S3)
return ConstantExpr::getCast(Op, DestTy);
}
} else if (CE->getOpcode() == Instruction::GetElementPtr) {
// If all of the indexes in the GEP are null values, there is no pointer
// adjustment going on. We might as well cast the source pointer.
bool isAllNull = true;
for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
if (!CE->getOperand(i)->isNullValue()) {
isAllNull = false;
break;
}
if (isAllNull)
return ConstantExpr::getCast(CE->getOperand(0), DestTy);
}
ConstRules &Rules = ConstRules::get(V, V);
switch (DestTy->getPrimitiveID()) {
case Type::BoolTyID: return Rules.castToBool(V);
case Type::UByteTyID: return Rules.castToUByte(V);
case Type::SByteTyID: return Rules.castToSByte(V);
case Type::UShortTyID: return Rules.castToUShort(V);
case Type::ShortTyID: return Rules.castToShort(V);
case Type::UIntTyID: return Rules.castToUInt(V);
case Type::IntTyID: return Rules.castToInt(V);
case Type::ULongTyID: return Rules.castToULong(V);
case Type::LongTyID: return Rules.castToLong(V);
case Type::FloatTyID: return Rules.castToFloat(V);
case Type::DoubleTyID: return Rules.castToDouble(V);
case Type::PointerTyID:
return Rules.castToPointer(V, cast<PointerType>(DestTy));
default: return 0;
}
}
Constant *llvm::ConstantFoldSelectInstruction(const Constant *Cond,
const Constant *V1,
const Constant *V2) {
if (Cond == ConstantBool::True)
return const_cast<Constant*>(V1);
else if (Cond == ConstantBool::False)
return const_cast<Constant*>(V2);
return 0;
}
/// IdxCompare - Compare the two constants as though they were getelementptr
/// indices. This allows coersion of the types to be the same thing.
///
/// If the two constants are the "same" (after coersion), return 0. If the
/// first is less than the second, return -1, if the second is less than the
/// first, return 1. If the constants are not integral, return -2.
///
static int IdxCompare(Constant *C1, Constant *C2) {
if (C1 == C2) return 0;
// Ok, we found a different index. Are either of the operands
// ConstantExprs? If so, we can't do anything with them.
if (!isa<ConstantInt>(C1) || !isa<ConstantInt>(C2))
return -2; // don't know!
// Ok, we have two differing integer indices. Sign extend them to be the same
// type. Long is always big enough, so we use it.
C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
if (C1 == C2) return 0; // Are they just differing types?
// If they are really different, now that they are the same type, then we
// found a difference!
if (cast<ConstantSInt>(C1)->getValue() < cast<ConstantSInt>(C2)->getValue())
return -1;
else
return 1;
}
/// evaluateRelation - This function determines if there is anything we can
/// decide about the two constants provided. This doesn't need to handle simple
/// things like integer comparisons, but should instead handle ConstantExpr's
/// and ConstantPointerRef's. If we can determine that the two constants have a
/// particular relation to each other, we should return the corresponding SetCC
/// code, otherwise return Instruction::BinaryOpsEnd.
///
/// To simplify this code we canonicalize the relation so that the first
/// operand is always the most "complex" of the two. We consider simple
/// constants (like ConstantInt) to be the simplest, followed by
/// ConstantPointerRef's, followed by ConstantExpr's (the most complex).
///
static Instruction::BinaryOps evaluateRelation(const Constant *V1,
const Constant *V2) {
assert(V1->getType() == V2->getType() &&
"Cannot compare different types of values!");
if (V1 == V2) return Instruction::SetEQ;
if (!isa<ConstantExpr>(V1) && !isa<ConstantPointerRef>(V1)) {
// If the first operand is simple, swap operands.
assert((isa<ConstantPointerRef>(V2) || isa<ConstantExpr>(V2)) &&
"Simple cases should have been handled by caller!");
Instruction::BinaryOps SwappedRelation = evaluateRelation(V2, V1);
if (SwappedRelation != Instruction::BinaryOpsEnd)
return SetCondInst::getSwappedCondition(SwappedRelation);
} else if (const ConstantPointerRef *CPR1 = dyn_cast<ConstantPointerRef>(V1)){
if (isa<ConstantExpr>(V2)) { // Swap as necessary.
Instruction::BinaryOps SwappedRelation = evaluateRelation(V2, V1);
if (SwappedRelation != Instruction::BinaryOpsEnd)
return SetCondInst::getSwappedCondition(SwappedRelation);
else
return Instruction::BinaryOpsEnd;
}
// Now we know that the RHS is a ConstantPointerRef or simple constant,
// which (since the types must match) means that it's a ConstantPointerNull.
if (const ConstantPointerRef *CPR2 = dyn_cast<ConstantPointerRef>(V2)) {
assert(CPR1->getValue() != CPR2->getValue() &&
"CPRs for the same value exist at different addresses??");
// FIXME: If both globals are external weak, they might both be null!
return Instruction::SetNE;
} else {
assert(isa<ConstantPointerNull>(V2) && "Canonicalization guarantee!");
// Global can never be null. FIXME: if we implement external weak
// linkage, this is not necessarily true!
return Instruction::SetNE;
}
} else {
// Ok, the LHS is known to be a constantexpr. The RHS can be any of a
// constantexpr, a CPR, or a simple constant.
const ConstantExpr *CE1 = cast<ConstantExpr>(V1);
Constant *CE1Op0 = CE1->getOperand(0);
switch (CE1->getOpcode()) {
case Instruction::Cast:
// If the cast is not actually changing bits, and the second operand is a
// null pointer, do the comparison with the pre-casted value.
if (V2->isNullValue() &&
CE1->getType()->isLosslesslyConvertibleTo(CE1Op0->getType()))
return evaluateRelation(CE1Op0,
Constant::getNullValue(CE1Op0->getType()));
break;
case Instruction::GetElementPtr:
// Ok, since this is a getelementptr, we know that the constant has a
// pointer type. Check the various cases.
if (isa<ConstantPointerNull>(V2)) {
// If we are comparing a GEP to a null pointer, check to see if the base
// of the GEP equals the null pointer.
if (isa<ConstantPointerRef>(CE1Op0)) {
// FIXME: this is not true when we have external weak references!
// No offset can go from a global to a null pointer.
return Instruction::SetGT;
} else if (isa<ConstantPointerNull>(CE1Op0)) {
// If we are indexing from a null pointer, check to see if we have any
// non-zero indices.
for (unsigned i = 1, e = CE1->getNumOperands(); i != e; ++i)
if (!CE1->getOperand(i)->isNullValue())
// Offsetting from null, must not be equal.
return Instruction::SetGT;
// Only zero indexes from null, must still be zero.
return Instruction::SetEQ;
}
// Otherwise, we can't really say if the first operand is null or not.
} else if (const ConstantPointerRef *CPR2 =
dyn_cast<ConstantPointerRef>(V2)) {
if (isa<ConstantPointerNull>(CE1Op0)) {
// FIXME: This is not true with external weak references.
return Instruction::SetLT;
} else if (const ConstantPointerRef *CPR1 =
dyn_cast<ConstantPointerRef>(CE1Op0)) {
if (CPR1 == CPR2) {
// If this is a getelementptr of the same global, then it must be
// different. Because the types must match, the getelementptr could
// only have at most one index, and because we fold getelementptr's
// with a single zero index, it must be nonzero.
assert(CE1->getNumOperands() == 2 &&
!CE1->getOperand(1)->isNullValue() &&
"Suprising getelementptr!");
return Instruction::SetGT;
} else {
// If they are different globals, we don't know what the value is,
// but they can't be equal.
return Instruction::SetNE;
}
}
} else {
const ConstantExpr *CE2 = cast<ConstantExpr>(V2);
const Constant *CE2Op0 = CE2->getOperand(0);
// There are MANY other foldings that we could perform here. They will
// probably be added on demand, as they seem needed.
switch (CE2->getOpcode()) {
default: break;
case Instruction::GetElementPtr:
// By far the most common case to handle is when the base pointers are
// obviously to the same or different globals.
if (isa<ConstantPointerRef>(CE1Op0) &&
isa<ConstantPointerRef>(CE2Op0)) {
if (CE1Op0 != CE2Op0) // Don't know relative ordering, but not equal
return Instruction::SetNE;
// Ok, we know that both getelementptr instructions are based on the
// same global. From this, we can precisely determine the relative
// ordering of the resultant pointers.
unsigned i = 1;
// Compare all of the operands the GEP's have in common.
for (;i != CE1->getNumOperands() && i != CE2->getNumOperands(); ++i)
switch (IdxCompare(CE1->getOperand(i), CE2->getOperand(i))) {
case -1: return Instruction::SetLT;
case 1: return Instruction::SetGT;
case -2: return Instruction::BinaryOpsEnd;
}
// Ok, we ran out of things they have in common. If any leftovers
// are non-zero then we have a difference, otherwise we are equal.
for (; i < CE1->getNumOperands(); ++i)
if (!CE1->getOperand(i)->isNullValue())
return Instruction::SetGT;
for (; i < CE2->getNumOperands(); ++i)
if (!CE2->getOperand(i)->isNullValue())
return Instruction::SetLT;
return Instruction::SetEQ;
}
}
}
default:
break;
}
}
return Instruction::BinaryOpsEnd;
}
Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
const Constant *V1,
const Constant *V2) {
Constant *C = 0;
switch (Opcode) {
default: break;
case Instruction::Add: C = ConstRules::get(V1, V2).add(V1, V2); break;
case Instruction::Sub: C = ConstRules::get(V1, V2).sub(V1, V2); break;
case Instruction::Mul: C = ConstRules::get(V1, V2).mul(V1, V2); break;
case Instruction::Div: C = ConstRules::get(V1, V2).div(V1, V2); break;
case Instruction::Rem: C = ConstRules::get(V1, V2).rem(V1, V2); break;
case Instruction::And: C = ConstRules::get(V1, V2).op_and(V1, V2); break;
case Instruction::Or: C = ConstRules::get(V1, V2).op_or (V1, V2); break;
case Instruction::Xor: C = ConstRules::get(V1, V2).op_xor(V1, V2); break;
case Instruction::Shl: C = ConstRules::get(V1, V2).shl(V1, V2); break;
case Instruction::Shr: C = ConstRules::get(V1, V2).shr(V1, V2); break;
case Instruction::SetEQ: C = ConstRules::get(V1, V2).equalto(V1, V2); break;
case Instruction::SetLT: C = ConstRules::get(V1, V2).lessthan(V1, V2);break;
case Instruction::SetGT: C = ConstRules::get(V1, V2).lessthan(V2, V1);break;
case Instruction::SetNE: // V1 != V2 === !(V1 == V2)
C = ConstRules::get(V1, V2).equalto(V1, V2);
if (C) return ConstantExpr::get(Instruction::Xor, C, ConstantBool::True);
break;
case Instruction::SetLE: // V1 <= V2 === !(V2 < V1)
C = ConstRules::get(V1, V2).lessthan(V2, V1);
if (C) return ConstantExpr::get(Instruction::Xor, C, ConstantBool::True);
break;
case Instruction::SetGE: // V1 >= V2 === !(V1 < V2)
C = ConstRules::get(V1, V2).lessthan(V1, V2);
if (C) return ConstantExpr::get(Instruction::Xor, C, ConstantBool::True);
break;
}
// If we successfully folded the expression, return it now.
if (C) return C;
if (SetCondInst::isRelational(Opcode))
switch (evaluateRelation(V1, V2)) {
default: assert(0 && "Unknown relational!");
case Instruction::BinaryOpsEnd:
break; // Couldn't determine anything about these constants.
case Instruction::SetEQ: // We know the constants are equal!
// If we know the constants are equal, we can decide the result of this
// computation precisely.
return ConstantBool::get(Opcode == Instruction::SetEQ ||
Opcode == Instruction::SetLE ||
Opcode == Instruction::SetGE);
case Instruction::SetLT:
// If we know that V1 < V2, we can decide the result of this computation
// precisely.
return ConstantBool::get(Opcode == Instruction::SetLT ||
Opcode == Instruction::SetNE ||
Opcode == Instruction::SetLE);
case Instruction::SetGT:
// If we know that V1 > V2, we can decide the result of this computation
// precisely.
return ConstantBool::get(Opcode == Instruction::SetGT ||
Opcode == Instruction::SetNE ||
Opcode == Instruction::SetGE);
case Instruction::SetLE:
// If we know that V1 <= V2, we can only partially decide this relation.
if (Opcode == Instruction::SetGT) return ConstantBool::False;
if (Opcode == Instruction::SetLT) return ConstantBool::True;
break;
case Instruction::SetGE:
// If we know that V1 >= V2, we can only partially decide this relation.
if (Opcode == Instruction::SetLT) return ConstantBool::False;
if (Opcode == Instruction::SetGT) return ConstantBool::True;
break;
case Instruction::SetNE:
// If we know that V1 != V2, we can only partially decide this relation.
if (Opcode == Instruction::SetEQ) return ConstantBool::False;
if (Opcode == Instruction::SetNE) return ConstantBool::True;
break;
}
if (const ConstantExpr *CE1 = dyn_cast<ConstantExpr>(V1)) {
if (const ConstantExpr *CE2 = dyn_cast<ConstantExpr>(V2)) {
// There are many possible foldings we could do here. We should probably
// at least fold add of a pointer with an integer into the appropriate
// getelementptr. This will improve alias analysis a bit.
} else {
// Just implement a couple of simple identities.
switch (Opcode) {
case Instruction::Add:
if (V2->isNullValue()) return const_cast<Constant*>(V1); // X + 0 == X
break;
case Instruction::Sub:
if (V2->isNullValue()) return const_cast<Constant*>(V1); // X - 0 == X
break;
case Instruction::Mul:
if (V2->isNullValue()) return const_cast<Constant*>(V2); // X * 0 == 0
if (const ConstantInt *CI = dyn_cast<ConstantInt>(V2))
if (CI->getRawValue() == 1)
return const_cast<Constant*>(V1); // X * 1 == X
break;
case Instruction::Div:
if (const ConstantInt *CI = dyn_cast<ConstantInt>(V2))
if (CI->getRawValue() == 1)
return const_cast<Constant*>(V1); // X / 1 == X
break;
case Instruction::Rem:
if (const ConstantInt *CI = dyn_cast<ConstantInt>(V2))
if (CI->getRawValue() == 1)
return Constant::getNullValue(CI->getType()); // X % 1 == 0
break;
case Instruction::And:
if (cast<ConstantIntegral>(V2)->isAllOnesValue())
return const_cast<Constant*>(V1); // X & -1 == X
if (V2->isNullValue()) return const_cast<Constant*>(V2); // X & 0 == 0
if (CE1->getOpcode() == Instruction::Cast &&
isa<ConstantPointerRef>(CE1->getOperand(0))) {
ConstantPointerRef *CPR =cast<ConstantPointerRef>(CE1->getOperand(0));
// Functions are at least 4-byte aligned. If and'ing the address of a
// function with a constant < 4, fold it to zero.
if (const ConstantInt *CI = dyn_cast<ConstantInt>(V2))
if (CI->getRawValue() < 4 && isa<Function>(CPR->getValue()))
return Constant::getNullValue(CI->getType());
}
break;
case Instruction::Or:
if (V2->isNullValue()) return const_cast<Constant*>(V1); // X | 0 == X
if (cast<ConstantIntegral>(V2)->isAllOnesValue())
return const_cast<Constant*>(V2); // X | -1 == -1
break;
case Instruction::Xor:
if (V2->isNullValue()) return const_cast<Constant*>(V1); // X ^ 0 == X
break;
}
}
} else if (const ConstantExpr *CE2 = dyn_cast<ConstantExpr>(V2)) {
// If V2 is a constant expr and V1 isn't, flop them around and fold the
// other way if possible.
switch (Opcode) {
case Instruction::Add:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::SetEQ:
case Instruction::SetNE:
// No change of opcode required.
return ConstantFoldBinaryInstruction(Opcode, V2, V1);
case Instruction::SetLT:
case Instruction::SetGT:
case Instruction::SetLE:
case Instruction::SetGE:
// Change the opcode as necessary to swap the operands.
Opcode = SetCondInst::getSwappedCondition((Instruction::BinaryOps)Opcode);
return ConstantFoldBinaryInstruction(Opcode, V2, V1);
case Instruction::Shl:
case Instruction::Shr:
case Instruction::Sub:
case Instruction::Div:
case Instruction::Rem:
default: // These instructions cannot be flopped around.
break;
}
}
return 0;
}
Constant *llvm::ConstantFoldGetElementPtr(const Constant *C,
const std::vector<Constant*> &IdxList) {
if (IdxList.size() == 0 ||
(IdxList.size() == 1 && IdxList[0]->isNullValue()))
return const_cast<Constant*>(C);
if (C->isNullValue()) {
bool isNull = true;
for (unsigned i = 0, e = IdxList.size(); i != e; ++i)
if (!IdxList[i]->isNullValue()) {
isNull = false;
break;
}
if (isNull) {
std::vector<Value*> VIdxList(IdxList.begin(), IdxList.end());
const Type *Ty = GetElementPtrInst::getIndexedType(C->getType(), VIdxList,
true);
assert(Ty != 0 && "Invalid indices for GEP!");
return ConstantPointerNull::get(PointerType::get(Ty));
}
}
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(const_cast<Constant*>(C))) {
// Combine Indices - If the source pointer to this getelementptr instruction
// is a getelementptr instruction, combine the indices of the two
// getelementptr instructions into a single instruction.
//
if (CE->getOpcode() == Instruction::GetElementPtr) {
const Type *LastTy = 0;
for (gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
I != E; ++I)
LastTy = *I;
if ((LastTy && isa<ArrayType>(LastTy)) || IdxList[0]->isNullValue()) {
std::vector<Constant*> NewIndices;
NewIndices.reserve(IdxList.size() + CE->getNumOperands());
for (unsigned i = 1, e = CE->getNumOperands()-1; i != e; ++i)
NewIndices.push_back(cast<Constant>(CE->getOperand(i)));
// Add the last index of the source with the first index of the new GEP.
// Make sure to handle the case when they are actually different types.
Constant *Combined = CE->getOperand(CE->getNumOperands()-1);
if (!IdxList[0]->isNullValue()) // Otherwise it must be an array
Combined =
ConstantExpr::get(Instruction::Add,
ConstantExpr::getCast(IdxList[0], Type::LongTy),
ConstantExpr::getCast(Combined, Type::LongTy));
NewIndices.push_back(Combined);
NewIndices.insert(NewIndices.end(), IdxList.begin()+1, IdxList.end());
return ConstantExpr::getGetElementPtr(CE->getOperand(0), NewIndices);
}
}
// Implement folding of:
// int* getelementptr ([2 x int]* cast ([3 x int]* %X to [2 x int]*),
// long 0, long 0)
// To: int* getelementptr ([3 x int]* %X, long 0, long 0)
//
if (CE->getOpcode() == Instruction::Cast && IdxList.size() > 1 &&
IdxList[0]->isNullValue())
if (const PointerType *SPT =
dyn_cast<PointerType>(CE->getOperand(0)->getType()))
if (const ArrayType *SAT = dyn_cast<ArrayType>(SPT->getElementType()))
if (const ArrayType *CAT =
dyn_cast<ArrayType>(cast<PointerType>(C->getType())->getElementType()))
if (CAT->getElementType() == SAT->getElementType())
return ConstantExpr::getGetElementPtr(
(Constant*)CE->getOperand(0), IdxList);
}
return 0;
}
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