// (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/iPHINode.h"
-#include "llvm/InstrTypes.h"
+#include "llvm/Instructions.h"
#include "llvm/DerivedTypes.h"
+#include "llvm/Function.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include <cmath>
using namespace llvm;
-static unsigned getSize(const Type *Ty) {
- unsigned S = Ty->getPrimitiveSize();
- return S ? S : 8; // Treat pointers at 8 bytes
-}
-
namespace {
struct ConstRules {
ConstRules() {}
}
-Constant *llvm::ConstantFoldCastInstruction(const Constant *V,
- const Type *DestTy) {
- if (V->getType() == DestTy) return (Constant*)V;
-
- 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::ConstantFoldBinaryInstruction(unsigned Opcode,
- const Constant *V1,
- const Constant *V2) {
- Constant *C;
- switch (Opcode) {
- default: return 0;
- case Instruction::Add: return ConstRules::get(V1, V2).add(V1, V2);
- case Instruction::Sub: return ConstRules::get(V1, V2).sub(V1, V2);
- case Instruction::Mul: return ConstRules::get(V1, V2).mul(V1, V2);
- case Instruction::Div: return ConstRules::get(V1, V2).div(V1, V2);
- case Instruction::Rem: return ConstRules::get(V1, V2).rem(V1, V2);
- case Instruction::And: return ConstRules::get(V1, V2).op_and(V1, V2);
- case Instruction::Or: return ConstRules::get(V1, V2).op_or (V1, V2);
- case Instruction::Xor: return ConstRules::get(V1, V2).op_xor(V1, V2);
-
- case Instruction::Shl: return ConstRules::get(V1, V2).shl(V1, V2);
- case Instruction::Shr: return ConstRules::get(V1, V2).shr(V1, V2);
-
- case Instruction::SetEQ: return ConstRules::get(V1, V2).equalto(V1, V2);
- case Instruction::SetLT: return ConstRules::get(V1, V2).lessthan(V1, V2);
- case Instruction::SetGT: return ConstRules::get(V1, V2).lessthan(V2, V1);
- case Instruction::SetNE: // V1 != V2 === !(V1 == V2)
- C = ConstRules::get(V1, V2).equalto(V1, V2);
- break;
- case Instruction::SetLE: // V1 <= V2 === !(V2 < V1)
- C = ConstRules::get(V1, V2).lessthan(V2, V1);
- break;
- case Instruction::SetGE: // V1 >= V2 === !(V1 < V2)
- C = ConstRules::get(V1, V2).lessthan(V1, V2);
- break;
- }
-
- // If the folder broke out of the switch statement, invert the boolean
- // constant value, if it exists, and return it.
- if (!C) return 0;
- return ConstantExpr::get(Instruction::Xor, ConstantBool::True, C);
-}
-
-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);
-
- // TODO If C is null and all idx's are null, return null of the right type.
-
-
- 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;
-}
-
-
//===----------------------------------------------------------------------===//
// TemplateRules Class
//===----------------------------------------------------------------------===//
// DirectFPRules Class
//===----------------------------------------------------------------------===//
//
-// DirectFPRules provides implementations of functions that are valid on
-// floating point types, but not all types in general.
-//
+/// 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,
}
};
+
+/// 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;
isa<ConstantPointerRef>(V1) || isa<ConstantPointerRef>(V2))
return EmptyR;
- switch (V1->getType()->getPrimitiveID()) {
+ switch (V1->getType()->getTypeID()) {
default: assert(0 && "Unknown value type for constant folding!");
case Type::BoolTyID: return BoolR;
case Type::PointerTyID: return NullPointerR;
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->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->getTypeID()) {
+ 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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