#include "ConstantFolding.h"
#include "llvm/Constants.h"
#include "llvm/iPHINode.h"
+#include "llvm/iOperators.h"
#include "llvm/InstrTypes.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
}
}
+/// 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. Convert them to
+ // be the same type. Long is always big enough, so we use it.
+ C1 = ConstantExpr::getCast(C1, Type::LongTy);
+ C2 = ConstantExpr::getCast(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!");
+ return SetCondInst::getSwappedCondition(evaluateRelation(V2, V1));
+
+ } else if (const ConstantPointerRef *CPR1 = dyn_cast<ConstantPointerRef>(V1)){
+ if (isa<ConstantExpr>(V2)) // Swap as necessary.
+ return SetCondInst::getSwappedCondition(evaluateRelation(V2, V1));
+
+ // 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()));
+
+ 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;
+ Constant *C = 0;
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);
+ 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 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);
+ // 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
+ 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,
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