#define DEBUG_TYPE "reassociate"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Constants.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/Pass.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/Assembly/Writer.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Pass.h"
#include "llvm/Support/CFG.h"
-#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/PostOrderIterator.h"
-#include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/SmallMap.h"
-#include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/Statistic.h"
+#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
using namespace llvm;
private:
void BuildRankMap(Function &F);
unsigned getRank(Value *V);
- Value *ReassociateExpression(BinaryOperator *I);
+ void ReassociateExpression(BinaryOperator *I);
void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
Value *OptimizeExpression(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops);
Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
SmallVectorImpl<Factor> &Factors);
Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
- void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
Value *RemoveFactorFromExpression(Value *V, Value *Factor);
+ void EraseInst(Instruction *I);
void OptimizeInst(Instruction *I);
};
}
BinaryOperator *Res =
BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
+ Neg->setOperand(1, Constant::getNullValue(Neg->getType())); // Drop use of op.
Res->takeName(Neg);
Neg->replaceAllUsesWith(Res);
Res->setDebugLoc(Neg->getDebugLoc());
return Res;
}
+/// CarmichaelShift - Returns k such that lambda(2^Bitwidth) = 2^k, where lambda
+/// is the Carmichael function. This means that x^(2^k) === 1 mod 2^Bitwidth for
+/// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic.
+/// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every
+/// even x in Bitwidth-bit arithmetic.
+static unsigned CarmichaelShift(unsigned Bitwidth) {
+ if (Bitwidth < 3)
+ return Bitwidth - 1;
+ return Bitwidth - 2;
+}
+
+/// IncorporateWeight - Add the extra weight 'RHS' to the existing weight 'LHS',
+/// reducing the combined weight using any special properties of the operation.
+/// The existing weight LHS represents the computation X op X op ... op X where
+/// X occurs LHS times. The combined weight represents X op X op ... op X with
+/// X occurring LHS + RHS times. If op is "Xor" for example then the combined
+/// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even;
+/// the routine returns 1 in LHS in the first case, and 0 in LHS in the second.
+static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) {
+ // If we were working with infinite precision arithmetic then the combined
+ // weight would be LHS + RHS. But we are using finite precision arithmetic,
+ // and the APInt sum LHS + RHS may not be correct if it wraps (it is correct
+ // for nilpotent operations and addition, but not for idempotent operations
+ // and multiplication), so it is important to correctly reduce the combined
+ // weight back into range if wrapping would be wrong.
+
+ // If RHS is zero then the weight didn't change.
+ if (RHS.isMinValue())
+ return;
+ // If LHS is zero then the combined weight is RHS.
+ if (LHS.isMinValue()) {
+ LHS = RHS;
+ return;
+ }
+ // From this point on we know that neither LHS nor RHS is zero.
+
+ if (Instruction::isIdempotent(Opcode)) {
+ // Idempotent means X op X === X, so any non-zero weight is equivalent to a
+ // weight of 1. Keeping weights at zero or one also means that wrapping is
+ // not a problem.
+ assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
+ return; // Return a weight of 1.
+ }
+ if (Instruction::isNilpotent(Opcode)) {
+ // Nilpotent means X op X === 0, so reduce weights modulo 2.
+ assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
+ LHS = 0; // 1 + 1 === 0 modulo 2.
+ return;
+ }
+ if (Opcode == Instruction::Add) {
+ // TODO: Reduce the weight by exploiting nsw/nuw?
+ LHS += RHS;
+ return;
+ }
+
+ assert(Opcode == Instruction::Mul && "Unknown associative operation!");
+ unsigned Bitwidth = LHS.getBitWidth();
+ // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth
+ // can be replaced with W-CM. That's because x^W=x^(W-CM) for every Bitwidth
+ // bit number x, since either x is odd in which case x^CM = 1, or x is even in
+ // which case both x^W and x^(W - CM) are zero. By subtracting off multiples
+ // of CM like this weights can always be reduced to the range [0, CM+Bitwidth)
+ // which by a happy accident means that they can always be represented using
+ // Bitwidth bits.
+ // TODO: Reduce the weight by exploiting nsw/nuw? (Could do much better than
+ // the Carmichael number).
+ if (Bitwidth > 3) {
+ /// CM - The value of Carmichael's lambda function.
+ APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth));
+ // Any weight W >= Threshold can be replaced with W - CM.
+ APInt Threshold = CM + Bitwidth;
+ assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!");
+ // For Bitwidth 4 or more the following sum does not overflow.
+ LHS += RHS;
+ while (LHS.uge(Threshold))
+ LHS -= CM;
+ } else {
+ // To avoid problems with overflow do everything the same as above but using
+ // a larger type.
+ unsigned CM = 1U << CarmichaelShift(Bitwidth);
+ unsigned Threshold = CM + Bitwidth;
+ assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold &&
+ "Weights not reduced!");
+ unsigned Total = LHS.getZExtValue() + RHS.getZExtValue();
+ while (Total >= Threshold)
+ Total -= CM;
+ LHS = Total;
+ }
+}
+
+typedef std::pair<Value*, APInt> RepeatedValue;
+
/// LinearizeExprTree - Given an associative binary expression, return the leaf
-/// nodes in Ops. The original expression is the same as Ops[0] op ... Ops[N].
-/// Note that a node may occur multiple times in Ops, but if so all occurrences
-/// are consecutive in the vector.
+/// nodes in Ops along with their weights (how many times the leaf occurs). The
+/// original expression is the same as
+/// (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times
+/// op
+/// (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times
+/// op
+/// ...
+/// op
+/// (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times
+///
+/// Note that the values Ops[0].first, ..., Ops[N].first are all distinct.
+///
+/// This routine may modify the function, in which case it returns 'true'. The
+/// changes it makes may well be destructive, changing the value computed by 'I'
+/// to something completely different. Thus if the routine returns 'true' then
+/// you MUST either replace I with a new expression computed from the Ops array,
+/// or use RewriteExprTree to put the values back in.
///
/// A leaf node is either not a binary operation of the same kind as the root
/// node 'I' (i.e. is not a binary operator at all, or is, but with a different
/// + * | F, G
///
/// The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in
-/// that order) C, E, F, F, G, G.
+/// that order) (C, 1), (E, 1), (F, 2), (G, 2).
///
/// The expression is maximal: if some instruction is a binary operator of the
/// same kind as 'I', and all of its uses are non-leaf nodes of the expression,
/// order to ensure that every non-root node in the expression has *exactly one*
/// use by a non-leaf node of the expression. This destruction means that the
/// caller MUST either replace 'I' with a new expression or use something like
-/// RewriteExprTree to put the values back in.
+/// RewriteExprTree to put the values back in if the routine indicates that it
+/// made a change by returning 'true'.
///
/// In the above example either the right operand of A or the left operand of B
/// will be replaced by undef. If it is B's operand then this gives:
/// of the expression) if it can turn them into binary operators of the right
/// type and thus make the expression bigger.
-void Reassociate::LinearizeExprTree(BinaryOperator *I,
- SmallVectorImpl<ValueEntry> &Ops) {
+static bool LinearizeExprTree(BinaryOperator *I,
+ SmallVectorImpl<RepeatedValue> &Ops) {
DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
+ unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
+ unsigned Opcode = I->getOpcode();
+ assert(Instruction::isAssociative(Opcode) &&
+ Instruction::isCommutative(Opcode) &&
+ "Expected an associative and commutative operation!");
// Visit all operands of the expression, keeping track of their weight (the
// number of paths from the expression root to the operand, or if you like
// with their weights, representing a certain number of paths to the operator.
// If an operator occurs in the worklist multiple times then we found multiple
// ways to get to it.
- SmallVector<std::pair<BinaryOperator*, unsigned>, 8> Worklist; // (Op, Weight)
- Worklist.push_back(std::make_pair(I, 1));
- unsigned Opcode = I->getOpcode();
+ SmallVector<std::pair<BinaryOperator*, APInt>, 8> Worklist; // (Op, Weight)
+ Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1)));
+ bool MadeChange = false;
// Leaves of the expression are values that either aren't the right kind of
// operation (eg: a constant, or a multiply in an add tree), or are, but have
// Leaves - Keeps track of the set of putative leaves as well as the number of
// paths to each leaf seen so far.
- typedef SmallMap<Value*, unsigned, 8> LeafMap;
+ typedef DenseMap<Value*, APInt> LeafMap;
LeafMap Leaves; // Leaf -> Total weight so far.
SmallVector<Value*, 8> LeafOrder; // Ensure deterministic leaf output order.
SmallPtrSet<Value*, 8> Visited; // For sanity checking the iteration scheme.
#endif
while (!Worklist.empty()) {
- std::pair<BinaryOperator*, unsigned> P = Worklist.pop_back_val();
+ std::pair<BinaryOperator*, APInt> P = Worklist.pop_back_val();
I = P.first; // We examine the operands of this binary operator.
- assert(P.second >= 1 && "No paths to here, so how did we get here?!");
for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands.
Value *Op = I->getOperand(OpIdx);
- unsigned Weight = P.second; // Number of paths to this operand.
+ APInt Weight = P.second; // Number of paths to this operand.
DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n");
assert(!Op->use_empty() && "No uses, so how did we get to it?!");
assert(Visited.count(Op) && "In leaf map but not visited!");
// Update the number of paths to the leaf.
- It->second += Weight;
+ IncorporateWeight(It->second, Weight, Opcode);
+#if 0 // TODO: Re-enable once PR13021 is fixed.
// The leaf already has one use from inside the expression. As we want
// exactly one such use, drop this new use of the leaf.
assert(!Op->hasOneUse() && "Only one use, but we got here twice!");
Leaves.erase(It);
continue;
}
+#endif
// If we still have uses that are not accounted for by the expression
// then it is not safe to modify the value.
Value *V = LeafOrder[i];
LeafMap::iterator It = Leaves.find(V);
if (It == Leaves.end())
- // Leaf already output, or node initially thought to be a leaf wasn't.
+ // Node initially thought to be a leaf wasn't.
continue;
assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!");
- unsigned Weight = It->second;
- assert(Weight > 0 && "No paths to this value!");
- // FIXME: Rather than repeating values Weight times, use a vector of
- // (ValueEntry, multiplicity) pairs.
- Ops.append(Weight, ValueEntry(getRank(V), V));
+ APInt Weight = It->second;
+ if (Weight.isMinValue())
+ // Leaf already output or weight reduction eliminated it.
+ continue;
// Ensure the leaf is only output once.
- Leaves.erase(It);
+ It->second = 0;
+ Ops.push_back(std::make_pair(V, Weight));
+ }
+
+ // For nilpotent operations or addition there may be no operands, for example
+ // because the expression was "X xor X" or consisted of 2^Bitwidth additions:
+ // in both cases the weight reduces to 0 causing the value to be skipped.
+ if (Ops.empty()) {
+ Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
+ assert(Identity && "Associative operation without identity!");
+ Ops.push_back(std::make_pair(Identity, APInt(Bitwidth, 1)));
}
+
+ return MadeChange;
}
// RewriteExprTree - Now that the operands for this expression tree are
SmallVectorImpl<ValueEntry> &Ops) {
assert(Ops.size() > 1 && "Single values should be used directly!");
- // Since our optimizations never increase the number of operations, the new
- // expression can always be written by reusing the existing binary operators
+ // Since our optimizations should never increase the number of operations, the
+ // new expression can usually be written reusing the existing binary operators
// from the original expression tree, without creating any new instructions,
// though the rewritten expression may have a completely different topology.
// We take care to not change anything if the new expression will be the same
/// the new expression into.
SmallVector<BinaryOperator*, 8> NodesToRewrite;
unsigned Opcode = I->getOpcode();
- NodesToRewrite.push_back(I);
+ BinaryOperator *Op = I;
+
+ /// NotRewritable - The operands being written will be the leaves of the new
+ /// expression and must not be used as inner nodes (via NodesToRewrite) by
+ /// mistake. Inner nodes are always reassociable, and usually leaves are not
+ /// (if they were they would have been incorporated into the expression and so
+ /// would not be leaves), so most of the time there is no danger of this. But
+ /// in rare cases a leaf may become reassociable if an optimization kills uses
+ /// of it, or it may momentarily become reassociable during rewriting (below)
+ /// due it being removed as an operand of one of its uses. Ensure that misuse
+ /// of leaf nodes as inner nodes cannot occur by remembering all of the future
+ /// leaves and refusing to reuse any of them as inner nodes.
+ SmallPtrSet<Value*, 8> NotRewritable;
+ for (unsigned i = 0, e = Ops.size(); i != e; ++i)
+ NotRewritable.insert(Ops[i].Op);
// ExpressionChanged - Non-null if the rewritten expression differs from the
// original in some non-trivial way, requiring the clearing of optional flags.
// Flags are cleared from the operator in ExpressionChanged up to I inclusive.
BinaryOperator *ExpressionChanged = 0;
- BinaryOperator *Previous;
- BinaryOperator *Op = 0;
- for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
- assert(!NodesToRewrite.empty() &&
- "Optimized expressions has more nodes than original!");
- Previous = Op; Op = NodesToRewrite.pop_back_val();
- if (ExpressionChanged)
- // Compactify the tree instructions together with each other to guarantee
- // that the expression tree is dominated by all of Ops.
- Op->moveBefore(Previous);
-
+ for (unsigned i = 0; ; ++i) {
// The last operation (which comes earliest in the IR) is special as both
// operands will come from Ops, rather than just one with the other being
// a subexpression.
// the old operands with the new ones.
DEBUG(dbgs() << "RA: " << *Op << '\n');
if (NewLHS != OldLHS) {
- if (BinaryOperator *BO = isReassociableOp(OldLHS, Opcode))
+ BinaryOperator *BO = isReassociableOp(OldLHS, Opcode);
+ if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(0, NewLHS);
}
if (NewRHS != OldRHS) {
- if (BinaryOperator *BO = isReassociableOp(OldRHS, Opcode))
+ BinaryOperator *BO = isReassociableOp(OldRHS, Opcode);
+ if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
}
Op->swapOperands();
} else {
// Overwrite with the new right-hand side.
- if (BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode))
+ BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode);
+ if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
ExpressionChanged = Op;
// Now deal with the left-hand side. If this is already an operation node
// from the original expression then just rewrite the rest of the expression
// into it.
- if (BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode)) {
- NodesToRewrite.push_back(BO);
+ BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode);
+ if (BO && !NotRewritable.count(BO)) {
+ Op = BO;
continue;
}
// Otherwise, grab a spare node from the original expression and use that as
- // the left-hand side.
- assert(!NodesToRewrite.empty() &&
- "Optimized expressions has more nodes than original!");
+ // the left-hand side. If there are no nodes left then the optimizers made
+ // an expression with more nodes than the original! This usually means that
+ // they did something stupid but it might mean that the problem was just too
+ // hard (finding the mimimal number of multiplications needed to realize a
+ // multiplication expression is NP-complete). Whatever the reason, smart or
+ // stupid, create a new node if there are none left.
+ BinaryOperator *NewOp;
+ if (NodesToRewrite.empty()) {
+ Constant *Undef = UndefValue::get(I->getType());
+ NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode),
+ Undef, Undef, "", I);
+ } else {
+ NewOp = NodesToRewrite.pop_back_val();
+ }
+
DEBUG(dbgs() << "RA: " << *Op << '\n');
- Op->setOperand(0, NodesToRewrite.back());
+ Op->setOperand(0, NewOp);
DEBUG(dbgs() << "TO: " << *Op << '\n');
ExpressionChanged = Op;
MadeChange = true;
++NumChanged;
+ Op = NewOp;
}
// If the expression changed non-trivially then clear out all subclass data
- // starting from the operator specified in ExpressionChanged.
- if (ExpressionChanged) {
+ // starting from the operator specified in ExpressionChanged, and compactify
+ // the operators to just before the expression root to guarantee that the
+ // expression tree is dominated by all of Ops.
+ if (ExpressionChanged)
do {
ExpressionChanged->clearSubclassOptionalData();
if (ExpressionChanged == I)
break;
+ ExpressionChanged->moveBefore(I);
ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->use_begin());
} while (1);
- }
// Throw away any left over nodes from the original expression.
for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
BinaryOperator *New =
BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
+ Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op.
+ Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op.
New->takeName(Sub);
// Everyone now refers to the add instruction.
BinaryOperator *Mul =
BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
+ Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
Mul->takeName(Shl);
Shl->replaceAllUsesWith(Mul);
Mul->setDebugLoc(Shl->getDebugLoc());
BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
if (!BO) return 0;
+ SmallVector<RepeatedValue, 8> Tree;
+ MadeChange |= LinearizeExprTree(BO, Tree);
SmallVector<ValueEntry, 8> Factors;
- LinearizeExprTree(BO, Factors);
+ Factors.reserve(Tree.size());
+ for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
+ RepeatedValue E = Tree[i];
+ Factors.append(E.second.getZExtValue(),
+ ValueEntry(getRank(E.first), E.first));
+ }
bool FoundFactor = false;
bool NeedsNegate = false;
SmallVectorImpl<ValueEntry> &Ops) {
// Now that we have the linearized expression tree, try to optimize it.
// Start by folding any constants that we found.
- if (Ops.size() == 1) return Ops[0].Op;
-
+ Constant *Cst = 0;
unsigned Opcode = I->getOpcode();
+ while (!Ops.empty() && isa<Constant>(Ops.back().Op)) {
+ Constant *C = cast<Constant>(Ops.pop_back_val().Op);
+ Cst = Cst ? ConstantExpr::get(Opcode, C, Cst) : C;
+ }
+ // If there was nothing but constants then we are done.
+ if (Ops.empty())
+ return Cst;
+
+ // Put the combined constant back at the end of the operand list, except if
+ // there is no point. For example, an add of 0 gets dropped here, while a
+ // multiplication by zero turns the whole expression into zero.
+ if (Cst && Cst != ConstantExpr::getBinOpIdentity(Opcode, I->getType())) {
+ if (Cst == ConstantExpr::getBinOpAbsorber(Opcode, I->getType()))
+ return Cst;
+ Ops.push_back(ValueEntry(0, Cst));
+ }
- if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
- if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
- Ops.pop_back();
- Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
- return OptimizeExpression(I, Ops);
- }
-
- // Check for destructive annihilation due to a constant being used.
- if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
- switch (Opcode) {
- default: break;
- case Instruction::And:
- if (CstVal->isZero()) // X & 0 -> 0
- return CstVal;
- if (CstVal->isAllOnesValue()) // X & -1 -> X
- Ops.pop_back();
- break;
- case Instruction::Mul:
- if (CstVal->isZero()) { // X * 0 -> 0
- ++NumAnnihil;
- return CstVal;
- }
-
- if (cast<ConstantInt>(CstVal)->isOne())
- Ops.pop_back(); // X * 1 -> X
- break;
- case Instruction::Or:
- if (CstVal->isAllOnesValue()) // X | -1 -> -1
- return CstVal;
- // FALLTHROUGH!
- case Instruction::Add:
- case Instruction::Xor:
- if (CstVal->isZero()) // X [|^+] 0 -> X
- Ops.pop_back();
- break;
- }
if (Ops.size() == 1) return Ops[0].Op;
// Handle destructive annihilation due to identities between elements in the
return 0;
}
-/// OptimizeInst - Inspect and optimize the given instruction, possibly erasing
-/// it.
-void Reassociate::OptimizeInst(Instruction *I) {
- // Reassociation can expose instructions as dead. Erasing them, removing uses,
- // can free up their operands for reassociation.
- if (isInstructionTriviallyDead(I)) {
- SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
- // Erase the dead instruction.
- ValueRankMap.erase(I);
- I->eraseFromParent();
- // Optimize its operands.
- for (unsigned i = 0, e = Ops.size(); i != e; ++i)
- if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) {
- // If this is a node in an expression tree, climb to the expression root
- // and add that since that's where optimization actually happens.
- unsigned Opcode = Op->getOpcode();
- while (Op->hasOneUse() && Op->use_back()->getOpcode() == Opcode)
- Op = Op->use_back();
- RedoInsts.insert(Op);
- }
- return;
- }
+/// EraseInst - Zap the given instruction, adding interesting operands to the
+/// work list.
+void Reassociate::EraseInst(Instruction *I) {
+ assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
+ SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
+ // Erase the dead instruction.
+ ValueRankMap.erase(I);
+ RedoInsts.remove(I);
+ I->eraseFromParent();
+ // Optimize its operands.
+ SmallPtrSet<Instruction *, 8> Visited; // Detect self-referential nodes.
+ for (unsigned i = 0, e = Ops.size(); i != e; ++i)
+ if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) {
+ // If this is a node in an expression tree, climb to the expression root
+ // and add that since that's where optimization actually happens.
+ unsigned Opcode = Op->getOpcode();
+ while (Op->hasOneUse() && Op->use_back()->getOpcode() == Opcode &&
+ Visited.insert(Op))
+ Op = Op->use_back();
+ RedoInsts.insert(Op);
+ }
+}
+/// OptimizeInst - Inspect and optimize the given instruction. Note that erasing
+/// instructions is not allowed.
+void Reassociate::OptimizeInst(Instruction *I) {
// Only consider operations that we understand.
if (!isa<BinaryOperator>(I))
return;
(isReassociableOp(I->use_back(), Instruction::Mul) ||
isReassociableOp(I->use_back(), Instruction::Add)))) {
Instruction *NI = ConvertShiftToMul(I);
- ValueRankMap.erase(I);
- I->eraseFromParent();
+ RedoInsts.insert(I);
MadeChange = true;
I = NI;
}
if (I->getOpcode() == Instruction::Sub) {
if (ShouldBreakUpSubtract(I)) {
Instruction *NI = BreakUpSubtract(I);
- ValueRankMap.erase(I);
- I->eraseFromParent();
+ RedoInsts.insert(I);
MadeChange = true;
I = NI;
} else if (BinaryOperator::isNeg(I)) {
(!I->hasOneUse() ||
!isReassociableOp(I->use_back(), Instruction::Mul))) {
Instruction *NI = LowerNegateToMultiply(I);
- ValueRankMap.erase(I);
- I->eraseFromParent();
+ RedoInsts.insert(I);
MadeChange = true;
I = NI;
}
// If this is an interior node of a reassociable tree, ignore it until we
// get to the root of the tree, to avoid N^2 analysis.
- if (BO->hasOneUse() && BO->use_back()->getOpcode() == BO->getOpcode())
+ unsigned Opcode = BO->getOpcode();
+ if (BO->hasOneUse() && BO->use_back()->getOpcode() == Opcode)
return;
// If this is an add tree that is used by a sub instruction, ignore it
ReassociateExpression(BO);
}
-Value *Reassociate::ReassociateExpression(BinaryOperator *I) {
+void Reassociate::ReassociateExpression(BinaryOperator *I) {
// First, walk the expression tree, linearizing the tree, collecting the
// operand information.
+ SmallVector<RepeatedValue, 8> Tree;
+ MadeChange |= LinearizeExprTree(I, Tree);
SmallVector<ValueEntry, 8> Ops;
- LinearizeExprTree(I, Ops);
+ Ops.reserve(Tree.size());
+ for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
+ RepeatedValue E = Tree[i];
+ Ops.append(E.second.getZExtValue(),
+ ValueEntry(getRank(E.first), E.first));
+ }
DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
// OptimizeExpression - Now that we have the expression tree in a convenient
// sorted form, optimize it globally if possible.
if (Value *V = OptimizeExpression(I, Ops)) {
+ if (V == I)
+ // Self-referential expression in unreachable code.
+ return;
// This expression tree simplified to something that isn't a tree,
// eliminate it.
DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
VI->setDebugLoc(I->getDebugLoc());
RedoInsts.insert(I);
++NumAnnihil;
- return V;
+ return;
}
// We want to sink immediates as deeply as possible except in the case where
DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
if (Ops.size() == 1) {
+ if (Ops[0].Op == I)
+ // Self-referential expression in unreachable code.
+ return;
+
// This expression tree simplified to something that isn't a tree,
// eliminate it.
I->replaceAllUsesWith(Ops[0].Op);
if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op))
OI->setDebugLoc(I->getDebugLoc());
RedoInsts.insert(I);
- return Ops[0].Op;
+ return;
}
// Now that we ordered and optimized the expressions, splat them back into
// the expression tree, removing any unneeded nodes.
RewriteExprTree(I, Ops);
- return I;
}
bool Reassociate::runOnFunction(Function &F) {
BuildRankMap(F);
MadeChange = false;
- for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI)
- for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; ) {
- // Optimize the current instruction, possibly erasing it. If this creates
- // new instructions that need optimizing then optimize all such too before
- // moving on to the next instruction.
- RedoInsts.insert(AssertingVH<Instruction>(II));
- while (!RedoInsts.empty()) {
- Instruction *I = RedoInsts.pop_back_val();
- if ((Instruction*)II == I)
- ++II;
- OptimizeInst(I);
+ for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
+ // Optimize every instruction in the basic block.
+ for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; )
+ if (isInstructionTriviallyDead(II)) {
+ EraseInst(II++);
+ } else {
+ OptimizeInst(II);
+ assert(II->getParent() == BI && "Moved to a different block!");
+ ++II;
}
+
+ // If this produced extra instructions to optimize, handle them now.
+ while (!RedoInsts.empty()) {
+ Instruction *I = RedoInsts.pop_back_val();
+ if (isInstructionTriviallyDead(I))
+ EraseInst(I);
+ else
+ OptimizeInst(I);
}
+ }
// We are done with the rank map.
RankMap.clear();
projects / oota-llvm.git / blobdiff