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+//===- Reassociate.cpp - Reassociate binary expressions -------------------===//
+//
+// 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 pass reassociates commutative expressions in an order that is designed
+// to promote better constant propagation, GCSE, LICM, PRE...
+//
+// For example: 4 + (x + 5) -> x + (4 + 5)
+//
+// In the implementation of this algorithm, constants are assigned rank = 0,
+// function arguments are rank = 1, and other values are assigned ranks
+// corresponding to the reverse post order traversal of current function
+// (starting at 2), which effectively gives values in deep loops higher rank
+// than values not in loops.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "reassociate"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
+#include "llvm/Function.h"
+#include "llvm/Instructions.h"
+#include "llvm/Pass.h"
+#include "llvm/Type.h"
+#include "llvm/Assembly/Writer.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/Statistic.h"
+#include <algorithm>
+using namespace llvm;
+
+namespace {
+ Statistic<> NumLinear ("reassociate","Number of insts linearized");
+ Statistic<> NumChanged("reassociate","Number of insts reassociated");
+ Statistic<> NumSwapped("reassociate","Number of insts with operands swapped");
+ Statistic<> NumAnnihil("reassociate","Number of expr tree annihilated");
+
+ struct ValueEntry {
+ unsigned Rank;
+ Value *Op;
+ ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
+ };
+ inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
+ return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
+ }
+
+ class Reassociate : public FunctionPass {
+ std::map<BasicBlock*, unsigned> RankMap;
+ std::map<Value*, unsigned> ValueRankMap;
+ bool MadeChange;
+ public:
+ bool runOnFunction(Function &F);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ }
+ private:
+ void BuildRankMap(Function &F);
+ unsigned getRank(Value *V);
+ void RewriteExprTree(BinaryOperator *I, unsigned Idx,
+ std::vector<ValueEntry> &Ops);
+ void OptimizeExpression(unsigned Opcode, std::vector<ValueEntry> &Ops);
+ void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops);
+ void LinearizeExpr(BinaryOperator *I);
+ void ReassociateBB(BasicBlock *BB);
+ };
+
+ RegisterOpt<Reassociate> X("reassociate", "Reassociate expressions");
+}
+
+// Public interface to the Reassociate pass
+FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
+
+
+static bool isUnmovableInstruction(Instruction *I) {
+ if (I->getOpcode() == Instruction::PHI ||
+ I->getOpcode() == Instruction::Alloca ||
+ I->getOpcode() == Instruction::Load ||
+ I->getOpcode() == Instruction::Malloc ||
+ I->getOpcode() == Instruction::Invoke ||
+ I->getOpcode() == Instruction::Call ||
+ I->getOpcode() == Instruction::Div ||
+ I->getOpcode() == Instruction::Rem)
+ return true;
+ return false;
+}
+
+void Reassociate::BuildRankMap(Function &F) {
+ unsigned i = 2;
+
+ // Assign distinct ranks to function arguments
+ for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
+ ValueRankMap[I] = ++i;
+
+ ReversePostOrderTraversal<Function*> RPOT(&F);
+ for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
+ E = RPOT.end(); I != E; ++I) {
+ BasicBlock *BB = *I;
+ unsigned BBRank = RankMap[BB] = ++i << 16;
+
+ // Walk the basic block, adding precomputed ranks for any instructions that
+ // we cannot move. This ensures that the ranks for these instructions are
+ // all different in the block.
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (isUnmovableInstruction(I))
+ ValueRankMap[I] = ++BBRank;
+ }
+}
+
+unsigned Reassociate::getRank(Value *V) {
+ if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument...
+
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (I == 0) return 0; // Otherwise it's a global or constant, rank 0.
+
+ unsigned &CachedRank = ValueRankMap[I];
+ if (CachedRank) return CachedRank; // Rank already known?
+
+ // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
+ // we can reassociate expressions for code motion! Since we do not recurse
+ // for PHI nodes, we cannot have infinite recursion here, because there
+ // cannot be loops in the value graph that do not go through PHI nodes.
+ unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
+ for (unsigned i = 0, e = I->getNumOperands();
+ i != e && Rank != MaxRank; ++i)
+ Rank = std::max(Rank, getRank(I->getOperand(i)));
+
+ // If this is a not or neg instruction, do not count it for rank. This
+ // assures us that X and ~X will have the same rank.
+ if (!I->getType()->isIntegral() ||
+ (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
+ ++Rank;
+
+ //DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = "
+ //<< Rank << "\n");
+
+ return CachedRank = Rank;
+}
+
+/// isReassociableOp - Return true if V is an instruction of the specified
+/// opcode and if it only has one use.
+static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
+ if (V->hasOneUse() && isa<Instruction>(V) &&
+ cast<Instruction>(V)->getOpcode() == Opcode)
+ return cast<BinaryOperator>(V);
+ return 0;
+}
+
+/// LowerNegateToMultiply - Replace 0-X with X*-1.
+///
+static Instruction *LowerNegateToMultiply(Instruction *Neg) {
+ Constant *Cst;
+ if (Neg->getType()->isFloatingPoint())
+ Cst = ConstantFP::get(Neg->getType(), -1);
+ else
+ Cst = ConstantInt::getAllOnesValue(Neg->getType());
+
+ std::string NegName = Neg->getName(); Neg->setName("");
+ Instruction *Res = BinaryOperator::createMul(Neg->getOperand(1), Cst, NegName,
+ Neg);
+ Neg->replaceAllUsesWith(Res);
+ Neg->eraseFromParent();
+ return Res;
+}
+
+// Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
+// Note that if D is also part of the expression tree that we recurse to
+// linearize it as well. Besides that case, this does not recurse into A,B, or
+// C.
+void Reassociate::LinearizeExpr(BinaryOperator *I) {
+ BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
+ BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
+ assert(isReassociableOp(LHS, I->getOpcode()) &&
+ isReassociableOp(RHS, I->getOpcode()) &&
+ "Not an expression that needs linearization?");
+
+ DEBUG(std::cerr << "Linear" << *LHS << *RHS << *I);
+
+ // Move the RHS instruction to live immediately before I, avoiding breaking
+ // dominator properties.
+ RHS->moveBefore(I);
+
+ // Move operands around to do the linearization.
+ I->setOperand(1, RHS->getOperand(0));
+ RHS->setOperand(0, LHS);
+ I->setOperand(0, RHS);
+
+ ++NumLinear;
+ MadeChange = true;
+ DEBUG(std::cerr << "Linearized: " << *I);
+
+ // If D is part of this expression tree, tail recurse.
+ if (isReassociableOp(I->getOperand(1), I->getOpcode()))
+ LinearizeExpr(I);
+}
+
+
+/// LinearizeExprTree - Given an associative binary expression tree, traverse
+/// all of the uses putting it into canonical form. This forces a left-linear
+/// form of the the expression (((a+b)+c)+d), and collects information about the
+/// rank of the non-tree operands.
+///
+/// This returns the rank of the RHS operand, which is known to be the highest
+/// rank value in the expression tree.
+///
+void Reassociate::LinearizeExprTree(BinaryOperator *I,
+ std::vector<ValueEntry> &Ops) {
+ Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
+ unsigned Opcode = I->getOpcode();
+
+ // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
+ BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
+ BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
+
+ // If this is a multiply expression tree and it contains internal negations,
+ // transform them into multiplies by -1 so they can be reassociated.
+ if (I->getOpcode() == Instruction::Mul) {
+ if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
+ LHS = LowerNegateToMultiply(cast<Instruction>(LHS));
+ LHSBO = isReassociableOp(LHS, Opcode);
+ }
+ if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
+ RHS = LowerNegateToMultiply(cast<Instruction>(RHS));
+ RHSBO = isReassociableOp(RHS, Opcode);
+ }
+ }
+
+ if (!LHSBO) {
+ if (!RHSBO) {
+ // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
+ // such, just remember these operands and their rank.
+ Ops.push_back(ValueEntry(getRank(LHS), LHS));
+ Ops.push_back(ValueEntry(getRank(RHS), RHS));
+ return;
+ } else {
+ // Turn X+(Y+Z) -> (Y+Z)+X
+ std::swap(LHSBO, RHSBO);
+ std::swap(LHS, RHS);
+ bool Success = !I->swapOperands();
+ assert(Success && "swapOperands failed");
+ MadeChange = true;
+ }
+ } else if (RHSBO) {
+ // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not
+ // part of the expression tree.
+ LinearizeExpr(I);
+ LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
+ RHS = I->getOperand(1);
+ RHSBO = 0;
+ }
+
+ // Okay, now we know that the LHS is a nested expression and that the RHS is
+ // not. Perform reassociation.
+ assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
+
+ // Move LHS right before I to make sure that the tree expression dominates all
+ // values.
+ LHSBO->moveBefore(I);
+
+ // Linearize the expression tree on the LHS.
+ LinearizeExprTree(LHSBO, Ops);
+
+ // Remember the RHS operand and its rank.
+ Ops.push_back(ValueEntry(getRank(RHS), RHS));
+}
+
+// RewriteExprTree - Now that the operands for this expression tree are
+// linearized and optimized, emit them in-order. This function is written to be
+// tail recursive.
+void Reassociate::RewriteExprTree(BinaryOperator *I, unsigned i,
+ std::vector<ValueEntry> &Ops) {
+ if (i+2 == Ops.size()) {
+ if (I->getOperand(0) != Ops[i].Op ||
+ I->getOperand(1) != Ops[i+1].Op) {
+ DEBUG(std::cerr << "RA: " << *I);
+ I->setOperand(0, Ops[i].Op);
+ I->setOperand(1, Ops[i+1].Op);
+ DEBUG(std::cerr << "TO: " << *I);
+ MadeChange = true;
+ ++NumChanged;
+ }
+ return;
+ }
+ assert(i+2 < Ops.size() && "Ops index out of range!");
+
+ if (I->getOperand(1) != Ops[i].Op) {
+ DEBUG(std::cerr << "RA: " << *I);
+ I->setOperand(1, Ops[i].Op);
+ DEBUG(std::cerr << "TO: " << *I);
+ MadeChange = true;
+ ++NumChanged;
+ }
+ RewriteExprTree(cast<BinaryOperator>(I->getOperand(0)), i+1, Ops);
+}
+
+
+
+// NegateValue - Insert instructions before the instruction pointed to by BI,
+// that computes the negative version of the value specified. The negative
+// version of the value is returned, and BI is left pointing at the instruction
+// that should be processed next by the reassociation pass.
+//
+static Value *NegateValue(Value *V, Instruction *BI) {
+ // We are trying to expose opportunity for reassociation. One of the things
+ // that we want to do to achieve this is to push a negation as deep into an
+ // expression chain as possible, to expose the add instructions. In practice,
+ // this means that we turn this:
+ // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
+ // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
+ // the constants. We assume that instcombine will clean up the mess later if
+ // we introduce tons of unnecessary negation instructions...
+ //
+ if (Instruction *I = dyn_cast<Instruction>(V))
+ if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
+ // Push the negates through the add.
+ I->setOperand(0, NegateValue(I->getOperand(0), BI));
+ I->setOperand(1, NegateValue(I->getOperand(1), BI));
+
+ // We must move the add instruction here, because the neg instructions do
+ // not dominate the old add instruction in general. By moving it, we are
+ // assured that the neg instructions we just inserted dominate the
+ // instruction we are about to insert after them.
+ //
+ I->moveBefore(BI);
+ I->setName(I->getName()+".neg");
+ return I;
+ }
+
+ // Insert a 'neg' instruction that subtracts the value from zero to get the
+ // negation.
+ //
+ return BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
+}
+
+/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
+/// only used by an add, transform this into (X+(0-Y)) to promote better
+/// reassociation.
+static Instruction *BreakUpSubtract(Instruction *Sub) {
+ // Don't bother to break this up unless either the LHS is an associable add or
+ // if this is only used by one.
+ if (!isReassociableOp(Sub->getOperand(0), Instruction::Add) &&
+ !isReassociableOp(Sub->getOperand(1), Instruction::Add) &&
+ !(Sub->hasOneUse() &&isReassociableOp(Sub->use_back(), Instruction::Add)))
+ return 0;
+
+ // Convert a subtract into an add and a neg instruction... so that sub
+ // instructions can be commuted with other add instructions...
+ //
+ // Calculate the negative value of Operand 1 of the sub instruction...
+ // and set it as the RHS of the add instruction we just made...
+ //
+ std::string Name = Sub->getName();
+ Sub->setName("");
+ Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
+ Instruction *New =
+ BinaryOperator::createAdd(Sub->getOperand(0), NegVal, Name, Sub);
+
+ // Everyone now refers to the add instruction.
+ Sub->replaceAllUsesWith(New);
+ Sub->eraseFromParent();
+
+ DEBUG(std::cerr << "Negated: " << *New);
+ return New;
+}
+
+/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
+/// by one, change this into a multiply by a constant to assist with further
+/// reassociation.
+static Instruction *ConvertShiftToMul(Instruction *Shl) {
+ if (!isReassociableOp(Shl->getOperand(0), Instruction::Mul) &&
+ !(Shl->hasOneUse() && isReassociableOp(Shl->use_back(),Instruction::Mul)))
+ return 0;
+
+ Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
+ MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
+
+ std::string Name = Shl->getName(); Shl->setName("");
+ Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst,
+ Name, Shl);
+ Shl->replaceAllUsesWith(Mul);
+ Shl->eraseFromParent();
+ return Mul;
+}
+
+// Scan backwards and forwards among values with the same rank as element i to
+// see if X exists. If X does not exist, return i.
+static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i,
+ Value *X) {
+ unsigned XRank = Ops[i].Rank;
+ unsigned e = Ops.size();
+ for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
+ if (Ops[j].Op == X)
+ return j;
+ // Scan backwards
+ for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
+ if (Ops[j].Op == X)
+ return j;
+ return i;
+}
+
+void Reassociate::OptimizeExpression(unsigned Opcode,
+ std::vector<ValueEntry> &Ops) {
+ // Now that we have the linearized expression tree, try to optimize it.
+ // Start by folding any constants that we found.
+ bool IterateOptimization = false;
+ if (Ops.size() == 1) return;
+
+ 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);
+ OptimizeExpression(Opcode, Ops);
+ return;
+ }
+
+ // Check for destructive annihilation due to a constant being used.
+ if (ConstantIntegral *CstVal = dyn_cast<ConstantIntegral>(Ops.back().Op))
+ switch (Opcode) {
+ default: break;
+ case Instruction::And:
+ if (CstVal->isNullValue()) { // ... & 0 -> 0
+ Ops[0].Op = CstVal;
+ Ops.erase(Ops.begin()+1, Ops.end());
+ ++NumAnnihil;
+ return;
+ } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ...
+ Ops.pop_back();
+ }
+ break;
+ case Instruction::Mul:
+ if (CstVal->isNullValue()) { // ... * 0 -> 0
+ Ops[0].Op = CstVal;
+ Ops.erase(Ops.begin()+1, Ops.end());
+ ++NumAnnihil;
+ return;
+ } else if (cast<ConstantInt>(CstVal)->getRawValue() == 1) {
+ Ops.pop_back(); // ... * 1 -> ...
+ }
+ break;
+ case Instruction::Or:
+ if (CstVal->isAllOnesValue()) { // ... | -1 -> -1
+ Ops[0].Op = CstVal;
+ Ops.erase(Ops.begin()+1, Ops.end());
+ ++NumAnnihil;
+ return;
+ }
+ // FALLTHROUGH!
+ case Instruction::Add:
+ case Instruction::Xor:
+ if (CstVal->isNullValue()) // ... [|^+] 0 -> ...
+ Ops.pop_back();
+ break;
+ }
+ if (Ops.size() == 1) return;
+
+ // Handle destructive annihilation do to identities between elements in the
+ // argument list here.
+ switch (Opcode) {
+ default: break;
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor:
+ // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
+ // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
+ for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
+ // First, check for X and ~X in the operand list.
+ assert(i < Ops.size());
+ if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
+ Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
+ unsigned FoundX = FindInOperandList(Ops, i, X);
+ if (FoundX != i) {
+ if (Opcode == Instruction::And) { // ...&X&~X = 0
+ Ops[0].Op = Constant::getNullValue(X->getType());
+ Ops.erase(Ops.begin()+1, Ops.end());
+ ++NumAnnihil;
+ return;
+ } else if (Opcode == Instruction::Or) { // ...|X|~X = -1
+ Ops[0].Op = ConstantIntegral::getAllOnesValue(X->getType());
+ Ops.erase(Ops.begin()+1, Ops.end());
+ ++NumAnnihil;
+ return;
+ }
+ }
+ }
+
+ // Next, check for duplicate pairs of values, which we assume are next to
+ // each other, due to our sorting criteria.
+ assert(i < Ops.size());
+ if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
+ if (Opcode == Instruction::And || Opcode == Instruction::Or) {
+ // Drop duplicate values.
+ Ops.erase(Ops.begin()+i);
+ --i; --e;
+ IterateOptimization = true;
+ ++NumAnnihil;
+ } else {
+ assert(Opcode == Instruction::Xor);
+ if (e == 2) {
+ Ops[0].Op = Constant::getNullValue(Ops[0].Op->getType());
+ Ops.erase(Ops.begin()+1, Ops.end());
+ ++NumAnnihil;
+ return;
+ }
+ // ... X^X -> ...
+ Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
+ i -= 1; e -= 2;
+ IterateOptimization = true;
+ ++NumAnnihil;
+ }
+ }
+ }
+ break;
+
+ case Instruction::Add:
+ // Scan the operand lists looking for X and -X pairs. If we find any, we
+ // can simplify the expression. X+-X == 0
+ for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
+ assert(i < Ops.size());
+ // Check for X and -X in the operand list.
+ if (BinaryOperator::isNeg(Ops[i].Op)) {
+ Value *X = BinaryOperator::getNegArgument(Ops[i].Op);
+ unsigned FoundX = FindInOperandList(Ops, i, X);
+ if (FoundX != i) {
+ // Remove X and -X from the operand list.
+ if (Ops.size() == 2) {
+ Ops[0].Op = Constant::getNullValue(X->getType());
+ Ops.pop_back();
+ ++NumAnnihil;
+ return;
+ } else {
+ Ops.erase(Ops.begin()+i);
+ if (i < FoundX)
+ --FoundX;
+ else
+ --i; // Need to back up an extra one.
+ Ops.erase(Ops.begin()+FoundX);
+ IterateOptimization = true;
+ ++NumAnnihil;
+ --i; // Revisit element.
+ e -= 2; // Removed two elements.
+ }
+ }
+ }
+ }
+ break;
+ //case Instruction::Mul:
+ }
+
+ if (IterateOptimization)
+ OptimizeExpression(Opcode, Ops);
+}
+
+/// PrintOps - Print out the expression identified in the Ops list.
+///
+static void PrintOps(unsigned Opcode, const std::vector<ValueEntry> &Ops,
+ BasicBlock *BB) {
+ Module *M = BB->getParent()->getParent();
+ std::cerr << Instruction::getOpcodeName(Opcode) << " "
+ << *Ops[0].Op->getType();
+ for (unsigned i = 0, e = Ops.size(); i != e; ++i)
+ WriteAsOperand(std::cerr << " ", Ops[i].Op, false, true, M)
+ << "," << Ops[i].Rank;
+}
+
+/// ReassociateBB - Inspect all of the instructions in this basic block,
+/// reassociating them as we go.
+void Reassociate::ReassociateBB(BasicBlock *BB) {
+ for (BasicBlock::iterator BI = BB->begin(); BI != BB->end(); ++BI) {
+ if (BI->getOpcode() == Instruction::Shl &&
+ isa<ConstantInt>(BI->getOperand(1)))
+ if (Instruction *NI = ConvertShiftToMul(BI)) {
+ MadeChange = true;
+ BI = NI;
+ }
+
+ // Reject cases where it is pointless to do this.
+ if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint())
+ continue; // Floating point ops are not associative.
+
+ // If this is a subtract instruction which is not already in negate form,
+ // see if we can convert it to X+-Y.
+ if (BI->getOpcode() == Instruction::Sub) {
+ if (!BinaryOperator::isNeg(BI)) {
+ if (Instruction *NI = BreakUpSubtract(BI)) {
+ MadeChange = true;
+ BI = NI;
+ }
+ } else {
+ // Otherwise, this is a negation. See if the operand is a multiply tree
+ // and if this is not an inner node of a multiply tree.
+ if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
+ (!BI->hasOneUse() ||
+ !isReassociableOp(BI->use_back(), Instruction::Mul))) {
+ BI = LowerNegateToMultiply(BI);
+ MadeChange = true;
+ }
+ }
+ }
+
+ // If this instruction is a commutative binary operator, process it.
+ if (!BI->isAssociative()) continue;
+ BinaryOperator *I = cast<BinaryOperator>(BI);
+
+ // 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 (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
+ continue;
+
+ // If this is an add tree that is used by a sub instruction, ignore it
+ // until we process the subtract.
+ if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
+ cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
+ continue;
+
+ // First, walk the expression tree, linearizing the tree, collecting
+ std::vector<ValueEntry> Ops;
+ LinearizeExprTree(I, Ops);
+
+ DEBUG(std::cerr << "RAIn:\t"; PrintOps(I->getOpcode(), Ops, BB);
+ std::cerr << "\n");
+
+ // Now that we have linearized the tree to a list and have gathered all of
+ // the operands and their ranks, sort the operands by their rank. Use a
+ // stable_sort so that values with equal ranks will have their relative
+ // positions maintained (and so the compiler is deterministic). Note that
+ // this sorts so that the highest ranking values end up at the beginning of
+ // the vector.
+ std::stable_sort(Ops.begin(), Ops.end());
+
+ // OptimizeExpression - Now that we have the expression tree in a convenient
+ // sorted form, optimize it globally if possible.
+ OptimizeExpression(I->getOpcode(), Ops);
+
+ // We want to sink immediates as deeply as possible except in the case where
+ // this is a multiply tree used only by an add, and the immediate is a -1.
+ // In this case we reassociate to put the negation on the outside so that we
+ // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
+ if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
+ cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
+ isa<ConstantInt>(Ops.back().Op) &&
+ cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
+ Ops.insert(Ops.begin(), Ops.back());
+ Ops.pop_back();
+ }
+
+ DEBUG(std::cerr << "RAOut:\t"; PrintOps(I->getOpcode(), Ops, BB);
+ std::cerr << "\n");
+
+ if (Ops.size() == 1) {
+ // This expression tree simplified to something that isn't a tree,
+ // eliminate it.
+ I->replaceAllUsesWith(Ops[0].Op);
+ } else {
+ // Now that we ordered and optimized the expressions, splat them back into
+ // the expression tree, removing any unneeded nodes.
+ RewriteExprTree(I, 0, Ops);
+ }
+ }
+}
+
+
+bool Reassociate::runOnFunction(Function &F) {
+ // Recalculate the rank map for F
+ BuildRankMap(F);
+
+ MadeChange = false;
+ for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
+ ReassociateBB(FI);
+
+ // We are done with the rank map...
+ RankMap.clear();
+ ValueRankMap.clear();
+ return MadeChange;
+}
+
generated by cgit v1.2.3-70-g09d2 (git 2.46.0) at 2025-09-07 16:32:57 +0000