//===- 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 propogation, GCSE, LICM, PRE...
+// to promote better constant propagation, GCSE, LICM, PRE...
//
// For example: 4 + (x + 5) -> x + (4 + 5)
//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Function.h"
-#include "llvm/BasicBlock.h"
#include "llvm/iOperators.h"
#include "llvm/Type.h"
#include "llvm/Pass.h"
#include "llvm/Constant.h"
#include "llvm/Support/CFG.h"
+#include "Support/Debug.h"
#include "Support/PostOrderIterator.h"
-#include "Support/StatisticReporter.h"
-
-static Statistic<> NumChanged("reassociate\t- Number of insts reassociated");
-static Statistic<> NumSwapped("reassociate\t- Number of insts with operands swapped");
+#include "Support/Statistic.h"
namespace {
+ Statistic<> NumLinear ("reassociate","Number of insts linearized");
+ Statistic<> NumChanged("reassociate","Number of insts reassociated");
+ Statistic<> NumSwapped("reassociate","Number of insts with operands swapped");
+
class Reassociate : public FunctionPass {
- map<BasicBlock*, unsigned> RankMap;
+ std::map<BasicBlock*, unsigned> RankMap;
+ std::map<Value*, unsigned> ValueRankMap;
public:
- const char *getPassName() const {
- return "Expression Reassociation";
- }
-
- bool runOnFunction(Function *F);
+ bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.preservesCFG();
+ AU.setPreservesCFG();
}
private:
- void BuildRankMap(Function *F);
+ void BuildRankMap(Function &F);
unsigned getRank(Value *V);
bool ReassociateExpr(BinaryOperator *I);
bool ReassociateBB(BasicBlock *BB);
};
+
+ RegisterOpt<Reassociate> X("reassociate", "Reassociate expressions");
}
Pass *createReassociatePass() { return new Reassociate(); }
-void Reassociate::BuildRankMap(Function *F) {
- unsigned i = 1;
- ReversePostOrderTraversal<Function*> RPOT(F);
+void Reassociate::BuildRankMap(Function &F) {
+ unsigned i = 2;
+
+ // Assign distinct ranks to function arguments
+ for (Function::aiterator I = F.abegin(), E = F.aend(); I != E; ++I)
+ ValueRankMap[I] = ++i;
+
+ ReversePostOrderTraversal<Function*> RPOT(&F);
for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
E = RPOT.end(); I != E; ++I)
- RankMap[*I] = ++i;
+ RankMap[*I] = ++i << 16;
}
unsigned Reassociate::getRank(Value *V) {
- if (isa<Argument>(V)) return 1; // Function argument...
+ if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument...
+
if (Instruction *I = dyn_cast<Instruction>(V)) {
- // If this is an expression, return the 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 (except for PHI nodes).
+ // 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.
//
- if (I->getOpcode() == Instruction::PHINode ||
+ if (I->getOpcode() == Instruction::PHI ||
I->getOpcode() == Instruction::Alloca ||
I->getOpcode() == Instruction::Malloc || isa<TerminatorInst>(I) ||
- I->hasSideEffects())
+ I->mayWriteToMemory()) // Cannot move inst if it writes to memory!
return RankMap[I->getParent()];
- unsigned Rank = 0;
- for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ unsigned &CachedRank = ValueRankMap[I];
+ if (CachedRank) return CachedRank; // Rank already known?
+
+ // If not, compute it!
+ 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)));
- return Rank;
+ DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = "
+ << Rank+1 << "\n");
+
+ return CachedRank = Rank+1;
}
// Otherwise it's a global or constant, rank 0.
}
-// isCommutativeOperator - Return true if the specified instruction is
-// commutative and associative. If the instruction is not commutative and
-// associative, we can not reorder its operands!
-//
-static inline BinaryOperator *isCommutativeOperator(Instruction *I) {
- // Floating point operations do not commute!
- if (I->getType()->isFloatingPoint()) return 0;
-
- if (I->getOpcode() == Instruction::Add ||
- I->getOpcode() == Instruction::Mul ||
- I->getOpcode() == Instruction::And ||
- I->getOpcode() == Instruction::Or ||
- I->getOpcode() == Instruction::Xor)
- return cast<BinaryOperator>(I);
- return 0;
-}
-
-
bool Reassociate::ReassociateExpr(BinaryOperator *I) {
Value *LHS = I->getOperand(0);
Value *RHS = I->getOperand(1);
// Make sure the LHS of the operand always has the greater rank...
if (LHSRank < RHSRank) {
- I->swapOperands();
+ bool Success = !I->swapOperands();
+ assert(Success && "swapOperands failed");
+
std::swap(LHS, RHS);
std::swap(LHSRank, RHSRank);
Changed = true;
++NumSwapped;
- //cerr << "Transposed: " << I << " Result BB: " << I->getParent();
+ DEBUG(std::cerr << "Transposed: " << I
+ /* << " Result BB: " << I->getParent()*/);
}
// If the LHS is the same operator as the current one is, and if we are the
// only expression using it...
//
if (BinaryOperator *LHSI = dyn_cast<BinaryOperator>(LHS))
- if (LHSI->getOpcode() == I->getOpcode() && LHSI->use_size() == 1) {
+ if (LHSI->getOpcode() == I->getOpcode() && LHSI->hasOneUse()) {
// If the rank of our current RHS is less than the rank of the LHS's LHS,
// then we reassociate the two instructions...
- if (RHSRank < getRank(LHSI->getOperand(0))) {
- unsigned TakeOp = 0;
- if (BinaryOperator *IOp = dyn_cast<BinaryOperator>(LHSI->getOperand(0)))
- if (IOp->getOpcode() == LHSI->getOpcode())
- TakeOp = 1; // Hoist out non-tree portion
+ unsigned TakeOp = 0;
+ if (BinaryOperator *IOp = dyn_cast<BinaryOperator>(LHSI->getOperand(0)))
+ if (IOp->getOpcode() == LHSI->getOpcode())
+ TakeOp = 1; // Hoist out non-tree portion
+
+ if (RHSRank < getRank(LHSI->getOperand(TakeOp))) {
// Convert ((a + 12) + 10) into (a + (12 + 10))
I->setOperand(0, LHSI->getOperand(TakeOp));
LHSI->setOperand(TakeOp, RHS);
I->setOperand(1, LHSI);
+ // Move the LHS expression forward, to ensure that it is dominated by
+ // its operands.
+ LHSI->getParent()->getInstList().remove(LHSI);
+ I->getParent()->getInstList().insert(I, LHSI);
+
++NumChanged;
- //cerr << "Reassociated: " << I << " Result BB: " << I->getParent();
+ DEBUG(std::cerr << "Reassociated: " << I/* << " Result BB: "
+ << I->getParent()*/);
// Since we modified the RHS instruction, make sure that we recheck it.
ReassociateExpr(LHSI);
+ ReassociateExpr(I);
return true;
}
}
}
+// 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, BasicBlock::iterator &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()) {
+ Value *RHS = NegateValue(I->getOperand(1), BI);
+ Value *LHS = NegateValue(I->getOperand(0), BI);
+
+ // We must actually insert a new add instruction here, because the neg
+ // instructions do not dominate the old add instruction in general. By
+ // adding it now, we are assured that the neg instructions we just
+ // inserted dominate the instruction we are about to insert after them.
+ //
+ return BinaryOperator::create(Instruction::Add, LHS, RHS,
+ I->getName()+".neg",
+ cast<Instruction>(RHS)->getNext());
+ }
+
+ // Insert a 'neg' instruction that subtracts the value from zero to get the
+ // negation.
+ //
+ return BI = BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
+}
+
+
bool Reassociate::ReassociateBB(BasicBlock *BB) {
bool Changed = false;
for (BasicBlock::iterator BI = BB->begin(); BI != BB->end(); ++BI) {
- Instruction *Inst = *BI;
-
- // If this instruction is a commutative binary operator, and the ranks of
- // the two operands are sorted incorrectly, fix it now.
- //
- if (BinaryOperator *I = isCommutativeOperator(Inst)) {
- // Make sure that this expression is correctly reassociated with respect
- // to it's used values...
- //
- Changed |= ReassociateExpr(I);
- } else if (Inst->getOpcode() == Instruction::Sub &&
- Inst->getOperand(0) != Constant::getNullValue(Inst->getType())) {
+ DEBUG(std::cerr << "Processing: " << *BI);
+ if (BI->getOpcode() == Instruction::Sub && !BinaryOperator::isNeg(BI)) {
// Convert a subtract into an add and a neg instruction... so that sub
// instructions can be commuted with other add instructions...
//
- Instruction *New = BinaryOperator::create(Instruction::Add,
- Inst->getOperand(0), Inst,
- Inst->getName());
+ // 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 = BI->getName();
+ BI->setName("");
+ Instruction *New =
+ BinaryOperator::create(Instruction::Add, BI->getOperand(0),
+ BI->getOperand(1), Name, BI);
+
// Everyone now refers to the add instruction...
- Inst->replaceAllUsesWith(New);
- Inst->setName(Inst->getOperand(1)->getName()+".neg");
- New->setOperand(1, Inst); // Except for the add inst itself!
+ BI->replaceAllUsesWith(New);
+
+ // Put the new add in the place of the subtract... deleting the subtract
+ BB->getInstList().erase(BI);
- BI = BB->getInstList().insert(BI+1, New)-1; // Add to the basic block...
- Inst->setOperand(0, Constant::getNullValue(Inst->getType()));
+ BI = New;
+ New->setOperand(1, NegateValue(New->getOperand(1), BI));
+
Changed = true;
+ DEBUG(std::cerr << "Negated: " << New /*<< " Result BB: " << BB*/);
+ }
+
+ // If this instruction is a commutative binary operator, and the ranks of
+ // the two operands are sorted incorrectly, fix it now.
+ //
+ if (BI->isAssociative()) {
+ BinaryOperator *I = cast<BinaryOperator>(BI);
+ if (!I->use_empty()) {
+ // Make sure that we don't have a tree-shaped computation. If we do,
+ // linearize it. Convert (A+B)+(C+D) into ((A+B)+C)+D
+ //
+ Instruction *LHSI = dyn_cast<Instruction>(I->getOperand(0));
+ Instruction *RHSI = dyn_cast<Instruction>(I->getOperand(1));
+ if (LHSI && (int)LHSI->getOpcode() == I->getOpcode() &&
+ RHSI && (int)RHSI->getOpcode() == I->getOpcode() &&
+ RHSI->hasOneUse()) {
+ // Insert a new temporary instruction... (A+B)+C
+ BinaryOperator *Tmp = BinaryOperator::create(I->getOpcode(), LHSI,
+ RHSI->getOperand(0),
+ RHSI->getName()+".ra",
+ BI);
+ BI = Tmp;
+ I->setOperand(0, Tmp);
+ I->setOperand(1, RHSI->getOperand(1));
+
+ // Process the temporary instruction for reassociation now.
+ I = Tmp;
+ ++NumLinear;
+ Changed = true;
+ DEBUG(std::cerr << "Linearized: " << I/* << " Result BB: " << BB*/);
+ }
+
+ // Make sure that this expression is correctly reassociated with respect
+ // to it's used values...
+ //
+ Changed |= ReassociateExpr(I);
+ }
}
}
}
-bool Reassociate::runOnFunction(Function *F) {
+bool Reassociate::runOnFunction(Function &F) {
// Recalculate the rank map for F
BuildRankMap(F);
bool Changed = false;
- for (Function::iterator FI = F->begin(), FE = F->end(); FI != FE; ++FI)
- Changed |= ReassociateBB(*FI);
+ for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
+ Changed |= ReassociateBB(FI);
// We are done with the rank map...
RankMap.clear();
+ ValueRankMap.clear();
return Changed;
}
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