#include "llvm/Constant.h"
#include "llvm/Support/CFG.h"
#include "Support/PostOrderIterator.h"
+#include "Support/StatisticReporter.h"
+
+static Statistic<> NumLinear ("reassociate\t- Number of insts linearized");
+static Statistic<> NumChanged("reassociate\t- Number of insts reassociated");
+static Statistic<> NumSwapped("reassociate\t- Number of insts with operands swapped");
namespace {
class Reassociate : public FunctionPass {
- map<BasicBlock*, unsigned> RankMap;
+ std::map<BasicBlock*, unsigned> RankMap;
public:
- const char *getPassName() const {
- return "Expression Reassociation";
- }
-
- bool runOnFunction(Function *F);
+ bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.preservesCFG();
}
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) {
+void Reassociate::BuildRankMap(Function &F) {
unsigned i = 1;
- ReversePostOrderTraversal<Function*> RPOT(F);
+ ReversePostOrderTraversal<Function*> RPOT(&F);
for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
E = RPOT.end(); I != E; ++I)
RankMap[*I] = ++i;
I->hasSideEffects())
return RankMap[I->getParent()];
- unsigned Rank = 0;
- for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ 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;
std::swap(LHS, RHS);
std::swap(LHSRank, RHSRank);
Changed = true;
- //cerr << "Transposed: " << I << " Result BB: " << I->getParent();
+ ++NumSwapped;
+ 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
LHSI->setOperand(TakeOp, RHS);
I->setOperand(1, LHSI);
- //cerr << "Reassociated: " << I << " Result BB: " << I->getParent();
+ ++NumChanged;
+ DEBUG(std::cerr << "Reassociated: " << I << " Result BB: "
+ << I->getParent());
// Since we modified the RHS instruction, make sure that we recheck it.
ReassociateExpr(LHSI);
}
+// 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 *BB, 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 unneccesary negation instructions...
+ //
+ if (Instruction *I = dyn_cast<Instruction>(V))
+ if (I->getOpcode() == Instruction::Add && I->use_size() == 1) {
+ Value *RHS = NegateValue(I->getOperand(1), BB, BI);
+ Value *LHS = NegateValue(I->getOperand(0), BB, 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.
+ //
+ BasicBlock::iterator NBI = cast<Instruction>(RHS);
+
+ Instruction *Add =
+ BinaryOperator::create(Instruction::Add, LHS, RHS, I->getName()+".neg");
+ BB->getInstList().insert(++NBI, Add); // Add to the basic block...
+ return Add;
+ }
+
+ // Insert a 'neg' instruction that subtracts the value from zero to get the
+ // negation.
+ //
+ Instruction *Neg =
+ BinaryOperator::create(Instruction::Sub,
+ Constant::getNullValue(V->getType()), V,
+ V->getName()+".neg");
+ BI = BB->getInstList().insert(BI, Neg); // Add to the basic block...
+ return Neg;
+}
+
+
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);
+ if (BinaryOperator *I = isCommutativeOperator(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->use_size() == 1) {
+ // Insert a new temporary instruction... (A+B)+C
+ BinaryOperator *Tmp = BinaryOperator::create(I->getOpcode(), LHSI,
+ RHSI->getOperand(0),
+ RHSI->getName()+".ra");
+ BI = BB->getInstList().insert(BI, Tmp); // Add to the basic block...
+ I->setOperand(0, Tmp);
+ I->setOperand(1, RHSI->getOperand(1));
- } else if (Inst->getOpcode() == Instruction::Sub &&
- Inst->getOperand(0) != Constant::getNullValue(Inst->getType())) {
+ // 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);
+ }
+
+ } else if (BI->getOpcode() == Instruction::Sub &&
+ BI->getOperand(0) != Constant::getNullValue(BI->getType())) {
// 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()+".add");
+ BI->getOperand(0),
+ BI->getOperand(1),
+ BI->getName());
+ Value *NegatedValue = BI->getOperand(1);
+
// Everyone now refers to the add instruction...
- Inst->replaceAllUsesWith(New);
- 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
+ BI = BB->getInstList().erase(BI);
+ BI = ++BB->getInstList().insert(BI, New);
- BI = BB->getInstList().insert(BI+1, New)-1; // Add to the basic block...
- Inst->setOperand(0, Constant::getNullValue(Inst->getType()));
+ // Calculate the negative value of Operand 1 of the sub instruction...
+ // and set it as the RHS of the add instruction we just made...
+ New->setOperand(1, NegateValue(NegatedValue, BB, BI));
+ --BI;
Changed = true;
+ DEBUG(std::cerr << "Negated: " << New << " Result BB: " << BB);
}
}
}
-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();
projects / oota-llvm.git / blobdiff