#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");
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(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
I->setOperand(1, 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);
}
+// 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 = BI;
+
+ // Scan through the inserted instructions, looking for RHS, which must be
+ // after LHS in the instruction list.
+ while (*NBI != RHS) ++NBI;
+
+ Instruction *Add =
+ BinaryOperator::create(Instruction::Add, LHS, RHS, I->getName()+".neg");
+ BB->getInstList().insert(NBI+1, 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) {
// 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 (!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));
+
+ // 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 (Inst->getOpcode() == Instruction::Sub &&
Inst->getOperand(0) != Constant::getNullValue(Inst->getType())) {
// instructions can be commuted with other add instructions...
//
Instruction *New = BinaryOperator::create(Instruction::Add,
- Inst->getOperand(0), Inst,
+ Inst->getOperand(0),
+ Inst->getOperand(1),
Inst->getName());
+ Value *NegatedValue = Inst->getOperand(1);
+
// 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 = BB->getInstList().insert(BI+1, New)-1; // Add to the basic block...
- Inst->setOperand(0, Constant::getNullValue(Inst->getType()));
+ // Put the new add in the place of the subtract... deleting the subtract
+ delete BB->getInstList().replaceWith(BI, New);
+
+ // 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);
}
}
projects / oota-llvm.git / blobdiff