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https://github.com/c64scene-ar/llvm-6502.git
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the command line git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2601 91177308-0d34-0410-b5e6-96231b3b80d8
206 lines
6.9 KiB
C++
206 lines
6.9 KiB
C++
//===- Reassociate.cpp - Reassociate binary expressions -------------------===//
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//
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// This pass reassociates commutative expressions in an order that is designed
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// to promote better constant propogation, GCSE, LICM, PRE...
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//
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// For example: 4 + (x + 5) -> x + (4 + 5)
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//
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// Note that this pass works best if left shifts have been promoted to explicit
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// multiplies before this pass executes.
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//
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// In the implementation of this algorithm, constants are assigned rank = 0,
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// function arguments are rank = 1, and other values are assigned ranks
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// corresponding to the reverse post order traversal of current function
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// (starting at 2), which effectively gives values in deep loops higher rank
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// than values not in loops.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Function.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/iOperators.h"
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#include "llvm/Type.h"
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#include "llvm/Pass.h"
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#include "llvm/Constant.h"
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#include "llvm/Support/CFG.h"
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#include "Support/PostOrderIterator.h"
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#include "Support/StatisticReporter.h"
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static Statistic<> NumChanged("reassociate\t- Number of insts reassociated");
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static Statistic<> NumSwapped("reassociate\t- Number of insts with operands swapped");
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namespace {
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class Reassociate : public FunctionPass {
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map<BasicBlock*, unsigned> RankMap;
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public:
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const char *getPassName() const {
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return "Expression Reassociation";
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}
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bool runOnFunction(Function *F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.preservesCFG();
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}
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private:
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void BuildRankMap(Function *F);
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unsigned getRank(Value *V);
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bool ReassociateExpr(BinaryOperator *I);
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bool ReassociateBB(BasicBlock *BB);
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};
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}
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Pass *createReassociatePass() { return new Reassociate(); }
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void Reassociate::BuildRankMap(Function *F) {
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unsigned i = 1;
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ReversePostOrderTraversal<Function*> RPOT(F);
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for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
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E = RPOT.end(); I != E; ++I)
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RankMap[*I] = ++i;
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}
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unsigned Reassociate::getRank(Value *V) {
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if (isa<Argument>(V)) return 1; // Function argument...
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if (Instruction *I = dyn_cast<Instruction>(V)) {
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// If this is an expression, return the MAX(rank(LHS), rank(RHS)) so that we
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// can reassociate expressions for code motion! Since we do not recurse for
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// PHI nodes, we cannot have infinite recursion here, because there cannot
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// be loops in the value graph (except for PHI nodes).
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//
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if (I->getOpcode() == Instruction::PHINode ||
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I->getOpcode() == Instruction::Alloca ||
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I->getOpcode() == Instruction::Malloc || isa<TerminatorInst>(I) ||
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I->hasSideEffects())
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return RankMap[I->getParent()];
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unsigned Rank = 0;
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
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Rank = std::max(Rank, getRank(I->getOperand(i)));
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return Rank;
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}
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// Otherwise it's a global or constant, rank 0.
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return 0;
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}
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// isCommutativeOperator - Return true if the specified instruction is
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// commutative and associative. If the instruction is not commutative and
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// associative, we can not reorder its operands!
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//
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static inline BinaryOperator *isCommutativeOperator(Instruction *I) {
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// Floating point operations do not commute!
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if (I->getType()->isFloatingPoint()) return 0;
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if (I->getOpcode() == Instruction::Add ||
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I->getOpcode() == Instruction::Mul ||
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I->getOpcode() == Instruction::And ||
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I->getOpcode() == Instruction::Or ||
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I->getOpcode() == Instruction::Xor)
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return cast<BinaryOperator>(I);
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return 0;
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}
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bool Reassociate::ReassociateExpr(BinaryOperator *I) {
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Value *LHS = I->getOperand(0);
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Value *RHS = I->getOperand(1);
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unsigned LHSRank = getRank(LHS);
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unsigned RHSRank = getRank(RHS);
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bool Changed = false;
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// Make sure the LHS of the operand always has the greater rank...
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if (LHSRank < RHSRank) {
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I->swapOperands();
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std::swap(LHS, RHS);
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std::swap(LHSRank, RHSRank);
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Changed = true;
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++NumSwapped;
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//cerr << "Transposed: " << I << " Result BB: " << I->getParent();
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}
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// If the LHS is the same operator as the current one is, and if we are the
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// only expression using it...
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//
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if (BinaryOperator *LHSI = dyn_cast<BinaryOperator>(LHS))
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if (LHSI->getOpcode() == I->getOpcode() && LHSI->use_size() == 1) {
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// If the rank of our current RHS is less than the rank of the LHS's LHS,
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// then we reassociate the two instructions...
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if (RHSRank < getRank(LHSI->getOperand(0))) {
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unsigned TakeOp = 0;
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if (BinaryOperator *IOp = dyn_cast<BinaryOperator>(LHSI->getOperand(0)))
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if (IOp->getOpcode() == LHSI->getOpcode())
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TakeOp = 1; // Hoist out non-tree portion
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// Convert ((a + 12) + 10) into (a + (12 + 10))
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I->setOperand(0, LHSI->getOperand(TakeOp));
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LHSI->setOperand(TakeOp, RHS);
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I->setOperand(1, LHSI);
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++NumChanged;
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//cerr << "Reassociated: " << I << " Result BB: " << I->getParent();
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// Since we modified the RHS instruction, make sure that we recheck it.
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ReassociateExpr(LHSI);
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return true;
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}
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}
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return Changed;
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}
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bool Reassociate::ReassociateBB(BasicBlock *BB) {
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bool Changed = false;
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for (BasicBlock::iterator BI = BB->begin(); BI != BB->end(); ++BI) {
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Instruction *Inst = *BI;
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// If this instruction is a commutative binary operator, and the ranks of
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// the two operands are sorted incorrectly, fix it now.
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//
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if (BinaryOperator *I = isCommutativeOperator(Inst)) {
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// Make sure that this expression is correctly reassociated with respect
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// to it's used values...
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//
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Changed |= ReassociateExpr(I);
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} else if (Inst->getOpcode() == Instruction::Sub &&
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Inst->getOperand(0) != Constant::getNullValue(Inst->getType())) {
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// Convert a subtract into an add and a neg instruction... so that sub
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// instructions can be commuted with other add instructions...
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//
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Instruction *New = BinaryOperator::create(Instruction::Add,
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Inst->getOperand(0), Inst,
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Inst->getName());
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// Everyone now refers to the add instruction...
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Inst->replaceAllUsesWith(New);
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Inst->setName(Inst->getOperand(1)->getName()+".neg");
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New->setOperand(1, Inst); // Except for the add inst itself!
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BI = BB->getInstList().insert(BI+1, New)-1; // Add to the basic block...
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Inst->setOperand(0, Constant::getNullValue(Inst->getType()));
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Changed = true;
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}
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}
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return Changed;
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}
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bool Reassociate::runOnFunction(Function *F) {
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// Recalculate the rank map for F
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BuildRankMap(F);
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bool Changed = false;
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for (Function::iterator FI = F->begin(), FE = F->end(); FI != FE; ++FI)
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Changed |= ReassociateBB(*FI);
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// We are done with the rank map...
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RankMap.clear();
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return Changed;
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}
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