mirror of
https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5983 91177308-0d34-0410-b5e6-96231b3b80d8
278 lines
10 KiB
C++
278 lines
10 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 propagation, 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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// This code was originally written by Chris Lattner, and was then cleaned up
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// and perfected by Casey Carter.
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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/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/Statistic.h"
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namespace {
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Statistic<> NumLinear ("reassociate","Number of insts linearized");
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Statistic<> NumChanged("reassociate","Number of insts reassociated");
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Statistic<> NumSwapped("reassociate","Number of insts with operands swapped");
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class Reassociate : public FunctionPass {
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std::map<BasicBlock*, unsigned> RankMap;
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std::map<Instruction*, unsigned> InstRankMap;
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public:
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bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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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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RegisterOpt<Reassociate> X("reassociate", "Reassociate expressions");
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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 that do not go through 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->mayWriteToMemory()) // Cannot move inst if it writes to memory!
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return RankMap[I->getParent()];
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unsigned &CachedRank = InstRankMap[I];
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if (CachedRank) return CachedRank; // Rank already known?
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// If not, compute it!
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unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
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for (unsigned i = 0, e = I->getNumOperands();
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i != e && Rank != MaxRank; ++i)
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Rank = std::max(Rank, getRank(I->getOperand(i)));
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return CachedRank = 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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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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bool Success = !I->swapOperands();
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assert(Success && "swapOperands failed");
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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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DEBUG(std::cerr << "Transposed: " << I
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/* << " 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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// Move the LHS expression forward, to ensure that it is dominated by
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// its operands.
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LHSI->getParent()->getInstList().remove(LHSI);
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I->getParent()->getInstList().insert(I, LHSI);
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++NumChanged;
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DEBUG(std::cerr << "Reassociated: " << I/* << " Result BB: "
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<< 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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// NegateValue - Insert instructions before the instruction pointed to by BI,
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// that computes the negative version of the value specified. The negative
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// version of the value is returned, and BI is left pointing at the instruction
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// that should be processed next by the reassociation pass.
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//
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static Value *NegateValue(Value *V, BasicBlock::iterator &BI) {
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// We are trying to expose opportunity for reassociation. One of the things
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// that we want to do to achieve this is to push a negation as deep into an
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// expression chain as possible, to expose the add instructions. In practice,
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// this means that we turn this:
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// X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
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// so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
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// the constants. We assume that instcombine will clean up the mess later if
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// we introduce tons of unneccesary negation instructions...
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//
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if (Instruction *I = dyn_cast<Instruction>(V))
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if (I->getOpcode() == Instruction::Add && I->use_size() == 1) {
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Value *RHS = NegateValue(I->getOperand(1), BI);
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Value *LHS = NegateValue(I->getOperand(0), BI);
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// We must actually insert a new add instruction here, because the neg
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// instructions do not dominate the old add instruction in general. By
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// adding it now, we are assured that the neg instructions we just
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// inserted dominate the instruction we are about to insert after them.
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//
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return BinaryOperator::create(Instruction::Add, LHS, RHS,
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I->getName()+".neg",
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cast<Instruction>(RHS)->getNext());
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}
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// Insert a 'neg' instruction that subtracts the value from zero to get the
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// negation.
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//
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return BI = BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
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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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DEBUG(std::cerr << "Processing: " << *BI);
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if (BI->getOpcode() == Instruction::Sub && !BinaryOperator::isNeg(BI)) {
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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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// Calculate the negative value of Operand 1 of the sub instruction...
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// and set it as the RHS of the add instruction we just made...
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//
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std::string Name = BI->getName();
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BI->setName("");
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Instruction *New =
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BinaryOperator::create(Instruction::Add, BI->getOperand(0),
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BI->getOperand(1), Name, BI);
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// Everyone now refers to the add instruction...
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BI->replaceAllUsesWith(New);
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// Put the new add in the place of the subtract... deleting the subtract
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BB->getInstList().erase(BI);
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BI = New;
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New->setOperand(1, NegateValue(New->getOperand(1), BI));
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Changed = true;
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DEBUG(std::cerr << "Negated: " << New /*<< " Result BB: " << BB*/);
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}
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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 (BI->isAssociative()) {
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BinaryOperator *I = cast<BinaryOperator>(BI);
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if (!I->use_empty()) {
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// Make sure that we don't have a tree-shaped computation. If we do,
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// linearize it. Convert (A+B)+(C+D) into ((A+B)+C)+D
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//
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Instruction *LHSI = dyn_cast<Instruction>(I->getOperand(0));
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Instruction *RHSI = dyn_cast<Instruction>(I->getOperand(1));
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if (LHSI && (int)LHSI->getOpcode() == I->getOpcode() &&
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RHSI && (int)RHSI->getOpcode() == I->getOpcode() &&
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RHSI->use_size() == 1) {
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// Insert a new temporary instruction... (A+B)+C
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BinaryOperator *Tmp = BinaryOperator::create(I->getOpcode(), LHSI,
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RHSI->getOperand(0),
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RHSI->getName()+".ra",
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BI);
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BI = Tmp;
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I->setOperand(0, Tmp);
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I->setOperand(1, RHSI->getOperand(1));
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// Process the temporary instruction for reassociation now.
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I = Tmp;
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++NumLinear;
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Changed = true;
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DEBUG(std::cerr << "Linearized: " << I/* << " Result BB: " << BB*/);
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}
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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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}
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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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InstRankMap.clear();
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return Changed;
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}
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