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https://github.com/c64scene-ar/llvm-6502.git
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Simplify the code and rearrange it. No major functionality changes here.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21759 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -12,9 +12,6 @@
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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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@ -23,6 +20,7 @@
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "reassociate"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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@ -78,35 +76,33 @@ void Reassociate::BuildRankMap(Function &F) {
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unsigned Reassociate::getRank(Value *V) {
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if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument...
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if (Instruction *I = dyn_cast<Instruction>(V)) {
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// If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
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// we can reassociate expressions for code motion! Since we do not recurse
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// for PHI nodes, we cannot have infinite recursion here, because there
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// cannot 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::PHI ||
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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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Instruction *I = dyn_cast<Instruction>(V);
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if (I == 0) return 0; // Otherwise it's a global or constant, rank 0.
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unsigned &CachedRank = ValueRankMap[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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DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = "
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<< Rank+1 << "\n");
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return CachedRank = Rank+1;
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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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unsigned &CachedRank = ValueRankMap[I];
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if (CachedRank) return CachedRank; // Rank already known?
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// If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
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// we can reassociate expressions for code motion! Since we do not recurse
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// for PHI nodes, we cannot have infinite recursion here, because there
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// cannot 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::PHI ||
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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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// 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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DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = "
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<< Rank+1 << "\n");
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return CachedRank = Rank+1;
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}
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@ -175,7 +171,7 @@ bool Reassociate::ReassociateExpr(BinaryOperator *I) {
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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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static Value *NegateValue(Value *V, Instruction *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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@ -196,52 +192,76 @@ static Value *NegateValue(Value *V, BasicBlock::iterator &BI) {
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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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I->getName()+".neg", BI);
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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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return BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
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}
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/// isReassociableOp - Return true if V is an instruction of the specified
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/// opcode and if it only has one use.
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static bool isReassociableOp(Value *V, unsigned Opcode) {
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return V->hasOneUse() && isa<Instruction>(V) &&
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cast<Instruction>(V)->getOpcode() == Opcode;
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}
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/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
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/// only used by an add, transform this into (X+(0-Y)) to promote better
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/// reassociation.
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static Instruction *BreakUpSubtract(Instruction *Sub) {
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// Reject cases where it is pointless to do this.
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if (Sub->getType()->isFloatingPoint())
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return 0; // Floating point adds are not associative.
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// Don't bother to break this up unless either the LHS is an associable add or
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// if this is only used by one.
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if (!isReassociableOp(Sub->getOperand(0), Instruction::Add) &&
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!isReassociableOp(Sub->getOperand(1), Instruction::Add) &&
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!(Sub->hasOneUse() &&isReassociableOp(Sub->use_back(), Instruction::Add)))
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return 0;
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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 = Sub->getName();
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Sub->setName("");
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Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
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Instruction *New =
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BinaryOperator::createAdd(Sub->getOperand(0), NegVal, Name, Sub);
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// Everyone now refers to the add instruction.
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Sub->replaceAllUsesWith(New);
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Sub->eraseFromParent();
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DEBUG(std::cerr << "Negated: " << *New);
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return New;
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}
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/// ReassociateBB - Inspect all of the instructions in this basic block,
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/// reassociating them as we go.
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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 << "Reassociating: " << *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 is a subtract instruction which is not already in negate form,
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// see if we can convert it to X+-Y.
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if (BI->getOpcode() == Instruction::Sub && !BinaryOperator::isNeg(BI))
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if (Instruction *NI = BreakUpSubtract(BI)) {
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Changed = true;
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BI = NI;
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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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DEBUG(std::cerr << "Reassociating: " << *BI);
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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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