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llvm-6502/lib/Transforms/Scalar/Reassociate.cpp
Duncan Sands 0fd120b970 Make the reassociation pass more powerful so that it can handle expressions 
with arbitrary topologies (previously it would give up when hitting a diamond
in the use graph for example).  The testcase from PR12764 is now reduced from
a pile of additions to the optimal 1617*%x0+208.  In doing this I changed the
previous strategy of dropping all uses for expression leaves to one of dropping
all but one use.  This works out more neatly (but required a bunch of tweaks)
and is also safer: some recently fixed bugs during recursive linearization were
because the linearization code thinks it completely owns a node if it has no uses
outside the expression it is linearizing.  But if the node was also in another
expression that had been linearized (and thus all uses of the node from that
expression dropped) then the conclusion that it is completely owned by the
expression currently being linearized is wrong.  Keeping one use from within each
linearized expression avoids this kind of mistake.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157467 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-25 12:03:02 +00:00

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//===- Reassociate.cpp - Reassociate binary expressions -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass reassociates commutative expressions in an order that is designed
// to promote better constant propagation, GCSE, LICM, PRE, etc.
//
// For example: 4 + (x + 5) -> x + (4 + 5)
//
// In the implementation of this algorithm, constants are assigned rank = 0,
// function arguments are rank = 1, and other values are assigned ranks
// corresponding to the reverse post order traversal of current function
// (starting at 2), which effectively gives values in deep loops higher rank
// than values not in loops.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "reassociate"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SmallMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumChanged, "Number of insts reassociated");
STATISTIC(NumAnnihil, "Number of expr tree annihilated");
STATISTIC(NumFactor , "Number of multiplies factored");
namespace {
struct ValueEntry {
unsigned Rank;
Value *Op;
ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
};
inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
}
}
#ifndef NDEBUG
/// PrintOps - Print out the expression identified in the Ops list.
///
static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) {
Module *M = I->getParent()->getParent()->getParent();
dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " "
<< *Ops[0].Op->getType() << '\t';
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
dbgs() << "[ ";
WriteAsOperand(dbgs(), Ops[i].Op, false, M);
dbgs() << ", #" << Ops[i].Rank << "] ";
}
}
#endif
namespace {
/// \brief Utility class representing a base and exponent pair which form one
/// factor of some product.
struct Factor {
Value *Base;
unsigned Power;
Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {}
/// \brief Sort factors by their Base.
struct BaseSorter {
bool operator()(const Factor &LHS, const Factor &RHS) {
return LHS.Base < RHS.Base;
}
};
/// \brief Compare factors for equal bases.
struct BaseEqual {
bool operator()(const Factor &LHS, const Factor &RHS) {
return LHS.Base == RHS.Base;
}
};
/// \brief Sort factors in descending order by their power.
struct PowerDescendingSorter {
bool operator()(const Factor &LHS, const Factor &RHS) {
return LHS.Power > RHS.Power;
}
};
/// \brief Compare factors for equal powers.
struct PowerEqual {
bool operator()(const Factor &LHS, const Factor &RHS) {
return LHS.Power == RHS.Power;
}
};
};
}
namespace {
class Reassociate : public FunctionPass {
DenseMap<BasicBlock*, unsigned> RankMap;
DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
SmallVector<WeakVH, 8> RedoInsts;
SmallVector<WeakVH, 8> DeadInsts;
bool MadeChange;
public:
static char ID; // Pass identification, replacement for typeid
Reassociate() : FunctionPass(ID) {
initializeReassociatePass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
private:
void BuildRankMap(Function &F);
unsigned getRank(Value *V);
Value *ReassociateExpression(BinaryOperator *I);
void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
Value *OptimizeExpression(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops);
Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
bool collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
SmallVectorImpl<Factor> &Factors);
Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
SmallVectorImpl<Factor> &Factors);
Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
Value *RemoveFactorFromExpression(Value *V, Value *Factor);
void ReassociateInst(BasicBlock::iterator &BBI);
void RemoveDeadBinaryOp(Value *V);
};
}
char Reassociate::ID = 0;
INITIALIZE_PASS(Reassociate, "reassociate",
"Reassociate expressions", false, false)
// Public interface to the Reassociate pass
FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
/// isReassociableOp - Return true if V is an instruction of the specified
/// opcode and if it only has one use.
static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
if (V->hasOneUse() && isa<Instruction>(V) &&
cast<Instruction>(V)->getOpcode() == Opcode)
return cast<BinaryOperator>(V);
return 0;
}
void Reassociate::RemoveDeadBinaryOp(Value *V) {
BinaryOperator *Op = dyn_cast<BinaryOperator>(V);
if (!Op)
return;
ValueRankMap.erase(Op);
DeadInsts.push_back(Op);
BinaryOperator *LHS = isReassociableOp(Op->getOperand(0), Op->getOpcode());
BinaryOperator *RHS = isReassociableOp(Op->getOperand(1), Op->getOpcode());
Op->setOperand(0, UndefValue::get(Op->getType()));
Op->setOperand(1, UndefValue::get(Op->getType()));
if (LHS)
RemoveDeadBinaryOp(LHS);
if (RHS)
RemoveDeadBinaryOp(RHS);
}
static bool isUnmovableInstruction(Instruction *I) {
if (I->getOpcode() == Instruction::PHI ||
I->getOpcode() == Instruction::LandingPad ||
I->getOpcode() == Instruction::Alloca ||
I->getOpcode() == Instruction::Load ||
I->getOpcode() == Instruction::Invoke ||
(I->getOpcode() == Instruction::Call &&
!isa<DbgInfoIntrinsic>(I)) ||
I->getOpcode() == Instruction::UDiv ||
I->getOpcode() == Instruction::SDiv ||
I->getOpcode() == Instruction::FDiv ||
I->getOpcode() == Instruction::URem ||
I->getOpcode() == Instruction::SRem ||
I->getOpcode() == Instruction::FRem)
return true;
return false;
}
void Reassociate::BuildRankMap(Function &F) {
unsigned i = 2;
// Assign distinct ranks to function arguments
for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
ValueRankMap[&*I] = ++i;
ReversePostOrderTraversal<Function*> RPOT(&F);
for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
E = RPOT.end(); I != E; ++I) {
BasicBlock *BB = *I;
unsigned BBRank = RankMap[BB] = ++i << 16;
// Walk the basic block, adding precomputed ranks for any instructions that
// we cannot move. This ensures that the ranks for these instructions are
// all different in the block.
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
if (isUnmovableInstruction(I))
ValueRankMap[&*I] = ++BBRank;
}
}
unsigned Reassociate::getRank(Value *V) {
Instruction *I = dyn_cast<Instruction>(V);
if (I == 0) {
if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
return 0; // Otherwise it's a global or constant, rank 0.
}
if (unsigned Rank = ValueRankMap[I])
return Rank; // Rank already known?
// If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
// we can reassociate expressions for code motion! Since we do not recurse
// for PHI nodes, we cannot have infinite recursion here, because there
// cannot be loops in the value graph that do not go through PHI nodes.
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)));
// If this is a not or neg instruction, do not count it for rank. This
// assures us that X and ~X will have the same rank.
if (!I->getType()->isIntegerTy() ||
(!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
++Rank;
//DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
// << Rank << "\n");
return ValueRankMap[I] = Rank;
}
/// LowerNegateToMultiply - Replace 0-X with X*-1.
///
static BinaryOperator *LowerNegateToMultiply(Instruction *Neg,
DenseMap<AssertingVH<Value>, unsigned> &ValueRankMap) {
Constant *Cst = Constant::getAllOnesValue(Neg->getType());
BinaryOperator *Res =
BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
ValueRankMap.erase(Neg);
Res->takeName(Neg);
Neg->replaceAllUsesWith(Res);
Res->setDebugLoc(Neg->getDebugLoc());
Neg->eraseFromParent();
return Res;
}
/// LinearizeExprTree - Given an associative binary expression, return the leaf
/// nodes in Ops. The original expression is the same as Ops[0] op ... Ops[N].
/// Note that a node may occur multiple times in Ops, but if so all occurrences
/// are consecutive in the vector.
///
/// A leaf node is either not a binary operation of the same kind as the root
/// node 'I' (i.e. is not a binary operator at all, or is, but with a different
/// opcode), or is the same kind of binary operator but has a use which either
/// does not belong to the expression, or does belong to the expression but is
/// a leaf node. Every leaf node has at least one use that is a non-leaf node
/// of the expression, while for non-leaf nodes (except for the root 'I') every
/// use is a non-leaf node of the expression.
///
/// For example:
/// expression graph node names
///
/// + | I
/// / \ |
/// + + | A, B
/// / \ / \ |
/// * + * | C, D, E
/// / \ / \ / \ |
/// + * | F, G
///
/// The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in
/// that order) C, E, F, F, G, G.
///
/// The expression is maximal: if some instruction is a binary operator of the
/// same kind as 'I', and all of its uses are non-leaf nodes of the expression,
/// then the instruction also belongs to the expression, is not a leaf node of
/// it, and its operands also belong to the expression (but may be leaf nodes).
///
/// NOTE: This routine will set operands of non-leaf non-root nodes to undef in
/// order to ensure that every non-root node in the expression has *exactly one*
/// use by a non-leaf node of the expression. This destruction means that the
/// caller MUST use something like RewriteExprTree to put the values back in.
///
/// In the above example either the right operand of A or the left operand of B
/// will be replaced by undef. If it is B's operand then this gives:
///
/// + | I
/// / \ |
/// + + | A, B - operand of B replaced with undef
/// / \ \ |
/// * + * | C, D, E
/// / \ / \ / \ |
/// + * | F, G
///
/// Note that if you visit operands recursively starting from a leaf node then
/// you will never encounter such an undef operand unless you get back to 'I',
/// which requires passing through a phi node.
///
/// Note that this routine may also mutate binary operators of the wrong type
/// that have all uses inside the expression (i.e. only used by non-leaf nodes
/// of the expression) if it can turn them into binary operators of the right
/// type and thus make the expression bigger.
void Reassociate::LinearizeExprTree(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops) {
DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
// Visit all operands of the expression, keeping track of their weight (the
// number of paths from the expression root to the operand, or if you like
// the number of times that operand occurs in the linearized expression).
// For example, if I = X + A, where X = A + B, then I, X and B have weight 1
// while A has weight two.
// Worklist of non-leaf nodes (their operands are in the expression too) along
// with their weights, representing a certain number of paths to the operator.
// If an operator occurs in the worklist multiple times then we found multiple
// ways to get to it.
SmallVector<std::pair<BinaryOperator*, unsigned>, 8> Worklist; // (Op, Weight)
Worklist.push_back(std::make_pair(I, 1));
unsigned Opcode = I->getOpcode();
// Leaves of the expression are values that either aren't the right kind of
// operation (eg: a constant, or a multiply in an add tree), or are, but have
// some uses that are not inside the expression. For example, in I = X + X,
// X = A + B, the value X has two uses (by I) that are in the expression. If
// X has any other uses, for example in a return instruction, then we consider
// X to be a leaf, and won't analyze it further. When we first visit a value,
// if it has more than one use then at first we conservatively consider it to
// be a leaf. Later, as the expression is explored, we may discover some more
// uses of the value from inside the expression. If all uses turn out to be
// from within the expression (and the value is a binary operator of the right
// kind) then the value is no longer considered to be a leaf, and its operands
// are explored.
// Leaves - Keeps track of the set of putative leaves as well as the number of
// paths to each leaf seen so far.
typedef SmallMap<Value*, unsigned, 8> LeafMap;
LeafMap Leaves; // Leaf -> Total weight so far.
SmallVector<Value*, 8> LeafOrder; // Ensure deterministic leaf output order.
#ifndef NDEBUG
SmallPtrSet<Value*, 8> Visited; // For sanity checking the iteration scheme.
#endif
while (!Worklist.empty()) {
std::pair<BinaryOperator*, unsigned> P = Worklist.pop_back_val();
I = P.first; // We examine the operands of this binary operator.
assert(P.second >= 1 && "No paths to here, so how did we get here?!");
for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands.
Value *Op = I->getOperand(OpIdx);
unsigned Weight = P.second; // Number of paths to this operand.
DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n");
assert(!Op->use_empty() && "No uses, so how did we get to it?!");
// If this is a binary operation of the right kind with only one use then
// add its operands to the expression.
if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
assert(Visited.insert(Op) && "Not first visit!");
DEBUG(dbgs() << "DIRECT ADD: " << *Op << " (" << Weight << ")\n");
Worklist.push_back(std::make_pair(BO, Weight));
continue;
}
// Appears to be a leaf. Is the operand already in the set of leaves?
LeafMap::iterator It = Leaves.find(Op);
if (It == Leaves.end()) {
// Not in the leaf map. Must be the first time we saw this operand.
assert(Visited.insert(Op) && "Not first visit!");
if (!Op->hasOneUse()) {
// This value has uses not accounted for by the expression, so it is
// not safe to modify. Mark it as being a leaf.
DEBUG(dbgs() << "ADD USES LEAF: " << *Op << " (" << Weight << ")\n");
LeafOrder.push_back(Op);
Leaves[Op] = Weight;
continue;
}
// No uses outside the expression, try morphing it.
} else if (It != Leaves.end()) {
// Already in the leaf map.
assert(Visited.count(Op) && "In leaf map but not visited!");
// Update the number of paths to the leaf.
It->second += Weight;
// The leaf already has one use from inside the expression. As we want
// exactly one such use, drop this new use of the leaf.
assert(!Op->hasOneUse() && "Only one use, but we got here twice!");
I->setOperand(OpIdx, UndefValue::get(I->getType()));
MadeChange = true;
// If the leaf is a binary operation of the right kind and we now see
// that its multiple original uses were in fact all by nodes belonging
// to the expression, then no longer consider it to be a leaf and add
// its operands to the expression.
if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n");
Worklist.push_back(std::make_pair(BO, It->second));
Leaves.erase(It);
continue;
}
// If we still have uses that are not accounted for by the expression
// then it is not safe to modify the value.
if (!Op->hasOneUse())
continue;
// No uses outside the expression, try morphing it.
Weight = It->second;
Leaves.erase(It); // Since the value may be morphed below.
}
// At this point we have a value which, first of all, is not a binary
// expression of the right kind, and secondly, is only used inside the
// expression. This means that it can safely be modified. See if we
// can usefully morph it into an expression of the right kind.
assert((!isa<Instruction>(Op) ||
cast<Instruction>(Op)->getOpcode() != Opcode) &&
"Should have been handled above!");
assert(Op->hasOneUse() && "Has uses outside the expression tree!");
// If this is a multiply expression, turn any internal negations into
// multiplies by -1 so they can be reassociated.
BinaryOperator *BO = dyn_cast<BinaryOperator>(Op);
if (Opcode == Instruction::Mul && BO && BinaryOperator::isNeg(BO)) {
DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
BO = LowerNegateToMultiply(BO, ValueRankMap);
DEBUG(dbgs() << *BO << 'n');
Worklist.push_back(std::make_pair(BO, Weight));
MadeChange = true;
continue;
}
// Failed to morph into an expression of the right type. This really is
// a leaf.
DEBUG(dbgs() << "ADD LEAF: " << *Op << " (" << Weight << ")\n");
assert(!isReassociableOp(Op, Opcode) && "Value was morphed?");
LeafOrder.push_back(Op);
Leaves[Op] = Weight;
}
}
// The leaves, repeated according to their weights, represent the linearized
// form of the expression.
for (unsigned i = 0, e = LeafOrder.size(); i != e; ++i) {
Value *V = LeafOrder[i];
LeafMap::iterator It = Leaves.find(V);
if (It == Leaves.end())
// Leaf already output, or node initially thought to be a leaf wasn't.
continue;
assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!");
unsigned Weight = It->second;
assert(Weight > 0 && "No paths to this value!");
// FIXME: Rather than repeating values Weight times, use a vector of
// (ValueEntry, multiplicity) pairs.
Ops.append(Weight, ValueEntry(getRank(V), V));
// Ensure the leaf is only output once.
Leaves.erase(It);
}
}
// RewriteExprTree - Now that the operands for this expression tree are
// linearized and optimized, emit them in-order.
void Reassociate::RewriteExprTree(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops) {
assert(Ops.size() > 1 && "Single values should be used directly!");
// Since our optimizations never increase the number of operations, the new
// expression can always be written by reusing the existing binary operators
// from the original expression tree, without creating any new instructions,
// though the rewritten expression may have a completely different topology.
// We take care to not change anything if the new expression will be the same
// as the original. If more than trivial changes (like commuting operands)
// were made then we are obliged to clear out any optional subclass data like
// nsw flags.
/// NodesToRewrite - Nodes from the original expression available for writing
/// the new expression into.
SmallVector<BinaryOperator*, 8> NodesToRewrite;
unsigned Opcode = I->getOpcode();
NodesToRewrite.push_back(I);
// ExpressionChanged - Whether the rewritten expression differs non-trivially
// from the original, requiring the clearing of all optional flags.
bool ExpressionChanged = false;
BinaryOperator *Previous;
BinaryOperator *Op = 0;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
assert(!NodesToRewrite.empty() &&
"Optimized expressions has more nodes than original!");
Previous = Op; Op = NodesToRewrite.pop_back_val();
// Compactify the tree instructions together with each other to guarantee
// that the expression tree is dominated by all of Ops.
if (Previous)
Op->moveBefore(Previous);
// The last operation (which comes earliest in the IR) is special as both
// operands will come from Ops, rather than just one with the other being
// a subexpression.
if (i+2 == Ops.size()) {
Value *NewLHS = Ops[i].Op;
Value *NewRHS = Ops[i+1].Op;
Value *OldLHS = Op->getOperand(0);
Value *OldRHS = Op->getOperand(1);
if (NewLHS == OldLHS && NewRHS == OldRHS)
// Nothing changed, leave it alone.
break;
if (NewLHS == OldRHS && NewRHS == OldLHS) {
// The order of the operands was reversed. Swap them.
DEBUG(dbgs() << "RA: " << *Op << '\n');
Op->swapOperands();
DEBUG(dbgs() << "TO: " << *Op << '\n');
MadeChange = true;
++NumChanged;
break;
}
// The new operation differs non-trivially from the original. Overwrite
// the old operands with the new ones.
DEBUG(dbgs() << "RA: " << *Op << '\n');
if (NewLHS != OldLHS) {
if (BinaryOperator *BO = isReassociableOp(OldLHS, Opcode))
NodesToRewrite.push_back(BO);
Op->setOperand(0, NewLHS);
}
if (NewRHS != OldRHS) {
if (BinaryOperator *BO = isReassociableOp(OldRHS, Opcode))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
}
DEBUG(dbgs() << "TO: " << *Op << '\n');
ExpressionChanged = true;
MadeChange = true;
++NumChanged;
break;
}
// Not the last operation. The left-hand side will be a sub-expression
// while the right-hand side will be the current element of Ops.
Value *NewRHS = Ops[i].Op;
if (NewRHS != Op->getOperand(1)) {
DEBUG(dbgs() << "RA: " << *Op << '\n');
if (NewRHS == Op->getOperand(0)) {
// The new right-hand side was already present as the left operand. If
// we are lucky then swapping the operands will sort out both of them.
Op->swapOperands();
} else {
// Overwrite with the new right-hand side.
if (BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
ExpressionChanged = true;
}
DEBUG(dbgs() << "TO: " << *Op << '\n');
MadeChange = true;
++NumChanged;
}
// Now deal with the left-hand side. If this is already an operation node
// from the original expression then just rewrite the rest of the expression
// into it.
if (BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode)) {
NodesToRewrite.push_back(BO);
continue;
}
// Otherwise, grab a spare node from the original expression and use that as
// the left-hand side.
assert(!NodesToRewrite.empty() &&
"Optimized expressions has more nodes than original!");
DEBUG(dbgs() << "RA: " << *Op << '\n');
Op->setOperand(0, NodesToRewrite.back());
DEBUG(dbgs() << "TO: " << *Op << '\n');
ExpressionChanged = true;
MadeChange = true;
++NumChanged;
}
// If the expression changed non-trivially then clear out all subclass data in
// the entire rewritten expression.
if (ExpressionChanged) {
do {
Op->clearSubclassOptionalData();
if (Op == I)
break;
Op = cast<BinaryOperator>(*Op->use_begin());
} while (1);
}
// Throw away any left over nodes from the original expression.
for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
RemoveDeadBinaryOp(NodesToRewrite[i]);
}
/// 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, Instruction *BI) {
if (Constant *C = dyn_cast<Constant>(V))
return ConstantExpr::getNeg(C);
// 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 unnecessary negation instructions.
//
if (BinaryOperator *I = isReassociableOp(V, Instruction::Add)) {
// Push the negates through the add.
I->setOperand(0, NegateValue(I->getOperand(0), BI));
I->setOperand(1, NegateValue(I->getOperand(1), BI));
// We must move the add instruction here, because the neg instructions do
// not dominate the old add instruction in general. By moving it, we are
// assured that the neg instructions we just inserted dominate the
// instruction we are about to insert after them.
//
I->moveBefore(BI);
I->setName(I->getName()+".neg");
return I;
}
// Okay, we need to materialize a negated version of V with an instruction.
// Scan the use lists of V to see if we have one already.
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
User *U = *UI;
if (!BinaryOperator::isNeg(U)) continue;
// We found one! Now we have to make sure that the definition dominates
// this use. We do this by moving it to the entry block (if it is a
// non-instruction value) or right after the definition. These negates will
// be zapped by reassociate later, so we don't need much finesse here.
BinaryOperator *TheNeg = cast<BinaryOperator>(U);
// Verify that the negate is in this function, V might be a constant expr.
if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
continue;
BasicBlock::iterator InsertPt;
if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
InsertPt = II->getNormalDest()->begin();
} else {
InsertPt = InstInput;
++InsertPt;
}
while (isa<PHINode>(InsertPt)) ++InsertPt;
} else {
InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
}
TheNeg->moveBefore(InsertPt);
return TheNeg;
}
// Insert a 'neg' instruction that subtracts the value from zero to get the
// negation.
return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
}
/// ShouldBreakUpSubtract - Return true if we should break up this subtract of
/// X-Y into (X + -Y).
static bool ShouldBreakUpSubtract(Instruction *Sub) {
// If this is a negation, we can't split it up!
if (BinaryOperator::isNeg(Sub))
return false;
// Don't bother to break this up unless either the LHS is an associable add or
// subtract or if this is only used by one.
if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
isReassociableOp(Sub->getOperand(0), Instruction::Sub))
return true;
if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
isReassociableOp(Sub->getOperand(1), Instruction::Sub))
return true;
if (Sub->hasOneUse() &&
(isReassociableOp(Sub->use_back(), Instruction::Add) ||
isReassociableOp(Sub->use_back(), Instruction::Sub)))
return true;
return false;
}
/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
/// only used by an add, transform this into (X+(0-Y)) to promote better
/// reassociation.
static Instruction *BreakUpSubtract(Instruction *Sub,
DenseMap<AssertingVH<Value>, unsigned> &ValueRankMap) {
// Convert a subtract into an add and a neg instruction. This allows sub
// instructions to be commuted with other add instructions.
//
// Calculate the negative value of Operand 1 of the sub instruction,
// and set it as the RHS of the add instruction we just made.
//
Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
Instruction *New =
BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
New->takeName(Sub);
// Everyone now refers to the add instruction.
ValueRankMap.erase(Sub);
Sub->replaceAllUsesWith(New);
New->setDebugLoc(Sub->getDebugLoc());
Sub->eraseFromParent();
DEBUG(dbgs() << "Negated: " << *New << '\n');
return New;
}
/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
/// by one, change this into a multiply by a constant to assist with further
/// reassociation.
static Instruction *ConvertShiftToMul(Instruction *Shl,
DenseMap<AssertingVH<Value>, unsigned> &ValueRankMap) {
// If an operand of this shift is a reassociable multiply, or if the shift
// is used by a reassociable multiply or add, turn into a multiply.
if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
(Shl->hasOneUse() &&
(isReassociableOp(Shl->use_back(), Instruction::Mul) ||
isReassociableOp(Shl->use_back(), Instruction::Add)))) {
Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
Instruction *Mul =
BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
ValueRankMap.erase(Shl);
Mul->takeName(Shl);
Shl->replaceAllUsesWith(Mul);
Mul->setDebugLoc(Shl->getDebugLoc());
Shl->eraseFromParent();
return Mul;
}
return 0;
}
/// FindInOperandList - Scan backwards and forwards among values with the same
/// rank as element i to see if X exists. If X does not exist, return i. This
/// is useful when scanning for 'x' when we see '-x' because they both get the
/// same rank.
static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
Value *X) {
unsigned XRank = Ops[i].Rank;
unsigned e = Ops.size();
for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
if (Ops[j].Op == X)
return j;
// Scan backwards.
for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
if (Ops[j].Op == X)
return j;
return i;
}
/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
/// and returning the result. Insert the tree before I.
static Value *EmitAddTreeOfValues(Instruction *I,
SmallVectorImpl<WeakVH> &Ops){
if (Ops.size() == 1) return Ops.back();
Value *V1 = Ops.back();
Ops.pop_back();
Value *V2 = EmitAddTreeOfValues(I, Ops);
return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
}
/// RemoveFactorFromExpression - If V is an expression tree that is a
/// multiplication sequence, and if this sequence contains a multiply by Factor,
/// remove Factor from the tree and return the new tree.
Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
if (!BO) return 0;
SmallVector<ValueEntry, 8> Factors;
LinearizeExprTree(BO, Factors);
bool FoundFactor = false;
bool NeedsNegate = false;
for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
if (Factors[i].Op == Factor) {
FoundFactor = true;
Factors.erase(Factors.begin()+i);
break;
}
// If this is a negative version of this factor, remove it.
if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
if (FC1->getValue() == -FC2->getValue()) {
FoundFactor = NeedsNegate = true;
Factors.erase(Factors.begin()+i);
break;
}
}
if (!FoundFactor) {
// Make sure to restore the operands to the expression tree.
RewriteExprTree(BO, Factors);
return 0;
}
BasicBlock::iterator InsertPt = BO; ++InsertPt;
// If this was just a single multiply, remove the multiply and return the only
// remaining operand.
if (Factors.size() == 1) {
RemoveDeadBinaryOp(BO);
V = Factors[0].Op;
} else {
RewriteExprTree(BO, Factors);
V = BO;
}
if (NeedsNegate)
V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
return V;
}
/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
/// add its operands as factors, otherwise add V to the list of factors.
///
/// Ops is the top-level list of add operands we're trying to factor.
static void FindSingleUseMultiplyFactors(Value *V,
SmallVectorImpl<Value*> &Factors,
const SmallVectorImpl<ValueEntry> &Ops) {
BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
if (!BO) {
Factors.push_back(V);
return;
}
// Otherwise, add the LHS and RHS to the list of factors.
FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops);
FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops);
}
/// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
/// instruction. This optimizes based on identities. If it can be reduced to
/// a single Value, it is returned, otherwise the Ops list is mutated as
/// necessary.
static Value *OptimizeAndOrXor(unsigned Opcode,
SmallVectorImpl<ValueEntry> &Ops) {
// Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
// If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
// First, check for X and ~X in the operand list.
assert(i < Ops.size());
if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
unsigned FoundX = FindInOperandList(Ops, i, X);
if (FoundX != i) {
if (Opcode == Instruction::And) // ...&X&~X = 0
return Constant::getNullValue(X->getType());
if (Opcode == Instruction::Or) // ...|X|~X = -1
return Constant::getAllOnesValue(X->getType());
}
}
// Next, check for duplicate pairs of values, which we assume are next to
// each other, due to our sorting criteria.
assert(i < Ops.size());
if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
if (Opcode == Instruction::And || Opcode == Instruction::Or) {
// Drop duplicate values for And and Or.
Ops.erase(Ops.begin()+i);
--i; --e;
++NumAnnihil;
continue;
}
// Drop pairs of values for Xor.
assert(Opcode == Instruction::Xor);
if (e == 2)
return Constant::getNullValue(Ops[0].Op->getType());
// Y ^ X^X -> Y
Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
i -= 1; e -= 2;
++NumAnnihil;
}
}
return 0;
}
/// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
/// optimizes based on identities. If it can be reduced to a single Value, it
/// is returned, otherwise the Ops list is mutated as necessary.
Value *Reassociate::OptimizeAdd(Instruction *I,
SmallVectorImpl<ValueEntry> &Ops) {
// Scan the operand lists looking for X and -X pairs. If we find any, we
// can simplify the expression. X+-X == 0. While we're at it, scan for any
// duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
//
// TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
//
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
Value *TheOp = Ops[i].Op;
// Check to see if we've seen this operand before. If so, we factor all
// instances of the operand together. Due to our sorting criteria, we know
// that these need to be next to each other in the vector.
if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
// Rescan the list, remove all instances of this operand from the expr.
unsigned NumFound = 0;
do {
Ops.erase(Ops.begin()+i);
++NumFound;
} while (i != Ops.size() && Ops[i].Op == TheOp);
DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
++NumFactor;
// Insert a new multiply.
Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
// Now that we have inserted a multiply, optimize it. This allows us to
// handle cases that require multiple factoring steps, such as this:
// (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
RedoInsts.push_back(Mul);
// If every add operand was a duplicate, return the multiply.
if (Ops.empty())
return Mul;
// Otherwise, we had some input that didn't have the dupe, such as
// "A + A + B" -> "A*2 + B". Add the new multiply to the list of
// things being added by this operation.
Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
--i;
e = Ops.size();
continue;
}
// Check for X and -X in the operand list.
if (!BinaryOperator::isNeg(TheOp))
continue;
Value *X = BinaryOperator::getNegArgument(TheOp);
unsigned FoundX = FindInOperandList(Ops, i, X);
if (FoundX == i)
continue;
// Remove X and -X from the operand list.
if (Ops.size() == 2)
return Constant::getNullValue(X->getType());
Ops.erase(Ops.begin()+i);
if (i < FoundX)
--FoundX;
else
--i; // Need to back up an extra one.
Ops.erase(Ops.begin()+FoundX);
++NumAnnihil;
--i; // Revisit element.
e -= 2; // Removed two elements.
}
// Scan the operand list, checking to see if there are any common factors
// between operands. Consider something like A*A+A*B*C+D. We would like to
// reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
// To efficiently find this, we count the number of times a factor occurs
// for any ADD operands that are MULs.
DenseMap<Value*, unsigned> FactorOccurrences;
// Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
// where they are actually the same multiply.
unsigned MaxOcc = 0;
Value *MaxOccVal = 0;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
if (!BOp)
continue;
// Compute all of the factors of this added value.
SmallVector<Value*, 8> Factors;
FindSingleUseMultiplyFactors(BOp, Factors, Ops);
assert(Factors.size() > 1 && "Bad linearize!");
// Add one to FactorOccurrences for each unique factor in this op.
SmallPtrSet<Value*, 8> Duplicates;
for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
Value *Factor = Factors[i];
if (!Duplicates.insert(Factor)) continue;
unsigned Occ = ++FactorOccurrences[Factor];
if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
// If Factor is a negative constant, add the negated value as a factor
// because we can percolate the negate out. Watch for minint, which
// cannot be positivified.
if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
if (CI->isNegative() && !CI->isMinValue(true)) {
Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
assert(!Duplicates.count(Factor) &&
"Shouldn't have two constant factors, missed a canonicalize");
unsigned Occ = ++FactorOccurrences[Factor];
if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
}
}
}
// If any factor occurred more than one time, we can pull it out.
if (MaxOcc > 1) {
DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
++NumFactor;
// Create a new instruction that uses the MaxOccVal twice. If we don't do
// this, we could otherwise run into situations where removing a factor
// from an expression will drop a use of maxocc, and this can cause
// RemoveFactorFromExpression on successive values to behave differently.
Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
SmallVector<WeakVH, 4> NewMulOps;
for (unsigned i = 0; i != Ops.size(); ++i) {
// Only try to remove factors from expressions we're allowed to.
BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
if (!BOp)
continue;
if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
// The factorized operand may occur several times. Convert them all in
// one fell swoop.
for (unsigned j = Ops.size(); j != i;) {
--j;
if (Ops[j].Op == Ops[i].Op) {
NewMulOps.push_back(V);
Ops.erase(Ops.begin()+j);
}
}
--i;
}
}
// No need for extra uses anymore.
delete DummyInst;
unsigned NumAddedValues = NewMulOps.size();
Value *V = EmitAddTreeOfValues(I, NewMulOps);
// Now that we have inserted the add tree, optimize it. This allows us to
// handle cases that require multiple factoring steps, such as this:
// A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
(void)NumAddedValues;
RedoInsts.push_back(V);
// Create the multiply.
Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
// Rerun associate on the multiply in case the inner expression turned into
// a multiply. We want to make sure that we keep things in canonical form.
RedoInsts.push_back(V2);
// If every add operand included the factor (e.g. "A*B + A*C"), then the
// entire result expression is just the multiply "A*(B+C)".
if (Ops.empty())
return V2;
// Otherwise, we had some input that didn't have the factor, such as
// "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
// things being added by this operation.
Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
}
return 0;
}
namespace {
/// \brief Predicate tests whether a ValueEntry's op is in a map.
struct IsValueInMap {
const DenseMap<Value *, unsigned> &Map;
IsValueInMap(const DenseMap<Value *, unsigned> &Map) : Map(Map) {}
bool operator()(const ValueEntry &Entry) {
return Map.find(Entry.Op) != Map.end();
}
};
}
/// \brief Build up a vector of value/power pairs factoring a product.
///
/// Given a series of multiplication operands, build a vector of factors and
/// the powers each is raised to when forming the final product. Sort them in
/// the order of descending power.
///
/// (x*x) -> [(x, 2)]
/// ((x*x)*x) -> [(x, 3)]
/// ((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)]
///
/// \returns Whether any factors have a power greater than one.
bool Reassociate::collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
SmallVectorImpl<Factor> &Factors) {
// FIXME: Have Ops be (ValueEntry, Multiplicity) pairs, simplifying this.
// Compute the sum of powers of simplifiable factors.
unsigned FactorPowerSum = 0;
for (unsigned Idx = 1, Size = Ops.size(); Idx < Size; ++Idx) {
Value *Op = Ops[Idx-1].Op;
// Count the number of occurrences of this value.
unsigned Count = 1;
for (; Idx < Size && Ops[Idx].Op == Op; ++Idx)
++Count;
// Track for simplification all factors which occur 2 or more times.
if (Count > 1)
FactorPowerSum += Count;
}
// We can only simplify factors if the sum of the powers of our simplifiable
// factors is 4 or higher. When that is the case, we will *always* have
// a simplification. This is an important invariant to prevent cyclicly
// trying to simplify already minimal formations.
if (FactorPowerSum < 4)
return false;
// Now gather the simplifiable factors, removing them from Ops.
FactorPowerSum = 0;
for (unsigned Idx = 1; Idx < Ops.size(); ++Idx) {
Value *Op = Ops[Idx-1].Op;
// Count the number of occurrences of this value.
unsigned Count = 1;
for (; Idx < Ops.size() && Ops[Idx].Op == Op; ++Idx)
++Count;
if (Count == 1)
continue;
// Move an even number of occurences to Factors.
Count &= ~1U;
Idx -= Count;
FactorPowerSum += Count;
Factors.push_back(Factor(Op, Count));
Ops.erase(Ops.begin()+Idx, Ops.begin()+Idx+Count);
}
// None of the adjustments above should have reduced the sum of factor powers
// below our mininum of '4'.
assert(FactorPowerSum >= 4);
std::sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter());
return true;
}
/// \brief Build a tree of multiplies, computing the product of Ops.
static Value *buildMultiplyTree(IRBuilder<> &Builder,
SmallVectorImpl<Value*> &Ops) {
if (Ops.size() == 1)
return Ops.back();
Value *LHS = Ops.pop_back_val();
do {
LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
} while (!Ops.empty());
return LHS;
}
/// \brief Build a minimal multiplication DAG for (a^x)*(b^y)*(c^z)*...
///
/// Given a vector of values raised to various powers, where no two values are
/// equal and the powers are sorted in decreasing order, compute the minimal
/// DAG of multiplies to compute the final product, and return that product
/// value.
Value *Reassociate::buildMinimalMultiplyDAG(IRBuilder<> &Builder,
SmallVectorImpl<Factor> &Factors) {
assert(Factors[0].Power);
SmallVector<Value *, 4> OuterProduct;
for (unsigned LastIdx = 0, Idx = 1, Size = Factors.size();
Idx < Size && Factors[Idx].Power > 0; ++Idx) {
if (Factors[Idx].Power != Factors[LastIdx].Power) {
LastIdx = Idx;
continue;
}
// We want to multiply across all the factors with the same power so that
// we can raise them to that power as a single entity. Build a mini tree
// for that.
SmallVector<Value *, 4> InnerProduct;
InnerProduct.push_back(Factors[LastIdx].Base);
do {
InnerProduct.push_back(Factors[Idx].Base);
++Idx;
} while (Idx < Size && Factors[Idx].Power == Factors[LastIdx].Power);
// Reset the base value of the first factor to the new expression tree.
// We'll remove all the factors with the same power in a second pass.
Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct);
RedoInsts.push_back(Factors[LastIdx].Base);
LastIdx = Idx;
}
// Unique factors with equal powers -- we've folded them into the first one's
// base.
Factors.erase(std::unique(Factors.begin(), Factors.end(),
Factor::PowerEqual()),
Factors.end());
// Iteratively collect the base of each factor with an add power into the
// outer product, and halve each power in preparation for squaring the
// expression.
for (unsigned Idx = 0, Size = Factors.size(); Idx != Size; ++Idx) {
if (Factors[Idx].Power & 1)
OuterProduct.push_back(Factors[Idx].Base);
Factors[Idx].Power >>= 1;
}
if (Factors[0].Power) {
Value *SquareRoot = buildMinimalMultiplyDAG(Builder, Factors);
OuterProduct.push_back(SquareRoot);
OuterProduct.push_back(SquareRoot);
}
if (OuterProduct.size() == 1)
return OuterProduct.front();
Value *V = buildMultiplyTree(Builder, OuterProduct);
return V;
}
Value *Reassociate::OptimizeMul(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops) {
// We can only optimize the multiplies when there is a chain of more than
// three, such that a balanced tree might require fewer total multiplies.
if (Ops.size() < 4)
return 0;
// Try to turn linear trees of multiplies without other uses of the
// intermediate stages into minimal multiply DAGs with perfect sub-expression
// re-use.
SmallVector<Factor, 4> Factors;
if (!collectMultiplyFactors(Ops, Factors))
return 0; // All distinct factors, so nothing left for us to do.
IRBuilder<> Builder(I);
Value *V = buildMinimalMultiplyDAG(Builder, Factors);
if (Ops.empty())
return V;
ValueEntry NewEntry = ValueEntry(getRank(V), V);
Ops.insert(std::lower_bound(Ops.begin(), Ops.end(), NewEntry), NewEntry);
return 0;
}
Value *Reassociate::OptimizeExpression(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops) {
// Now that we have the linearized expression tree, try to optimize it.
// Start by folding any constants that we found.
bool IterateOptimization = false;
if (Ops.size() == 1) return Ops[0].Op;
unsigned Opcode = I->getOpcode();
if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
Ops.pop_back();
Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
return OptimizeExpression(I, Ops);
}
// Check for destructive annihilation due to a constant being used.
if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
switch (Opcode) {
default: break;
case Instruction::And:
if (CstVal->isZero()) // X & 0 -> 0
return CstVal;
if (CstVal->isAllOnesValue()) // X & -1 -> X
Ops.pop_back();
break;
case Instruction::Mul:
if (CstVal->isZero()) { // X * 0 -> 0
++NumAnnihil;
return CstVal;
}
if (cast<ConstantInt>(CstVal)->isOne())
Ops.pop_back(); // X * 1 -> X
break;
case Instruction::Or:
if (CstVal->isAllOnesValue()) // X | -1 -> -1
return CstVal;
// FALLTHROUGH!
case Instruction::Add:
case Instruction::Xor:
if (CstVal->isZero()) // X [|^+] 0 -> X
Ops.pop_back();
break;
}
if (Ops.size() == 1) return Ops[0].Op;
// Handle destructive annihilation due to identities between elements in the
// argument list here.
unsigned NumOps = Ops.size();
switch (Opcode) {
default: break;
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
return Result;
break;
case Instruction::Add:
if (Value *Result = OptimizeAdd(I, Ops))
return Result;
break;
case Instruction::Mul:
if (Value *Result = OptimizeMul(I, Ops))
return Result;
break;
}
if (IterateOptimization || Ops.size() != NumOps)
return OptimizeExpression(I, Ops);
return 0;
}
/// ReassociateInst - Inspect and reassociate the instruction at the
/// given position, post-incrementing the position.
void Reassociate::ReassociateInst(BasicBlock::iterator &BBI) {
Instruction *BI = BBI++;
if (BI->getOpcode() == Instruction::Shl &&
isa<ConstantInt>(BI->getOperand(1)))
if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) {
MadeChange = true;
BI = NI;
}
// Floating point binary operators are not associative, but we can still
// commute (some) of them, to canonicalize the order of their operands.
// This can potentially expose more CSE opportunities, and makes writing
// other transformations simpler.
if (isa<BinaryOperator>(BI) &&
(BI->getType()->isFloatingPointTy() || BI->getType()->isVectorTy())) {
// FAdd and FMul can be commuted.
if (BI->getOpcode() != Instruction::FMul &&
BI->getOpcode() != Instruction::FAdd)
return;
Value *LHS = BI->getOperand(0);
Value *RHS = BI->getOperand(1);
unsigned LHSRank = getRank(LHS);
unsigned RHSRank = getRank(RHS);
// Sort the operands by rank.
if (RHSRank < LHSRank) {
BI->setOperand(0, RHS);
BI->setOperand(1, LHS);
}
return;
}
// Do not reassociate operations that we do not understand.
if (!isa<BinaryOperator>(BI))
return;
// Do not reassociate boolean (i1) expressions. We want to preserve the
// original order of evaluation for short-circuited comparisons that
// SimplifyCFG has folded to AND/OR expressions. If the expression
// is not further optimized, it is likely to be transformed back to a
// short-circuited form for code gen, and the source order may have been
// optimized for the most likely conditions.
if (BI->getType()->isIntegerTy(1))
return;
// If this is a subtract instruction which is not already in negate form,
// see if we can convert it to X+-Y.
if (BI->getOpcode() == Instruction::Sub) {
if (ShouldBreakUpSubtract(BI)) {
BI = BreakUpSubtract(BI, ValueRankMap);
// Reset the BBI iterator in case BreakUpSubtract changed the
// instruction it points to.
BBI = BI;
++BBI;
MadeChange = true;
} else if (BinaryOperator::isNeg(BI)) {
// Otherwise, this is a negation. See if the operand is a multiply tree
// and if this is not an inner node of a multiply tree.
if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
(!BI->hasOneUse() ||
!isReassociableOp(BI->use_back(), Instruction::Mul))) {
BI = LowerNegateToMultiply(BI, ValueRankMap);
MadeChange = true;
}
}
}
// If this instruction is a commutative binary operator, process it.
if (!BI->isAssociative()) return;
BinaryOperator *I = cast<BinaryOperator>(BI);
// If this is an interior node of a reassociable tree, ignore it until we
// get to the root of the tree, to avoid N^2 analysis.
if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
return;
// If this is an add tree that is used by a sub instruction, ignore it
// until we process the subtract.
if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
return;
ReassociateExpression(I);
}
Value *Reassociate::ReassociateExpression(BinaryOperator *I) {
// First, walk the expression tree, linearizing the tree, collecting the
// operand information.
SmallVector<ValueEntry, 8> Ops;
LinearizeExprTree(I, Ops);
// Now that we have linearized the tree to a list and have gathered all of
// the operands and their ranks, sort the operands by their rank. Use a
// stable_sort so that values with equal ranks will have their relative
// positions maintained (and so the compiler is deterministic). Note that
// this sorts so that the highest ranking values end up at the beginning of
// the vector.
std::stable_sort(Ops.begin(), Ops.end());
DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
// OptimizeExpression - Now that we have the expression tree in a convenient
// sorted form, optimize it globally if possible.
if (Value *V = OptimizeExpression(I, Ops)) {
// This expression tree simplified to something that isn't a tree,
// eliminate it.
DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
I->replaceAllUsesWith(V);
if (Instruction *VI = dyn_cast<Instruction>(V))
VI->setDebugLoc(I->getDebugLoc());
RemoveDeadBinaryOp(I);
++NumAnnihil;
return V;
}
// We want to sink immediates as deeply as possible except in the case where
// this is a multiply tree used only by an add, and the immediate is a -1.
// In this case we reassociate to put the negation on the outside so that we
// can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
isa<ConstantInt>(Ops.back().Op) &&
cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
ValueEntry Tmp = Ops.pop_back_val();
Ops.insert(Ops.begin(), Tmp);
}
DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
if (Ops.size() == 1) {
// This expression tree simplified to something that isn't a tree,
// eliminate it.
I->replaceAllUsesWith(Ops[0].Op);
if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op))
OI->setDebugLoc(I->getDebugLoc());
RemoveDeadBinaryOp(I);
return Ops[0].Op;
}
// Now that we ordered and optimized the expressions, splat them back into
// the expression tree, removing any unneeded nodes.
RewriteExprTree(I, Ops);
return I;
}
bool Reassociate::runOnFunction(Function &F) {
// Recalculate the rank map for F
BuildRankMap(F);
MadeChange = false;
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
for (BasicBlock::iterator BBI = FI->begin(); BBI != FI->end(); )
ReassociateInst(BBI);
// Now that we're done, revisit any instructions which are likely to
// have secondary reassociation opportunities.
while (!RedoInsts.empty())
if (Value *V = RedoInsts.pop_back_val()) {
BasicBlock::iterator BBI = cast<Instruction>(V);
ReassociateInst(BBI);
}
// We are done with the rank map.
RankMap.clear();
ValueRankMap.clear();
// Now that we're done, delete any instructions which are no longer used.
while (!DeadInsts.empty())
if (Value *V = DeadInsts.pop_back_val())
RecursivelyDeleteTriviallyDeadInstructions(V);
return MadeChange;
}
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