llvm-6502/lib/Transforms/Scalar/Reassociate.cpp
Bob Wilson fc375d2200 Do not reassociate expressions with i1 type. SimplifyCFG converts some
short-circuited conditions to AND/OR expressions, and those expressions
are often converted back to a short-circuited form in code gen.  The
original source order may have been optimized to take advantage of the
expected values, and if we reassociate them, we change the order and
subvert that optimization.  Radar 7497329.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95333 91177308-0d34-0410-b5e6-96231b3b80d8
2010-02-04 23:32:37 +00:00

1058 lines
38 KiB
C++

//===- 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/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/Debug.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/DenseMap.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumLinear , "Number of insts linearized");
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 {
class Reassociate : public FunctionPass {
DenseMap<BasicBlock*, unsigned> RankMap;
DenseMap<AssertingVH<>, unsigned> ValueRankMap;
bool MadeChange;
public:
static char ID; // Pass identification, replacement for typeid
Reassociate() : FunctionPass(&ID) {}
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,
unsigned Idx = 0);
Value *OptimizeExpression(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops);
Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
void LinearizeExpr(BinaryOperator *I);
Value *RemoveFactorFromExpression(Value *V, Value *Factor);
void ReassociateBB(BasicBlock *BB);
void RemoveDeadBinaryOp(Value *V);
};
}
char Reassociate::ID = 0;
static RegisterPass<Reassociate> X("reassociate", "Reassociate expressions");
// Public interface to the Reassociate pass
FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
void Reassociate::RemoveDeadBinaryOp(Value *V) {
Instruction *Op = dyn_cast<Instruction>(V);
if (!Op || !isa<BinaryOperator>(Op) || !Op->use_empty())
return;
Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
ValueRankMap.erase(Op);
Op->eraseFromParent();
RemoveDeadBinaryOp(LHS);
RemoveDeadBinaryOp(RHS);
}
static bool isUnmovableInstruction(Instruction *I) {
if (I->getOpcode() == Instruction::PHI ||
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()->isInteger() ||
(!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
++Rank;
//DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
// << Rank << "\n");
return ValueRankMap[I] = Rank;
}
/// 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() || V->use_empty()) && isa<Instruction>(V) &&
cast<Instruction>(V)->getOpcode() == Opcode)
return cast<BinaryOperator>(V);
return 0;
}
/// LowerNegateToMultiply - Replace 0-X with X*-1.
///
static Instruction *LowerNegateToMultiply(Instruction *Neg,
DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
Constant *Cst = Constant::getAllOnesValue(Neg->getType());
Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
ValueRankMap.erase(Neg);
Res->takeName(Neg);
Neg->replaceAllUsesWith(Res);
Neg->eraseFromParent();
return Res;
}
// Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
// Note that if D is also part of the expression tree that we recurse to
// linearize it as well. Besides that case, this does not recurse into A,B, or
// C.
void Reassociate::LinearizeExpr(BinaryOperator *I) {
BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
assert(isReassociableOp(LHS, I->getOpcode()) &&
isReassociableOp(RHS, I->getOpcode()) &&
"Not an expression that needs linearization?");
DEBUG(dbgs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n');
// Move the RHS instruction to live immediately before I, avoiding breaking
// dominator properties.
RHS->moveBefore(I);
// Move operands around to do the linearization.
I->setOperand(1, RHS->getOperand(0));
RHS->setOperand(0, LHS);
I->setOperand(0, RHS);
++NumLinear;
MadeChange = true;
DEBUG(dbgs() << "Linearized: " << *I << '\n');
// If D is part of this expression tree, tail recurse.
if (isReassociableOp(I->getOperand(1), I->getOpcode()))
LinearizeExpr(I);
}
/// LinearizeExprTree - Given an associative binary expression tree, traverse
/// all of the uses putting it into canonical form. This forces a left-linear
/// form of the the expression (((a+b)+c)+d), and collects information about the
/// rank of the non-tree operands.
///
/// NOTE: These intentionally destroys the expression tree operands (turning
/// them into undef values) to reduce #uses of the values. This means that the
/// caller MUST use something like RewriteExprTree to put the values back in.
///
void Reassociate::LinearizeExprTree(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops) {
Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
unsigned Opcode = I->getOpcode();
// First step, linearize the expression if it is in ((A+B)+(C+D)) form.
BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
// If this is a multiply expression tree and it contains internal negations,
// transform them into multiplies by -1 so they can be reassociated.
if (I->getOpcode() == Instruction::Mul) {
if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap);
LHSBO = isReassociableOp(LHS, Opcode);
}
if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap);
RHSBO = isReassociableOp(RHS, Opcode);
}
}
if (!LHSBO) {
if (!RHSBO) {
// Neither the LHS or RHS as part of the tree, thus this is a leaf. As
// such, just remember these operands and their rank.
Ops.push_back(ValueEntry(getRank(LHS), LHS));
Ops.push_back(ValueEntry(getRank(RHS), RHS));
// Clear the leaves out.
I->setOperand(0, UndefValue::get(I->getType()));
I->setOperand(1, UndefValue::get(I->getType()));
return;
}
// Turn X+(Y+Z) -> (Y+Z)+X
std::swap(LHSBO, RHSBO);
std::swap(LHS, RHS);
bool Success = !I->swapOperands();
assert(Success && "swapOperands failed");
Success = false;
MadeChange = true;
} else if (RHSBO) {
// Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not
// part of the expression tree.
LinearizeExpr(I);
LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
RHS = I->getOperand(1);
RHSBO = 0;
}
// Okay, now we know that the LHS is a nested expression and that the RHS is
// not. Perform reassociation.
assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
// Move LHS right before I to make sure that the tree expression dominates all
// values.
LHSBO->moveBefore(I);
// Linearize the expression tree on the LHS.
LinearizeExprTree(LHSBO, Ops);
// Remember the RHS operand and its rank.
Ops.push_back(ValueEntry(getRank(RHS), RHS));
// Clear the RHS leaf out.
I->setOperand(1, UndefValue::get(I->getType()));
}
// RewriteExprTree - Now that the operands for this expression tree are
// linearized and optimized, emit them in-order. This function is written to be
// tail recursive.
void Reassociate::RewriteExprTree(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops,
unsigned i) {
if (i+2 == Ops.size()) {
if (I->getOperand(0) != Ops[i].Op ||
I->getOperand(1) != Ops[i+1].Op) {
Value *OldLHS = I->getOperand(0);
DEBUG(dbgs() << "RA: " << *I << '\n');
I->setOperand(0, Ops[i].Op);
I->setOperand(1, Ops[i+1].Op);
DEBUG(dbgs() << "TO: " << *I << '\n');
MadeChange = true;
++NumChanged;
// If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
// delete the extra, now dead, nodes.
RemoveDeadBinaryOp(OldLHS);
}
return;
}
assert(i+2 < Ops.size() && "Ops index out of range!");
if (I->getOperand(1) != Ops[i].Op) {
DEBUG(dbgs() << "RA: " << *I << '\n');
I->setOperand(1, Ops[i].Op);
DEBUG(dbgs() << "TO: " << *I << '\n');
MadeChange = true;
++NumChanged;
}
BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
assert(LHS->getOpcode() == I->getOpcode() &&
"Improper expression tree!");
// Compactify the tree instructions together with each other to guarantee
// that the expression tree is dominated by all of Ops.
LHS->moveBefore(I);
RewriteExprTree(LHS, Ops, i+1);
}
// 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 (Instruction *I = dyn_cast<Instruction>(V))
if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
// 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){
if (!BinaryOperator::isNeg(*UI)) 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>(*UI);
// 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<>, 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);
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<>, 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);
Shl->eraseFromParent();
return Mul;
}
return 0;
}
// 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<Value*> &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) {
ValueRankMap.erase(BO);
BO->eraseFromParent();
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.
static void FindSingleUseMultiplyFactors(Value *V,
SmallVectorImpl<Value*> &Factors) {
BinaryOperator *BO;
if ((!V->hasOneUse() && !V->use_empty()) ||
!(BO = dyn_cast<BinaryOperator>(V)) ||
BO->getOpcode() != Instruction::Mul) {
Factors.push_back(V);
return;
}
// Otherwise, add the LHS and RHS to the list of factors.
FindSingleUseMultiplyFactors(BO->getOperand(1), Factors);
FindSingleUseMultiplyFactors(BO->getOperand(0), Factors);
}
/// 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
Mul = ReassociateExpression(cast<BinaryOperator>(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 = dyn_cast<BinaryOperator>(Ops[i].Op);
if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
continue;
// Compute all of the factors of this added value.
SmallVector<Value*, 8> Factors;
FindSingleUseMultiplyFactors(BOp, Factors);
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->getValue().isNegative() && !CI->getValue().isMinSignedValue()) {
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<Value*, 4> NewMulOps;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
// Only try to remove factors from expressions we're allowed to.
BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
continue;
if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
NewMulOps.push_back(V);
Ops.erase(Ops.begin()+i);
--i; --e;
}
}
// 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;
V = ReassociateExpression(cast<BinaryOperator>(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.
V2 = ReassociateExpression(cast<BinaryOperator>(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;
}
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.
switch (Opcode) {
default: break;
case Instruction::And:
case Instruction::Or:
case Instruction::Xor: {
unsigned NumOps = Ops.size();
if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
return Result;
IterateOptimization |= Ops.size() != NumOps;
break;
}
case Instruction::Add: {
unsigned NumOps = Ops.size();
if (Value *Result = OptimizeAdd(I, Ops))
return Result;
IterateOptimization |= Ops.size() != NumOps;
}
break;
//case Instruction::Mul:
}
if (IterateOptimization)
return OptimizeExpression(I, Ops);
return 0;
}
/// ReassociateBB - Inspect all of the instructions in this basic block,
/// reassociating them as we go.
void Reassociate::ReassociateBB(BasicBlock *BB) {
for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
Instruction *BI = BBI++;
if (BI->getOpcode() == Instruction::Shl &&
isa<ConstantInt>(BI->getOperand(1)))
if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) {
MadeChange = true;
BI = NI;
}
// Reject cases where it is pointless to do this.
if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() ||
isa<VectorType>(BI->getType()))
continue; // Floating point ops are not associative.
// 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()->isInteger(1))
continue;
// 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()) continue;
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()))
continue;
// 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)
continue;
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);
DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
// 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());
// 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);
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);
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)
ReassociateBB(FI);
// We are done with the rank map.
RankMap.clear();
ValueRankMap.clear();
return MadeChange;
}