//===- Reassociate.cpp - Reassociate binary expressions -------------------===//
//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and 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...
//
// For example: 4 + (x + 5) -> x + (4 + 5)
//
-// Note that this pass works best if left shifts have been promoted to explicit
-// multiplies before this pass executes.
-//
// 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.
//
-// This code was originally written by Chris Lattner, and was then cleaned up
-// and perfected by Casey Carter.
-//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "reassociate"
#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
#include "llvm/Function.h"
-#include "llvm/iOperators.h"
-#include "llvm/Type.h"
+#include "llvm/Instructions.h"
#include "llvm/Pass.h"
-#include "llvm/Constant.h"
+#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
-#include "Support/Debug.h"
-#include "Support/PostOrderIterator.h"
-#include "Support/Statistic.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
namespace {
Statistic<> NumLinear ("reassociate","Number of insts linearized");
class Reassociate : public FunctionPass {
std::map<BasicBlock*, unsigned> RankMap;
- std::map<Instruction*, unsigned> InstRankMap;
+ std::map<Value*, unsigned> ValueRankMap;
public:
bool runOnFunction(Function &F);
RegisterOpt<Reassociate> X("reassociate", "Reassociate expressions");
}
-Pass *createReassociatePass() { return new Reassociate(); }
+// Public interface to the Reassociate pass
+FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
void Reassociate::BuildRankMap(Function &F) {
- unsigned i = 1;
+ 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)
- RankMap[*I] = ++i;
+ RankMap[*I] = ++i << 16;
}
unsigned Reassociate::getRank(Value *V) {
- if (isa<Argument>(V)) return 1; // Function argument...
- if (Instruction *I = dyn_cast<Instruction>(V)) {
- // If this is an expression, return the 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.
- //
- if (I->getOpcode() == Instruction::PHINode ||
- I->getOpcode() == Instruction::Alloca ||
- I->getOpcode() == Instruction::Malloc || isa<TerminatorInst>(I) ||
- I->mayWriteToMemory()) // Cannot move inst if it writes to memory!
- return RankMap[I->getParent()];
-
- unsigned &CachedRank = InstRankMap[I];
- if (CachedRank) return CachedRank; // Rank already known?
-
- // If not, compute it!
- 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)));
-
- return CachedRank = Rank;
- }
+ if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument...
+
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (I == 0) return 0; // Otherwise it's a global or constant, rank 0.
- // Otherwise it's a global or constant, rank 0.
- return 0;
+ unsigned &CachedRank = ValueRankMap[I];
+ if (CachedRank) return CachedRank; // 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.
+ //
+ if (I->getOpcode() == Instruction::PHI ||
+ I->getOpcode() == Instruction::Alloca ||
+ I->getOpcode() == Instruction::Malloc || isa<TerminatorInst>(I) ||
+ I->mayWriteToMemory()) // Cannot move inst if it writes to memory!
+ return RankMap[I->getParent()];
+
+ // If not, compute it!
+ 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)));
+
+ DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = "
+ << Rank+1 << "\n");
+
+ return CachedRank = Rank+1;
}
Value *RHS = I->getOperand(1);
unsigned LHSRank = getRank(LHS);
unsigned RHSRank = getRank(RHS);
-
+
bool Changed = false;
// Make sure the LHS of the operand always has the greater rank...
std::swap(LHSRank, RHSRank);
Changed = true;
++NumSwapped;
- DEBUG(std::cerr << "Transposed: " << I
+ DEBUG(std::cerr << "Transposed: " << *I
/* << " Result BB: " << I->getParent()*/);
}
-
+
// If the LHS is the same operator as the current one is, and if we are the
// only expression using it...
//
if (BinaryOperator *LHSI = dyn_cast<BinaryOperator>(LHS))
- if (LHSI->getOpcode() == I->getOpcode() && LHSI->use_size() == 1) {
+ if (LHSI->getOpcode() == I->getOpcode() && LHSI->hasOneUse()) {
// If the rank of our current RHS is less than the rank of the LHS's LHS,
// then we reassociate the two instructions...
- if (RHSRank < getRank(LHSI->getOperand(0))) {
- unsigned TakeOp = 0;
- if (BinaryOperator *IOp = dyn_cast<BinaryOperator>(LHSI->getOperand(0)))
- if (IOp->getOpcode() == LHSI->getOpcode())
- TakeOp = 1; // Hoist out non-tree portion
+ unsigned TakeOp = 0;
+ if (BinaryOperator *IOp = dyn_cast<BinaryOperator>(LHSI->getOperand(0)))
+ if (IOp->getOpcode() == LHSI->getOpcode())
+ TakeOp = 1; // Hoist out non-tree portion
+
+ if (RHSRank < getRank(LHSI->getOperand(TakeOp))) {
// Convert ((a + 12) + 10) into (a + (12 + 10))
I->setOperand(0, LHSI->getOperand(TakeOp));
LHSI->setOperand(TakeOp, RHS);
I->getParent()->getInstList().insert(I, LHSI);
++NumChanged;
- DEBUG(std::cerr << "Reassociated: " << I/* << " Result BB: "
+ DEBUG(std::cerr << "Reassociated: " << *I/* << " Result BB: "
<< I->getParent()*/);
// Since we modified the RHS instruction, make sure that we recheck it.
ReassociateExpr(LHSI);
+ ReassociateExpr(I);
return true;
}
}
// 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, BasicBlock::iterator &BI) {
+static Value *NegateValue(Value *V, Instruction *BI) {
// 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,
// 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 unneccesary negation instructions...
+ // we introduce tons of unnecessary negation instructions...
//
if (Instruction *I = dyn_cast<Instruction>(V))
- if (I->getOpcode() == Instruction::Add && I->use_size() == 1) {
+ if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
Value *RHS = NegateValue(I->getOperand(1), BI);
Value *LHS = NegateValue(I->getOperand(0), BI);
// inserted dominate the instruction we are about to insert after them.
//
return BinaryOperator::create(Instruction::Add, LHS, RHS,
- I->getName()+".neg",
- cast<Instruction>(RHS)->getNext());
+ I->getName()+".neg", BI);
}
// Insert a 'neg' instruction that subtracts the value from zero to get the
// negation.
//
- return BI = BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
+ return BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
+}
+
+/// isReassociableOp - Return true if V is an instruction of the specified
+/// opcode and if it only has one use.
+static bool isReassociableOp(Value *V, unsigned Opcode) {
+ return V->hasOneUse() && isa<Instruction>(V) &&
+ cast<Instruction>(V)->getOpcode() == Opcode;
}
+/// 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) {
+ // Reject cases where it is pointless to do this.
+ if (Sub->getType()->isFloatingPoint())
+ return 0; // Floating point adds are not associative.
+
+ // Don't bother to break this up unless either the LHS is an associable add or
+ // if this is only used by one.
+ if (!isReassociableOp(Sub->getOperand(0), Instruction::Add) &&
+ !isReassociableOp(Sub->getOperand(1), Instruction::Add) &&
+ !(Sub->hasOneUse() &&isReassociableOp(Sub->use_back(), Instruction::Add)))
+ return 0;
+
+ // Convert a subtract into an add and a neg instruction... so that sub
+ // instructions can 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...
+ //
+ std::string Name = Sub->getName();
+ Sub->setName("");
+ Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
+ Instruction *New =
+ BinaryOperator::createAdd(Sub->getOperand(0), NegVal, Name, Sub);
+
+ // Everyone now refers to the add instruction.
+ Sub->replaceAllUsesWith(New);
+ Sub->eraseFromParent();
+
+ DEBUG(std::cerr << "Negated: " << *New);
+ 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) {
+ if (!isReassociableOp(Shl->getOperand(0), Instruction::Mul) &&
+ !(Shl->hasOneUse() && isReassociableOp(Shl->use_back(),Instruction::Mul)))
+ return 0;
+
+ Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
+ MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
+
+ std::string Name = Shl->getName(); Shl->setName("");
+ Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst,
+ Name, Shl);
+ Shl->replaceAllUsesWith(Mul);
+ Shl->eraseFromParent();
+ return Mul;
+}
+
+
+/// ReassociateBB - Inspect all of the instructions in this basic block,
+/// reassociating them as we go.
bool Reassociate::ReassociateBB(BasicBlock *BB) {
bool Changed = false;
for (BasicBlock::iterator BI = BB->begin(); BI != BB->end(); ++BI) {
-
- DEBUG(std::cerr << "Processing: " << *BI);
- if (BI->getOpcode() == Instruction::Sub && !BinaryOperator::isNeg(BI)) {
- // Convert a subtract into an add and a neg instruction... so that sub
- // instructions can 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...
- //
- std::string Name = BI->getName();
- BI->setName("");
- Instruction *New =
- BinaryOperator::create(Instruction::Add, BI->getOperand(0),
- BI->getOperand(1), Name, BI);
-
- // Everyone now refers to the add instruction...
- BI->replaceAllUsesWith(New);
-
- // Put the new add in the place of the subtract... deleting the subtract
- BB->getInstList().erase(BI);
-
- BI = New;
- New->setOperand(1, NegateValue(New->getOperand(1), BI));
-
- Changed = true;
- DEBUG(std::cerr << "Negated: " << New /*<< " Result BB: " << BB*/);
- }
+ // 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 && !BinaryOperator::isNeg(BI))
+ if (Instruction *NI = BreakUpSubtract(BI)) {
+ Changed = true;
+ BI = NI;
+ }
+ if (BI->getOpcode() == Instruction::Shl &&
+ isa<ConstantInt>(BI->getOperand(1)))
+ if (Instruction *NI = ConvertShiftToMul(BI)) {
+ Changed = true;
+ BI = NI;
+ }
// If this instruction is a commutative binary operator, and the ranks of
// the two operands are sorted incorrectly, fix it now.
//
if (BI->isAssociative()) {
+ DEBUG(std::cerr << "Reassociating: " << *BI);
BinaryOperator *I = cast<BinaryOperator>(BI);
if (!I->use_empty()) {
// Make sure that we don't have a tree-shaped computation. If we do,
Instruction *RHSI = dyn_cast<Instruction>(I->getOperand(1));
if (LHSI && (int)LHSI->getOpcode() == I->getOpcode() &&
RHSI && (int)RHSI->getOpcode() == I->getOpcode() &&
- RHSI->use_size() == 1) {
+ RHSI->hasOneUse()) {
// Insert a new temporary instruction... (A+B)+C
BinaryOperator *Tmp = BinaryOperator::create(I->getOpcode(), LHSI,
RHSI->getOperand(0),
I = Tmp;
++NumLinear;
Changed = true;
- DEBUG(std::cerr << "Linearized: " << I/* << " Result BB: " << BB*/);
+ DEBUG(std::cerr << "Linearized: " << *I/* << " Result BB: " << BB*/);
}
// Make sure that this expression is correctly reassociated with respect
// We are done with the rank map...
RankMap.clear();
- InstRankMap.clear();
+ ValueRankMap.clear();
return Changed;
}
+
projects / oota-llvm.git / blobdiff