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llvm-mirror/lib/Transforms/Scalar/Reassociate.cpp
Arthur Eubanks 7a1762f190 [NewPM] Don't mark AA analyses as preserved 
Currently all AA analyses marked as preserved are stateless, not taking
into account their dependent analyses. So there's no need to mark them
as preserved, they won't be invalidated unless their analyses are.

SCEVAAResults was the one exception to this, it was treated like a
typical analysis result. Make it like the others and don't invalidate
unless SCEV is invalidated.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D102032
2021-05-18 13:49:03 -07:00

2617 lines
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//===- Reassociate.cpp - Reassociate binary expressions -------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/Reassociate.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
#include <cassert>
#include <utility>
using namespace llvm;
using namespace reassociate;
using namespace PatternMatch;
#define DEBUG_TYPE "reassociate"
STATISTIC(NumChanged, "Number of insts reassociated");
STATISTIC(NumAnnihil, "Number of expr tree annihilated");
STATISTIC(NumFactor , "Number of multiplies factored");
#ifndef NDEBUG
/// Print out the expression identified in the Ops list.
static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) {
Module *M = I->getModule();
dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " "
<< *Ops[0].Op->getType() << '\t';
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
dbgs() << "[ ";
Ops[i].Op->printAsOperand(dbgs(), false, M);
dbgs() << ", #" << Ops[i].Rank << "] ";
}
}
#endif
/// Utility class representing a non-constant Xor-operand. We classify
/// non-constant Xor-Operands into two categories:
/// C1) The operand is in the form "X & C", where C is a constant and C != ~0
/// C2)
/// C2.1) The operand is in the form of "X | C", where C is a non-zero
/// constant.
/// C2.2) Any operand E which doesn't fall into C1 and C2.1, we view this
/// operand as "E | 0"
class llvm::reassociate::XorOpnd {
public:
XorOpnd(Value *V);
bool isInvalid() const { return SymbolicPart == nullptr; }
bool isOrExpr() const { return isOr; }
Value *getValue() const { return OrigVal; }
Value *getSymbolicPart() const { return SymbolicPart; }
unsigned getSymbolicRank() const { return SymbolicRank; }
const APInt &getConstPart() const { return ConstPart; }
void Invalidate() { SymbolicPart = OrigVal = nullptr; }
void setSymbolicRank(unsigned R) { SymbolicRank = R; }
private:
Value *OrigVal;
Value *SymbolicPart;
APInt ConstPart;
unsigned SymbolicRank;
bool isOr;
};
XorOpnd::XorOpnd(Value *V) {
assert(!isa<ConstantInt>(V) && "No ConstantInt");
OrigVal = V;
Instruction *I = dyn_cast<Instruction>(V);
SymbolicRank = 0;
if (I && (I->getOpcode() == Instruction::Or ||
I->getOpcode() == Instruction::And)) {
Value *V0 = I->getOperand(0);
Value *V1 = I->getOperand(1);
const APInt *C;
if (match(V0, m_APInt(C)))
std::swap(V0, V1);
if (match(V1, m_APInt(C))) {
ConstPart = *C;
SymbolicPart = V0;
isOr = (I->getOpcode() == Instruction::Or);
return;
}
}
// view the operand as "V | 0"
SymbolicPart = V;
ConstPart = APInt::getNullValue(V->getType()->getScalarSizeInBits());
isOr = true;
}
/// 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) {
auto *I = dyn_cast<Instruction>(V);
if (I && I->hasOneUse() && I->getOpcode() == Opcode)
if (!isa<FPMathOperator>(I) || I->isFast())
return cast<BinaryOperator>(I);
return nullptr;
}
static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode1,
unsigned Opcode2) {
auto *I = dyn_cast<Instruction>(V);
if (I && I->hasOneUse() &&
(I->getOpcode() == Opcode1 || I->getOpcode() == Opcode2))
if (!isa<FPMathOperator>(I) || I->isFast())
return cast<BinaryOperator>(I);
return nullptr;
}
void ReassociatePass::BuildRankMap(Function &F,
ReversePostOrderTraversal<Function*> &RPOT) {
unsigned Rank = 2;
// Assign distinct ranks to function arguments.
for (auto &Arg : F.args()) {
ValueRankMap[&Arg] = ++Rank;
LLVM_DEBUG(dbgs() << "Calculated Rank[" << Arg.getName() << "] = " << Rank
<< "\n");
}
// Traverse basic blocks in ReversePostOrder.
for (BasicBlock *BB : RPOT) {
unsigned BBRank = RankMap[BB] = ++Rank << 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 (Instruction &I : *BB)
if (mayBeMemoryDependent(I))
ValueRankMap[&I] = ++BBRank;
}
}
unsigned ReassociatePass::getRank(Value *V) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) {
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 (!match(I, m_Not(m_Value())) && !match(I, m_Neg(m_Value())) &&
!match(I, m_FNeg(m_Value())))
++Rank;
LLVM_DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = " << Rank
<< "\n");
return ValueRankMap[I] = Rank;
}
// Canonicalize constants to RHS. Otherwise, sort the operands by rank.
void ReassociatePass::canonicalizeOperands(Instruction *I) {
assert(isa<BinaryOperator>(I) && "Expected binary operator.");
assert(I->isCommutative() && "Expected commutative operator.");
Value *LHS = I->getOperand(0);
Value *RHS = I->getOperand(1);
if (LHS == RHS || isa<Constant>(RHS))
return;
if (isa<Constant>(LHS) || getRank(RHS) < getRank(LHS))
cast<BinaryOperator>(I)->swapOperands();
}
static BinaryOperator *CreateAdd(Value *S1, Value *S2, const Twine &Name,
Instruction *InsertBefore, Value *FlagsOp) {
if (S1->getType()->isIntOrIntVectorTy())
return BinaryOperator::CreateAdd(S1, S2, Name, InsertBefore);
else {
BinaryOperator *Res =
BinaryOperator::CreateFAdd(S1, S2, Name, InsertBefore);
Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
return Res;
}
}
static BinaryOperator *CreateMul(Value *S1, Value *S2, const Twine &Name,
Instruction *InsertBefore, Value *FlagsOp) {
if (S1->getType()->isIntOrIntVectorTy())
return BinaryOperator::CreateMul(S1, S2, Name, InsertBefore);
else {
BinaryOperator *Res =
BinaryOperator::CreateFMul(S1, S2, Name, InsertBefore);
Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
return Res;
}
}
static Instruction *CreateNeg(Value *S1, const Twine &Name,
Instruction *InsertBefore, Value *FlagsOp) {
if (S1->getType()->isIntOrIntVectorTy())
return BinaryOperator::CreateNeg(S1, Name, InsertBefore);
if (auto *FMFSource = dyn_cast<Instruction>(FlagsOp))
return UnaryOperator::CreateFNegFMF(S1, FMFSource, Name, InsertBefore);
return UnaryOperator::CreateFNeg(S1, Name, InsertBefore);
}
/// Replace 0-X with X*-1.
static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) {
assert((isa<UnaryOperator>(Neg) || isa<BinaryOperator>(Neg)) &&
"Expected a Negate!");
// FIXME: It's not safe to lower a unary FNeg into a FMul by -1.0.
unsigned OpNo = isa<BinaryOperator>(Neg) ? 1 : 0;
Type *Ty = Neg->getType();
Constant *NegOne = Ty->isIntOrIntVectorTy() ?
ConstantInt::getAllOnesValue(Ty) : ConstantFP::get(Ty, -1.0);
BinaryOperator *Res = CreateMul(Neg->getOperand(OpNo), NegOne, "", Neg, Neg);
Neg->setOperand(OpNo, Constant::getNullValue(Ty)); // Drop use of op.
Res->takeName(Neg);
Neg->replaceAllUsesWith(Res);
Res->setDebugLoc(Neg->getDebugLoc());
return Res;
}
/// Returns k such that lambda(2^Bitwidth) = 2^k, where lambda is the Carmichael
/// function. This means that x^(2^k) === 1 mod 2^Bitwidth for
/// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic.
/// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every
/// even x in Bitwidth-bit arithmetic.
static unsigned CarmichaelShift(unsigned Bitwidth) {
if (Bitwidth < 3)
return Bitwidth - 1;
return Bitwidth - 2;
}
/// Add the extra weight 'RHS' to the existing weight 'LHS',
/// reducing the combined weight using any special properties of the operation.
/// The existing weight LHS represents the computation X op X op ... op X where
/// X occurs LHS times. The combined weight represents X op X op ... op X with
/// X occurring LHS + RHS times. If op is "Xor" for example then the combined
/// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even;
/// the routine returns 1 in LHS in the first case, and 0 in LHS in the second.
static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) {
// If we were working with infinite precision arithmetic then the combined
// weight would be LHS + RHS. But we are using finite precision arithmetic,
// and the APInt sum LHS + RHS may not be correct if it wraps (it is correct
// for nilpotent operations and addition, but not for idempotent operations
// and multiplication), so it is important to correctly reduce the combined
// weight back into range if wrapping would be wrong.
// If RHS is zero then the weight didn't change.
if (RHS.isMinValue())
return;
// If LHS is zero then the combined weight is RHS.
if (LHS.isMinValue()) {
LHS = RHS;
return;
}
// From this point on we know that neither LHS nor RHS is zero.
if (Instruction::isIdempotent(Opcode)) {
// Idempotent means X op X === X, so any non-zero weight is equivalent to a
// weight of 1. Keeping weights at zero or one also means that wrapping is
// not a problem.
assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
return; // Return a weight of 1.
}
if (Instruction::isNilpotent(Opcode)) {
// Nilpotent means X op X === 0, so reduce weights modulo 2.
assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
LHS = 0; // 1 + 1 === 0 modulo 2.
return;
}
if (Opcode == Instruction::Add || Opcode == Instruction::FAdd) {
// TODO: Reduce the weight by exploiting nsw/nuw?
LHS += RHS;
return;
}
assert((Opcode == Instruction::Mul || Opcode == Instruction::FMul) &&
"Unknown associative operation!");
unsigned Bitwidth = LHS.getBitWidth();
// If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth
// can be replaced with W-CM. That's because x^W=x^(W-CM) for every Bitwidth
// bit number x, since either x is odd in which case x^CM = 1, or x is even in
// which case both x^W and x^(W - CM) are zero. By subtracting off multiples
// of CM like this weights can always be reduced to the range [0, CM+Bitwidth)
// which by a happy accident means that they can always be represented using
// Bitwidth bits.
// TODO: Reduce the weight by exploiting nsw/nuw? (Could do much better than
// the Carmichael number).
if (Bitwidth > 3) {
/// CM - The value of Carmichael's lambda function.
APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth));
// Any weight W >= Threshold can be replaced with W - CM.
APInt Threshold = CM + Bitwidth;
assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!");
// For Bitwidth 4 or more the following sum does not overflow.
LHS += RHS;
while (LHS.uge(Threshold))
LHS -= CM;
} else {
// To avoid problems with overflow do everything the same as above but using
// a larger type.
unsigned CM = 1U << CarmichaelShift(Bitwidth);
unsigned Threshold = CM + Bitwidth;
assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold &&
"Weights not reduced!");
unsigned Total = LHS.getZExtValue() + RHS.getZExtValue();
while (Total >= Threshold)
Total -= CM;
LHS = Total;
}
}
using RepeatedValue = std::pair<Value*, APInt>;
/// Given an associative binary expression, return the leaf
/// nodes in Ops along with their weights (how many times the leaf occurs). The
/// original expression is the same as
/// (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times
/// op
/// (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times
/// op
/// ...
/// op
/// (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times
///
/// Note that the values Ops[0].first, ..., Ops[N].first are all distinct.
///
/// This routine may modify the function, in which case it returns 'true'. The
/// changes it makes may well be destructive, changing the value computed by 'I'
/// to something completely different. Thus if the routine returns 'true' then
/// you MUST either replace I with a new expression computed from the Ops array,
/// or use RewriteExprTree to put the values back in.
///
/// 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, 1), (E, 1), (F, 2), (G, 2).
///
/// 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 either replace 'I' with a new expression or use something like
/// RewriteExprTree to put the values back in if the routine indicates that it
/// made a change by returning 'true'.
///
/// 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 such undef operands can only be reached by passing through 'I'.
/// For example, if you visit operands recursively starting from a leaf node
/// then you will never see 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.
static bool LinearizeExprTree(Instruction *I,
SmallVectorImpl<RepeatedValue> &Ops) {
assert((isa<UnaryOperator>(I) || isa<BinaryOperator>(I)) &&
"Expected a UnaryOperator or BinaryOperator!");
LLVM_DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
unsigned Opcode = I->getOpcode();
assert(I->isAssociative() && I->isCommutative() &&
"Expected an associative and commutative operation!");
// 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<Instruction*, APInt>, 8> Worklist; // (Op, Weight)
Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1)));
bool Changed = false;
// 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.
using LeafMap = DenseMap<Value *, APInt>;
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<Instruction*, APInt> P = Worklist.pop_back_val();
I = P.first; // We examine the operands of this binary operator.
for (unsigned OpIdx = 0; OpIdx < I->getNumOperands(); ++OpIdx) { // Visit operands.
Value *Op = I->getOperand(OpIdx);
APInt Weight = P.second; // Number of paths to this operand.
LLVM_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).second && "Not first visit!");
LLVM_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).second && "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.
LLVM_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 {
// Already in the leaf map.
assert(It != Leaves.end() && Visited.count(Op) &&
"In leaf map but not visited!");
// Update the number of paths to the leaf.
IncorporateWeight(It->second, Weight, Opcode);
#if 0 // TODO: Re-enable once PR13021 is fixed.
// 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()));
Changed = 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)) {
LLVM_DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n");
Worklist.push_back(std::make_pair(BO, It->second));
Leaves.erase(It);
continue;
}
#endif
// 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
|| (isa<FPMathOperator>(Op) &&
!cast<Instruction>(Op)->isFast())) &&
"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.
if (Instruction *Tmp = dyn_cast<Instruction>(Op))
if ((Opcode == Instruction::Mul && match(Tmp, m_Neg(m_Value()))) ||
(Opcode == Instruction::FMul && match(Tmp, m_FNeg(m_Value())))) {
LLVM_DEBUG(dbgs()
<< "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
Tmp = LowerNegateToMultiply(Tmp);
LLVM_DEBUG(dbgs() << *Tmp << '\n');
Worklist.push_back(std::make_pair(Tmp, Weight));
Changed = true;
continue;
}
// Failed to morph into an expression of the right type. This really is
// a leaf.
LLVM_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())
// Node initially thought to be a leaf wasn't.
continue;
assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!");
APInt Weight = It->second;
if (Weight.isMinValue())
// Leaf already output or weight reduction eliminated it.
continue;
// Ensure the leaf is only output once.
It->second = 0;
Ops.push_back(std::make_pair(V, Weight));
}
// For nilpotent operations or addition there may be no operands, for example
// because the expression was "X xor X" or consisted of 2^Bitwidth additions:
// in both cases the weight reduces to 0 causing the value to be skipped.
if (Ops.empty()) {
Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
assert(Identity && "Associative operation without identity!");
Ops.emplace_back(Identity, APInt(Bitwidth, 1));
}
return Changed;
}
/// Now that the operands for this expression tree are
/// linearized and optimized, emit them in-order.
void ReassociatePass::RewriteExprTree(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops) {
assert(Ops.size() > 1 && "Single values should be used directly!");
// Since our optimizations should never increase the number of operations, the
// new expression can usually be written 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();
BinaryOperator *Op = I;
/// NotRewritable - The operands being written will be the leaves of the new
/// expression and must not be used as inner nodes (via NodesToRewrite) by
/// mistake. Inner nodes are always reassociable, and usually leaves are not
/// (if they were they would have been incorporated into the expression and so
/// would not be leaves), so most of the time there is no danger of this. But
/// in rare cases a leaf may become reassociable if an optimization kills uses
/// of it, or it may momentarily become reassociable during rewriting (below)
/// due it being removed as an operand of one of its uses. Ensure that misuse
/// of leaf nodes as inner nodes cannot occur by remembering all of the future
/// leaves and refusing to reuse any of them as inner nodes.
SmallPtrSet<Value*, 8> NotRewritable;
for (unsigned i = 0, e = Ops.size(); i != e; ++i)
NotRewritable.insert(Ops[i].Op);
// ExpressionChanged - Non-null if the rewritten expression differs from the
// original in some non-trivial way, requiring the clearing of optional flags.
// Flags are cleared from the operator in ExpressionChanged up to I inclusive.
BinaryOperator *ExpressionChanged = nullptr;
for (unsigned i = 0; ; ++i) {
// 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.
LLVM_DEBUG(dbgs() << "RA: " << *Op << '\n');
Op->swapOperands();
LLVM_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.
LLVM_DEBUG(dbgs() << "RA: " << *Op << '\n');
if (NewLHS != OldLHS) {
BinaryOperator *BO = isReassociableOp(OldLHS, Opcode);
if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(0, NewLHS);
}
if (NewRHS != OldRHS) {
BinaryOperator *BO = isReassociableOp(OldRHS, Opcode);
if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
}
LLVM_DEBUG(dbgs() << "TO: " << *Op << '\n');
ExpressionChanged = Op;
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)) {
LLVM_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.
BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode);
if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
ExpressionChanged = Op;
}
LLVM_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.
BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode);
if (BO && !NotRewritable.count(BO)) {
Op = BO;
continue;
}
// Otherwise, grab a spare node from the original expression and use that as
// the left-hand side. If there are no nodes left then the optimizers made
// an expression with more nodes than the original! This usually means that
// they did something stupid but it might mean that the problem was just too
// hard (finding the mimimal number of multiplications needed to realize a
// multiplication expression is NP-complete). Whatever the reason, smart or
// stupid, create a new node if there are none left.
BinaryOperator *NewOp;
if (NodesToRewrite.empty()) {
Constant *Undef = UndefValue::get(I->getType());
NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode),
Undef, Undef, "", I);
if (NewOp->getType()->isFPOrFPVectorTy())
NewOp->setFastMathFlags(I->getFastMathFlags());
} else {
NewOp = NodesToRewrite.pop_back_val();
}
LLVM_DEBUG(dbgs() << "RA: " << *Op << '\n');
Op->setOperand(0, NewOp);
LLVM_DEBUG(dbgs() << "TO: " << *Op << '\n');
ExpressionChanged = Op;
MadeChange = true;
++NumChanged;
Op = NewOp;
}
// If the expression changed non-trivially then clear out all subclass data
// starting from the operator specified in ExpressionChanged, and compactify
// the operators to just before the expression root to guarantee that the
// expression tree is dominated by all of Ops.
if (ExpressionChanged)
do {
// Preserve FastMathFlags.
if (isa<FPMathOperator>(I)) {
FastMathFlags Flags = I->getFastMathFlags();
ExpressionChanged->clearSubclassOptionalData();
ExpressionChanged->setFastMathFlags(Flags);
} else
ExpressionChanged->clearSubclassOptionalData();
if (ExpressionChanged == I)
break;
// Discard any debug info related to the expressions that has changed (we
// can leave debug infor related to the root, since the result of the
// expression tree should be the same even after reassociation).
replaceDbgUsesWithUndef(ExpressionChanged);
ExpressionChanged->moveBefore(I);
ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->user_begin());
} while (true);
// Throw away any left over nodes from the original expression.
for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
RedoInsts.insert(NodesToRewrite[i]);
}
/// 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.
/// Also add intermediate instructions to the redo list that are modified while
/// pushing the negates through adds. These will be revisited to see if
/// additional opportunities have been exposed.
static Value *NegateValue(Value *V, Instruction *BI,
ReassociatePass::OrderedSet &ToRedo) {
if (auto *C = dyn_cast<Constant>(V))
return C->getType()->isFPOrFPVectorTy() ? ConstantExpr::getFNeg(C) :
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, Instruction::FAdd)) {
// Push the negates through the add.
I->setOperand(0, NegateValue(I->getOperand(0), BI, ToRedo));
I->setOperand(1, NegateValue(I->getOperand(1), BI, ToRedo));
if (I->getOpcode() == Instruction::Add) {
I->setHasNoUnsignedWrap(false);
I->setHasNoSignedWrap(false);
}
// 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");
// Add the intermediate negates to the redo list as processing them later
// could expose more reassociating opportunities.
ToRedo.insert(I);
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 (User *U : V->users()) {
if (!match(U, m_Neg(m_Value())) && !match(U, m_FNeg(m_Value())))
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.
Instruction *TheNeg = cast<Instruction>(U);
// Verify that the negate is in this function, V might be a constant expr.
if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
continue;
bool FoundCatchSwitch = false;
BasicBlock::iterator InsertPt;
if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
InsertPt = II->getNormalDest()->begin();
} else {
InsertPt = ++InstInput->getIterator();
}
const BasicBlock *BB = InsertPt->getParent();
// Make sure we don't move anything before PHIs or exception
// handling pads.
while (InsertPt != BB->end() && (isa<PHINode>(InsertPt) ||
InsertPt->isEHPad())) {
if (isa<CatchSwitchInst>(InsertPt))
// A catchswitch cannot have anything in the block except
// itself and PHIs. We'll bail out below.
FoundCatchSwitch = true;
++InsertPt;
}
} else {
InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
}
// We found a catchswitch in the block where we want to move the
// neg. We cannot move anything into that block. Bail and just
// create the neg before BI, as if we hadn't found an existing
// neg.
if (FoundCatchSwitch)
break;
TheNeg->moveBefore(&*InsertPt);
if (TheNeg->getOpcode() == Instruction::Sub) {
TheNeg->setHasNoUnsignedWrap(false);
TheNeg->setHasNoSignedWrap(false);
} else {
TheNeg->andIRFlags(BI);
}
ToRedo.insert(TheNeg);
return TheNeg;
}
// Insert a 'neg' instruction that subtracts the value from zero to get the
// negation.
Instruction *NewNeg = CreateNeg(V, V->getName() + ".neg", BI, BI);
ToRedo.insert(NewNeg);
return NewNeg;
}
// See if this `or` looks like an load widening reduction, i.e. that it
// consists of an `or`/`shl`/`zext`/`load` nodes only. Note that we don't
// ensure that the pattern is *really* a load widening reduction,
// we do not ensure that it can really be replaced with a widened load,
// only that it mostly looks like one.
static bool isLoadCombineCandidate(Instruction *Or) {
SmallVector<Instruction *, 8> Worklist;
SmallSet<Instruction *, 8> Visited;
auto Enqueue = [&](Value *V) {
auto *I = dyn_cast<Instruction>(V);
// Each node of an `or` reduction must be an instruction,
if (!I)
return false; // Node is certainly not part of an `or` load reduction.
// Only process instructions we have never processed before.
if (Visited.insert(I).second)
Worklist.emplace_back(I);
return true; // Will need to look at parent nodes.
};
if (!Enqueue(Or))
return false; // Not an `or` reduction pattern.
while (!Worklist.empty()) {
auto *I = Worklist.pop_back_val();
// Okay, which instruction is this node?
switch (I->getOpcode()) {
case Instruction::Or:
// Got an `or` node. That's fine, just recurse into it's operands.
for (Value *Op : I->operands())
if (!Enqueue(Op))
return false; // Not an `or` reduction pattern.
continue;
case Instruction::Shl:
case Instruction::ZExt:
// `shl`/`zext` nodes are fine, just recurse into their base operand.
if (!Enqueue(I->getOperand(0)))
return false; // Not an `or` reduction pattern.
continue;
case Instruction::Load:
// Perfect, `load` node means we've reached an edge of the graph.
continue;
default: // Unknown node.
return false; // Not an `or` reduction pattern.
}
}
return true;
}
/// Return true if it may be profitable to convert this (X|Y) into (X+Y).
static bool shouldConvertOrWithNoCommonBitsToAdd(Instruction *Or) {
// Don't bother to convert this up unless either the LHS is an associable add
// or subtract or mul or if this is only used by one of the above.
// This is only a compile-time improvement, it is not needed for correctness!
auto isInteresting = [](Value *V) {
for (auto Op : {Instruction::Add, Instruction::Sub, Instruction::Mul,
Instruction::Shl})
if (isReassociableOp(V, Op))
return true;
return false;
};
if (any_of(Or->operands(), isInteresting))
return true;
Value *VB = Or->user_back();
if (Or->hasOneUse() && isInteresting(VB))
return true;
return false;
}
/// If we have (X|Y), and iff X and Y have no common bits set,
/// transform this into (X+Y) to allow arithmetics reassociation.
static BinaryOperator *convertOrWithNoCommonBitsToAdd(Instruction *Or) {
// Convert an or into an add.
BinaryOperator *New =
CreateAdd(Or->getOperand(0), Or->getOperand(1), "", Or, Or);
New->setHasNoSignedWrap();
New->setHasNoUnsignedWrap();
New->takeName(Or);
// Everyone now refers to the add instruction.
Or->replaceAllUsesWith(New);
New->setDebugLoc(Or->getDebugLoc());
LLVM_DEBUG(dbgs() << "Converted or into an add: " << *New << '\n');
return New;
}
/// 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 (match(Sub, m_Neg(m_Value())) || match(Sub, m_FNeg(m_Value())))
return false;
// Don't breakup X - undef.
if (isa<UndefValue>(Sub->getOperand(1)))
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.
Value *V0 = Sub->getOperand(0);
if (isReassociableOp(V0, Instruction::Add, Instruction::FAdd) ||
isReassociableOp(V0, Instruction::Sub, Instruction::FSub))
return true;
Value *V1 = Sub->getOperand(1);
if (isReassociableOp(V1, Instruction::Add, Instruction::FAdd) ||
isReassociableOp(V1, Instruction::Sub, Instruction::FSub))
return true;
Value *VB = Sub->user_back();
if (Sub->hasOneUse() &&
(isReassociableOp(VB, Instruction::Add, Instruction::FAdd) ||
isReassociableOp(VB, Instruction::Sub, Instruction::FSub)))
return true;
return false;
}
/// 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 BinaryOperator *BreakUpSubtract(Instruction *Sub,
ReassociatePass::OrderedSet &ToRedo) {
// 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, ToRedo);
BinaryOperator *New = CreateAdd(Sub->getOperand(0), NegVal, "", Sub, Sub);
Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op.
Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op.
New->takeName(Sub);
// Everyone now refers to the add instruction.
Sub->replaceAllUsesWith(New);
New->setDebugLoc(Sub->getDebugLoc());
LLVM_DEBUG(dbgs() << "Negated: " << *New << '\n');
return New;
}
/// 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 BinaryOperator *ConvertShiftToMul(Instruction *Shl) {
Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
auto *SA = cast<ConstantInt>(Shl->getOperand(1));
MulCst = ConstantExpr::getShl(MulCst, SA);
BinaryOperator *Mul =
BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
Mul->takeName(Shl);
// Everyone now refers to the mul instruction.
Shl->replaceAllUsesWith(Mul);
Mul->setDebugLoc(Shl->getDebugLoc());
// We can safely preserve the nuw flag in all cases. It's also safe to turn a
// nuw nsw shl into a nuw nsw mul. However, nsw in isolation requires special
// handling. It can be preserved as long as we're not left shifting by
// bitwidth - 1.
bool NSW = cast<BinaryOperator>(Shl)->hasNoSignedWrap();
bool NUW = cast<BinaryOperator>(Shl)->hasNoUnsignedWrap();
unsigned BitWidth = Shl->getType()->getIntegerBitWidth();
if (NSW && (NUW || SA->getValue().ult(BitWidth - 1)))
Mul->setHasNoSignedWrap(true);
Mul->setHasNoUnsignedWrap(NUW);
return Mul;
}
/// 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(const 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;
if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op))
if (Instruction *I2 = dyn_cast<Instruction>(X))
if (I1->isIdenticalTo(I2))
return j;
}
// Scan backwards.
for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) {
if (Ops[j].Op == X)
return j;
if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op))
if (Instruction *I2 = dyn_cast<Instruction>(X))
if (I1->isIdenticalTo(I2))
return j;
}
return i;
}
/// Emit a tree of add instructions, summing Ops together
/// and returning the result. Insert the tree before I.
static Value *EmitAddTreeOfValues(Instruction *I,
SmallVectorImpl<WeakTrackingVH> &Ops) {
if (Ops.size() == 1) return Ops.back();
Value *V1 = Ops.pop_back_val();
Value *V2 = EmitAddTreeOfValues(I, Ops);
return CreateAdd(V2, V1, "reass.add", I, I);
}
/// 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 *ReassociatePass::RemoveFactorFromExpression(Value *V, Value *Factor) {
BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul);
if (!BO)
return nullptr;
SmallVector<RepeatedValue, 8> Tree;
MadeChange |= LinearizeExprTree(BO, Tree);
SmallVector<ValueEntry, 8> Factors;
Factors.reserve(Tree.size());
for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
RepeatedValue E = Tree[i];
Factors.append(E.second.getZExtValue(),
ValueEntry(getRank(E.first), E.first));
}
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;
}
} else if (ConstantFP *FC1 = dyn_cast<ConstantFP>(Factor)) {
if (ConstantFP *FC2 = dyn_cast<ConstantFP>(Factors[i].Op)) {
const APFloat &F1 = FC1->getValueAPF();
APFloat F2(FC2->getValueAPF());
F2.changeSign();
if (F1 == F2) {
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 nullptr;
}
BasicBlock::iterator InsertPt = ++BO->getIterator();
// If this was just a single multiply, remove the multiply and return the only
// remaining operand.
if (Factors.size() == 1) {
RedoInsts.insert(BO);
V = Factors[0].Op;
} else {
RewriteExprTree(BO, Factors);
V = BO;
}
if (NeedsNegate)
V = CreateNeg(V, "neg", &*InsertPt, BO);
return V;
}
/// 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) {
BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul);
if (!BO) {
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);
}
/// 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());
Value *X;
if (match(Ops[i].Op, m_Not(m_Value(X)))) { // Cannot occur for ^.
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 nullptr;
}
/// Helper function of CombineXorOpnd(). It creates a bitwise-and
/// instruction with the given two operands, and return the resulting
/// instruction. There are two special cases: 1) if the constant operand is 0,
/// it will return NULL. 2) if the constant is ~0, the symbolic operand will
/// be returned.
static Value *createAndInstr(Instruction *InsertBefore, Value *Opnd,
const APInt &ConstOpnd) {
if (ConstOpnd.isNullValue())
return nullptr;
if (ConstOpnd.isAllOnesValue())
return Opnd;
Instruction *I = BinaryOperator::CreateAnd(
Opnd, ConstantInt::get(Opnd->getType(), ConstOpnd), "and.ra",
InsertBefore);
I->setDebugLoc(InsertBefore->getDebugLoc());
return I;
}
// Helper function of OptimizeXor(). It tries to simplify "Opnd1 ^ ConstOpnd"
// into "R ^ C", where C would be 0, and R is a symbolic value.
//
// If it was successful, true is returned, and the "R" and "C" is returned
// via "Res" and "ConstOpnd", respectively; otherwise, false is returned,
// and both "Res" and "ConstOpnd" remain unchanged.
bool ReassociatePass::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1,
APInt &ConstOpnd, Value *&Res) {
// Xor-Rule 1: (x | c1) ^ c2 = (x | c1) ^ (c1 ^ c1) ^ c2
// = ((x | c1) ^ c1) ^ (c1 ^ c2)
// = (x & ~c1) ^ (c1 ^ c2)
// It is useful only when c1 == c2.
if (!Opnd1->isOrExpr() || Opnd1->getConstPart().isNullValue())
return false;
if (!Opnd1->getValue()->hasOneUse())
return false;
const APInt &C1 = Opnd1->getConstPart();
if (C1 != ConstOpnd)
return false;
Value *X = Opnd1->getSymbolicPart();
Res = createAndInstr(I, X, ~C1);
// ConstOpnd was C2, now C1 ^ C2.
ConstOpnd ^= C1;
if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue()))
RedoInsts.insert(T);
return true;
}
// Helper function of OptimizeXor(). It tries to simplify
// "Opnd1 ^ Opnd2 ^ ConstOpnd" into "R ^ C", where C would be 0, and R is a
// symbolic value.
//
// If it was successful, true is returned, and the "R" and "C" is returned
// via "Res" and "ConstOpnd", respectively (If the entire expression is
// evaluated to a constant, the Res is set to NULL); otherwise, false is
// returned, and both "Res" and "ConstOpnd" remain unchanged.
bool ReassociatePass::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1,
XorOpnd *Opnd2, APInt &ConstOpnd,
Value *&Res) {
Value *X = Opnd1->getSymbolicPart();
if (X != Opnd2->getSymbolicPart())
return false;
// This many instruction become dead.(At least "Opnd1 ^ Opnd2" will die.)
int DeadInstNum = 1;
if (Opnd1->getValue()->hasOneUse())
DeadInstNum++;
if (Opnd2->getValue()->hasOneUse())
DeadInstNum++;
// Xor-Rule 2:
// (x | c1) ^ (x & c2)
// = (x|c1) ^ (x&c2) ^ (c1 ^ c1) = ((x|c1) ^ c1) ^ (x & c2) ^ c1
// = (x & ~c1) ^ (x & c2) ^ c1 // Xor-Rule 1
// = (x & c3) ^ c1, where c3 = ~c1 ^ c2 // Xor-rule 3
//
if (Opnd1->isOrExpr() != Opnd2->isOrExpr()) {
if (Opnd2->isOrExpr())
std::swap(Opnd1, Opnd2);
const APInt &C1 = Opnd1->getConstPart();
const APInt &C2 = Opnd2->getConstPart();
APInt C3((~C1) ^ C2);
// Do not increase code size!
if (!C3.isNullValue() && !C3.isAllOnesValue()) {
int NewInstNum = ConstOpnd.getBoolValue() ? 1 : 2;
if (NewInstNum > DeadInstNum)
return false;
}
Res = createAndInstr(I, X, C3);
ConstOpnd ^= C1;
} else if (Opnd1->isOrExpr()) {
// Xor-Rule 3: (x | c1) ^ (x | c2) = (x & c3) ^ c3 where c3 = c1 ^ c2
//
const APInt &C1 = Opnd1->getConstPart();
const APInt &C2 = Opnd2->getConstPart();
APInt C3 = C1 ^ C2;
// Do not increase code size
if (!C3.isNullValue() && !C3.isAllOnesValue()) {
int NewInstNum = ConstOpnd.getBoolValue() ? 1 : 2;
if (NewInstNum > DeadInstNum)
return false;
}
Res = createAndInstr(I, X, C3);
ConstOpnd ^= C3;
} else {
// Xor-Rule 4: (x & c1) ^ (x & c2) = (x & (c1^c2))
//
const APInt &C1 = Opnd1->getConstPart();
const APInt &C2 = Opnd2->getConstPart();
APInt C3 = C1 ^ C2;
Res = createAndInstr(I, X, C3);
}
// Put the original operands in the Redo list; hope they will be deleted
// as dead code.
if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue()))
RedoInsts.insert(T);
if (Instruction *T = dyn_cast<Instruction>(Opnd2->getValue()))
RedoInsts.insert(T);
return true;
}
/// Optimize a series of operands to an 'xor' instruction. If it can be reduced
/// to a single Value, it is returned, otherwise the Ops list is mutated as
/// necessary.
Value *ReassociatePass::OptimizeXor(Instruction *I,
SmallVectorImpl<ValueEntry> &Ops) {
if (Value *V = OptimizeAndOrXor(Instruction::Xor, Ops))
return V;
if (Ops.size() == 1)
return nullptr;
SmallVector<XorOpnd, 8> Opnds;
SmallVector<XorOpnd*, 8> OpndPtrs;
Type *Ty = Ops[0].Op->getType();
APInt ConstOpnd(Ty->getScalarSizeInBits(), 0);
// Step 1: Convert ValueEntry to XorOpnd
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
Value *V = Ops[i].Op;
const APInt *C;
// TODO: Support non-splat vectors.
if (match(V, m_APInt(C))) {
ConstOpnd ^= *C;
} else {
XorOpnd O(V);
O.setSymbolicRank(getRank(O.getSymbolicPart()));
Opnds.push_back(O);
}
}
// NOTE: From this point on, do *NOT* add/delete element to/from "Opnds".
// It would otherwise invalidate the "Opnds"'s iterator, and hence invalidate
// the "OpndPtrs" as well. For the similar reason, do not fuse this loop
// with the previous loop --- the iterator of the "Opnds" may be invalidated
// when new elements are added to the vector.
for (unsigned i = 0, e = Opnds.size(); i != e; ++i)
OpndPtrs.push_back(&Opnds[i]);
// Step 2: Sort the Xor-Operands in a way such that the operands containing
// the same symbolic value cluster together. For instance, the input operand
// sequence ("x | 123", "y & 456", "x & 789") will be sorted into:
// ("x | 123", "x & 789", "y & 456").
//
// The purpose is twofold:
// 1) Cluster together the operands sharing the same symbolic-value.
// 2) Operand having smaller symbolic-value-rank is permuted earlier, which
// could potentially shorten crital path, and expose more loop-invariants.
// Note that values' rank are basically defined in RPO order (FIXME).
// So, if Rank(X) < Rank(Y) < Rank(Z), it means X is defined earlier
// than Y which is defined earlier than Z. Permute "x | 1", "Y & 2",
// "z" in the order of X-Y-Z is better than any other orders.
llvm::stable_sort(OpndPtrs, [](XorOpnd *LHS, XorOpnd *RHS) {
return LHS->getSymbolicRank() < RHS->getSymbolicRank();
});
// Step 3: Combine adjacent operands
XorOpnd *PrevOpnd = nullptr;
bool Changed = false;
for (unsigned i = 0, e = Opnds.size(); i < e; i++) {
XorOpnd *CurrOpnd = OpndPtrs[i];
// The combined value
Value *CV;
// Step 3.1: Try simplifying "CurrOpnd ^ ConstOpnd"
if (!ConstOpnd.isNullValue() &&
CombineXorOpnd(I, CurrOpnd, ConstOpnd, CV)) {
Changed = true;
if (CV)
*CurrOpnd = XorOpnd(CV);
else {
CurrOpnd->Invalidate();
continue;
}
}
if (!PrevOpnd || CurrOpnd->getSymbolicPart() != PrevOpnd->getSymbolicPart()) {
PrevOpnd = CurrOpnd;
continue;
}
// step 3.2: When previous and current operands share the same symbolic
// value, try to simplify "PrevOpnd ^ CurrOpnd ^ ConstOpnd"
if (CombineXorOpnd(I, CurrOpnd, PrevOpnd, ConstOpnd, CV)) {
// Remove previous operand
PrevOpnd->Invalidate();
if (CV) {
*CurrOpnd = XorOpnd(CV);
PrevOpnd = CurrOpnd;
} else {
CurrOpnd->Invalidate();
PrevOpnd = nullptr;
}
Changed = true;
}
}
// Step 4: Reassemble the Ops
if (Changed) {
Ops.clear();
for (unsigned int i = 0, e = Opnds.size(); i < e; i++) {
XorOpnd &O = Opnds[i];
if (O.isInvalid())
continue;
ValueEntry VE(getRank(O.getValue()), O.getValue());
Ops.push_back(VE);
}
if (!ConstOpnd.isNullValue()) {
Value *C = ConstantInt::get(Ty, ConstOpnd);
ValueEntry VE(getRank(C), C);
Ops.push_back(VE);
}
unsigned Sz = Ops.size();
if (Sz == 1)
return Ops.back().Op;
if (Sz == 0) {
assert(ConstOpnd.isNullValue());
return ConstantInt::get(Ty, ConstOpnd);
}
}
return nullptr;
}
/// 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 *ReassociatePass::OptimizeAdd(Instruction *I,
SmallVectorImpl<ValueEntry> &Ops) {
// Scan the operand lists looking for X and -X pairs. If we find any, we
// can simplify expressions like X+-X == 0 and X+~X ==-1. While we're at it,
// scan for any
// duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
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);
LLVM_DEBUG(dbgs() << "\nFACTORING [" << NumFound << "]: " << *TheOp
<< '\n');
++NumFactor;
// Insert a new multiply.
Type *Ty = TheOp->getType();
Constant *C = Ty->isIntOrIntVectorTy() ?
ConstantInt::get(Ty, NumFound) : ConstantFP::get(Ty, NumFound);
Instruction *Mul = CreateMul(TheOp, C, "factor", I, 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.insert(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 or X and ~X in the operand list.
Value *X;
if (!match(TheOp, m_Neg(m_Value(X))) && !match(TheOp, m_Not(m_Value(X))) &&
!match(TheOp, m_FNeg(m_Value(X))))
continue;
unsigned FoundX = FindInOperandList(Ops, i, X);
if (FoundX == i)
continue;
// Remove X and -X from the operand list.
if (Ops.size() == 2 &&
(match(TheOp, m_Neg(m_Value())) || match(TheOp, m_FNeg(m_Value()))))
return Constant::getNullValue(X->getType());
// Remove X and ~X from the operand list.
if (Ops.size() == 2 && match(TheOp, m_Not(m_Value())))
return Constant::getAllOnesValue(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.
// if X and ~X we append -1 to the operand list.
if (match(TheOp, m_Not(m_Value()))) {
Value *V = Constant::getAllOnesValue(X->getType());
Ops.insert(Ops.end(), ValueEntry(getRank(V), V));
e += 1;
}
}
// 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 = nullptr;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
BinaryOperator *BOp =
isReassociableOp(Ops[i].Op, Instruction::Mul, Instruction::FMul);
if (!BOp)
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).second)
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());
if (!Duplicates.insert(Factor).second)
continue;
unsigned Occ = ++FactorOccurrences[Factor];
if (Occ > MaxOcc) {
MaxOcc = Occ;
MaxOccVal = Factor;
}
}
} else if (ConstantFP *CF = dyn_cast<ConstantFP>(Factor)) {
if (CF->isNegative()) {
APFloat F(CF->getValueAPF());
F.changeSign();
Factor = ConstantFP::get(CF->getContext(), F);
if (!Duplicates.insert(Factor).second)
continue;
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) {
LLVM_DEBUG(dbgs() << "\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 =
I->getType()->isIntOrIntVectorTy()
? BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal)
: BinaryOperator::CreateFAdd(MaxOccVal, MaxOccVal);
SmallVector<WeakTrackingVH, 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, Instruction::FMul);
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.
DummyInst->deleteValue();
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;
if (Instruction *VI = dyn_cast<Instruction>(V))
RedoInsts.insert(VI);
// Create the multiply.
Instruction *V2 = CreateMul(V, MaxOccVal, "reass.mul", I, 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.insert(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 nullptr;
}
/// 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.
static bool 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 occurrences 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);
llvm::stable_sort(Factors, [](const Factor &LHS, const Factor &RHS) {
return LHS.Power > RHS.Power;
});
return true;
}
/// Build a tree of multiplies, computing the product of Ops.
static Value *buildMultiplyTree(IRBuilderBase &Builder,
SmallVectorImpl<Value*> &Ops) {
if (Ops.size() == 1)
return Ops.back();
Value *LHS = Ops.pop_back_val();
do {
if (LHS->getType()->isIntOrIntVectorTy())
LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
else
LHS = Builder.CreateFMul(LHS, Ops.pop_back_val());
} while (!Ops.empty());
return LHS;
}
/// 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 *
ReassociatePass::buildMinimalMultiplyDAG(IRBuilderBase &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.
Value *M = Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct);
if (Instruction *MI = dyn_cast<Instruction>(M))
RedoInsts.insert(MI);
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(),
[](const Factor &LHS, const Factor &RHS) {
return LHS.Power == RHS.Power;
}),
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 *ReassociatePass::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 nullptr;
// 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 nullptr; // All distinct factors, so nothing left for us to do.
IRBuilder<> Builder(I);
// The reassociate transformation for FP operations is performed only
// if unsafe algebra is permitted by FastMathFlags. Propagate those flags
// to the newly generated operations.
if (auto FPI = dyn_cast<FPMathOperator>(I))
Builder.setFastMathFlags(FPI->getFastMathFlags());
Value *V = buildMinimalMultiplyDAG(Builder, Factors);
if (Ops.empty())
return V;
ValueEntry NewEntry = ValueEntry(getRank(V), V);
Ops.insert(llvm::lower_bound(Ops, NewEntry), NewEntry);
return nullptr;
}
Value *ReassociatePass::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.
Constant *Cst = nullptr;
unsigned Opcode = I->getOpcode();
while (!Ops.empty() && isa<Constant>(Ops.back().Op)) {
Constant *C = cast<Constant>(Ops.pop_back_val().Op);
Cst = Cst ? ConstantExpr::get(Opcode, C, Cst) : C;
}
// If there was nothing but constants then we are done.
if (Ops.empty())
return Cst;
// Put the combined constant back at the end of the operand list, except if
// there is no point. For example, an add of 0 gets dropped here, while a
// multiplication by zero turns the whole expression into zero.
if (Cst && Cst != ConstantExpr::getBinOpIdentity(Opcode, I->getType())) {
if (Cst == ConstantExpr::getBinOpAbsorber(Opcode, I->getType()))
return Cst;
Ops.push_back(ValueEntry(0, Cst));
}
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:
if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
return Result;
break;
case Instruction::Xor:
if (Value *Result = OptimizeXor(I, Ops))
return Result;
break;
case Instruction::Add:
case Instruction::FAdd:
if (Value *Result = OptimizeAdd(I, Ops))
return Result;
break;
case Instruction::Mul:
case Instruction::FMul:
if (Value *Result = OptimizeMul(I, Ops))
return Result;
break;
}
if (Ops.size() != NumOps)
return OptimizeExpression(I, Ops);
return nullptr;
}
// Remove dead instructions and if any operands are trivially dead add them to
// Insts so they will be removed as well.
void ReassociatePass::RecursivelyEraseDeadInsts(Instruction *I,
OrderedSet &Insts) {
assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
SmallVector<Value *, 4> Ops(I->operands());
ValueRankMap.erase(I);
Insts.remove(I);
RedoInsts.remove(I);
llvm::salvageDebugInfo(*I);
I->eraseFromParent();
for (auto Op : Ops)
if (Instruction *OpInst = dyn_cast<Instruction>(Op))
if (OpInst->use_empty())
Insts.insert(OpInst);
}
/// Zap the given instruction, adding interesting operands to the work list.
void ReassociatePass::EraseInst(Instruction *I) {
assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
LLVM_DEBUG(dbgs() << "Erasing dead inst: "; I->dump());
SmallVector<Value *, 8> Ops(I->operands());
// Erase the dead instruction.
ValueRankMap.erase(I);
RedoInsts.remove(I);
llvm::salvageDebugInfo(*I);
I->eraseFromParent();
// Optimize its operands.
SmallPtrSet<Instruction *, 8> Visited; // Detect self-referential nodes.
for (unsigned i = 0, e = Ops.size(); i != e; ++i)
if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) {
// If this is a node in an expression tree, climb to the expression root
// and add that since that's where optimization actually happens.
unsigned Opcode = Op->getOpcode();
while (Op->hasOneUse() && Op->user_back()->getOpcode() == Opcode &&
Visited.insert(Op).second)
Op = Op->user_back();
// The instruction we're going to push may be coming from a
// dead block, and Reassociate skips the processing of unreachable
// blocks because it's a waste of time and also because it can
// lead to infinite loop due to LLVM's non-standard definition
// of dominance.
if (ValueRankMap.find(Op) != ValueRankMap.end())
RedoInsts.insert(Op);
}
MadeChange = true;
}
/// Recursively analyze an expression to build a list of instructions that have
/// negative floating-point constant operands. The caller can then transform
/// the list to create positive constants for better reassociation and CSE.
static void getNegatibleInsts(Value *V,
SmallVectorImpl<Instruction *> &Candidates) {
// Handle only one-use instructions. Combining negations does not justify
// replicating instructions.
Instruction *I;
if (!match(V, m_OneUse(m_Instruction(I))))
return;
// Handle expressions of multiplications and divisions.
// TODO: This could look through floating-point casts.
const APFloat *C;
switch (I->getOpcode()) {
case Instruction::FMul:
// Not expecting non-canonical code here. Bail out and wait.
if (match(I->getOperand(0), m_Constant()))
break;
if (match(I->getOperand(1), m_APFloat(C)) && C->isNegative()) {
Candidates.push_back(I);
LLVM_DEBUG(dbgs() << "FMul with negative constant: " << *I << '\n');
}
getNegatibleInsts(I->getOperand(0), Candidates);
getNegatibleInsts(I->getOperand(1), Candidates);
break;
case Instruction::FDiv:
// Not expecting non-canonical code here. Bail out and wait.
if (match(I->getOperand(0), m_Constant()) &&
match(I->getOperand(1), m_Constant()))
break;
if ((match(I->getOperand(0), m_APFloat(C)) && C->isNegative()) ||
(match(I->getOperand(1), m_APFloat(C)) && C->isNegative())) {
Candidates.push_back(I);
LLVM_DEBUG(dbgs() << "FDiv with negative constant: " << *I << '\n');
}
getNegatibleInsts(I->getOperand(0), Candidates);
getNegatibleInsts(I->getOperand(1), Candidates);
break;
default:
break;
}
}
/// Given an fadd/fsub with an operand that is a one-use instruction
/// (the fadd/fsub), try to change negative floating-point constants into
/// positive constants to increase potential for reassociation and CSE.
Instruction *ReassociatePass::canonicalizeNegFPConstantsForOp(Instruction *I,
Instruction *Op,
Value *OtherOp) {
assert((I->getOpcode() == Instruction::FAdd ||
I->getOpcode() == Instruction::FSub) && "Expected fadd/fsub");
// Collect instructions with negative FP constants from the subtree that ends
// in Op.
SmallVector<Instruction *, 4> Candidates;
getNegatibleInsts(Op, Candidates);
if (Candidates.empty())
return nullptr;
// Don't canonicalize x + (-Constant * y) -> x - (Constant * y), if the
// resulting subtract will be broken up later. This can get us into an
// infinite loop during reassociation.
bool IsFSub = I->getOpcode() == Instruction::FSub;
bool NeedsSubtract = !IsFSub && Candidates.size() % 2 == 1;
if (NeedsSubtract && ShouldBreakUpSubtract(I))
return nullptr;
for (Instruction *Negatible : Candidates) {
const APFloat *C;
if (match(Negatible->getOperand(0), m_APFloat(C))) {
assert(!match(Negatible->getOperand(1), m_Constant()) &&
"Expecting only 1 constant operand");
assert(C->isNegative() && "Expected negative FP constant");
Negatible->setOperand(0, ConstantFP::get(Negatible->getType(), abs(*C)));
MadeChange = true;
}
if (match(Negatible->getOperand(1), m_APFloat(C))) {
assert(!match(Negatible->getOperand(0), m_Constant()) &&
"Expecting only 1 constant operand");
assert(C->isNegative() && "Expected negative FP constant");
Negatible->setOperand(1, ConstantFP::get(Negatible->getType(), abs(*C)));
MadeChange = true;
}
}
assert(MadeChange == true && "Negative constant candidate was not changed");
// Negations cancelled out.
if (Candidates.size() % 2 == 0)
return I;
// Negate the final operand in the expression by flipping the opcode of this
// fadd/fsub.
assert(Candidates.size() % 2 == 1 && "Expected odd number");
IRBuilder<> Builder(I);
Value *NewInst = IsFSub ? Builder.CreateFAddFMF(OtherOp, Op, I)
: Builder.CreateFSubFMF(OtherOp, Op, I);
I->replaceAllUsesWith(NewInst);
RedoInsts.insert(I);
return dyn_cast<Instruction>(NewInst);
}
/// Canonicalize expressions that contain a negative floating-point constant
/// of the following form:
/// OtherOp + (subtree) -> OtherOp {+/-} (canonical subtree)
/// (subtree) + OtherOp -> OtherOp {+/-} (canonical subtree)
/// OtherOp - (subtree) -> OtherOp {+/-} (canonical subtree)
///
/// The fadd/fsub opcode may be switched to allow folding a negation into the
/// input instruction.
Instruction *ReassociatePass::canonicalizeNegFPConstants(Instruction *I) {
LLVM_DEBUG(dbgs() << "Combine negations for: " << *I << '\n');
Value *X;
Instruction *Op;
if (match(I, m_FAdd(m_Value(X), m_OneUse(m_Instruction(Op)))))
if (Instruction *R = canonicalizeNegFPConstantsForOp(I, Op, X))
I = R;
if (match(I, m_FAdd(m_OneUse(m_Instruction(Op)), m_Value(X))))
if (Instruction *R = canonicalizeNegFPConstantsForOp(I, Op, X))
I = R;
if (match(I, m_FSub(m_Value(X), m_OneUse(m_Instruction(Op)))))
if (Instruction *R = canonicalizeNegFPConstantsForOp(I, Op, X))
I = R;
return I;
}
/// Inspect and optimize the given instruction. Note that erasing
/// instructions is not allowed.
void ReassociatePass::OptimizeInst(Instruction *I) {
// Only consider operations that we understand.
if (!isa<UnaryOperator>(I) && !isa<BinaryOperator>(I))
return;
if (I->getOpcode() == Instruction::Shl && isa<ConstantInt>(I->getOperand(1)))
// 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(I->getOperand(0), Instruction::Mul) ||
(I->hasOneUse() &&
(isReassociableOp(I->user_back(), Instruction::Mul) ||
isReassociableOp(I->user_back(), Instruction::Add)))) {
Instruction *NI = ConvertShiftToMul(I);
RedoInsts.insert(I);
MadeChange = true;
I = NI;
}
// Commute binary operators, to canonicalize the order of their operands.
// This can potentially expose more CSE opportunities, and makes writing other
// transformations simpler.
if (I->isCommutative())
canonicalizeOperands(I);
// Canonicalize negative constants out of expressions.
if (Instruction *Res = canonicalizeNegFPConstants(I))
I = Res;
// Don't optimize floating-point instructions unless they are 'fast'.
if (I->getType()->isFPOrFPVectorTy() && !I->isFast())
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 (I->getType()->isIntegerTy(1))
return;
// If this is a bitwise or instruction of operands
// with no common bits set, convert it to X+Y.
if (I->getOpcode() == Instruction::Or &&
shouldConvertOrWithNoCommonBitsToAdd(I) && !isLoadCombineCandidate(I) &&
haveNoCommonBitsSet(I->getOperand(0), I->getOperand(1),
I->getModule()->getDataLayout(), /*AC=*/nullptr, I,
/*DT=*/nullptr)) {
Instruction *NI = convertOrWithNoCommonBitsToAdd(I);
RedoInsts.insert(I);
MadeChange = true;
I = NI;
}
// If this is a subtract instruction which is not already in negate form,
// see if we can convert it to X+-Y.
if (I->getOpcode() == Instruction::Sub) {
if (ShouldBreakUpSubtract(I)) {
Instruction *NI = BreakUpSubtract(I, RedoInsts);
RedoInsts.insert(I);
MadeChange = true;
I = NI;
} else if (match(I, m_Neg(m_Value()))) {
// 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(I->getOperand(1), Instruction::Mul) &&
(!I->hasOneUse() ||
!isReassociableOp(I->user_back(), Instruction::Mul))) {
Instruction *NI = LowerNegateToMultiply(I);
// If the negate was simplified, revisit the users to see if we can
// reassociate further.
for (User *U : NI->users()) {
if (BinaryOperator *Tmp = dyn_cast<BinaryOperator>(U))
RedoInsts.insert(Tmp);
}
RedoInsts.insert(I);
MadeChange = true;
I = NI;
}
}
} else if (I->getOpcode() == Instruction::FNeg ||
I->getOpcode() == Instruction::FSub) {
if (ShouldBreakUpSubtract(I)) {
Instruction *NI = BreakUpSubtract(I, RedoInsts);
RedoInsts.insert(I);
MadeChange = true;
I = NI;
} else if (match(I, m_FNeg(m_Value()))) {
// 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.
Value *Op = isa<BinaryOperator>(I) ? I->getOperand(1) :
I->getOperand(0);
if (isReassociableOp(Op, Instruction::FMul) &&
(!I->hasOneUse() ||
!isReassociableOp(I->user_back(), Instruction::FMul))) {
// If the negate was simplified, revisit the users to see if we can
// reassociate further.
Instruction *NI = LowerNegateToMultiply(I);
for (User *U : NI->users()) {
if (BinaryOperator *Tmp = dyn_cast<BinaryOperator>(U))
RedoInsts.insert(Tmp);
}
RedoInsts.insert(I);
MadeChange = true;
I = NI;
}
}
}
// If this instruction is an associative binary operator, process it.
if (!I->isAssociative()) return;
BinaryOperator *BO = cast<BinaryOperator>(I);
// 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.
unsigned Opcode = BO->getOpcode();
if (BO->hasOneUse() && BO->user_back()->getOpcode() == Opcode) {
// During the initial run we will get to the root of the tree.
// But if we get here while we are redoing instructions, there is no
// guarantee that the root will be visited. So Redo later
if (BO->user_back() != BO &&
BO->getParent() == BO->user_back()->getParent())
RedoInsts.insert(BO->user_back());
return;
}
// If this is an add tree that is used by a sub instruction, ignore it
// until we process the subtract.
if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add &&
cast<Instruction>(BO->user_back())->getOpcode() == Instruction::Sub)
return;
if (BO->hasOneUse() && BO->getOpcode() == Instruction::FAdd &&
cast<Instruction>(BO->user_back())->getOpcode() == Instruction::FSub)
return;
ReassociateExpression(BO);
}
void ReassociatePass::ReassociateExpression(BinaryOperator *I) {
// First, walk the expression tree, linearizing the tree, collecting the
// operand information.
SmallVector<RepeatedValue, 8> Tree;
MadeChange |= LinearizeExprTree(I, Tree);
SmallVector<ValueEntry, 8> Ops;
Ops.reserve(Tree.size());
for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
RepeatedValue E = Tree[i];
Ops.append(E.second.getZExtValue(),
ValueEntry(getRank(E.first), E.first));
}
LLVM_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.
llvm::stable_sort(Ops);
// Now that we have the expression tree in a convenient
// sorted form, optimize it globally if possible.
if (Value *V = OptimizeExpression(I, Ops)) {
if (V == I)
// Self-referential expression in unreachable code.
return;
// This expression tree simplified to something that isn't a tree,
// eliminate it.
LLVM_DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
I->replaceAllUsesWith(V);
if (Instruction *VI = dyn_cast<Instruction>(V))
if (I->getDebugLoc())
VI->setDebugLoc(I->getDebugLoc());
RedoInsts.insert(I);
++NumAnnihil;
return;
}
// 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->hasOneUse()) {
if (I->getOpcode() == Instruction::Mul &&
cast<Instruction>(I->user_back())->getOpcode() == Instruction::Add &&
isa<ConstantInt>(Ops.back().Op) &&
cast<ConstantInt>(Ops.back().Op)->isMinusOne()) {
ValueEntry Tmp = Ops.pop_back_val();
Ops.insert(Ops.begin(), Tmp);
} else if (I->getOpcode() == Instruction::FMul &&
cast<Instruction>(I->user_back())->getOpcode() ==
Instruction::FAdd &&
isa<ConstantFP>(Ops.back().Op) &&
cast<ConstantFP>(Ops.back().Op)->isExactlyValue(-1.0)) {
ValueEntry Tmp = Ops.pop_back_val();
Ops.insert(Ops.begin(), Tmp);
}
}
LLVM_DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
if (Ops.size() == 1) {
if (Ops[0].Op == I)
// Self-referential expression in unreachable code.
return;
// 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());
RedoInsts.insert(I);
return;
}
if (Ops.size() > 2 && Ops.size() <= GlobalReassociateLimit) {
// Find the pair with the highest count in the pairmap and move it to the
// back of the list so that it can later be CSE'd.
// example:
// a*b*c*d*e
// if c*e is the most "popular" pair, we can express this as
// (((c*e)*d)*b)*a
unsigned Max = 1;
unsigned BestRank = 0;
std::pair<unsigned, unsigned> BestPair;
unsigned Idx = I->getOpcode() - Instruction::BinaryOpsBegin;
for (unsigned i = 0; i < Ops.size() - 1; ++i)
for (unsigned j = i + 1; j < Ops.size(); ++j) {
unsigned Score = 0;
Value *Op0 = Ops[i].Op;
Value *Op1 = Ops[j].Op;
if (std::less<Value *>()(Op1, Op0))
std::swap(Op0, Op1);
auto it = PairMap[Idx].find({Op0, Op1});
if (it != PairMap[Idx].end()) {
// Functions like BreakUpSubtract() can erase the Values we're using
// as keys and create new Values after we built the PairMap. There's a
// small chance that the new nodes can have the same address as
// something already in the table. We shouldn't accumulate the stored
// score in that case as it refers to the wrong Value.
if (it->second.isValid())
Score += it->second.Score;
}
unsigned MaxRank = std::max(Ops[i].Rank, Ops[j].Rank);
if (Score > Max || (Score == Max && MaxRank < BestRank)) {
BestPair = {i, j};
Max = Score;
BestRank = MaxRank;
}
}
if (Max > 1) {
auto Op0 = Ops[BestPair.first];
auto Op1 = Ops[BestPair.second];
Ops.erase(&Ops[BestPair.second]);
Ops.erase(&Ops[BestPair.first]);
Ops.push_back(Op0);
Ops.push_back(Op1);
}
}
// Now that we ordered and optimized the expressions, splat them back into
// the expression tree, removing any unneeded nodes.
RewriteExprTree(I, Ops);
}
void
ReassociatePass::BuildPairMap(ReversePostOrderTraversal<Function *> &RPOT) {
// Make a "pairmap" of how often each operand pair occurs.
for (BasicBlock *BI : RPOT) {
for (Instruction &I : *BI) {
if (!I.isAssociative())
continue;
// Ignore nodes that aren't at the root of trees.
if (I.hasOneUse() && I.user_back()->getOpcode() == I.getOpcode())
continue;
// Collect all operands in a single reassociable expression.
// Since Reassociate has already been run once, we can assume things
// are already canonical according to Reassociation's regime.
SmallVector<Value *, 8> Worklist = { I.getOperand(0), I.getOperand(1) };
SmallVector<Value *, 8> Ops;
while (!Worklist.empty() && Ops.size() <= GlobalReassociateLimit) {
Value *Op = Worklist.pop_back_val();
Instruction *OpI = dyn_cast<Instruction>(Op);
if (!OpI || OpI->getOpcode() != I.getOpcode() || !OpI->hasOneUse()) {
Ops.push_back(Op);
continue;
}
// Be paranoid about self-referencing expressions in unreachable code.
if (OpI->getOperand(0) != OpI)
Worklist.push_back(OpI->getOperand(0));
if (OpI->getOperand(1) != OpI)
Worklist.push_back(OpI->getOperand(1));
}
// Skip extremely long expressions.
if (Ops.size() > GlobalReassociateLimit)
continue;
// Add all pairwise combinations of operands to the pair map.
unsigned BinaryIdx = I.getOpcode() - Instruction::BinaryOpsBegin;
SmallSet<std::pair<Value *, Value*>, 32> Visited;
for (unsigned i = 0; i < Ops.size() - 1; ++i) {
for (unsigned j = i + 1; j < Ops.size(); ++j) {
// Canonicalize operand orderings.
Value *Op0 = Ops[i];
Value *Op1 = Ops[j];
if (std::less<Value *>()(Op1, Op0))
std::swap(Op0, Op1);
if (!Visited.insert({Op0, Op1}).second)
continue;
auto res = PairMap[BinaryIdx].insert({{Op0, Op1}, {Op0, Op1, 1}});
if (!res.second) {
// If either key value has been erased then we've got the same
// address by coincidence. That can't happen here because nothing is
// erasing values but it can happen by the time we're querying the
// map.
assert(res.first->second.isValid() && "WeakVH invalidated");
++res.first->second.Score;
}
}
}
}
}
}
PreservedAnalyses ReassociatePass::run(Function &F, FunctionAnalysisManager &) {
// Get the functions basic blocks in Reverse Post Order. This order is used by
// BuildRankMap to pre calculate ranks correctly. It also excludes dead basic
// blocks (it has been seen that the analysis in this pass could hang when
// analysing dead basic blocks).
ReversePostOrderTraversal<Function *> RPOT(&F);
// Calculate the rank map for F.
BuildRankMap(F, RPOT);
// Build the pair map before running reassociate.
// Technically this would be more accurate if we did it after one round
// of reassociation, but in practice it doesn't seem to help much on
// real-world code, so don't waste the compile time running reassociate
// twice.
// If a user wants, they could expicitly run reassociate twice in their
// pass pipeline for further potential gains.
// It might also be possible to update the pair map during runtime, but the
// overhead of that may be large if there's many reassociable chains.
BuildPairMap(RPOT);
MadeChange = false;
// Traverse the same blocks that were analysed by BuildRankMap.
for (BasicBlock *BI : RPOT) {
assert(RankMap.count(&*BI) && "BB should be ranked.");
// Optimize every instruction in the basic block.
for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE;)
if (isInstructionTriviallyDead(&*II)) {
EraseInst(&*II++);
} else {
OptimizeInst(&*II);
assert(II->getParent() == &*BI && "Moved to a different block!");
++II;
}
// Make a copy of all the instructions to be redone so we can remove dead
// instructions.
OrderedSet ToRedo(RedoInsts);
// Iterate over all instructions to be reevaluated and remove trivially dead
// instructions. If any operand of the trivially dead instruction becomes
// dead mark it for deletion as well. Continue this process until all
// trivially dead instructions have been removed.
while (!ToRedo.empty()) {
Instruction *I = ToRedo.pop_back_val();
if (isInstructionTriviallyDead(I)) {
RecursivelyEraseDeadInsts(I, ToRedo);
MadeChange = true;
}
}
// Now that we have removed dead instructions, we can reoptimize the
// remaining instructions.
while (!RedoInsts.empty()) {
Instruction *I = RedoInsts.front();
RedoInsts.erase(RedoInsts.begin());
if (isInstructionTriviallyDead(I))
EraseInst(I);
else
OptimizeInst(I);
}
}
// We are done with the rank map and pair map.
RankMap.clear();
ValueRankMap.clear();
for (auto &Entry : PairMap)
Entry.clear();
if (MadeChange) {
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
return PA;
}
return PreservedAnalyses::all();
}
namespace {
class ReassociateLegacyPass : public FunctionPass {
ReassociatePass Impl;
public:
static char ID; // Pass identification, replacement for typeid
ReassociateLegacyPass() : FunctionPass(ID) {
initializeReassociateLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
FunctionAnalysisManager DummyFAM;
auto PA = Impl.run(F, DummyFAM);
return !PA.areAllPreserved();
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addPreserved<AAResultsWrapperPass>();
AU.addPreserved<BasicAAWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
}
};
} // end anonymous namespace
char ReassociateLegacyPass::ID = 0;
INITIALIZE_PASS(ReassociateLegacyPass, "reassociate",
"Reassociate expressions", false, false)
// Public interface to the Reassociate pass
FunctionPass *llvm::createReassociatePass() {
return new ReassociateLegacyPass();
}
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