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llvm-project/llvm/lib/Transforms/Scalar/PredicateSimplifier.cpp

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//===-- PredicateSimplifier.cpp - Path Sensitive Simplifier -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Nick Lewycky and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===------------------------------------------------------------------===//
//
// Path-sensitive optimizer. In a branch where x == y, replace uses of
// x with y. Permits further optimization, such as the elimination of
// the unreachable call:
//
// void test(int *p, int *q)
// {
// if (p != q)
// return;
//
// if (*p != *q)
// foo(); // unreachable
// }
//
//===------------------------------------------------------------------===//
//
// This optimization works by substituting %q for %p when protected by a
// conditional that assures us of that fact. Properties are stored as
// relationships between two values.
//
//===------------------------------------------------------------------===//
// TODO:
// * Check handling of NAN in floating point types
#define DEBUG_TYPE "predsimplify"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include <iostream>
using namespace llvm;
namespace {
Statistic<>
NumVarsReplaced("predsimplify", "Number of argument substitutions");
Statistic<>
NumInstruction("predsimplify", "Number of instructions removed");
Statistic<>
NumSwitchCases("predsimplify", "Number of switch cases removed");
Statistic<>
NumBranches("predsimplify", "Number of branches made unconditional");
/// Used for choosing the canonical Value in a synonym set.
/// Leaves the better one in V1. Returns whether a swap took place.
static void order(Value *&V1, Value *&V2) {
if (isa<Constant>(V2)) {
if (!isa<Constant>(V1)) {
std::swap(V1, V2);
return;
}
} else if (isa<Argument>(V2)) {
if (!isa<Constant>(V1) && !isa<Argument>(V1)) {
std::swap(V1, V2);
return;
}
}
if (User *U1 = dyn_cast<User>(V1)) {
for (User::const_op_iterator I = U1->op_begin(), E = U1->op_end();
I != E; ++I) {
if (*I == V2) {
std::swap(V1, V2);
return;
}
}
}
return;
}
/// Represents the set of equivalent Value*s and provides insertion
/// and fast lookup. Also stores the set of inequality relationships.
class PropertySet {
struct Property;
class EquivalenceClasses<Value *> union_find;
public:
typedef std::vector<Property>::iterator PropertyIterator;
typedef std::vector<Property>::const_iterator ConstPropertyIterator;
enum Ops {
EQ,
NE
};
Value *canonicalize(Value *V) const {
Value *C = lookup(V);
return C ? C : V;
}
Value *lookup(Value *V) const {
EquivalenceClasses<Value *>::member_iterator SI =
union_find.findLeader(V);
if (SI == union_find.member_end()) return NULL;
return *SI;
}
bool empty() const {
return union_find.empty();
}
void addEqual(Value *V1, Value *V2) {
order(V1, V2);
if (isa<Constant>(V2)) return; // refuse to set false == true.
union_find.unionSets(V1, V2);
addImpliedProperties(EQ, V1, V2);
}
void addNotEqual(Value *V1, Value *V2) {
DEBUG(std::cerr << "not equal: " << *V1 << " and " << *V2 << "\n");
if (findProperty(NE, V1, V2) != Properties.end())
return; // found.
// Add the property.
Properties.push_back(Property(NE, V1, V2));
addImpliedProperties(NE, V1, V2);
}
PropertyIterator findProperty(Ops Opcode, Value *V1, Value *V2) {
assert(Opcode != EQ && "Can't findProperty on EQ."
"Use the lookup method instead.");
V1 = canonicalize(V1);
V2 = canonicalize(V2);
// Does the property already exist?
for (PropertyIterator I = Properties.begin(), E = Properties.end();
I != E; ++I) {
if (I->Opcode != Opcode) continue;
I->V1 = canonicalize(I->V1);
I->V2 = canonicalize(I->V2);
if ((I->V1 == V1 && I->V2 == V2) ||
(I->V1 == V2 && I->V2 == V1)) {
return I; // Found.
}
}
return Properties.end();
}
ConstPropertyIterator
findProperty(Ops Opcode, Value *V1, Value *V2) const {
assert(Opcode != EQ && "Can't findProperty on EQ."
"Use the lookup method instead.");
V1 = canonicalize(V1);
V2 = canonicalize(V2);
// Does the property already exist?
for (ConstPropertyIterator I = Properties.begin(),
E = Properties.end(); I != E; ++I) {
if (I->Opcode != Opcode) continue;
Value *v1 = canonicalize(I->V1),
*v2 = canonicalize(I->V2);
if ((v1 == V1 && v2 == V2) ||
(v1 == V2 && v2 == V1)) {
return I; // Found.
}
}
return Properties.end();
}
private:
// Represents Head OP [Tail1, Tail2, ...]
// For example: %x != %a, %x != %b.
struct Property {
Property(Ops opcode, Value *v1, Value *v2)
: Opcode(opcode), V1(v1), V2(v2)
{ assert(opcode != EQ && "Equality belongs in the synonym set,"
"not a property."); }
bool operator<(const Property &rhs) const {
if (Opcode != rhs.Opcode) return Opcode < rhs.Opcode;
if (V1 != rhs.V1) return V1 < rhs.V1;
return V2 < rhs.V2;
}
Ops Opcode;
Value *V1, *V2;
};
void add(Ops Opcode, Value *V1, Value *V2, bool invert) {
switch (Opcode) {
case EQ:
if (invert) addNotEqual(V1, V2);
else addEqual(V1, V2);
break;
case NE:
if (invert) addEqual(V1, V2);
else addNotEqual(V1, V2);
break;
default:
assert(0 && "Unknown property opcode.");
}
}
// Finds the properties implied by a synonym and adds them too.
// Example: ("seteq %a, %b", true, EQ) --> (%a, %b, EQ)
// ("seteq %a, %b", false, EQ) --> (%a, %b, NE)
void addImpliedProperties(Ops Opcode, Value *V1, Value *V2) {
order(V1, V2);
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V2)) {
switch (BO->getOpcode()) {
case Instruction::SetEQ:
if (V1 == ConstantBool::True)
add(Opcode, BO->getOperand(0), BO->getOperand(1), false);
if (V1 == ConstantBool::False)
add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
break;
case Instruction::SetNE:
if (V1 == ConstantBool::True)
add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
if (V1 == ConstantBool::False)
add(Opcode, BO->getOperand(0), BO->getOperand(1), false);
break;
case Instruction::SetLT:
case Instruction::SetGT:
if (V1 == ConstantBool::True)
add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
break;
case Instruction::SetLE:
case Instruction::SetGE:
if (V1 == ConstantBool::False)
add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
break;
case Instruction::And:
if (V1 == ConstantBool::True) {
add(Opcode, ConstantBool::True, BO->getOperand(0), false);
add(Opcode, ConstantBool::True, BO->getOperand(1), false);
}
break;
case Instruction::Or:
if (V1 == ConstantBool::False) {
add(Opcode, ConstantBool::False, BO->getOperand(0), false);
add(Opcode, ConstantBool::False, BO->getOperand(1), false);
}
break;
case Instruction::Xor:
if (V1 == ConstantBool::True) {
if (BO->getOperand(0) == ConstantBool::True)
add(Opcode, ConstantBool::False, BO->getOperand(1), false);
if (BO->getOperand(1) == ConstantBool::True)
add(Opcode, ConstantBool::False, BO->getOperand(0), false);
}
if (V1 == ConstantBool::False) {
if (BO->getOperand(0) == ConstantBool::True)
add(Opcode, ConstantBool::True, BO->getOperand(1), false);
if (BO->getOperand(1) == ConstantBool::True)
add(Opcode, ConstantBool::True, BO->getOperand(0), false);
}
break;
default:
break;
}
}
}
std::map<Value *, unsigned> SynonymMap;
std::vector<Value *> Synonyms;
public:
void debug(std::ostream &os) const {
for (EquivalenceClasses<Value*>::iterator I = union_find.begin(),
E = union_find.end(); I != E; ++I) {
if (!I->isLeader()) continue;
for (EquivalenceClasses<Value*>::member_iterator MI =
union_find.member_begin(I); MI != union_find.member_end(); ++MI)
std::cerr << **MI << " ";
std::cerr << "\n--\n";
}
}
std::vector<Property> Properties;
};
/// PredicateSimplifier - This class is a simplifier that replaces
/// one equivalent variable with another. It also tracks what
/// can't be equal and will solve setcc instructions when possible.
class PredicateSimplifier : public FunctionPass {
public:
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
private:
// Try to replace the Use of the instruction with something simpler.
Value *resolve(SetCondInst *SCI, const PropertySet &);
Value *resolve(BinaryOperator *BO, const PropertySet &);
Value *resolve(SelectInst *SI, const PropertySet &);
Value *resolve(Value *V, const PropertySet &);
// Used by terminator instructions to proceed from the current basic
// block to the next. Verifies that "current" dominates "next",
// then calls visitBasicBlock.
void proceedToSuccessor(PropertySet &CurrentPS, PropertySet &NextPS,
DominatorTree::Node *Current, DominatorTree::Node *Next);
void proceedToSuccessor(PropertySet &CurrentPS,
DominatorTree::Node *Current, DominatorTree::Node *Next);
// Visits each instruction in the basic block.
void visitBasicBlock(DominatorTree::Node *DTNode,
PropertySet &KnownProperties);
// For each instruction, add the properties to KnownProperties.
void visit(Instruction *I, DominatorTree::Node *, PropertySet &);
void visit(TerminatorInst *TI, DominatorTree::Node *, PropertySet &);
void visit(BranchInst *BI, DominatorTree::Node *, PropertySet &);
void visit(SwitchInst *SI, DominatorTree::Node *, PropertySet);
void visit(LoadInst *LI, DominatorTree::Node *, PropertySet &);
void visit(StoreInst *SI, DominatorTree::Node *, PropertySet &);
void visit(BinaryOperator *BO, DominatorTree::Node *, PropertySet &);
DominatorTree *DT;
bool modified;
};
RegisterPass<PredicateSimplifier> X("predsimplify",
"Predicate Simplifier");
}
FunctionPass *llvm::createPredicateSimplifierPass() {
return new PredicateSimplifier();
}
bool PredicateSimplifier::runOnFunction(Function &F) {
DT = &getAnalysis<DominatorTree>();
modified = false;
PropertySet KnownProperties;
visitBasicBlock(DT->getRootNode(), KnownProperties);
return modified;
}
void PredicateSimplifier::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
}
// resolve catches cases addProperty won't because it wasn't used as a
// condition in the branch, and that visit won't, because the instruction
// was defined outside of the range that the properties apply to.
Value *PredicateSimplifier::resolve(SetCondInst *SCI,
const PropertySet &KP) {
// Attempt to resolve the SetCondInst to a boolean.
Value *SCI0 = SCI->getOperand(0),
*SCI1 = SCI->getOperand(1);
PropertySet::ConstPropertyIterator NE =
KP.findProperty(PropertySet::NE, SCI0, SCI1);
if (NE != KP.Properties.end()) {
switch (SCI->getOpcode()) {
case Instruction::SetEQ:
return ConstantBool::False;
case Instruction::SetNE:
return ConstantBool::True;
case Instruction::SetLE:
case Instruction::SetGE:
case Instruction::SetLT:
case Instruction::SetGT:
break;
default:
assert(0 && "Unknown opcode in SetCondInst.");
break;
}
}
SCI0 = KP.canonicalize(SCI0);
SCI1 = KP.canonicalize(SCI1);
ConstantIntegral *CI1 = dyn_cast<ConstantIntegral>(SCI0),
*CI2 = dyn_cast<ConstantIntegral>(SCI1);
if (!CI1 || !CI2) return SCI;
switch(SCI->getOpcode()) {
case Instruction::SetLE:
case Instruction::SetGE:
case Instruction::SetEQ:
if (CI1->getRawValue() == CI2->getRawValue())
return ConstantBool::True;
else
return ConstantBool::False;
case Instruction::SetLT:
case Instruction::SetGT:
case Instruction::SetNE:
if (CI1->getRawValue() == CI2->getRawValue())
return ConstantBool::False;
else
return ConstantBool::True;
default:
assert(0 && "Unknown opcode in SetContInst.");
break;
}
}
Value *PredicateSimplifier::resolve(BinaryOperator *BO,
const PropertySet &KP) {
if (SetCondInst *SCI = dyn_cast<SetCondInst>(BO))
return resolve(SCI, KP);
DEBUG(std::cerr << "BO->getOperand(1) = " << *BO->getOperand(1) << "\n");
Value *lhs = resolve(BO->getOperand(0), KP),
*rhs = resolve(BO->getOperand(1), KP);
ConstantIntegral *CI1 = dyn_cast<ConstantIntegral>(lhs);
ConstantIntegral *CI2 = dyn_cast<ConstantIntegral>(rhs);
DEBUG(std::cerr << "resolveBO: lhs = " << *lhs
<< ", rhs = " << *rhs << "\n");
if (CI1) DEBUG(std::cerr << "CI1 = " << *CI1);
if (CI2) DEBUG(std::cerr << "CI2 = " << *CI2);
if (!CI1 || !CI2) return BO;
Value *V = ConstantExpr::get(BO->getOpcode(), CI1, CI2);
if (V) return V;
return BO;
}
Value *PredicateSimplifier::resolve(SelectInst *SI, const PropertySet &KP) {
Value *Condition = resolve(SI->getCondition(), KP);
if (Condition == ConstantBool::True)
return resolve(SI->getTrueValue(), KP);
else if (Condition == ConstantBool::False)
return resolve(SI->getFalseValue(), KP);
return SI;
}
Value *PredicateSimplifier::resolve(Value *V, const PropertySet &KP) {
if (isa<Constant>(V) || isa<BasicBlock>(V) || KP.empty()) return V;
V = KP.canonicalize(V);
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
return resolve(BO, KP);
else if (SelectInst *SI = dyn_cast<SelectInst>(V))
return resolve(SI, KP);
return V;
}
void PredicateSimplifier::visitBasicBlock(DominatorTree::Node *DTNode,
PropertySet &KnownProperties) {
BasicBlock *BB = DTNode->getBlock();
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
visit(I, DTNode, KnownProperties);
}
}
void PredicateSimplifier::visit(Instruction *I, DominatorTree::Node *DTNode,
PropertySet &KnownProperties) {
DEBUG(std::cerr << "Considering instruction " << *I << "\n");
DEBUG(KnownProperties.debug(std::cerr));
// Substitute values known to be equal.
for (unsigned i = 0, E = I->getNumOperands(); i != E; ++i) {
Value *Oper = I->getOperand(i);
Value *V = resolve(Oper, KnownProperties);
assert(V && "resolve not supposed to return NULL.");
if (V != Oper) {
modified = true;
++NumVarsReplaced;
DEBUG(std::cerr << "resolving " << *I);
I->setOperand(i, V);
DEBUG(std::cerr << "into " << *I);
}
}
Value *V = resolve(I, KnownProperties);
assert(V && "resolve not supposed to return NULL.");
if (V != I) {
modified = true;
++NumInstruction;
I->replaceAllUsesWith(V);
I->eraseFromParent();
}
if (TerminatorInst *TI = dyn_cast<TerminatorInst>(I))
visit(TI, DTNode, KnownProperties);
else if (LoadInst *LI = dyn_cast<LoadInst>(I))
visit(LI, DTNode, KnownProperties);
else if (StoreInst *SI = dyn_cast<StoreInst>(I))
visit(SI, DTNode, KnownProperties);
else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I))
visit(BO, DTNode, KnownProperties);
}
void PredicateSimplifier::proceedToSuccessor(PropertySet &CurrentPS,
PropertySet &NextPS, DominatorTree::Node *Current,
DominatorTree::Node *Next) {
if (Next->getBlock()->getSinglePredecessor() == Current->getBlock())
proceedToSuccessor(NextPS, Current, Next);
else
proceedToSuccessor(CurrentPS, Current, Next);
}
void PredicateSimplifier::proceedToSuccessor(PropertySet &KP,
DominatorTree::Node *Current, DominatorTree::Node *Next) {
if (Current->properlyDominates(Next))
visitBasicBlock(Next, KP);
}
void PredicateSimplifier::visit(TerminatorInst *TI,
DominatorTree::Node *Node, PropertySet &KP){
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
visit(BI, Node, KP);
return;
}
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
visit(SI, Node, KP);
return;
}
for (unsigned i = 0, E = TI->getNumSuccessors(); i != E; ++i) {
BasicBlock *BB = TI->getSuccessor(i);
PropertySet KPcopy(KP);
proceedToSuccessor(KPcopy, Node, DT->getNode(TI->getSuccessor(i)));
}
}
void PredicateSimplifier::visit(BranchInst *BI,
DominatorTree::Node *Node, PropertySet &KP){
if (BI->isUnconditional()) {
proceedToSuccessor(KP, Node, DT->getNode(BI->getSuccessor(0)));
return;
}
Value *Condition = BI->getCondition();
BasicBlock *TrueDest = BI->getSuccessor(0),
*FalseDest = BI->getSuccessor(1);
if (Condition == ConstantBool::True) {
FalseDest->removePredecessor(BI->getParent());
BI->setUnconditionalDest(TrueDest);
modified = true;
++NumBranches;
proceedToSuccessor(KP, Node, DT->getNode(TrueDest));
return;
} else if (Condition == ConstantBool::False) {
TrueDest->removePredecessor(BI->getParent());
BI->setUnconditionalDest(FalseDest);
modified = true;
++NumBranches;
proceedToSuccessor(KP, Node, DT->getNode(FalseDest));
return;
}
PropertySet TrueProperties(KP), FalseProperties(KP);
DEBUG(std::cerr << "true set:\n");
TrueProperties.addEqual(ConstantBool::True, Condition);
DEBUG(TrueProperties.debug(std::cerr));
DEBUG(std::cerr << "false set:\n");
FalseProperties.addEqual(ConstantBool::False, Condition);
DEBUG(FalseProperties.debug(std::cerr));
PropertySet KPcopy(KP);
proceedToSuccessor(KP, TrueProperties, Node, DT->getNode(TrueDest));
proceedToSuccessor(KPcopy, FalseProperties, Node, DT->getNode(FalseDest));
}
void PredicateSimplifier::visit(SwitchInst *SI,
DominatorTree::Node *DTNode, PropertySet KP) {
Value *Condition = SI->getCondition();
// If there's an NEProperty covering this SwitchInst, we may be able to
// eliminate one of the cases.
if (Value *C = KP.lookup(Condition)) {
Condition = C;
for (PropertySet::ConstPropertyIterator I = KP.Properties.begin(),
E = KP.Properties.end(); I != E; ++I) {
if (I->Opcode != PropertySet::NE) continue;
Value *V1 = KP.lookup(I->V1),
*V2 = KP.lookup(I->V2);
if (V1 != C && V2 != C) continue;
// Is one side a number?
ConstantInt *CI = dyn_cast<ConstantInt>(KP.lookup(I->V1));
if (!CI) CI = dyn_cast<ConstantInt>(KP.lookup(I->V2));
if (CI) {
unsigned i = SI->findCaseValue(CI);
if (i != 0) {
SI->getSuccessor(i)->removePredecessor(SI->getParent());
SI->removeCase(i);
modified = true;
++NumSwitchCases;
}
}
}
}
// Set the EQProperty in each of the cases BBs,
// and the NEProperties in the default BB.
PropertySet DefaultProperties(KP);
DominatorTree::Node *Node = DT->getNode(SI->getParent()),
*DefaultNode = DT->getNode(SI->getSuccessor(0));
if (!Node->dominates(DefaultNode)) DefaultNode = NULL;
for (unsigned I = 1, E = SI->getNumCases(); I < E; ++I) {
ConstantInt *CI = SI->getCaseValue(I);
BasicBlock *SuccBB = SI->getSuccessor(I);
PropertySet copy(KP);
if (SuccBB->getSinglePredecessor()) {
PropertySet NewProperties(KP);
NewProperties.addEqual(Condition, CI);
proceedToSuccessor(copy, NewProperties, DTNode, DT->getNode(SuccBB));
} else
proceedToSuccessor(copy, DTNode, DT->getNode(SuccBB));
if (DefaultNode)
DefaultProperties.addNotEqual(Condition, CI);
}
if (DefaultNode)
proceedToSuccessor(DefaultProperties, DTNode, DefaultNode);
}
void PredicateSimplifier::visit(LoadInst *LI,
DominatorTree::Node *, PropertySet &KP) {
Value *Ptr = LI->getPointerOperand();
KP.addNotEqual(Constant::getNullValue(Ptr->getType()), Ptr);
}
void PredicateSimplifier::visit(StoreInst *SI,
DominatorTree::Node *, PropertySet &KP) {
Value *Ptr = SI->getPointerOperand();
KP.addNotEqual(Constant::getNullValue(Ptr->getType()), Ptr);
}
void PredicateSimplifier::visit(BinaryOperator *BO,
DominatorTree::Node *, PropertySet &KP) {
Instruction::BinaryOps ops = BO->getOpcode();
switch (ops) {
case Instruction::Div:
case Instruction::Rem: {
Value *Divisor = BO->getOperand(1);
KP.addNotEqual(Constant::getNullValue(Divisor->getType()), Divisor);
break;
}
default:
break;
}
// Some other things we could do:
// In f=x*y, if x != 1 && y != 1 then f != x && f != y.
// In f=x+y, if x != 0 then f != y and if y != 0 then f != x.
}
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