//===-- DifferenceEngine.cpp - Structural function/module comparison ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This header defines the implementation of the LLVM difference
// engine, which structurally compares global values within a module.
//
//===----------------------------------------------------------------------===//
#include "DifferenceEngine.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/type_traits.h"
#include <utility>
using namespace llvm;
namespace {
/// A priority queue, implemented as a heap.
template <class T, class Sorter, unsigned InlineCapacity>
class PriorityQueue {
Sorter Precedes;
llvm::SmallVector<T, InlineCapacity> Storage;
public:
PriorityQueue(const Sorter &Precedes) : Precedes(Precedes) {}
/// Checks whether the heap is empty.
bool empty() const { return Storage.empty(); }
/// Insert a new value on the heap.
void insert(const T &V) {
unsigned Index = Storage.size();
Storage.push_back(V);
if (Index == 0) return;
T *data = Storage.data();
while (true) {
unsigned Target = (Index + 1) / 2 - 1;
if (!Precedes(data[Index], data[Target])) return;
std::swap(data[Index], data[Target]);
if (Target == 0) return;
Index = Target;
}
}
/// Remove the minimum value in the heap. Only valid on a non-empty heap.
T remove_min() {
assert(!empty());
T tmp = Storage[0];
unsigned NewSize = Storage.size() - 1;
if (NewSize) {
// Move the slot at the end to the beginning.
if (isPodLike<T>::value)
Storage[0] = Storage[NewSize];
else
std::swap(Storage[0], Storage[NewSize]);
// Bubble the root up as necessary.
unsigned Index = 0;
while (true) {
// With a 1-based index, the children would be Index*2 and Index*2+1.
unsigned R = (Index + 1) * 2;
unsigned L = R - 1;
// If R is out of bounds, we're done after this in any case.
if (R >= NewSize) {
// If L is also out of bounds, we're done immediately.
if (L >= NewSize) break;
// Otherwise, test whether we should swap L and Index.
if (Precedes(Storage[L], Storage[Index]))
std::swap(Storage[L], Storage[Index]);
break;
}
// Otherwise, we need to compare with the smaller of L and R.
// Prefer R because it's closer to the end of the array.
unsigned IndexToTest = (Precedes(Storage[L], Storage[R]) ? L : R);
// If Index is >= the min of L and R, then heap ordering is restored.
if (!Precedes(Storage[IndexToTest], Storage[Index]))
break;
// Otherwise, keep bubbling up.
std::swap(Storage[IndexToTest], Storage[Index]);
Index = IndexToTest;
}
}
Storage.pop_back();
return tmp;
}
};
/// A function-scope difference engine.
class FunctionDifferenceEngine {
DifferenceEngine &Engine;
/// The current mapping from old local values to new local values.
DenseMap<Value*, Value*> Values;
/// The current mapping from old blocks to new blocks.
DenseMap<BasicBlock*, BasicBlock*> Blocks;
DenseSet<std::pair<Value*, Value*> > TentativeValues;
unsigned getUnprocPredCount(BasicBlock *Block) const {
unsigned Count = 0;
for (pred_iterator I = pred_begin(Block), E = pred_end(Block); I != E; ++I)
if (!Blocks.count(*I)) Count++;
return Count;
}
typedef std::pair<BasicBlock*, BasicBlock*> BlockPair;
/// A type which sorts a priority queue by the number of unprocessed
/// predecessor blocks it has remaining.
///
/// This is actually really expensive to calculate.
struct QueueSorter {
const FunctionDifferenceEngine &fde;
explicit QueueSorter(const FunctionDifferenceEngine &fde) : fde(fde) {}
bool operator()(const BlockPair &Old, const BlockPair &New) {
return fde.getUnprocPredCount(Old.first)
< fde.getUnprocPredCount(New.first);
}
};
/// A queue of unified blocks to process.
PriorityQueue<BlockPair, QueueSorter, 20> Queue;
/// Try to unify the given two blocks. Enqueues them for processing
/// if they haven't already been processed.
///
/// Returns true if there was a problem unifying them.
bool tryUnify(BasicBlock *L, BasicBlock *R) {
BasicBlock *&Ref = Blocks[L];
if (Ref) {
if (Ref == R) return false;
Engine.logf("successor %l cannot be equivalent to %r; "
"it's already equivalent to %r")
<< L << R << Ref;
return true;
}
Ref = R;
Queue.insert(BlockPair(L, R));
return false;
}
/// Unifies two instructions, given that they're known not to have
/// structural differences.
void unify(Instruction *L, Instruction *R) {
DifferenceEngine::Context C(Engine, L, R);
bool Result = diff(L, R, true, true);
assert(!Result && "structural differences second time around?");
(void) Result;
if (!L->use_empty())
Values[L] = R;
}
void processQueue() {
while (!Queue.empty()) {
BlockPair Pair = Queue.remove_min();
diff(Pair.first, Pair.second);
}
}
void diff(BasicBlock *L, BasicBlock *R) {
DifferenceEngine::Context C(Engine, L, R);
BasicBlock::iterator LI = L->begin(), LE = L->end();
BasicBlock::iterator RI = R->begin();
do {
assert(LI != LE && RI != R->end());
Instruction *LeftI = &*LI, *RightI = &*RI;
// If the instructions differ, start the more sophisticated diff
// algorithm at the start of the block.
if (diff(LeftI, RightI, false, false)) {
TentativeValues.clear();
return runBlockDiff(L->begin(), R->begin());
}
// Otherwise, tentatively unify them.
if (!LeftI->use_empty())
TentativeValues.insert(std::make_pair(LeftI, RightI));
++LI, ++RI;
} while (LI != LE); // This is sufficient: we can't get equality of
// terminators if there are residual instructions.
// Unify everything in the block, non-tentatively this time.
TentativeValues.clear();
for (LI = L->begin(), RI = R->begin(); LI != LE; ++LI, ++RI)
unify(&*LI, &*RI);
}
bool matchForBlockDiff(Instruction *L, Instruction *R);
void runBlockDiff(BasicBlock::iterator LI, BasicBlock::iterator RI);
bool diffCallSites(CallSite L, CallSite R, bool Complain) {
// FIXME: call attributes
if (!equivalentAsOperands(L.getCalledValue(), R.getCalledValue())) {
if (Complain) Engine.log("called functions differ");
return true;
}
if (L.arg_size() != R.arg_size()) {
if (Complain) Engine.log("argument counts differ");
return true;
}
for (unsigned I = 0, E = L.arg_size(); I != E; ++I)
if (!equivalentAsOperands(L.getArgument(I), R.getArgument(I))) {
if (Complain)
Engine.logf("arguments %l and %r differ")
<< L.getArgument(I) << R.getArgument(I);
return true;
}
return false;
}
bool diff(Instruction *L, Instruction *R, bool Complain, bool TryUnify) {
// FIXME: metadata (if Complain is set)
// Different opcodes always imply different operations.
if (L->getOpcode() != R->getOpcode()) {
if (Complain) Engine.log("different instruction types");
return true;
}
if (isa<CmpInst>(L)) {
if (cast<CmpInst>(L)->getPredicate()
!= cast<CmpInst>(R)->getPredicate()) {
if (Complain) Engine.log("different predicates");
return true;
}
} else if (isa<CallInst>(L)) {
return diffCallSites(CallSite(L), CallSite(R), Complain);
} else if (isa<PHINode>(L)) {
// FIXME: implement.
// This is really weird; type uniquing is broken?
if (L->getType() != R->getType()) {
if (!L->getType()->isPointerTy() || !R->getType()->isPointerTy()) {
if (Complain) Engine.log("different phi types");
return true;
}
}
return false;
// Terminators.
} else if (isa<InvokeInst>(L)) {
InvokeInst *LI = cast<InvokeInst>(L);
InvokeInst *RI = cast<InvokeInst>(R);
if (diffCallSites(CallSite(LI), CallSite(RI), Complain))
return true;
if (TryUnify) {
tryUnify(LI->getNormalDest(), RI->getNormalDest());
tryUnify(LI->getUnwindDest(), RI->getUnwindDest());
}
return false;
} else if (isa<BranchInst>(L)) {
BranchInst *LI = cast<BranchInst>(L);
BranchInst *RI = cast<BranchInst>(R);
if (LI->isConditional() != RI->isConditional()) {
if (Complain) Engine.log("branch conditionality differs");
return true;
}
if (LI->isConditional()) {
if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) {
if (Complain) Engine.log("branch conditions differ");
return true;
}
if (TryUnify) tryUnify(LI->getSuccessor(1), RI->getSuccessor(1));
}
if (TryUnify) tryUnify(LI->getSuccessor(0), RI->getSuccessor(0));
return false;
} else if (isa<SwitchInst>(L)) {
SwitchInst *LI = cast<SwitchInst>(L);
SwitchInst *RI = cast<SwitchInst>(R);
if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) {
if (Complain) Engine.log("switch conditions differ");
return true;
}
if (TryUnify) tryUnify(LI->getDefaultDest(), RI->getDefaultDest());
bool Difference = false;
DenseMap<ConstantInt*,BasicBlock*> LCases;
for (SwitchInst::CaseIt I = LI->case_begin(), E = LI->case_end();
I != E; ++I)
LCases[I.getCaseValue()] = I.getCaseSuccessor();
for (SwitchInst::CaseIt I = RI->case_begin(), E = RI->case_end();
I != E; ++I) {
ConstantInt *CaseValue = I.getCaseValue();
BasicBlock *LCase = LCases[CaseValue];
if (LCase) {
if (TryUnify) tryUnify(LCase, I.getCaseSuccessor());
LCases.erase(CaseValue);
} else if (Complain || !Difference) {
if (Complain)
Engine.logf("right switch has extra case %r") << CaseValue;
Difference = true;
}
}
if (!Difference)
for (DenseMap<ConstantInt*,BasicBlock*>::iterator
I = LCases.begin(), E = LCases.end(); I != E; ++I) {
if (Complain)
Engine.logf("left switch has extra case %l") << I->first;
Difference = true;
}
return Difference;
} else if (isa<UnreachableInst>(L)) {
return false;
}
if (L->getNumOperands() != R->getNumOperands()) {
if (Complain) Engine.log("instructions have different operand counts");
return true;
}
for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I) {
Value *LO = L->getOperand(I), *RO = R->getOperand(I);
if (!equivalentAsOperands(LO, RO)) {
if (Complain) Engine.logf("operands %l and %r differ") << LO << RO;
return true;
}
}
return false;
}
bool equivalentAsOperands(Constant *L, Constant *R) {
// Use equality as a preliminary filter.
if (L == R)
return true;
if (L->getValueID() != R->getValueID())
return false;
// Ask the engine about global values.
if (isa<GlobalValue>(L))
return Engine.equivalentAsOperands(cast<GlobalValue>(L),
cast<GlobalValue>(R));
// Compare constant expressions structurally.
if (isa<ConstantExpr>(L))
return equivalentAsOperands(cast<ConstantExpr>(L),
cast<ConstantExpr>(R));
// Nulls of the "same type" don't always actually have the same
// type; I don't know why. Just white-list them.
if (isa<ConstantPointerNull>(L))
return true;
// Block addresses only match if we've already encountered the
// block. FIXME: tentative matches?
if (isa<BlockAddress>(L))
return Blocks[cast<BlockAddress>(L)->getBasicBlock()]
== cast<BlockAddress>(R)->getBasicBlock();
return false;
}
bool equivalentAsOperands(ConstantExpr *L, ConstantExpr *R) {
if (L == R)
return true;
if (L->getOpcode() != R->getOpcode())
return false;
switch (L->getOpcode()) {
case Instruction::ICmp:
case Instruction::FCmp:
if (L->getPredicate() != R->getPredicate())
return false;
break;
case Instruction::GetElementPtr:
// FIXME: inbounds?
break;
default:
break;
}
if (L->getNumOperands() != R->getNumOperands())
return false;
for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I)
if (!equivalentAsOperands(L->getOperand(I), R->getOperand(I)))
return false;
return true;
}
bool equivalentAsOperands(Value *L, Value *R) {
// Fall out if the values have different kind.
// This possibly shouldn't take priority over oracles.
if (L->getValueID() != R->getValueID())
return false;
// Value subtypes: Argument, Constant, Instruction, BasicBlock,
// InlineAsm, MDNode, MDString, PseudoSourceValue
if (isa<Constant>(L))
return equivalentAsOperands(cast<Constant>(L), cast<Constant>(R));
if (isa<Instruction>(L))
return Values[L] == R || TentativeValues.count(std::make_pair(L, R));
if (isa<Argument>(L))
return Values[L] == R;
if (isa<BasicBlock>(L))
return Blocks[cast<BasicBlock>(L)] != R;
// Pretend everything else is identical.
return true;
}
// Avoid a gcc warning about accessing 'this' in an initializer.
FunctionDifferenceEngine *this_() { return this; }
public:
FunctionDifferenceEngine(DifferenceEngine &Engine) :
Engine(Engine), Queue(QueueSorter(*this_())) {}
void diff(Function *L, Function *R) {
if (L->arg_size() != R->arg_size())
Engine.log("different argument counts");
// Map the arguments.
for (Function::arg_iterator
LI = L->arg_begin(), LE = L->arg_end(),
RI = R->arg_begin(), RE = R->arg_end();
LI != LE && RI != RE; ++LI, ++RI)
Values[&*LI] = &*RI;
tryUnify(&*L->begin(), &*R->begin());
processQueue();
}
};
struct DiffEntry {
DiffEntry() : Cost(0) {}
unsigned Cost;
llvm::SmallVector<char, 8> Path; // actually of DifferenceEngine::DiffChange
};
bool FunctionDifferenceEngine::matchForBlockDiff(Instruction *L,
Instruction *R) {
return !diff(L, R, false, false);
}
void FunctionDifferenceEngine::runBlockDiff(BasicBlock::iterator LStart,
BasicBlock::iterator RStart) {
BasicBlock::iterator LE = LStart->getParent()->end();
BasicBlock::iterator RE = RStart->getParent()->end();
unsigned NL = std::distance(LStart, LE);
SmallVector<DiffEntry, 20> Paths1(NL+1);
SmallVector<DiffEntry, 20> Paths2(NL+1);
DiffEntry *Cur = Paths1.data();
DiffEntry *Next = Paths2.data();
const unsigned LeftCost = 2;
const unsigned RightCost = 2;
const unsigned MatchCost = 0;
assert(TentativeValues.empty());
// Initialize the first column.
for (unsigned I = 0; I != NL+1; ++I) {
Cur[I].Cost = I * LeftCost;
for (unsigned J = 0; J != I; ++J)
Cur[I].Path.push_back(DC_left);
}
for (BasicBlock::iterator RI = RStart; RI != RE; ++RI) {
// Initialize the first row.
Next[0] = Cur[0];
Next[0].Cost += RightCost;
Next[0].Path.push_back(DC_right);
unsigned Index = 1;
for (BasicBlock::iterator LI = LStart; LI != LE; ++LI, ++Index) {
if (matchForBlockDiff(&*LI, &*RI)) {
Next[Index] = Cur[Index-1];
Next[Index].Cost += MatchCost;
Next[Index].Path.push_back(DC_match);
TentativeValues.insert(std::make_pair(&*LI, &*RI));
} else if (Next[Index-1].Cost <= Cur[Index].Cost) {
Next[Index] = Next[Index-1];
Next[Index].Cost += LeftCost;
Next[Index].Path.push_back(DC_left);
} else {
Next[Index] = Cur[Index];
Next[Index].Cost += RightCost;
Next[Index].Path.push_back(DC_right);
}
}
std::swap(Cur, Next);
}
// We don't need the tentative values anymore; everything from here
// on out should be non-tentative.
TentativeValues.clear();
SmallVectorImpl<char> &Path = Cur[NL].Path;
BasicBlock::iterator LI = LStart, RI = RStart;
DiffLogBuilder Diff(Engine.getConsumer());
// Drop trailing matches.
while (Path.back() == DC_match)
Path.pop_back();
// Skip leading matches.
SmallVectorImpl<char>::iterator
PI = Path.begin(), PE = Path.end();
while (PI != PE && *PI == DC_match) {
unify(&*LI, &*RI);
++PI, ++LI, ++RI;
}
for (; PI != PE; ++PI) {
switch (static_cast<DiffChange>(*PI)) {
case DC_match:
assert(LI != LE && RI != RE);
{
Instruction *L = &*LI, *R = &*RI;
unify(L, R);
Diff.addMatch(L, R);
}
++LI; ++RI;
break;
case DC_left:
assert(LI != LE);
Diff.addLeft(&*LI);
++LI;
break;
case DC_right:
assert(RI != RE);
Diff.addRight(&*RI);
++RI;
break;
}
}
// Finishing unifying and complaining about the tails of the block,
// which should be matches all the way through.
while (LI != LE) {
assert(RI != RE);
unify(&*LI, &*RI);
++LI, ++RI;
}
// If the terminators have different kinds, but one is an invoke and the
// other is an unconditional branch immediately following a call, unify
// the results and the destinations.
TerminatorInst *LTerm = LStart->getParent()->getTerminator();
TerminatorInst *RTerm = RStart->getParent()->getTerminator();
if (isa<BranchInst>(LTerm) && isa<InvokeInst>(RTerm)) {
if (cast<BranchInst>(LTerm)->isConditional()) return;
BasicBlock::iterator I = LTerm;
if (I == LStart->getParent()->begin()) return;
--I;
if (!isa<CallInst>(*I)) return;
CallInst *LCall = cast<CallInst>(&*I);
InvokeInst *RInvoke = cast<InvokeInst>(RTerm);
if (!equivalentAsOperands(LCall->getCalledValue(), RInvoke->getCalledValue()))
return;
if (!LCall->use_empty())
Values[LCall] = RInvoke;
tryUnify(LTerm->getSuccessor(0), RInvoke->getNormalDest());
} else if (isa<InvokeInst>(LTerm) && isa<BranchInst>(RTerm)) {
if (cast<BranchInst>(RTerm)->isConditional()) return;
BasicBlock::iterator I = RTerm;
if (I == RStart->getParent()->begin()) return;
--I;
if (!isa<CallInst>(*I)) return;
CallInst *RCall = cast<CallInst>(I);
InvokeInst *LInvoke = cast<InvokeInst>(LTerm);
if (!equivalentAsOperands(LInvoke->getCalledValue(), RCall->getCalledValue()))
return;
if (!LInvoke->use_empty())
Values[LInvoke] = RCall;
tryUnify(LInvoke->getNormalDest(), RTerm->getSuccessor(0));
}
}
}
void DifferenceEngine::Oracle::anchor() { }
void DifferenceEngine::diff(Function *L, Function *R) {
Context C(*this, L, R);
// FIXME: types
// FIXME: attributes and CC
// FIXME: parameter attributes
// If both are declarations, we're done.
if (L->empty() && R->empty())
return;
else if (L->empty())
log("left function is declaration, right function is definition");
else if (R->empty())
log("right function is declaration, left function is definition");
else
FunctionDifferenceEngine(*this).diff(L, R);
}
void DifferenceEngine::diff(Module *L, Module *R) {
StringSet<> LNames;
SmallVector<std::pair<Function*,Function*>, 20> Queue;
for (Module::iterator I = L->begin(), E = L->end(); I != E; ++I) {
Function *LFn = &*I;
LNames.insert(LFn->getName());
if (Function *RFn = R->getFunction(LFn->getName()))
Queue.push_back(std::make_pair(LFn, RFn));
else
logf("function %l exists only in left module") << LFn;
}
for (Module::iterator I = R->begin(), E = R->end(); I != E; ++I) {
Function *RFn = &*I;
if (!LNames.count(RFn->getName()))
logf("function %r exists only in right module") << RFn;
}
for (SmallVectorImpl<std::pair<Function*,Function*> >::iterator
I = Queue.begin(), E = Queue.end(); I != E; ++I)
diff(I->first, I->second);
}
bool DifferenceEngine::equivalentAsOperands(GlobalValue *L, GlobalValue *R) {
if (globalValueOracle) return (*globalValueOracle)(L, R);
return L->getName() == R->getName();
}