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//===-- DifferenceEngine.cpp - Structural function/module comparison ------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// 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/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.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;
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();
if (Index == 0) return;
T *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() {
T tmp = Storage[0];
unsigned NewSize = Storage.size() - 1;
if (NewSize) {
// Move the slot at the end to the beginning.
if (std::is_trivially_copyable<T>::value)
Storage[0] = Storage[NewSize];
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]);
// 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]))
// Otherwise, keep bubbling up.
std::swap(Storage[IndexToTest], Storage[Index]);
Index = IndexToTest;
return tmp;
/// A function-scope difference engine.
class FunctionDifferenceEngine {
DifferenceEngine &Engine;
// Some initializers may reference the variable we're currently checking. This
// can cause an infinite loop. The Saved[LR]HS ivars can be checked to prevent
// recursing.
const Value *SavedLHS;
const Value *SavedRHS;
// The current mapping from old local values to new local values.
DenseMap<const Value *, const Value *> Values;
// The current mapping from old blocks to new blocks.
DenseMap<const BasicBlock *, const BasicBlock *> Blocks;
// The tentative mapping from old local values while comparing a pair of
// basic blocks. Once the pair has been processed, the tentative mapping is
// committed to the Values map.
DenseSet<std::pair<const Value *, const Value *>> TentativeValues;
// Equivalence Assumptions
// For basic blocks in loops, some values in phi nodes may depend on
// values from not yet processed basic blocks in the loop. When encountering
// such values, we optimistically asssume their equivalence and store this
// assumption in a BlockDiffCandidate for the pair of compared BBs.
// Once we have diffed all BBs, for every BlockDiffCandidate, we check all
// stored assumptions using the Values map that stores proven equivalences
// between the old and new values, and report a diff if an assumption cannot
// be proven to be true.
// Note that after having made an assumption, all further determined
// equivalences implicitly depend on that assumption. These will not be
// reverted or reported if the assumption proves to be false, because these
// are considered indirect diffs caused by earlier direct diffs.
// We aim to avoid false negatives in llvm-diff, that is, ensure that
// whenever no diff is reported, the functions are indeed equal. If
// assumptions were made, this is not entirely clear, because in principle we
// could end up with a circular proof where the proof of equivalence of two
// nodes is depending on the assumption of their equivalence.
// To see that assumptions do not add false negatives, note that if we do not
// report a diff, this means that there is an equivalence mapping between old
// and new values that is consistent with all assumptions made. The circular
// dependency that exists on an IR value level does not exist at run time,
// because the values selected by the phi nodes must always already have been
// computed. Hence, we can prove equivalence of the old and new functions by
// considering step-wise parallel execution, and incrementally proving
// equivalence of every new computed value. Another way to think about it is
// to imagine cloning the loop BBs for every iteration, turning the loops
// into (possibly infinite) DAGs, and proving equivalence by induction on the
// iteration, using the computed value mapping.
// The class BlockDiffCandidate stores pairs which either have already been
// proven to differ, or pairs whose equivalence depends on assumptions to be
// verified later.
struct BlockDiffCandidate {
const BasicBlock *LBB;
const BasicBlock *RBB;
// Maps old values to assumed-to-be-equivalent new values
SmallDenseMap<const Value *, const Value *> EquivalenceAssumptions;
// If set, we already know the blocks differ.
bool KnownToDiffer;
// List of block diff candidates in the order found by processing.
// We generate reports in this order.
// For every LBB, there may only be one corresponding RBB.
SmallVector<BlockDiffCandidate> BlockDiffCandidates;
// Maps LBB to the index of its BlockDiffCandidate, if existing.
DenseMap<const BasicBlock *, uint64_t> BlockDiffCandidateIndices;
// Note: Every LBB must always be queried together with the same RBB.
// The returned reference is not permanently valid and should not be stored.
BlockDiffCandidate &getOrCreateBlockDiffCandidate(const BasicBlock *LBB,
const BasicBlock *RBB) {
auto It = BlockDiffCandidateIndices.find(LBB);
// Check if LBB already has a diff candidate
if (It == BlockDiffCandidateIndices.end()) {
// Add new one
BlockDiffCandidateIndices[LBB] = BlockDiffCandidates.size();
{LBB, RBB, SmallDenseMap<const Value *, const Value *>(), false});
return BlockDiffCandidates.back();
// Use existing one
BlockDiffCandidate &Result = BlockDiffCandidates[It->second];
assert(Result.RBB == RBB && "Inconsistent basic block pairing!");
return Result;
// Optionally passed to equivalence checker functions, so these can add
// assumptions in BlockDiffCandidates. Its presence controls whether
// assumptions are generated.
struct AssumptionContext {
// The two basic blocks that need the two compared values to be equivalent.
const BasicBlock *LBB;
const BasicBlock *RBB;
unsigned getUnprocPredCount(const BasicBlock *Block) const {
unsigned Count = 0;
for (const_pred_iterator I = pred_begin(Block), E = pred_end(Block); I != E;
if (!Blocks.count(*I)) Count++;
return Count;
typedef std::pair<const BasicBlock *, const 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()(BlockPair &Old, 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(const BasicBlock *L, const BasicBlock *R) {
const 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(const Instruction *L, const Instruction *R) {
DifferenceEngine::Context C(Engine, L, R);
bool Result = diff(L, R, true, 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 checkAndReportDiffCandidates() {
for (BlockDiffCandidate &BDC : BlockDiffCandidates) {
// Check assumptions
for (const auto &[L, R] : BDC.EquivalenceAssumptions) {
auto It = Values.find(L);
if (It == Values.end() || It->second != R) {
BDC.KnownToDiffer = true;
// Run block diff if the BBs differ
if (BDC.KnownToDiffer) {
DifferenceEngine::Context C(Engine, BDC.LBB, BDC.RBB);
runBlockDiff(BDC.LBB->begin(), BDC.RBB->begin());
void diff(const BasicBlock *L, const BasicBlock *R) {
DifferenceEngine::Context C(Engine, L, R);
BasicBlock::const_iterator LI = L->begin(), LE = L->end();
BasicBlock::const_iterator RI = R->begin();
do {
assert(LI != LE && RI != R->end());
const 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, true)) {
// Register (L, R) as diffing pair. Note that we could directly emit a
// block diff here, but this way we ensure all diffs are emitted in one
// consistent order, independent of whether the diffs were detected
// immediately or via invalid assumptions.
getOrCreateBlockDiffCandidate(L, R).KnownToDiffer = true;
// Otherwise, tentatively unify them.
if (!LeftI->use_empty())
TentativeValues.insert(std::make_pair(LeftI, RightI));
} 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.
for (LI = L->begin(), RI = R->begin(); LI != LE; ++LI, ++RI)
unify(&*LI, &*RI);
bool matchForBlockDiff(const Instruction *L, const Instruction *R);
void runBlockDiff(BasicBlock::const_iterator LI,
BasicBlock::const_iterator RI);
bool diffCallSites(const CallBase &L, const CallBase &R, bool Complain) {
// FIXME: call attributes
AssumptionContext AC = {L.getParent(), R.getParent()};
if (!equivalentAsOperands(L.getCalledOperand(), R.getCalledOperand(),
&AC)) {
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.getArgOperand(I), R.getArgOperand(I), &AC)) {
if (Complain)
Engine.logf("arguments %l and %r differ")
<< L.getArgOperand(I) << R.getArgOperand(I);
return true;
return false;
// If AllowAssumptions is enabled, whenever we encounter a pair of values
// that we cannot prove to be equivalent, we assume equivalence and store that
// assumption to be checked later in BlockDiffCandidates.
bool diff(const Instruction *L, const Instruction *R, bool Complain,
bool TryUnify, bool AllowAssumptions) {
// FIXME: metadata (if Complain is set)
AssumptionContext ACValue = {L->getParent(), R->getParent()};
// nullptr AssumptionContext disables assumption generation.
const AssumptionContext *AC = AllowAssumptions ? &ACValue : nullptr;
// 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(cast<CallInst>(*L), cast<CallInst>(*R), Complain);
} else if (isa<PHINode>(L)) {
const PHINode &LI = cast<PHINode>(*L);
const PHINode &RI = cast<PHINode>(*R);
// This is really weird; type uniquing is broken?
if (LI.getType() != RI.getType()) {
if (!LI.getType()->isPointerTy() || !RI.getType()->isPointerTy()) {
if (Complain) Engine.log("different phi types");
return true;
if (LI.getNumIncomingValues() != RI.getNumIncomingValues()) {
if (Complain)
Engine.log("PHI node # of incoming values differ");
return true;
for (unsigned I = 0; I < LI.getNumIncomingValues(); ++I) {
if (TryUnify)
tryUnify(LI.getIncomingBlock(I), RI.getIncomingBlock(I));
if (!equivalentAsOperands(LI.getIncomingValue(I),
RI.getIncomingValue(I), AC)) {
if (Complain)
Engine.log("PHI node incoming values differ");
return true;
return false;
// Terminators.
} else if (isa<InvokeInst>(L)) {
const InvokeInst &LI = cast<InvokeInst>(*L);
const InvokeInst &RI = cast<InvokeInst>(*R);
if (diffCallSites(LI, RI, Complain))
return true;
if (TryUnify) {
tryUnify(LI.getNormalDest(), RI.getNormalDest());
tryUnify(LI.getUnwindDest(), RI.getUnwindDest());
return false;
} else if (isa<CallBrInst>(L)) {
const CallBrInst &LI = cast<CallBrInst>(*L);
const CallBrInst &RI = cast<CallBrInst>(*R);
if (LI.getNumIndirectDests() != RI.getNumIndirectDests()) {
if (Complain)
Engine.log("callbr # of indirect destinations differ");
return true;
// Perform the "try unify" step so that we can equate the indirect
// destinations before checking the call site.
for (unsigned I = 0; I < LI.getNumIndirectDests(); I++)
tryUnify(LI.getIndirectDest(I), RI.getIndirectDest(I));
if (diffCallSites(LI, RI, Complain))
return true;
if (TryUnify)
tryUnify(LI.getDefaultDest(), RI.getDefaultDest());
return false;
} else if (isa<BranchInst>(L)) {
const BranchInst *LI = cast<BranchInst>(L);
const 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(), AC)) {
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<IndirectBrInst>(L)) {
const IndirectBrInst *LI = cast<IndirectBrInst>(L);
const IndirectBrInst *RI = cast<IndirectBrInst>(R);
if (LI->getNumDestinations() != RI->getNumDestinations()) {
if (Complain) Engine.log("indirectbr # of destinations differ");
return true;
if (!equivalentAsOperands(LI->getAddress(), RI->getAddress(), AC)) {
if (Complain) Engine.log("indirectbr addresses differ");
return true;
if (TryUnify) {
for (unsigned i = 0; i < LI->getNumDestinations(); i++) {
tryUnify(LI->getDestination(i), RI->getDestination(i));
return false;
} else if (isa<SwitchInst>(L)) {
const SwitchInst *LI = cast<SwitchInst>(L);
const SwitchInst *RI = cast<SwitchInst>(R);
if (!equivalentAsOperands(LI->getCondition(), RI->getCondition(), AC)) {
if (Complain) Engine.log("switch conditions differ");
return true;
if (TryUnify) tryUnify(LI->getDefaultDest(), RI->getDefaultDest());
bool Difference = false;
DenseMap<const ConstantInt *, const BasicBlock *> LCases;
for (auto Case : LI->cases())
LCases[Case.getCaseValue()] = Case.getCaseSuccessor();
for (auto Case : RI->cases()) {
const ConstantInt *CaseValue = Case.getCaseValue();
const BasicBlock *LCase = LCases[CaseValue];
if (LCase) {
if (TryUnify)
tryUnify(LCase, Case.getCaseSuccessor());
} else if (Complain || !Difference) {
if (Complain)
Engine.logf("right switch has extra case %r") << CaseValue;
Difference = true;
if (!Difference)
for (DenseMap<const ConstantInt *, const 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, AC)) {
if (Complain) Engine.logf("operands %l and %r differ") << LO << RO;
return true;
return false;
bool equivalentAsOperands(const Constant *L, const Constant *R,
const AssumptionContext *AC) {
// 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),
// Compare constant expressions structurally.
if (isa<ConstantExpr>(L))
return equivalentAsOperands(cast<ConstantExpr>(L), cast<ConstantExpr>(R),
// Constants 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) || isa<UndefValue>(L) || isa<ConstantAggregateZero>(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();
// If L and R are ConstantVectors, compare each element
if (isa<ConstantVector>(L)) {
const ConstantVector *CVL = cast<ConstantVector>(L);
const ConstantVector *CVR = cast<ConstantVector>(R);
if (CVL->getType()->getNumElements() != CVR->getType()->getNumElements())
return false;
for (unsigned i = 0; i < CVL->getType()->getNumElements(); i++) {
if (!equivalentAsOperands(CVL->getOperand(i), CVR->getOperand(i), AC))
return false;
return true;
// If L and R are ConstantArrays, compare the element count and types.
if (isa<ConstantArray>(L)) {
const ConstantArray *CAL = cast<ConstantArray>(L);
const ConstantArray *CAR = cast<ConstantArray>(R);
// Sometimes a type may be equivalent, but not uniquified---e.g. it may
// contain a GEP instruction. Do a deeper comparison of the types.
if (CAL->getType()->getNumElements() != CAR->getType()->getNumElements())
return false;
for (unsigned I = 0; I < CAL->getType()->getNumElements(); ++I) {
if (!equivalentAsOperands(CAL->getAggregateElement(I),
CAR->getAggregateElement(I), AC))
return false;
return true;
// If L and R are ConstantStructs, compare each field and type.
if (isa<ConstantStruct>(L)) {
const ConstantStruct *CSL = cast<ConstantStruct>(L);
const ConstantStruct *CSR = cast<ConstantStruct>(R);
const StructType *LTy = cast<StructType>(CSL->getType());
const StructType *RTy = cast<StructType>(CSR->getType());
// The StructTypes should have the same attributes. Don't use
// isLayoutIdentical(), because that just checks the element pointers,
// which may not work here.
if (LTy->getNumElements() != RTy->getNumElements() ||
LTy->isPacked() != RTy->isPacked())
return false;
for (unsigned I = 0; I < LTy->getNumElements(); I++) {
const Value *LAgg = CSL->getAggregateElement(I);
const Value *RAgg = CSR->getAggregateElement(I);
if (LAgg == SavedLHS || RAgg == SavedRHS) {
if (LAgg != SavedLHS || RAgg != SavedRHS)
// If the left and right operands aren't both re-analyzing the
// variable, then the initialiers don't match, so report "false".
// Otherwise, we skip these operands..
return false;
if (!equivalentAsOperands(LAgg, RAgg, AC)) {
return false;
return true;
return false;
bool equivalentAsOperands(const ConstantExpr *L, const ConstantExpr *R,
const AssumptionContext *AC) {
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;
case Instruction::GetElementPtr:
// FIXME: inbounds?
if (L->getNumOperands() != R->getNumOperands())
return false;
for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I) {
const auto *LOp = L->getOperand(I);
const auto *ROp = R->getOperand(I);
if (LOp == SavedLHS || ROp == SavedRHS) {
if (LOp != SavedLHS || ROp != SavedRHS)
// If the left and right operands aren't both re-analyzing the
// variable, then the initialiers don't match, so report "false".
// Otherwise, we skip these operands..
return false;
if (!equivalentAsOperands(LOp, ROp, AC))
return false;
return true;
// There are cases where we cannot determine whether two values are
// equivalent, because it depends on not yet processed basic blocks -- see the
// documentation on assumptions.
// AC is the context in which we are currently performing a diff.
// When we encounter a pair of values for which we can neither prove
// equivalence nor the opposite, we do the following:
// * If AC is nullptr, we treat the pair as non-equivalent.
// * If AC is set, we add an assumption for the basic blocks given by AC,
// and treat the pair as equivalent. The assumption is checked later.
bool equivalentAsOperands(const Value *L, const Value *R,
const AssumptionContext *AC) {
// 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), AC);
if (isa<Instruction>(L)) {
auto It = Values.find(L);
if (It != Values.end())
return It->second == R;
if (TentativeValues.count(std::make_pair(L, R)))
return true;
// L and R might be equivalent, this could depend on not yet processed
// basic blocks, so we cannot decide here.
if (AC) {
// Add an assumption, unless there is a conflict with an existing one
BlockDiffCandidate &BDC =
getOrCreateBlockDiffCandidate(AC->LBB, AC->RBB);
auto InsertionResult = BDC.EquivalenceAssumptions.insert({L, R});
if (!InsertionResult.second && InsertionResult.first->second != R) {
// We already have a conflicting equivalence assumption for L, so at
// least one must be wrong, and we know that there is a diff.
BDC.KnownToDiffer = true;
return false;
// Optimistically assume equivalence, and check later once all BBs
// have been processed.
return true;
// Assumptions disabled, so pessimistically assume non-equivalence.
return false;
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; }
FunctionDifferenceEngine(DifferenceEngine &Engine,
const Value *SavedLHS = nullptr,
const Value *SavedRHS = nullptr)
: Engine(Engine), SavedLHS(SavedLHS), SavedRHS(SavedRHS),
Queue(QueueSorter(*this_())) {}
void diff(const Function *L, const Function *R) {
assert(Values.empty() && "Multiple diffs per engine are not supported!");
if (L->arg_size() != R->arg_size())
Engine.log("different argument counts");
// Map the arguments.
for (Function::const_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());
struct DiffEntry {
DiffEntry() : Cost(0) {}
unsigned Cost;
llvm::SmallVector<char, 8> Path; // actually of DifferenceEngine::DiffChange
bool FunctionDifferenceEngine::matchForBlockDiff(const Instruction *L,
const Instruction *R) {
return !diff(L, R, false, false, false);
void FunctionDifferenceEngine::runBlockDiff(BasicBlock::const_iterator LStart,
BasicBlock::const_iterator RStart) {
BasicBlock::const_iterator LE = LStart->getParent()->end();
BasicBlock::const_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 =;
DiffEntry *Next =;
const unsigned LeftCost = 2;
const unsigned RightCost = 2;
const unsigned MatchCost = 0;
// Initialize the first column.
for (unsigned I = 0; I != NL+1; ++I) {
Cur[I].Cost = I * LeftCost;
for (unsigned J = 0; J != I; ++J)
for (BasicBlock::const_iterator RI = RStart; RI != RE; ++RI) {
// Initialize the first row.
Next[0] = Cur[0];
Next[0].Cost += RightCost;
unsigned Index = 1;
for (BasicBlock::const_iterator LI = LStart; LI != LE; ++LI, ++Index) {
if (matchForBlockDiff(&*LI, &*RI)) {
Next[Index] = Cur[Index-1];
Next[Index].Cost += MatchCost;
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;
} else {
Next[Index] = Cur[Index];
Next[Index].Cost += RightCost;
std::swap(Cur, Next);
// We don't need the tentative values anymore; everything from here
// on out should be non-tentative.
SmallVectorImpl<char> &Path = Cur[NL].Path;
BasicBlock::const_iterator LI = LStart, RI = RStart;
DiffLogBuilder Diff(Engine.getConsumer());
// Drop trailing matches.
while (Path.size() && Path.back() == DC_match)
// Skip leading matches.
PI = Path.begin(), PE = Path.end();
while (PI != PE && *PI == DC_match) {
unify(&*LI, &*RI);
for (; PI != PE; ++PI) {
switch (static_cast<DiffChange>(*PI)) {
case DC_match:
assert(LI != LE && RI != RE);
const Instruction *L = &*LI, *R = &*RI;
unify(L, R);
Diff.addMatch(L, R);
++LI; ++RI;
case DC_left:
assert(LI != LE);
case DC_right:
assert(RI != RE);
// 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);
// 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.
const Instruction *LTerm = LStart->getParent()->getTerminator();
const Instruction *RTerm = RStart->getParent()->getTerminator();
if (isa<BranchInst>(LTerm) && isa<InvokeInst>(RTerm)) {
if (cast<BranchInst>(LTerm)->isConditional()) return;
BasicBlock::const_iterator I = LTerm->getIterator();
if (I == LStart->getParent()->begin()) return;
if (!isa<CallInst>(*I)) return;
const CallInst *LCall = cast<CallInst>(&*I);
const InvokeInst *RInvoke = cast<InvokeInst>(RTerm);
if (!equivalentAsOperands(LCall->getCalledOperand(),
RInvoke->getCalledOperand(), nullptr))
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::const_iterator I = RTerm->getIterator();
if (I == RStart->getParent()->begin()) return;
if (!isa<CallInst>(*I)) return;
const CallInst *RCall = cast<CallInst>(I);
const InvokeInst *LInvoke = cast<InvokeInst>(LTerm);
if (!equivalentAsOperands(LInvoke->getCalledOperand(),
RCall->getCalledOperand(), nullptr))
if (!LInvoke->use_empty())
Values[LInvoke] = RCall;
tryUnify(LInvoke->getNormalDest(), RTerm->getSuccessor(0));
void DifferenceEngine::Oracle::anchor() { }
void DifferenceEngine::diff(const Function *L, const 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())
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");
FunctionDifferenceEngine(*this).diff(L, R);
void DifferenceEngine::diff(const Module *L, const Module *R) {
StringSet<> LNames;
SmallVector<std::pair<const Function *, const Function *>, 20> Queue;
unsigned LeftAnonCount = 0;
unsigned RightAnonCount = 0;
for (Module::const_iterator I = L->begin(), E = L->end(); I != E; ++I) {
const Function *LFn = &*I;
StringRef Name = LFn->getName();
if (Name.empty()) {
if (Function *RFn = R->getFunction(LFn->getName()))
Queue.push_back(std::make_pair(LFn, RFn));
logf("function %l exists only in left module") << LFn;
for (Module::const_iterator I = R->begin(), E = R->end(); I != E; ++I) {
const Function *RFn = &*I;
StringRef Name = RFn->getName();
if (Name.empty()) {
if (!LNames.count(Name))
logf("function %r exists only in right module") << RFn;
if (LeftAnonCount != 0 || RightAnonCount != 0) {
SmallString<32> Tmp;
logf(("not comparing " + Twine(LeftAnonCount) +
" anonymous functions in the left module and " +
Twine(RightAnonCount) + " in the right module")
for (SmallVectorImpl<std::pair<const Function *, const Function *>>::iterator
I = Queue.begin(),
E = Queue.end();
I != E; ++I)
diff(I->first, I->second);
bool DifferenceEngine::equivalentAsOperands(const GlobalValue *L,
const GlobalValue *R) {
if (globalValueOracle) return (*globalValueOracle)(L, R);
if (isa<GlobalVariable>(L) && isa<GlobalVariable>(R)) {
const GlobalVariable *GVL = cast<GlobalVariable>(L);
const GlobalVariable *GVR = cast<GlobalVariable>(R);
if (GVL->hasLocalLinkage() && GVL->hasUniqueInitializer() &&
GVR->hasLocalLinkage() && GVR->hasUniqueInitializer())
return FunctionDifferenceEngine(*this, GVL, GVR)
.equivalentAsOperands(GVL->getInitializer(), GVR->getInitializer(),
return L->getName() == R->getName();