llvm16 targets

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diff --git a/contrib/libs/llvm16/tools/llvm-diff/lib/DifferenceEngine.cpp b/contrib/libs/llvm16/tools/llvm-diff/lib/DifferenceEngine.cpp
new file mode 100644
index 0000000000..6573bf010c
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+++ b/contrib/libs/llvm16/tools/llvm-diff/lib/DifferenceEngine.cpp
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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 https://llvm.org/LICENSE.txt 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;
+
+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 (std::is_trivially_copyable<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;
+
+  // 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();
+      BlockDiffCandidates.push_back(
+          {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;
+         ++I)
+      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;
+          break;
+        }
+      }
+
+      // 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)) {
+        TentativeValues.clear();
+        // 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;
+        return;
+      }
+
+      // 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(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());
+          LCases.erase(CaseValue);
+        } 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;
+  }
+
+public:
+  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),
+                                         cast<GlobalValue>(R));
+
+    // Compare constant expressions structurally.
+    if (isa<ConstantExpr>(L))
+      return equivalentAsOperands(cast<ConstantExpr>(L), cast<ConstantExpr>(R),
+                                  AC);
+
+    // 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;
+
+          continue;
+        }
+
+        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;
+      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) {
+      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;
+
+        continue;
+      }
+
+      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;
+          BDC.EquivalenceAssumptions.clear();
+          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; }
+
+public:
+  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());
+    processQueue();
+    checkAndReportDiffCandidates();
+  }
+};
+
+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 = 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::const_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::const_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::const_iterator LI = LStart, RI = RStart;
+
+  DiffLogBuilder Diff(Engine.getConsumer());
+
+  // Drop trailing matches.
+  while (Path.size() && 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);
+      {
+        const 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.
+  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;
+    --I;
+    if (!isa<CallInst>(*I)) return;
+    const CallInst *LCall = cast<CallInst>(&*I);
+    const InvokeInst *RInvoke = cast<InvokeInst>(RTerm);
+    if (!equivalentAsOperands(LCall->getCalledOperand(),
+                              RInvoke->getCalledOperand(), nullptr))
+      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::const_iterator I = RTerm->getIterator();
+    if (I == RStart->getParent()->begin()) return;
+    --I;
+    if (!isa<CallInst>(*I)) return;
+    const CallInst *RCall = cast<CallInst>(I);
+    const InvokeInst *LInvoke = cast<InvokeInst>(LTerm);
+    if (!equivalentAsOperands(LInvoke->getCalledOperand(),
+                              RCall->getCalledOperand(), nullptr))
+      return;
+    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())
+    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(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()) {
+      ++LeftAnonCount;
+      continue;
+    }
+
+    LNames.insert(Name);
+
+    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::const_iterator I = R->begin(), E = R->end(); I != E; ++I) {
+    const Function *RFn = &*I;
+    StringRef Name = RFn->getName();
+    if (Name.empty()) {
+      ++RightAnonCount;
+      continue;
+    }
+
+    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")
+             .toStringRef(Tmp));
+  }
+
+  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(),
+                                nullptr);
+  }
+
+  return L->getName() == R->getName();
+}