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+//===- Evaluator.h - LLVM IR evaluator --------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Function evaluator for LLVM IR.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_EVALUATOR_H
+#define LLVM_TRANSFORMS_UTILS_EVALUATOR_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/Value.h"
+#include "llvm/Support/Casting.h"
+#include <cassert>
+#include <deque>
+#include <memory>
+
+namespace llvm {
+
+class DataLayout;
+class Function;
+class TargetLibraryInfo;
+
+/// This class evaluates LLVM IR, producing the Constant representing each SSA
+/// instruction.  Changes to global variables are stored in a mapping that can
+/// be iterated over after the evaluation is complete.  Once an evaluation call
+/// fails, the evaluation object should not be reused.
+class Evaluator {
+public:
+  Evaluator(const DataLayout &DL, const TargetLibraryInfo *TLI)
+      : DL(DL), TLI(TLI) {
+    ValueStack.emplace_back();
+  }
+
+  ~Evaluator() {
+    for (auto &Tmp : AllocaTmps)
+      // If there are still users of the alloca, the program is doing something
+      // silly, e.g. storing the address of the alloca somewhere and using it
+      // later.  Since this is undefined, we'll just make it be null.
+      if (!Tmp->use_empty())
+        Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
+  }
+
+  /// Evaluate a call to function F, returning true if successful, false if we
+  /// can't evaluate it.  ActualArgs contains the formal arguments for the
+  /// function.
+  bool EvaluateFunction(Function *F, Constant *&RetVal,
+                        const SmallVectorImpl<Constant*> &ActualArgs);
+
+  /// Evaluate all instructions in block BB, returning true if successful, false
+  /// if we can't evaluate it.  NewBB returns the next BB that control flows
+  /// into, or null upon return.
+  bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
+
+  Constant *getVal(Value *V) {
+    if (Constant *CV = dyn_cast<Constant>(V)) return CV;
+    Constant *R = ValueStack.back().lookup(V);
+    assert(R && "Reference to an uncomputed value!");
+    return R;
+  }
+
+  void setVal(Value *V, Constant *C) {
+    ValueStack.back()[V] = C;
+  }
+
+  /// Given call site return callee and list of its formal arguments
+  Function *getCalleeWithFormalArgs(CallSite &CS,
+                                    SmallVector<Constant *, 8> &Formals);
+
+  /// Given call site and callee returns list of callee formal argument
+  /// values converting them when necessary
+  bool getFormalParams(CallSite &CS, Function *F,
+                       SmallVector<Constant *, 8> &Formals);
+
+  /// Casts call result to a type of bitcast call expression
+  Constant *castCallResultIfNeeded(Value *CallExpr, Constant *RV);
+
+  const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
+    return MutatedMemory;
+  }
+
+  const SmallPtrSetImpl<GlobalVariable*> &getInvariants() const {
+    return Invariants;
+  }
+
+private:
+  Constant *ComputeLoadResult(Constant *P);
+
+  /// As we compute SSA register values, we store their contents here. The back
+  /// of the deque contains the current function and the stack contains the
+  /// values in the calling frames.
+  std::deque<DenseMap<Value*, Constant*>> ValueStack;
+
+  /// This is used to detect recursion.  In pathological situations we could hit
+  /// exponential behavior, but at least there is nothing unbounded.
+  SmallVector<Function*, 4> CallStack;
+
+  /// For each store we execute, we update this map.  Loads check this to get
+  /// the most up-to-date value.  If evaluation is successful, this state is
+  /// committed to the process.
+  DenseMap<Constant*, Constant*> MutatedMemory;
+
+  /// To 'execute' an alloca, we create a temporary global variable to represent
+  /// its body.  This vector is needed so we can delete the temporary globals
+  /// when we are done.
+  SmallVector<std::unique_ptr<GlobalVariable>, 32> AllocaTmps;
+
+  /// These global variables have been marked invariant by the static
+  /// constructor.
+  SmallPtrSet<GlobalVariable*, 8> Invariants;
+
+  /// These are constants we have checked and know to be simple enough to live
+  /// in a static initializer of a global.
+  SmallPtrSet<Constant*, 8> SimpleConstants;
+
+  const DataLayout &DL;
+  const TargetLibraryInfo *TLI;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_EVALUATOR_H