Index: llvm/include/llvm/Analysis/InstructionCost.h
===================================================================
--- /dev/null
+++ llvm/include/llvm/Analysis/InstructionCost.h
@@ -0,0 +1,247 @@
+//===- InstructionCost.h ----------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file defines an InstructionCost class that is used when calculating
+/// the cost of an instruction, or a group of instructions. In addition to a
+/// numeric value representing the cost the class also contains a state that
+/// can be used to encode particular properties, i.e. a cost being invalid or
+/// unknown.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_INSTRUCTIONCOST_H
+#define LLVM_ANALYSIS_INSTRUCTIONCOST_H
+
+#include "llvm/ADT/Optional.h"
+
+namespace llvm {
+
+class raw_ostream;
+
+class InstructionCost {
+public:
+  using CostType = int;
+
+private:
+  // These states can currently be used to indicate whether a cost is valid or
+  // invalid. Examples of an invalid cost might be where the cost is
+  // prohibitively expensive and the user wants to prevent certain
+  // optimizations being performed. Or perhaps the cost is simply unknown
+  // because the operation makes no sense in certain circumstances. These states
+  // can be expanded in future to support other cases if necessary.
+  enum CostState { Valid, Invalid };
+
+  CostType Value;
+  CostState State;
+
+  void propagateState(const InstructionCost &RHS) {
+    if (RHS.State == Invalid)
+      State = Invalid;
+  }
+
+public:
+  InstructionCost() = default;
+
+  InstructionCost(CostType Val) : Value(Val), State(Valid) {}
+
+  static InstructionCost getInvalid(CostType Val = 0) {
+    InstructionCost Tmp(Val);
+    Tmp.setInvalid();
+    return Tmp;
+  }
+
+  bool isValid() const { return State == Valid; }
+  bool isInvalid() const { return State == Invalid; }
+  void setValid() { State = Valid; }
+  void setInvalid() { State = Invalid; }
+
+  // This function is intended to be used as sparingly as possible, since the
+  // class provides the full range of operator support required for arithmetic
+  // and comparisons. Users of this class can check for validity before trying
+  // to extract a value, for example using the isValid() interface provided
+  // above.
+  Optional<CostType> getValue() const {
+    if (isValid())
+      return Value;
+    return None;
+  }
+
+  // For all of the arithmetic operators provided here any invalid state is
+  // perpetuated and cannot be removed. Once a cost becomes invalid it stays
+  // invalid, and it also inherits any invalid state from the RHS. Regardless
+  // of the state, arithmetic and comparisons work on the actual values in the
+  // same way as they would on a basic type, such as integer.
+
+  InstructionCost &operator+=(const InstructionCost &RHS) {
+    propagateState(RHS);
+    Value += RHS.Value;
+    return *this;
+  }
+
+  InstructionCost &operator+=(const CostType RHS) {
+    InstructionCost RHS2(RHS);
+    *this += RHS2;
+    return *this;
+  }
+
+  InstructionCost &operator-=(const InstructionCost &RHS) {
+    propagateState(RHS);
+    Value -= RHS.Value;
+    return *this;
+  }
+
+  InstructionCost &operator-=(const CostType RHS) {
+    InstructionCost RHS2(RHS);
+    *this -= RHS2;
+    return *this;
+  }
+
+  InstructionCost &operator*=(const InstructionCost &RHS) {
+    propagateState(RHS);
+    Value *= RHS.Value;
+    return *this;
+  }
+
+  InstructionCost &operator*=(const CostType RHS) {
+    InstructionCost RHS2(RHS);
+    *this *= RHS2;
+    return *this;
+  }
+
+  InstructionCost &operator/=(const InstructionCost &RHS) {
+    propagateState(RHS);
+    Value /= RHS.Value;
+    return *this;
+  }
+
+  InstructionCost &operator/=(const CostType RHS) {
+    InstructionCost RHS2(RHS);
+    *this /= RHS2;
+    return *this;
+  }
+
+  InstructionCost &operator++() {
+    *this += 1;
+    return *this;
+  }
+
+  InstructionCost operator++(int) {
+    InstructionCost Copy = *this;
+    ++*this;
+    return Copy;
+  }
+
+  InstructionCost &operator--() {
+    *this -= 1;
+    return *this;
+  }
+
+  InstructionCost operator--(int) {
+    InstructionCost Copy = *this;
+    --*this;
+    return Copy;
+  }
+
+  bool operator==(const InstructionCost &RHS) const {
+    return State == RHS.State && Value == RHS.Value;
+  }
+
+  bool operator!=(const InstructionCost &RHS) const { return !(*this == RHS); }
+
+  bool operator==(const CostType RHS) const {
+    return State == Valid && Value == RHS;
+  }
+
+  bool operator!=(const CostType RHS) const { return !(*this == RHS); }
+
+  // For the comparison operators we have chosen to use total ordering with
+  // the following rules:
+  //  1. If either of the states != Valid then a lexicographical order is
+  //     applied based upon the state.
+  //  2. If both states are valid then order based upon value.
+  // This avoids having to add asserts the comparison operators that the states
+  // are valid and users can test for validity of the cost explicitly.
+  bool operator<(const InstructionCost &RHS) const {
+    if (State != Valid || RHS.State != Valid)
+      return State < RHS.State;
+    return Value < RHS.Value;
+  }
+
+  bool operator>(const InstructionCost &RHS) const { return RHS < *this; }
+
+  bool operator<=(const InstructionCost &RHS) const { return !(RHS < *this); }
+
+  bool operator>=(const InstructionCost &RHS) const { return !(*this < RHS); }
+
+  bool operator<(const CostType RHS) const {
+    InstructionCost RHS2(RHS);
+    return *this < RHS2;
+  }
+
+  bool operator>(const CostType RHS) const {
+    InstructionCost RHS2(RHS);
+    return *this > RHS2;
+  }
+
+  bool operator<=(const CostType RHS) const {
+    InstructionCost RHS2(RHS);
+    return *this <= RHS2;
+  }
+
+  bool operator>=(const CostType RHS) const {
+    InstructionCost RHS2(RHS);
+    return *this >= RHS2;
+  }
+
+  static InstructionCost min(InstructionCost LHS, InstructionCost RHS) {
+    return LHS < RHS ? LHS : RHS;
+  }
+
+  static InstructionCost max(InstructionCost LHS, InstructionCost RHS) {
+    return LHS > RHS ? LHS : RHS;
+  }
+
+  void print(raw_ostream &OS) const;
+};
+
+inline InstructionCost operator+(const InstructionCost &LHS,
+                                 const InstructionCost &RHS) {
+  InstructionCost LHS2(LHS);
+  LHS2 += RHS;
+  return LHS2;
+}
+
+inline InstructionCost operator-(const InstructionCost &LHS,
+                                 const InstructionCost &RHS) {
+  InstructionCost LHS2(LHS);
+  LHS2 -= RHS;
+  return LHS2;
+}
+
+inline InstructionCost operator*(const InstructionCost &LHS,
+                                 const InstructionCost &RHS) {
+  InstructionCost LHS2(LHS);
+  LHS2 *= RHS;
+  return LHS2;
+}
+
+inline InstructionCost operator/(const InstructionCost &LHS,
+                                 const InstructionCost &RHS) {
+  InstructionCost LHS2(LHS);
+  LHS2 /= RHS;
+  return LHS2;
+}
+
+inline raw_ostream &operator<<(raw_ostream &OS, const InstructionCost &V) {
+  V.print(OS);
+  return OS;
+}
+
+} // namespace llvm
+
+#endif
Index: llvm/include/llvm/Analysis/TargetTransformInfo.h
===================================================================
--- llvm/include/llvm/Analysis/TargetTransformInfo.h
+++ llvm/include/llvm/Analysis/TargetTransformInfo.h
@@ -21,6 +21,7 @@
 #ifndef LLVM_ANALYSIS_TARGETTRANSFORMINFO_H
 #define LLVM_ANALYSIS_TARGETTRANSFORMINFO_H
 
+#include "llvm/Analysis/InstructionCost.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/PassManager.h"
@@ -236,19 +237,26 @@
   ///
   /// Note, this method does not cache the cost calculation and it
   /// can be expensive in some cases.
-  int getInstructionCost(const Instruction *I, enum TargetCostKind kind) const {
+  InstructionCost getInstructionCost(const Instruction *I,
+                                     enum TargetCostKind kind) const {
+    InstructionCost Cost;
     switch (kind) {
     case TCK_RecipThroughput:
-      return getInstructionThroughput(I);
-
+      Cost = getInstructionThroughput(I);
+      break;
     case TCK_Latency:
-      return getInstructionLatency(I);
-
+      Cost = getInstructionLatency(I);
+      break;
     case TCK_CodeSize:
     case TCK_SizeAndLatency:
-      return getUserCost(I, kind);
+      Cost = getUserCost(I, kind);
+      break;
+    default:
+      llvm_unreachable("Unknown instruction cost kind");
     }
-    llvm_unreachable("Unknown instruction cost kind");
+    if (Cost == -1)
+      Cost.setInvalid();
+    return Cost;
   }
 
   /// Underlying constants for 'cost' values in this interface.
Index: llvm/include/llvm/IR/DiagnosticInfo.h
===================================================================
--- llvm/include/llvm/IR/DiagnosticInfo.h
+++ llvm/include/llvm/IR/DiagnosticInfo.h
@@ -38,6 +38,7 @@
 class LLVMContext;
 class Module;
 class SMDiagnostic;
+class InstructionCost;
 
 /// Defines the different supported severity of a diagnostic.
 enum DiagnosticSeverity : char {
@@ -437,6 +438,7 @@
     Argument(StringRef Key, ElementCount EC);
     Argument(StringRef Key, bool B) : Key(Key), Val(B ? "true" : "false") {}
     Argument(StringRef Key, DebugLoc dl);
+    Argument(StringRef Key, InstructionCost C);
   };
 
   /// \p PassName is the name of the pass emitting this diagnostic. \p
Index: llvm/lib/Analysis/CostModel.cpp
===================================================================
--- llvm/lib/Analysis/CostModel.cpp
+++ llvm/lib/Analysis/CostModel.cpp
@@ -57,7 +57,7 @@
     /// Returns -1 if the cost is unknown.
     /// Note, this method does not cache the cost calculation and it
     /// can be expensive in some cases.
-    unsigned getInstructionCost(const Instruction *I) const {
+    InstructionCost getInstructionCost(const Instruction *I) const {
       return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput);
     }
 
@@ -103,8 +103,8 @@
 
   for (BasicBlock &B : *F) {
     for (Instruction &Inst : B) {
-      unsigned Cost = TTI->getInstructionCost(&Inst, CostKind);
-      if (Cost != (unsigned)-1)
+      InstructionCost Cost = TTI->getInstructionCost(&Inst, CostKind);
+      if (!Cost.isInvalid())
         OS << "Cost Model: Found an estimated cost of " << Cost;
       else
         OS << "Cost Model: Unknown cost";
Index: llvm/lib/Analysis/TargetTransformInfo.cpp
===================================================================
--- llvm/lib/Analysis/TargetTransformInfo.cpp
+++ llvm/lib/Analysis/TargetTransformInfo.cpp
@@ -54,6 +54,13 @@
   return true;
 }
 
+void InstructionCost::print(raw_ostream &OS) const {
+  if (isInvalid())
+    OS << "Invalid";
+  else
+    OS << Value;
+}
+
 IntrinsicCostAttributes::IntrinsicCostAttributes(const IntrinsicInst &I) :
     II(&I), RetTy(I.getType()), IID(I.getIntrinsicID()) {
 
Index: llvm/lib/CodeGen/InterleavedLoadCombinePass.cpp
===================================================================
--- llvm/lib/CodeGen/InterleavedLoadCombinePass.cpp
+++ llvm/lib/CodeGen/InterleavedLoadCombinePass.cpp
@@ -1130,8 +1130,8 @@
   std::set<Instruction *> Is;
   std::set<Instruction *> SVIs;
 
-  unsigned InterleavedCost;
-  unsigned InstructionCost = 0;
+  InstructionCost InterleavedCost;
+  InstructionCost InstructionCost = 0;
 
   // Get the interleave factor
   unsigned Factor = InterleavedLoad.size();
@@ -1174,6 +1174,10 @@
     }
   }
 
+  // We need to have a valid cost in order to proceed.
+  if (InstructionCost.isInvalid())
+    return false;
+
   // We know that all LoadInst are within the same BB. This guarantees that
   // either everything or nothing is loaded.
   LoadInst *First = findFirstLoad(LIs);
Index: llvm/lib/IR/DiagnosticInfo.cpp
===================================================================
--- llvm/lib/IR/DiagnosticInfo.cpp
+++ llvm/lib/IR/DiagnosticInfo.cpp
@@ -16,6 +16,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/ADT/iterator_range.h"
+#include "llvm/Analysis/InstructionCost.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DebugInfoMetadata.h"
@@ -220,6 +221,13 @@
   EC.print(OS);
 }
 
+DiagnosticInfoOptimizationBase::Argument::Argument(StringRef Key,
+                                                   InstructionCost C)
+    : Key(std::string(Key)) {
+  raw_string_ostream OS(Val);
+  C.print(OS);
+}
+
 DiagnosticInfoOptimizationBase::Argument::Argument(StringRef Key, DebugLoc Loc)
     : Key(std::string(Key)), Loc(Loc) {
   if (Loc) {
Index: llvm/lib/Transforms/IPO/HotColdSplitting.cpp
===================================================================
--- llvm/lib/Transforms/IPO/HotColdSplitting.cpp
+++ llvm/lib/Transforms/IPO/HotColdSplitting.cpp
@@ -233,11 +233,11 @@
 }
 
 /// Get the benefit score of outlining \p Region.
-static int getOutliningBenefit(ArrayRef<BasicBlock *> Region,
-                               TargetTransformInfo &TTI) {
+static InstructionCost getOutliningBenefit(ArrayRef<BasicBlock *> Region,
+                                           TargetTransformInfo &TTI) {
   // Sum up the code size costs of non-terminator instructions. Tight coupling
   // with \ref getOutliningPenalty is needed to model the costs of terminators.
-  int Benefit = 0;
+  InstructionCost Benefit = 0;
   for (BasicBlock *BB : Region)
     for (Instruction &I : BB->instructionsWithoutDebug())
       if (&I != BB->getTerminator())
@@ -324,12 +324,12 @@
   // splitting.
   SetVector<Value *> Inputs, Outputs, Sinks;
   CE.findInputsOutputs(Inputs, Outputs, Sinks);
-  int OutliningBenefit = getOutliningBenefit(Region, TTI);
+  InstructionCost OutliningBenefit = getOutliningBenefit(Region, TTI);
   int OutliningPenalty =
       getOutliningPenalty(Region, Inputs.size(), Outputs.size());
   LLVM_DEBUG(dbgs() << "Split profitability: benefit = " << OutliningBenefit
                     << ", penalty = " << OutliningPenalty << "\n");
-  if (OutliningBenefit <= OutliningPenalty)
+  if (OutliningBenefit.isInvalid() || OutliningBenefit <= OutliningPenalty)
     return nullptr;
 
   Function *OrigF = Region[0]->getParent();
Index: llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
+++ llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -208,7 +208,7 @@
   // instructions before the call is less then DuplicationThreshold. The
   // instructions before the call will be duplicated in the split blocks and
   // corresponding uses will be updated.
-  unsigned Cost = 0;
+  InstructionCost Cost = 0;
   for (auto &InstBeforeCall :
        llvm::make_range(CallSiteBB->begin(), CB.getIterator())) {
     Cost += TTI.getInstructionCost(&InstBeforeCall,
Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -3781,17 +3781,17 @@
       if (NeedToShuffleReuses) {
         for (unsigned Idx : E->ReuseShuffleIndices) {
           Instruction *I = cast<Instruction>(VL[Idx]);
-          ReuseShuffleCost -= TTI->getInstructionCost(I, CostKind);
+          ReuseShuffleCost -= *(TTI->getInstructionCost(I, CostKind).getValue());
         }
         for (Value *V : VL) {
           Instruction *I = cast<Instruction>(V);
-          ReuseShuffleCost += TTI->getInstructionCost(I, CostKind);
+          ReuseShuffleCost += *(TTI->getInstructionCost(I, CostKind).getValue());
         }
       }
       for (Value *V : VL) {
         Instruction *I = cast<Instruction>(V);
         assert(E->isOpcodeOrAlt(I) && "Unexpected main/alternate opcode");
-        ScalarCost += TTI->getInstructionCost(I, CostKind);
+        ScalarCost += *(TTI->getInstructionCost(I, CostKind).getValue());
       }
       // VecCost is equal to sum of the cost of creating 2 vectors
       // and the cost of creating shuffle.
Index: llvm/unittests/Analysis/CMakeLists.txt
===================================================================
--- llvm/unittests/Analysis/CMakeLists.txt
+++ llvm/unittests/Analysis/CMakeLists.txt
@@ -29,6 +29,7 @@
   DomTreeUpdaterTest.cpp
   GlobalsModRefTest.cpp
   FunctionPropertiesAnalysisTest.cpp
+  InstructionCostTest.cpp
   IRSimilarityIdentifierTest.cpp
   IVDescriptorsTest.cpp
   LazyCallGraphTest.cpp
Index: llvm/unittests/Analysis/InstructionCostTest.cpp
===================================================================
--- /dev/null
+++ llvm/unittests/Analysis/InstructionCostTest.cpp
@@ -0,0 +1,51 @@
+//===- InstructionCostTest.cpp - InstructionCost tests --------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/InstructionCost.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+struct CostTest : public testing::Test {
+  CostTest() {}
+};
+
+} // namespace
+
+TEST_F(CostTest, Operators) {
+  InstructionCost VThree = 3;
+  InstructionCost VNegTwo = -2;
+  InstructionCost VSix = 6;
+  InstructionCost IThreeA = InstructionCost::getInvalid(3);
+  InstructionCost IThreeB = InstructionCost::getInvalid(3);
+  InstructionCost TmpCost;
+
+  EXPECT_NE(VThree, VNegTwo);
+  EXPECT_GT(VThree, VNegTwo);
+  EXPECT_NE(VThree, IThreeA);
+  EXPECT_EQ(IThreeA, IThreeB);
+  EXPECT_GE(IThreeA, VNegTwo);
+  EXPECT_LT(VSix, IThreeA);
+  EXPECT_EQ(VSix - IThreeA, IThreeB);
+  EXPECT_EQ(VThree - VNegTwo, 5);
+  EXPECT_EQ(VThree * VNegTwo, -6);
+  EXPECT_EQ(VSix / VThree, 2);
+
+  EXPECT_TRUE(IThreeA.isInvalid());
+
+  TmpCost = VThree + IThreeA;
+  EXPECT_TRUE(TmpCost.isInvalid());
+
+  TmpCost = VThree * IThreeA;
+  EXPECT_TRUE(TmpCost.isInvalid());
+
+  EXPECT_EQ(InstructionCost::min(VThree, VNegTwo), -2);
+  EXPECT_EQ(InstructionCost::max(VThree, VSix), 6);
+}