Index: llvm/trunk/include/llvm/Analysis/AssumptionCache.h
===================================================================
--- llvm/trunk/include/llvm/Analysis/AssumptionCache.h
+++ llvm/trunk/include/llvm/Analysis/AssumptionCache.h
@@ -46,6 +46,30 @@
   /// intrinsic.
   SmallVector<WeakVH, 4> AssumeHandles;
 
+  class AffectedValueCallbackVH final : public CallbackVH {
+    AssumptionCache *AC;
+    void deleted() override;
+    void allUsesReplacedWith(Value *) override;
+
+  public:
+    using DMI = DenseMapInfo<Value *>;
+
+    AffectedValueCallbackVH(Value *V, AssumptionCache *AC = nullptr)
+        : CallbackVH(V), AC(AC) {}
+  };
+
+  friend AffectedValueCallbackVH;
+
+  /// \brief A map of values about which an assumption might be providing
+  /// information to the relevant set of assumptions.
+  using AffectedValuesMap =
+    DenseMap<AffectedValueCallbackVH, SmallVector<WeakVH, 1>,
+             AffectedValueCallbackVH::DMI>;
+  AffectedValuesMap AffectedValues;
+
+  /// Get the vector of assumptions which affect a value from the cache.
+  SmallVector<WeakVH, 1> &getAffectedValues(Value *V);
+
   /// \brief Flag tracking whether we have scanned the function yet.
   ///
   /// We want to be as lazy about this as possible, and so we scan the function
@@ -66,11 +90,16 @@
   /// not already be in the cache.
   void registerAssumption(CallInst *CI);
 
+  /// \brief Update the cache of values being affected by this assumption (i.e.
+  /// the values about which this assumption provides information).
+  void updateAffectedValues(CallInst *CI);
+
   /// \brief Clear the cache of @llvm.assume intrinsics for a function.
   ///
   /// It will be re-scanned the next time it is requested.
   void clear() {
     AssumeHandles.clear();
+    AffectedValues.clear();
     Scanned = false;
   }
 
@@ -87,6 +116,18 @@
       scanFunction();
     return AssumeHandles;
   }
+
+  /// \brief Access the list of assumptions which affect this value.
+  MutableArrayRef<WeakVH> assumptionsFor(const Value *V) {
+    if (!Scanned)
+      scanFunction();
+
+    auto AVI = AffectedValues.find_as(const_cast<Value *>(V));
+    if (AVI == AffectedValues.end())
+      return MutableArrayRef<WeakVH>();
+
+    return AVI->second;
+  }
 };
 
 /// \brief A function analysis which provides an \c AssumptionCache.
Index: llvm/trunk/lib/Analysis/AssumptionCache.cpp
===================================================================
--- llvm/trunk/lib/Analysis/AssumptionCache.cpp
+++ llvm/trunk/lib/Analysis/AssumptionCache.cpp
@@ -24,6 +24,109 @@
 using namespace llvm;
 using namespace llvm::PatternMatch;
 
+SmallVector<WeakVH, 1> &AssumptionCache::getAffectedValues(Value *V) {
+  // Try using find_as first to avoid creating extra value handles just for the
+  // purpose of doing the lookup.
+  auto AVI = AffectedValues.find_as(V);
+  if (AVI != AffectedValues.end())
+    return AVI->second;
+
+  auto AVIP = AffectedValues.insert({
+      AffectedValueCallbackVH(V, this), SmallVector<WeakVH, 1>()});
+  return AVIP.first->second;
+}
+
+void AssumptionCache::updateAffectedValues(CallInst *CI) {
+  // Note: This code must be kept in-sync with the code in
+  // computeKnownBitsFromAssume in ValueTracking.
+
+  SmallVector<Value *, 16> Affected;
+  auto AddAffected = [&Affected](Value *V) {
+    if (isa<Argument>(V)) {
+      Affected.push_back(V);
+    } else if (auto *I = dyn_cast<Instruction>(V)) {
+      Affected.push_back(I);
+
+      if (I->getOpcode() == Instruction::BitCast ||
+          I->getOpcode() == Instruction::PtrToInt) {
+        auto *Op = I->getOperand(0);
+        if (isa<Instruction>(Op) || isa<Argument>(Op))
+          Affected.push_back(Op);
+      }
+    }
+  };
+
+  Value *Cond = CI->getArgOperand(0), *A, *B;
+  AddAffected(Cond);
+
+  CmpInst::Predicate Pred;
+  if (match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
+    AddAffected(A);
+    AddAffected(B);
+
+    if (Pred == ICmpInst::ICMP_EQ) {
+      // For equality comparisons, we handle the case of bit inversion.
+      auto AddAffectedFromEq = [&AddAffected](Value *V) {
+        Value *A;
+        if (match(V, m_Not(m_Value(A)))) {
+          AddAffected(A);
+          V = A;
+        }
+
+        Value *B;
+        ConstantInt *C;
+        // (A & B) or (A | B) or (A ^ B).
+        if (match(V,
+                  m_CombineOr(m_And(m_Value(A), m_Value(B)),
+                    m_CombineOr(m_Or(m_Value(A), m_Value(B)),
+                                m_Xor(m_Value(A), m_Value(B)))))) {
+          AddAffected(A);
+          AddAffected(B);
+        // (A << C) or (A >>_s C) or (A >>_u C) where C is some constant.
+        } else if (match(V,
+                         m_CombineOr(m_Shl(m_Value(A), m_ConstantInt(C)),
+                           m_CombineOr(m_LShr(m_Value(A), m_ConstantInt(C)),
+                                       m_AShr(m_Value(A),
+                                              m_ConstantInt(C)))))) {
+          AddAffected(A);
+        }
+      };
+
+      AddAffectedFromEq(A);
+      AddAffectedFromEq(B);
+    }
+  }
+
+  for (auto &AV : Affected) {
+    auto &AVV = getAffectedValues(AV);
+    if (std::find(AVV.begin(), AVV.end(), CI) == AVV.end())
+      AVV.push_back(CI);
+  }
+}
+
+void AssumptionCache::AffectedValueCallbackVH::deleted() {
+  auto AVI = AC->AffectedValues.find(getValPtr());
+  if (AVI != AC->AffectedValues.end())
+    AC->AffectedValues.erase(AVI);
+  // 'this' now dangles!
+}
+
+void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
+  if (!isa<Instruction>(NV) && !isa<Argument>(NV))
+    return;
+
+  // Any assumptions that affected this value now affect the new value.
+
+  auto &NAVV = AC->getAffectedValues(NV);
+  auto AVI = AC->AffectedValues.find(getValPtr());
+  if (AVI == AC->AffectedValues.end())
+    return;
+
+  for (auto &A : AVI->second)
+    if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
+      NAVV.push_back(A);
+}
+
 void AssumptionCache::scanFunction() {
   assert(!Scanned && "Tried to scan the function twice!");
   assert(AssumeHandles.empty() && "Already have assumes when scanning!");
@@ -37,6 +140,10 @@
 
   // Mark the scan as complete.
   Scanned = true;
+
+  // Update affected values.
+  for (auto &A : AssumeHandles)
+    updateAffectedValues(cast<CallInst>(A));
 }
 
 void AssumptionCache::registerAssumption(CallInst *CI) {
@@ -72,6 +179,8 @@
            "Cache contains multiple copies of a call!");
   }
 #endif
+
+  updateAffectedValues(CI);
 }
 
 AnalysisKey AssumptionAnalysis::Key;
Index: llvm/trunk/lib/Analysis/LazyValueInfo.cpp
===================================================================
--- llvm/trunk/lib/Analysis/LazyValueInfo.cpp
+++ llvm/trunk/lib/Analysis/LazyValueInfo.cpp
@@ -925,7 +925,7 @@
   if (!BBI)
     return;
 
-  for (auto &AssumeVH : AC->assumptions()) {
+  for (auto &AssumeVH : AC->assumptionsFor(Val)) {
     if (!AssumeVH)
       continue;
     auto *I = cast<CallInst>(AssumeVH);
Index: llvm/trunk/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp
@@ -526,7 +526,10 @@
 
   unsigned BitWidth = KnownZero.getBitWidth();
 
-  for (auto &AssumeVH : Q.AC->assumptions()) {
+  // Note that the patterns below need to be kept in sync with the code
+  // in AssumptionCache::updateAffectedValues.
+
+  for (auto &AssumeVH : Q.AC->assumptionsFor(V)) {
     if (!AssumeVH)
       continue;
     CallInst *I = cast<CallInst>(AssumeVH);
Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2756,6 +2756,9 @@
     if (KnownOne.isAllOnesValue())
       return eraseInstFromFunction(*II);
 
+    // Update the cache of affected values for this assumption (we might be
+    // here because we just simplified the condition).
+    AC.updateAffectedValues(II);
     break;
   }
   case Intrinsic::experimental_gc_relocate: {