Index: lib/Analysis/LazyValueInfo.cpp
===================================================================
--- lib/Analysis/LazyValueInfo.cpp
+++ lib/Analysis/LazyValueInfo.cpp
@@ -820,11 +820,16 @@
   if (!BBI)
     return;
 
+  BasicBlock *BB = BBI->getParent();
   for (auto &AssumeVH : AC->assumptionsFor(Val)) {
     if (!AssumeVH)
       continue;
+
+    // Only check assumes in the block of the context instruction. Other
+    // assumes will have already been taken into account when the value was
+    // propagated from predecessor blocks.
     auto *I = cast<CallInst>(AssumeVH);
-    if (!isValidAssumeForContext(I, BBI, DT))
+    if (I->getParent() != BB || !isValidAssumeForContext(I, BBI))
       continue;
 
     BBLV = intersect(BBLV, getValueFromCondition(Val, I->getArgOperand(0)));
@@ -836,10 +841,10 @@
   if (!GuardDecl || GuardDecl->use_empty())
     return;
 
-  if (BBI->getIterator() == BBI->getParent()->begin())
+  if (BBI->getIterator() == BB->begin())
     return;
   for (Instruction &I : make_range(std::next(BBI->getIterator().getReverse()),
-                                   BBI->getParent()->rend())) {
+                                   BB->rend())) {
     Value *Cond = nullptr;
     if (match(&I, m_Intrinsic<Intrinsic::experimental_guard>(m_Value(Cond))))
       BBLV = intersect(BBLV, getValueFromCondition(Val, Cond));