Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2242,6 +2242,27 @@
     return &BI;
   }
 
+  // See if we can determine the value of a use based on a dominating condition.
+  Value *Op0;
+  ConstantInt *C;
+  if (match(&BI, m_Br(m_ICmp(Pred, m_Value(Op0), m_ConstantInt(C)), TrueDest,
+                      FalseDest)) &&
+      (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) &&
+      Op0->getNumUses() >= 2) {
+    BasicBlock *TargetBB = Pred == ICmpInst::ICMP_EQ ? TrueDest : FalseDest;
+    if (TargetBB->getSinglePredecessor()) {
+      // This branch dominates TargetBB and we known that Op0 == C in TargetBB.
+      for (User *U : Op0->users())
+        if (Instruction *UI = dyn_cast<Instruction>(U))
+          if (UI->getParent() == TargetBB)
+            for (unsigned OpNum = 0; OpNum < UI->getNumOperands(); ++OpNum)
+              if (UI->getOperand(OpNum) == Op0)
+                U->setOperand(OpNum, C);
+
+      // FIXME: We've changed things, but not the branch. IC need to know this.
+    }
+  }
+
   return nullptr;
 }