Index: llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
===================================================================
--- llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
+++ llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
@@ -276,6 +276,7 @@
   std::function<TargetLibraryInfo &(Function &)> GetTLI;
 
   SmallPtrSet<Function *, 2> SpecializedFuncs;
+  SmallVector<Instruction *> ReplacedWithConstant;
 
 public:
   FunctionSpecializer(SCCPSolver &Solver,
@@ -320,6 +321,15 @@
     return Changed;
   }
 
+  void removeDeadInstructions() {
+    for (auto *I : ReplacedWithConstant) {
+      LLVM_DEBUG(dbgs() << "FnSpecialization: Removing dead instruction "
+                        << *I << "\n");
+      I->eraseFromParent();
+    }
+    ReplacedWithConstant.clear();
+  }
+
   bool tryToReplaceWithConstant(Value *V) {
     if (!V->getType()->isSingleValueType() || isa<CallBase>(V) ||
         V->user_empty())
@@ -330,6 +340,10 @@
       return false;
     auto *Const =
         isConstant(IV) ? Solver.getConstant(IV) : UndefValue::get(V->getType());
+
+    LLVM_DEBUG(dbgs() << "FnSpecialization: Replacing " << *V
+                      << "\nFnSpecialization: with " << *Const << "\n");
+
     V->replaceAllUsesWith(Const);
 
     for (auto *U : Const->users())
@@ -340,7 +354,7 @@
     // Remove the instruction from Block and Solver.
     if (auto *I = dyn_cast<Instruction>(V)) {
       if (I->isSafeToRemove()) {
-        I->eraseFromParent();
+        ReplacedWithConstant.push_back(I);
         Solver.removeLatticeValueFor(I);
       }
     }
@@ -886,7 +900,8 @@
     Changed = true;
   }
 
-  // Clean up the IR by removing ssa_copy intrinsics.
+  // Clean up the IR by removing dead instructions and ssa_copy intrinsics.
+  FS.removeDeadInstructions();
   removeSSACopy(M);
   return Changed;
 }