Index: llvm/lib/IR/Value.cpp
===================================================================
--- llvm/lib/IR/Value.cpp
+++ llvm/lib/IR/Value.cpp
@@ -315,45 +315,43 @@
 }
 
 void Value::setNameImpl(const Twine &NewName) {
-  // Fast-path: LLVMContext can be set to strip out non-GlobalValue names
-  if (getContext().shouldDiscardValueNames() && !isa<GlobalValue>(this))
-    return;
-
   // Fast path for common IRBuilder case of setName("") when there is no name.
   if (NewName.isTriviallyEmpty() && !hasName())
     return;
 
-  SmallString<256> NameData;
-  StringRef NameRef = NewName.toStringRef(NameData);
-  assert(NameRef.find_first_of(0) == StringRef::npos &&
-         "Null bytes are not allowed in names");
-
-  // Name isn't changing?
-  if (getName() == NameRef)
-    return;
-
-  assert(!getType()->isVoidTy() && "Cannot assign a name to void values!");
-
   // Get the symbol table to update for this object.
   ValueSymbolTable *ST;
   if (getSymTab(this, ST))
     return;  // Cannot set a name on this value (e.g. constant).
 
-  if (!ST) { // No symbol table to update?  Just do the change.
-    if (NameRef.empty()) {
-      // Free the name for this value.
-      destroyValueName();
+  // Avoiding NewName.toStringRef(NameData) initialize and use NameData and
+  // NameRef only if they are needed to set the new name. Even if the new name
+  // is not needed the current name still needs to be removed.
+  SmallString<256> NameData;
+  StringRef NameRef;
+
+  if ((!getContext().shouldDiscardValueNames() || isa<GlobalValue>(this)) &&
+      !NewName.isTriviallyEmpty()) {
+    NameRef = NewName.toStringRef(NameData);
+    assert(NameRef.find_first_of(0) == StringRef::npos &&
+           "Null bytes are not allowed in names");
+
+    // Name isn't changing?
+    if (getName() == NameRef)
       return;
-    }
+  }
 
-    // NOTE: Could optimize for the case the name is shrinking to not deallocate
-    // then reallocated.
-    destroyValueName();
+  assert((NameRef.empty() || !getType()->isVoidTy()) &&
+         "Cannot assign a name to void values!");
 
+  if (!ST) { // No symbol table to update?  Just do the change.
+    destroyValueName();
     // Create the new name.
-    MallocAllocator Allocator;
-    setValueName(ValueName::create(NameRef, Allocator));
-    getValueName()->setValue(this);
+    if (!NameRef.empty()) {
+      MallocAllocator Allocator;
+      setValueName(ValueName::create(NameRef, Allocator));
+      getValueName()->setValue(this);
+    }
     return;
   }
 
@@ -363,13 +361,11 @@
     // Remove old name.
     ST->removeValueName(getValueName());
     destroyValueName();
-
-    if (NameRef.empty())
-      return;
   }
 
   // Name is changing to something new.
-  setValueName(ST->createValueName(NameRef, this));
+  if (!NameRef.empty())
+    setValueName(ST->createValueName(NameRef, this));
 }
 
 void Value::setName(const Twine &NewName) {
Index: llvm/unittests/IR/BasicBlockTest.cpp
===================================================================
--- llvm/unittests/IR/BasicBlockTest.cpp
+++ llvm/unittests/IR/BasicBlockTest.cpp
@@ -541,5 +541,44 @@
   BB0->erase(BB0->begin(), BB0->end());
   EXPECT_TRUE(BB0->empty());
 }
+
+TEST(BasicBlockTest, DiscardValueNames) {
+  const char *ModuleString = "declare void @f(i32 %dangling)";
+  SMDiagnostic Err;
+  LLVMContext Ctx;
+  { // Scope of M.
+    auto M = parseAssemblyString(ModuleString, Err, Ctx);
+    ASSERT_TRUE(M.get());
+    ASSERT_FALSE(Ctx.shouldDiscardValueNames());
+  }
+  { // Scope of M.
+    auto M = parseAssemblyString(ModuleString, Err, Ctx);
+    ASSERT_TRUE(M.get());
+    Ctx.setDiscardValueNames(true);
+  }
+}
+
+TEST(BasicBlockTest, DiscardValueNames2) {
+  SMDiagnostic Err;
+  LLVMContext Ctx;
+  Module M("Mod", Ctx);
+  auto FTy = FunctionType::get(Type::getVoidTy(M.getContext()),
+                               {Type::getInt32Ty(Ctx)}, /*isVarArg=*/false);
+  { // Scope of F.
+    Function *F = Function::Create(FTy, Function::ExternalLinkage, "f", &M);
+    F->getArg(0)->setName("dangling");
+    F->removeFromParent();
+    ASSERT_FALSE(Ctx.shouldDiscardValueNames());
+    delete F;
+  }
+  { // Scope of F.
+    Function *F = Function::Create(FTy, Function::ExternalLinkage, "f", &M);
+    F->getArg(0)->setName("dangling");
+    F->removeFromParent();
+    Ctx.setDiscardValueNames(true);
+    delete F;
+  }
+}
+
 } // End anonymous namespace.
 } // End llvm namespace.