Index: llvm/lib/AsmParser/LLParser.cpp
===================================================================
--- llvm/lib/AsmParser/LLParser.cpp
+++ llvm/lib/AsmParser/LLParser.cpp
@@ -3439,9 +3439,23 @@
   // Set the name on the instruction.
   Inst->setName(NameStr);
 
-  if (Inst->getName() != NameStr)
+  if (Inst->getName() != NameStr) {
+
+    size_t InstNameSize = Inst->getName().size();
+    size_t NameStrSize = NameStr.size();
+
+    if (InstNameSize != NameStrSize + 1) {
+      // The name is too long and was trimmed when stored in SmallString with
+      // NonGlobalValueMaxNameSize
+      return P.error(NameLoc, "name length exceeds non global max name size, "
+                              "consider making the name shorter or "
+                              "increasing -non-global-value-max-name-size: '" +
+                                  NameStr + "'");
+    }
+
     return P.error(NameLoc, "multiple definition of local value named '" +
                                 NameStr + "'");
+  }
   return false;
 }
 
Index: llvm/test/Assembler/non-global-value-max-name-size.ll
===================================================================
--- llvm/test/Assembler/non-global-value-max-name-size.ll
+++ llvm/test/Assembler/non-global-value-max-name-size.ll
@@ -5,6 +5,7 @@
 
 define void @f() {
 bb0:
+  %length = alloca i32, align 4
   br label %testz
 
 testz: