diff --git a/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn b/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
index 6cd6c4f2af9e7..506c72b462e25 100644
--- a/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
+++ b/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
@@ -349,6 +349,7 @@ write_cmake_config("llvm-config") {
     "LLVM_NATIVE_TARGETINFO=1",
     "LLVM_NATIVE_TARGETMC=1",
     "LLVM_NATIVE_TARGETMCA=1",
+    "LLVM_UNREACHABLE_OPTIMIZE=1",
     "LLVM_USE_INTEL_JITEVENTS=",
     "LLVM_USE_OPROFILE=",
     "LLVM_USE_PERF=",