diff --git a/llvm/utils/gn/build/BUILD.gn b/llvm/utils/gn/build/BUILD.gn
--- a/llvm/utils/gn/build/BUILD.gn
+++ b/llvm/utils/gn/build/BUILD.gn
@@ -34,6 +34,10 @@
     defines += [ "NDEBUG" ]
   }
 
+  if (llvm_enable_expensive_checks) {
+    defines += [ "EXPENSIVE_CHECKS" ]
+  }
+
   asmflags = target_flags
   cflags = target_flags
   ldflags = target_flags + target_ldflags
diff --git a/llvm/utils/gn/build/buildflags.gni b/llvm/utils/gn/build/buildflags.gni
--- a/llvm/utils/gn/build/buildflags.gni
+++ b/llvm/utils/gn/build/buildflags.gni
@@ -10,4 +10,7 @@
 
   # Whether to enable assertions.
   llvm_enable_assertions = true
+
+  # Whether to enable expensive checks.
+  llvm_enable_expensive_checks = false
 }