1 files changed, 9 insertions, 0 deletions
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index a6e2329..c642af1 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1054,6 +1054,15 @@ compileModuleImpl(CompilerInstance &ImportingInstance, SourceLocation ImportLoc,
                       [](CompilerInstance &) {}) {
   llvm::TimeTraceScope TimeScope("Module Compile", ModuleName);
 
+  // Never compile a module that's already finalized - this would cause the
+  // existing module to be freed, causing crashes if it is later referenced
+  if (ImportingInstance.getModuleCache().isPCMFinal(ModuleFileName)) {
+    ImportingInstance.getDiagnostics().Report(
+        ImportLoc, diag::err_module_rebuild_finalized)
+        << ModuleName;
+    return false;
+  }
+
   // Construct a compiler invocation for creating this module.
   auto Invocation =
       std::make_shared<CompilerInvocation>(ImportingInstance.getInvocation());