[PATCH] D58497: Clear the KnownModules cache if the preprocessor is going away

[Nemanja Ivanovic via Phabricator via cfe-commits]

nemanjai created this revision.
nemanjai added a reviewer: rsmith.
Herald added a subscriber: jdoerfert.
Herald added a project: clang.

When the `Preprocessor (PP)` in compiler instance is going away, we should clear the cache of any pointers that it owns as they will be destroyed.

This is one possible fix for the issue I outlined in http://lists.llvm.org/pipermail/cfe-dev/2019-February/061293.html that received no responses. We have now encountered the issue in multiple internal buildbots and I have even seen it in external bots as well. This really should be fixed.

As outlined in my cfe-dev post, it is exceedingly difficult to produce a reliable test case for this (at least for me) so I have not provided one.

If others should be on the list of reviewers, please add them.


Repository:
  rC Clang

https://reviews.llvm.org/D58497

Files:
  lib/Frontend/CompilerInstance.cpp


Index: lib/Frontend/CompilerInstance.cpp
===================================================================
--- lib/Frontend/CompilerInstance.cpp
+++ lib/Frontend/CompilerInstance.cpp
@@ -374,7 +374,14 @@
   // The module manager holds a reference to the old preprocessor (if any).
   ModuleManager.reset();
 
-  // Create the Preprocessor.
+  // Create the Preprocessor. If this instance is replacing the existing
+  // preprocessor and that existing one is going away, we have to remove
+  // the Module* pointers it owns from KnownModules since they will be
+  // dangling. FIXME: Should this only remove pointers owned by the
+  // preprocessor that is going away or clear the entire map (or can
+  // the map even own any other Module* pointers)?
+  if (PP.unique())
+    KnownModules.clear();
   HeaderSearch *HeaderInfo =
       new HeaderSearch(getHeaderSearchOptsPtr(), getSourceManager(),
                        getDiagnostics(), getLangOpts(), &getTarget());


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