[PATCH] D140930: [dsymutil] Avoid invalid keep chains due to pruning

[Jonas Devlieghere via Phabricator via llvm-commits]

JDevlieghere created this revision.
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The pruning property that's part of the DIE info is fully computing during the `analyzeContextInfo` phase, but can be updated during the `lookForDIEsToKeep` phase.

  // Keep a module forward declaration if there is no definition.
  if (!(isODRAttribute(AttrSpec.Attr) && Info.Ctxt &&
        Info.Ctxt->hasCanonicalDIE()))
    Info.Prune = false;

When the pruning property is updated during the `lookForDIEsToKeep` phase, it's not propagated to the parent, unlike during the `analyzeContextInfo` phase. This can result in an invalid keep chain with the child DIE being marked as kept while its parent is still marked as pruned and therefore never kept, a situation that's now caught by 1b79bed8f532 <https://reviews.llvm.org/rG1b79bed8f53231144ad6e14f8cc3e8673c7fb469>.

This patch fixes this issue by updating the pruning properties of the parent DIE during the parent walk.

Similar to c9cbe6937b1f <https://reviews.llvm.org/rGc9cbe6937b1fe797f805648216257ae88bde4ad7>, this issue was caught in a big internal project that doesn't lend itself to reduction and so far I haven't been able to create an artificial test case where (1) a pruned DIE doesn't have a decl context and (2) is marked as kept.


https://reviews.llvm.org/D140930

Files:
  llvm/lib/DWARFLinker/DWARFLinker.cpp


Index: llvm/lib/DWARFLinker/DWARFLinker.cpp
===================================================================
--- llvm/lib/DWARFLinker/DWARFLinker.cpp
+++ llvm/lib/DWARFLinker/DWARFLinker.cpp
@@ -788,8 +788,12 @@
     unsigned Idx = Current.CU.getOrigUnit().getDIEIndex(Current.Die);
     CompileUnit::DIEInfo &MyInfo = Current.CU.getInfo(Idx);
 
-    if (MyInfo.Prune)
-      continue;
+    if (MyInfo.Prune) {
+      if (Current.Flags & TF_DependencyWalk)
+        MyInfo.Prune = false;
+      else
+        continue;
+    }
 
     // If the Keep flag is set, we are marking a required DIE's dependencies.
     // If our target is already marked as kept, we're all set.


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