[PATCH] D96996: [BasicAA] Add simple depth limit to avoid stack overflow (PR49151)

[Nikita Popov via Phabricator via llvm-commits]

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This is a simpler variant on D96647 <https://reviews.llvm.org/D96647>. It just adds a straightforward depth limit with a high cutoff, without introducing complex logic for BatchAA consistency. It accepts that we may cache a sub-optimal result if the depth limit is hit.

Eventually this should be more fully addressed by D96647 <https://reviews.llvm.org/D96647> or similar, but in the meantime this avoids stack overflows in a cheap way.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D96996

Files:
  llvm/lib/Analysis/BasicAliasAnalysis.cpp


Index: llvm/lib/Analysis/BasicAliasAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -1559,6 +1559,13 @@
     V2Size = LocationSize::afterPointer();
   }
 
+  // FIXME: If this depth limit is hit, then we may cache sub-optimal results
+  // for recursive queries. For this reason, this limit is chosen to be large
+  // enough to be very rarely hit, while still being small enough to avoid
+  // stack overflows.
+  if (AAQI.Depth >= 512)
+    return MayAlias;
+
   // Check the cache before climbing up use-def chains. This also terminates
   // otherwise infinitely recursive queries.
   AAQueryInfo::LocPair Locs(MemoryLocation(V1, V1Size, V1AAInfo),


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