[mlir] Add a null pointer check in symbol lookup

[shlmregev]

We (TensorFlow project) ran into a case where a dead code analysis crashed because a symbol that is called/used didn't appear in the symbol table. Added a nullptr check after symbol table lookup.

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[llvmbot]

@llvm/pr-subscribers-mlir

Author: Shlomi Regev (shlmregev)

Changes

We (TensorFlow project) ran into a case where a dead code analysis crashed because a symbol that is called/used didn't appear in the symbol table. Added a nullptr check after symbol table lookup.

---

Full diff: https://github.com/llvm/llvm-project/pull/115165.diff

1 Files Affected:

• (modified) mlir/lib/Analysis/DataFlow/DeadCodeAnalysis.cpp (+2)

diff --git a/mlir/lib/Analysis/DataFlow/DeadCodeAnalysis.cpp b/mlir/lib/Analysis/DataFlow/DeadCodeAnalysis.cpp
index 3c190d4e991919..e805e21d878bf9 100644
--- a/mlir/lib/Analysis/DataFlow/DeadCodeAnalysis.cpp
+++ b/mlir/lib/Analysis/DataFlow/DeadCodeAnalysis.cpp
@@ -186,6 +186,8 @@ void DeadCodeAnalysis::initializeSymbolCallables(Operation *top) {
       // If a callable symbol has a non-call use, then we can't be guaranteed to
       // know all callsites.
       Operation *symbol = symbolTable.lookupSymbolIn(top, use.getSymbolRef());
+      if (!symbol)
+        continue;
       auto *state = getOrCreate<PredecessorState>(getProgramPointAfter(symbol));
       propagateIfChanged(state, state->setHasUnknownPredecessors());
     }

[joker-eph]

Thanks for the fix!

Could we test?

If needed adding an op in the test dialect which implements the callable interface, and an IR that has the call but not the definition for the callee?

[shlmregev]

Sorry, but I'm not familiar with LLVM. Just tracked down this bug from my application code, written on top of TensorFlow.

[joker-eph]

Oh I see. You should many MLIR folks at Google I think: can you find one of your colleagues to assist with this maybe?

[jpienaar]

Added a test to very it doesn't crash.

[joker-eph]

Nice, didn't even need a change in the test dialect :)

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