[PATCH] D94180: [SimplifyCFG] Optimize CFG when null is passed to a function with nonnull argument.

[Nikita Popov via Phabricator via llvm-commits]

nikic added a reviewer: aqjune.
nikic added a subscriber: aqjune.
nikic added inline comments.


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Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6598
+      // Passing null to a nonnnull argument is undefined.
+      for (const llvm::Use &Arg : CB->args())
+        if (Arg == I &&
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Why `llvm::`?


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Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6600
+        if (Arg == I &&
+            CB->paramHasAttr(CB->getArgOperandNo(&Arg), Attribute::NonNull))
+          return true;
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Two issues:

1. I believe this is subtle incorrect in conjunction with the GEP rule above. Accessing memory at `gep null, x` is always UB, but passing it to a nonnull argument isn't UB as long as x is not zero.

2. I'm not sure what the current state on this is (@aqjune), but I believe the plan is to make passing null to nonnull argument poison rather than UB. This optimization would only be valid using nonnull + noundef.


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https://reviews.llvm.org/D94180