[PATCH] D103862: [Attributor] Simplify loads

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added inline comments.


================
Comment at: llvm/lib/Transforms/IPO/AttributorAttributes.cpp:4504
+        // A null pointer access can be undefined but any offset from null may
+        // be OK. We do not try to optimize the latter.
+        bool UsedAssumedInformation;
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kuter wrote:
> I don't understand why this case needs to be handled.  I don't see how we would get something different from the `getAssumedSimplified`. `getAssumedUnderlyingObjects` just does `genericValueTraversal` and strips away casts.
> 
The problem is that the object might be null but the pointer is not.

`p = nullptr; p[(intptr_t)q] = 1;` 
Uses a nullptr object and `q` as offset. The simplified pointer is not `null` but a gep (or q).
In this case we cannot ignore the object. We can only ignore `p = nullptr; q = p[10]; q[-10] = 1;` because the object and the simplified pointer (which is where the access happens) are both null.


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  https://reviews.llvm.org/D103862/new/

https://reviews.llvm.org/D103862