[PATCH] D68244: [InstCombine] don't assume 'inbounds' for bitcast pointer to GEP transform (PR43501)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp:2348
+      uint64_t DerefBytes = Src->getPointerDereferenceableBytes(DL, CanBeNull);
+      unsigned EltBitWidth = DstElTy->getPrimitiveSizeInBits();
+      if (!CanBeNull && EltBitWidth && EltBitWidth % 8 == 0 &&
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lebedev.ri wrote:
> ```
>   /// Note that this may not reflect the size of memory allocated for an
>   /// instance of the type or the number of bytes that are written when an
>   /// instance of the type is stored to memory. The DataLayout class provides
>   /// additional query functions to provide this information.
>   ///
>   unsigned getPrimitiveSizeInBits() const LLVM_READONLY;
> ```
> We are sure this is what we want?
Actually, what @jdoerfert was saying is that we don't care what the size of the type is.
We only need to check that we have at least one dereferenceable byte.


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  https://reviews.llvm.org/D68244/new/

https://reviews.llvm.org/D68244