[llvm-dev] Aliasing rules difference between GCC and Clang

Ivan Kosarev via llvm-dev llvm-dev at lists.llvm.org
Fri Jan 25 07:02:23 PST 2019

Hi, Jonas,

Sorry for the late answer.

As far as I'm aware, those proposals didn't result in any patches 
published. Here's the original message discussing the approach:

[llvm-dev] RFC: Representing unions in TBAA

Despite its title, it also suggests changes supposed to address the 
issue with representation of array-element accesses.

As to my own patches pending publication, they are all for the new TBAA 
format, which you said would be of no help in your case.


On 22/01/2019 16:02, Jonas Paulsson wrote:
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> Hi Ivan,
> On 2019-01-18 10:15, Ivan Kosarev wrote:
>> IIRC, there were proposals/attempts to represent accesses to array
>> elements as accesses to their first elements, which can technically be
>> encoded with the current TBAA format and thus may work as an
>> incremental improvement on top of the existing TBAA machinery you are
>> looking for. But this may need making sure there will be no
>> regressions for some tricky cases like those that involve GCC's type
>> punning and changing effective types within unions and in dynamic 
>> memory.
> It would be interesting for me to apply such a patch and evaluate if it
> really helps my test case. I would much appreciate any links to (or
> files of) your patches and the attempts you mentioned above.
> Thanks,
> Jonas

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