[llvm-dev] Full restrict support - status update

Jeroen Dobbelaere via llvm-dev
Sun, 03 Nov 2019 22:15:13 -0000

Hi Alexey,

Adding llvm-ir bitcode support means adding/adapting the tags for LOAD/STORE
instructions and adding
the support for the noalias_sidechannel at the right places.

I had a short attempt to implement it when preparing the public patches, but I
am not familiar with that
part of the llvm code. When I noticed that it would take a lot longer than
anticipated, I postponed it.
Also because it is likely that the way how the noalias_sidechannel was added to
LoadInst/StoreInst might
change.

At this moment, I am not planning to work on this. For the current
implementation, there might be
a number of possibilities for adding support :
  - maybe 2 new tags are needed (FUNC_CODE_INST_{LOAD_NOALIAS,STORE_NOALIAS})
  - or maybe it is sufficient to add the noalias_sidechannels as extra operands
and look at the number of
     operands to see if they are present or not
  - or maybe it is sufficient to look at the number of operands, and the
noalias_sidechannel operand should
    be added with an extra bit, indicating if it is really there or not...

Greetings,

Jeroen Dobbelaere


From: Alexey Zhikhartsev <alexey.zhikhar at gmail.com>
Sent: Thursday, October 31, 2019 16:21
To: Jeroen Dobbelaere <dobbel at synopsys.com>
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Full restrict support - status update

Hi Jeroen,

Thank you very much for the great work, it is much appreciated.

> - For now, there is still no llvm-ir bitcode support for the load/store
noalias_sidechannel argument.

Do you have plans to work on this in the near future? Do you know how much work
it is and if there are significant hurdles?

Thanks,
Alexey

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