[prev in list] [next in list] [prev in thread] [next in thread] 

List:       llvm-dev
Subject:    [llvm-dev] Extending StoreInst/LoadInst
From:       Jeroen Dobbelaere via llvm-dev <llvm-dev () lists ! llvm ! org>
Date:       2018-08-31 20:20:24
Message-ID: 19541D745B8D4845AA4E0B97499258E457E2B2A5 () de02wembxa ! internal ! synopsys ! com
[Download RAW message or body]

Hi,

I am trying to figure out the best way to add some extra metadata to the store and \
load llvm-ir instructions:

The metadata content is a 'Value*' expression representing a side channel, containing \
dependency information that is used to help the Scoped Alias Analysis. Optimizations \
that don't know about this side channel can safely drop it, where the only effect \
would be on the alias analysis not being able to prove that certain accesses will not \
alias.

As for the actual implementation, I am wondering what the recommended strategy is.

I am currently aware of:
1) 'metadata as value': this is supported for arguments (like in a call), but, as far \
as I see, not directly for generic metadata. Not sure how easy it is to add to \
StoreInst/LoadInst. 2) add an extra 'Value*' member to StoreInst and LoadInst \
(without changing the operands and the OperandTraits) 3) treat the side channel as \
(optional) operand 1 for load, and (optional) operand 2 for store. This involves \
changing the 'operator new' to always allocate for 2(load)/3(store) operands. Also  \
OperandTraits of StoreInst must be modfied as we now have an optional operand.  For \
the LoadInst, we also need to introduce an OperandTraits, to overrule the \
'UnaryInstruction' one. 4) Introduce a \
StoreWithSideChannelInst/LoadWithSideChannelInst that inherits from \
StoreInst/LoadInst, together with its appropriate OperandTraits. This makes it harder \
to add/remove sidechannel information.

Thanks,

Jeroen Dobbelaere



_______________________________________________
LLVM Developers mailing list
llvm-dev@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


[prev in list] [next in list] [prev in thread] [next in thread]