[Polly][PATCH 5/8] Allow the IslExprBuilder to build address of expressions

[Johannes Doerfert]

On 08/11, Tobias Grosser wrote:
> On 11/08/2014 10:52, Johannes Doerfert wrote:
> >On 08/11, Tobias Grosser wrote:
> >>On 11/08/2014 09:36, Johannes Doerfert wrote:
> >>>On 08/11, Tobias Grosser wrote:
> >>>>On 10/08/2014 09:50, Johannes Doerfert wrote:
> >>>In the future it might be applicable to more but the "types"
> >>>still have to match, thus in our code generation the operand should
> >>>result in a load/store (the store case is missing at the moment though).
> >>>If you want me to factor it out, sure...
> >>>
> >>>>Also, I am surprised that create(Op) actually returns a load instruction? My
> >>>>understanding is that we do not create load/stores for access expressions,
> >>>>but that we only create the ptr value?
> >>>I change the behaviour of createOpAccess to generate the load and the
> >>>reason is pretty simple:
> >>>   A isl_ast_expr which dumps like MemRef_sum[0] or MemRef_A[i] should
> >>>   not result in a LLVM-Value representing &MemRef_sum[0] or
> >>>   &MemRef_A[i]. What we did before for isl ast access expressions was
> >>>   actually implementing the address of the access not the actual
> >>>   access.
> >>
> >>Right. You should mention such things in your commit message. They are very
> >>helpful to understand what you are doing.
> >>
> >>Nevertheless, you change just makes the behaviour unintuitive in a different
> >>way.
> >>
> >>As proposed before, I would just assert if we see an isl_ast_access that
> >>is not surrounded by the address_of instruction.
> >How is that going to work?
> 
> We can move the code that computes the address expression into a subfunction
> getAddressOfAccess().
> 
> createOpAccess() becomes just an
> 
> // We currently do not have a need to create access expressions that
> // load or store to memory. If we at some point need to do this,
> // we need to a way to understand if an access is a load or a store
> // access.
> llvm_unreachable("Can not generate isl_op_access instructions")
>
> 
> >>And the address_of instruction could directly compute the address (using a
> >>subfunction), without having to create a load that is later removed.
> >We can do that.
> 
> And here we can just call getAddressOfAccess().
Could you just write the patch?

-- 

Johannes Doerfert
Researcher / PhD Student

Compiler Design Lab (Prof. Hack)
Saarland University, Computer Science
Building E1.3, Room 4.26

Tel. +49 (0)681 302-57521 : doerfert at cs.uni-saarland.de
Fax. +49 (0)681 302-3065  : http://www.cdl.uni-saarland.de/people/doerfert
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