[PATCH] D35754: [ForwardOpTree] Introduce the -polly-optree pass.

[Nandini Singhal via Phabricator via llvm-commits]

nandini12396 added a comment.

In https://reviews.llvm.org/D35754#818793, @Meinersbur wrote:

> In https://reviews.llvm.org/D35754#818516, @nandini12396 wrote:
>
> > Could you please explain what is the meaning of 'forwarding' of operand trees?
>
>
> Suppose you have two statements:
>
>   StmtA:
>     %add = fadd double 21.0,21.0
>     bl label %StmtB
>  
>   StmtB:
>     store double %add, double*A
>
>
> This would induce a scalar dependency from %StmtA to %StmtB. To avoid, we can recompute %add in %StmtB instead:
>
>   StmtA:
>     %add = fadd double 21.0,21.0
>     bl label %StmtB
>  
>   StmtB:
>     %add_ = fadd double 21.0,21.0
>     store double %add_, double*A
>
>
> This "forwards" %add (and its operand tree/DAG) to StmtB.


Thank you. This is really nice idea. Do you have some cost modeling for when to allow this forwarding?

> I am open to naming it differently. I considered "reverse code motion".




Repository:
  rL LLVM

https://reviews.llvm.org/D35754