[llvm] r290769 - Add a comment for a todo in LoopUnroll post cleanup

[Sean Silva via llvm-commits]

Sorry for the stupid question, but what's the difference between EarlyCSE
and GVN in this context? (and more generally in LLVM)

Is EarlyCSE just a "cheaper" GVN? If so then that makes NewGVN seem even
more attractive, because from reading the paper the algorithm is quite
tunable w.r.t. compile time cost vs accuracy so maybe it can replace both
EarlyCSE and CurrentGVN.

-- Sean Silva

On Fri, Dec 30, 2016 at 2:10 PM, Philip Reames via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: reames
> Date: Fri Dec 30 16:10:19 2016
> New Revision: 290769
>
> URL: http://llvm.org/viewvc/llvm-project?rev=290769&view=rev
> Log:
> Add a comment for a todo in LoopUnroll post cleanup
>
>
> Modified:
>     llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp
>
> Modified: llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/
> Transforms/Utils/LoopUnroll.cpp?rev=290769&r1=290768&r2=290769&view=diff
> ============================================================
> ==================
> --- llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp Fri Dec 30 16:10:19
> 2016
> @@ -673,6 +673,11 @@ bool llvm::UnrollLoop(Loop *L, unsigned
>      }
>    }
>
> +  // TODO: after peeling or unrolling, previously loop variant conditions
> are
> +  // likely to fold to constants, eagerly propagating those here will
> require
> +  // fewer cleanup passes to be run.  Alternatively, a LoopEarlyCSE might
> be
> +  // appropriate.
> +
>    NumCompletelyUnrolled += CompletelyUnroll;
>    ++NumUnrolled;
>
>
>
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