[LLVMdev] SimplifyCFG vs loops

[Dan Gohman]

On Wed, Oct 17, 2012 at 8:41 AM, Krzysztof Parzyszek <
kparzysz at codeaurora.org> wrote:

> Hello All,
>
> The current implementation of the CFG simplification is loop-agnostic. In
> the past I have observed that it can perform transformations that can be
> detrimental to the loop structure.  One example that I recall, is
> converting a loop like this:
>    while (...) {
>       ...
>       if (cond) continue;
>       ...
>    }
> into two nested loops.  Specifically, the "continue" branch would go back
> to the loop header making it appear as if there were two back edges.
>

Well, there really are two backedges there.


>
> What are your thoughts about either making the CFG simplification aware of
> loops in its entirety, or separating the "safe" transformations in a quick
> pass, and having a more aggressive pass that does preserve loop structure?


It's not clear what the problem is.

Dan
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20121017/756e0442/attachment.html>