[llvm-commits] [PATCH] Make SimplifyCFGPass preserve the dominator tree

[Chandler Carruth]

On Fri, Jun 8, 2012 at 10:47 AM, Peter Cooper <peter_cooper at apple.com>wrote:

> Hi all
>
> Attached is a pass to make the SimplifyCFGPass preserve the dominator
> tree.  Currently we see lots of recalculations of the dom tree right after
> simplify cfg runs, regardless of whether simplify cfg actually did anything.
>
> This pass explicitly recalculates the dom tree if simplify cfg did
> anything, but otherwise just leaves it preserved so we recalculate less
> often.
>
> Also, i'm open to suggestions for a better way to do this.  Ideally the
> pass manager could track this but not all passes return true from their run
> functions when they actually make a change.


Can we just go fix these passes and then teach the pass manager to preserve
analyses across passes that claim they didn't change anything? There aren't
*that* many optimization passes.

Anyways, I'm also interested in incrementally updating domtree, just wanted
to see if we could get the heavy hammer part in a more general way.
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