[LLVMdev] Find all backedges of CFG by MachineDominatorTree. please look at my jpg.

[任坤]

Hi:

I hope to cut all backedges of MachineFunction CFG, then topological sort MachineBasicBlocks.

1. MachineDominatorTree *domintree = new MachineDominatorTree();
domintree->runOnMachineFunction(mf);

2. Then travel mf one by one.
When domintree->dominates(next,current) is true, there is a backedge from current node to next node. move this backedge form CFG.

But I find A LOOP in some CFG, there is backedge from current to next, dominates function reture "FALSE". So my algorithm find Graph can not be
toplogical sort.

3. how do I find all backedges of CFG???

Thanks
renkun

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[Benoit Boissinot]

2010/1/25 任坤 <hbre...@yahoo.cn>:

> Hi:
>
> I hope to cut all backedges of MachineFunction CFG, then topological sort MachineBasicBlocks.
>
> 1. MachineDominatorTree *domintree = new MachineDominatorTree();
> domintree->runOnMachineFunction(mf);
>
> 2. Then travel mf one by one.
> When domintree->dominates(next,current) is true, there is a backedge from current node to next node. move this backedge form CFG.
>
> But I find A LOOP in some CFG, there is backedge from current to next, dominates function reture "FALSE". So my algorithm find Graph can not be
> toplogical sort.
>
> 3. how do I find all backedges of CFG???

For non-reducible graphs (as is the case for your example), it is no
longer true that the target of a back-edge dominates the source.

If you want back-edges, just do a depth-first search of the CFG, the
back-edges are the edges going to an already processed node. If you
want loop-edges (edges going to loop headers, that is more generic
than back-edges), you'll need to build the loop nesting forest.

Cheers,

Benoit

[任坤]

Dear Benoit:

Thanks for your answer.

Best Regards.

Ren Kun

--- 10年1月25日，周一, Benoit Boissinot <bboiss...@gmail.com> 写道：

> 发件人: Benoit Boissinot <bboiss...@gmail.com>
> 主题: Re: [LLVMdev] Find all backedges of CFG by MachineDominatorTree. please look at my jpg.
> 收件人: "任坤" <hbre...@yahoo.cn>
> 抄送: "llvm" <llv...@cs.uiuc.edu>
> 日期: 2010年1月25日,周一,下午6:14

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[任坤]

Hi, Dear Boissinot:

1. When I have irreducible CFG, I travel its nodes by DFS.
search backedge for every node. After I finish one node,
push it into a stack.
[0, 1, 2, M] <---push.
[0, 1, 2, M,...N] <---push.

When resolving node M, find a edge from node N to node M,
N is not in stack(M < N), It is a backedge.
N is in stack(M > N), It is NOT a backedge.

I treat these backedges as loop-edges. M is Loop header node.
If I cut these edges from CFG, CFG can be topological sort.

Am I right???

--- 10年1月26日，周二, Benoit Boissinot <bboiss...@gmail.com> 写道：

> 发件人: Benoit Boissinot <bboiss...@gmail.com>
> 主题: Re: [LLVMdev] Find all backedges of CFG by MachineDominatorTree. please look at my jpg.
> 收件人: "任坤" <hbre...@yahoo.cn>

> 日期: 2010年1月26日,周二,下午3:12
> On Tue, Jan 26, 2010 at 01:31:53PM
> +0800, 浠诲潳   wrote:
> > Hi, Dear Boissinot:
> >
> > If a graph(CFG) is irreducible, how to find every loop
> headers of CFG?
> >
> > If I have a simple algorithm to find them, I think it
> is easy to use
> > depth-first search to find all loop-edges.
>
> Since there are several definition of loops, the simplest
> way is to
> choose: backedge target are loop-headers.
>
> Backedge is then defined by a DFS of the CFG (you'll find
> that in most
> textbooks).
> http://www.personal.kent.edu/~rmuhamma/Algorithms/MyAlgorithms/GraphAlgor/depthSearch.htm
>
> regards,
>
> Benoit
>
> --
> :wq

[Benoit Boissinot]

On Tue, Jan 26, 2010 at 10:04:16PM +0800, 任坤 wrote:
> Hi, Dear Boissinot:
>
> 1. When I have irreducible CFG, I travel its nodes by DFS.
> search backedge for every node. After I finish one node,
> push it into a stack.
> [0, 1, 2, M] <---push.
> [0, 1, 2, M,...N] <---push.
>
> When resolving node M, find a edge from node N to node M,
> N is not in stack(M < N), It is a backedge.
> N is in stack(M > N), It is NOT a backedge.
>
> I treat these backedges as loop-edges. M is Loop header node.
> If I cut these edges from CFG, CFG can be topological sort.
>
> Am I right???

yes, exactly.

regards,

Benoit

--
:wq