llvm dev - Jun 2010 - [LLVMdev] [llvmdev] Whole function SelectionDAG

I am trying to build a DAG for a whole function. The first problem I met is
to assign a user for the last instruction of each basic block, be it BRCOND
or other node. There is no natural user for such nodes. Without user, it
will be removed in later phases. My idea is to use it as chain for nodes in
the next basic block. Is this reasonable?

-Zhongxing Xu
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The first question is code placement.  How is the compiler going to  
decide which block (or blocks) to emit an instruction in?  The answer  
to that will help determine how control relationships should be  
represented.

Dan

On Jun 7, 2010, at 11:56 PM, Zhongxing Xu <xuzhongxing at gmail.com>
wrote:
> I am trying to build a DAG for a whole function. The first problem I  
> met is to assign a user for the last instruction of each basic  
> block, be it BRCOND or other node. There is no natural user for such  
> nodes. Without user, it will be removed in later phases. My idea is  
> to use it as chain for nodes in the next basic block. Is this  
> reasonable?
>
> -Zhongxing Xu
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

At first I'll try the simplest strategy: put the instruction in the machine
BB corresponding to the LLVM BB where it comes from.

To implement this, I plan to add an operand to non-passive node which points
to the BasicBlockSDNode which the node belongs to.

Another idea is to use a side map to map each node to its block. But I guess
it's difficult to keep the map consistent when transforming the DAG.

On Wed, Jun 9, 2010 at 1:39 AM, Dan Gohman <gohman at apple.com> wrote:
> The first question is code placement.  How is the compiler going to decide
> which block (or blocks) to emit an instruction in?  The answer to that will
> help determine how control relationships should be represented.
>
> Dan
>
>
> On Jun 7, 2010, at 11:56 PM, Zhongxing Xu <xuzhongxing at gmail.com>
wrote:
>
>  I am trying to build a DAG for a whole function. The first problem I met
>> is to assign a user for the last instruction of each basic block, be it
>> BRCOND or other node. There is no natural user for such nodes. Without
user,
>> it will be removed in later phases. My idea is to use it as chain for
nodes
>> in the next basic block. Is this reasonable?
>>
>> -Zhongxing Xu
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>
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