[LLVMdev] [llvmdev] Whole function SelectionDAG

Zhongxing Xu xuzhongxing at gmail.com
Thu Jun 10 22:48:50 PDT 2010

I have another idea: let the BasicBlockSDNode points to the last node in its
predecessor blocks. But this will introduce cycles into the selection DAG,
making it not a DAG anymore.

So what's the impact of a non-DAG on the existing DAG legalizers and

On Wed, Jun 9, 2010 at 9:33 AM, Zhongxing Xu <xuzhongxing at gmail.com> wrote:

> 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
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