llvm dev - Mar 2010 - [LLVMdev] CFG as DOT: where do node addresses come from?

Hi,

The -dot-cfg option of opt will write a diagram of an analyzed  
function's CFG to DOT format. If you then open the DOT file, you will  
see that the BasicBlocks are uniquely identified with hexadecimal  
addresses. For example, an edge from one block to another may look like:

	Node0x10026b0:s0 -> Node0x1004c20;

I've been trying to figure out where these hexadecimal addresses come  
from. I've been up and down the code but remain at a loss. I can see  
where GraphWriter.h is actually writing the strings to the DOT file,  
and I can see that some of the DOT data is coming from DOTGraphTraits  
in CFGPrinter.h. But the hexadecimal addresses are a mystery. I  
thought perhaps a BasicBlock method, such as getName, might be  
producing the addresses, but no.

Can anyone shed some light on this for me? Thanks,

Trevor

On Mar 15, 2010, at 4:22 PM, Trevor Harmon wrote:
> Hi,
> 
> The -dot-cfg option of opt will write a diagram of an analyzed  
> function's CFG to DOT format. If you then open the DOT file, you will  
> see that the BasicBlocks are uniquely identified with hexadecimal  
> addresses. For example, an edge from one block to another may look like:
> 
> 	Node0x10026b0:s0 -> Node0x1004c20;
> 
> I've been trying to figure out where these hexadecimal addresses come  
> from. I've been up and down the code but remain at a loss. I can see  
> where GraphWriter.h is actually writing the strings to the DOT file,  
> and I can see that some of the DOT data is coming from DOTGraphTraits  
> in CFGPrinter.h. But the hexadecimal addresses are a mystery. I  
> thought perhaps a BasicBlock method, such as getName, might be  
> producing the addresses, but no.
>From GraphWriter.h:
    O << "\tNode" << static_cast<const void*>(Node)
<< " [shape=record,";

Printing a pointer on a raw_ostream produces a hexadecimal address.