llvm dev - Jun 2010 - [LLVMdev] Two quick questions on call graph nodes

Hello all, 

When I examined the callgraph generated by LLVM via this command: 

  opt -print-callgraph-sccs -dot-callgraph a.out.bc

I ran into two confusions: 

First, there is a "indirect call node" dominating all other nodes
(include "main"). My question is: what does this special node serves
for? 

Second, there are two identical functions except that the functions
have slightly different names. 

  define void @_ZN6StringC2Ev(%struct.String* %this) nounwind ssp {}
  define void @_ZN6StringC1Ev(%struct.String* %this) nounwind ssp {} 

So, why is it so? 

Thanks!

best, 
Xiaolong

PS: My running example is a simple code as below: 

  #include "string.h"

  int main()
  {
    String y, z;
    String x("Hello World!");
    y = x; // strongly update y
    z = y; // use y
    return 0;
  }

The string class definition is: 

  class String {
  public:
    // Default constructor
    String();

    // Copy constructor
    String(const String& that);

    // One argument constructor that takes a character array as the initial
    //  value for the string
    String(const char str[]);

    // Destructor
    ~String();

    // Assignment operator
    String& operator=(const String& that);
                                                                          
  private:
    int length;
    int capacity;
    char* buffer;
  };

  String::String() : capacity(0), length(0), buffer(0)
  {
    // Nothing else to do
  }
                                                                          
  String::String(const String& that) 
  {
    ...
  }

  ...

Hi Xiaolong,
> First, there is a "indirect call node" dominating all other nodes
> (include "main"). My question is: what does this special node
serves
> for?
what version of LLVM are you using?  I don't think LLVM 2.7 uses a
"indirect call node".  However it does use a "external
node", which
is used when a function external to the current module is called.
> Second, there are two identical functions except that the functions
> have slightly different names.
>
>    define void @_ZN6StringC2Ev(%struct.String* %this) nounwind ssp {}
>    define void @_ZN6StringC1Ev(%struct.String* %this) nounwind ssp {}
>
> So, why is it so?
These are generated by the C++ front-end, and represent the base object
constructor and the complete object constructor respectively.

Ciao,

Duncan.

Hello Duncan, 

Thanks!
> > First, there is a "indirect call node" dominating all other
nodes
> > (include "main"). My question is: what does this special
node serves
> > for?
> 
> what version of LLVM are you using?  I don't think LLVM 2.7 uses a
> "indirect call node".  However it does use a "external
node", which
> is used when a function external to the current module is called.
> 
The "external node" makes sense. However, I am using LLVM 2.8. (See
the output from "opt -version") and build it against Revision 105271
in the svn repository. So, can I say that the presence of "indirect
call node" is new in LLVM 2.8?
  
  
  Low Level Virtual Machine (http://llvm.org/):
    llvm version 2.8svn
    DEBUG build with assertions.
    Built Jun  1 2010 (12:21:00).
    Host: x86_64-apple-darwin10
    Host CPU: core2

Best, 
Xiaolong