[LLVMdev] Call graph node for function: 'main' Calls external node

[Duncan Sands]

Hi Gener,

> For the main function, the output of the above command is:
>
> Call graph node for function: 'main'
>    Calls external node

this means that callgraph saw that main calls something, but it doesn't
know what it is.  It might be any function, internal (eg: f2) or external.
The reason for this poor quality information is that the use of the forward
declaration "void f2();", which should be "void f2(void);", results in some
unpleasantness in the bitcode.  If you run the optimizers it will be cleaned
up.  Take a look at this: without optimization and with mild optimization:

$ llvm-gcc -c -o - cg.c -emit-llvm -O0 | opt -print-callgraph -disable-output 
2>&1 | grep "function: 'main'" -A 2
Call graph node for function: 'main'<<0x2f80c30>>  #uses=1
   CS<0x2f837b8> calls external node

$ llvm-gcc -c -o - cg.c -emit-llvm -O1 | opt -print-callgraph -disable-output 
2>&1 | grep "function: 'main'" -A 2
Call graph node for function: 'main'<<0x20536c0>>  #uses=1
   CS<0x2057468> calls function 'f2'

The callgraph code doesn't try to be clever.  It assumes that the optimizers
have been run.

Ciao,

Duncan.