[LLVMdev] BasicCallGraph patch

[Zhongxing Xu]

I am doing inter-procedural static analysis, so I need to do DFS of call
graph. llvm-gcc sometimes generates this kind of call instruction, which
cause the call graph to be incomplete.

But thanks for your information, instcombine really solves the problem.

On 7/17/07, Chris Lattner <sabre at nondot.org> wrote:
>
> On Thu, 12 Jul 2007, Zhongxing Xu wrote:
> > The current BasicCallGraph will miss call sites like this:
> > %tmp86 = call i8* (...)* bitcast (i8* ()* @find_ispell to i8* (...)*)( )
> >     ; <i8*> [#uses=1]
> >
> > Here the direct user of @find_ispell is a ConstantExpr.
> > I added several lines of code to address this case.
> > Below is the output of command: svn diff lib/Analysis/IPA/CallGraph.cpp
> > Attached is LLVM asm files with such function calls.
>
> This is problematic, because it's not checking for the type of constant
> expr (i.e. is it a bitcast, etc).  That can easily be fixed, but here's a
> basic question: when is this important?  The instcombine pass should fix
> up these bitcasts, so they shouldn't occur frequently in practice.  When
> have you found this to be important?
>
> Thanks,
>
> -Chris
>
> > Index: lib/Analysis/IPA/CallGraph.cpp
> > ===================================================================
> > --- lib/Analysis/IPA/CallGraph.cpp      (revision 39771)
> > +++ lib/Analysis/IPA/CallGraph.cpp      (working copy)
> > @@ -13,6 +13,7 @@
>
> >  //===----------------------------------------------------------------------===//
> >
> >
> > #include "llvm/Analysis/CallGraph.h"
> > +#include "llvm/Constants.h"
> > # include "llvm/Module.h"
> > # include "llvm/Instructions.h"
> > # include "llvm/Support/CallSite.h"
> > @@ -150,6 +151,19 @@
> >               -> addCalledFunction(CS, Node);
> >          else
> >          isUsedExternally = true;
> > +      } else if (ConstantExpr* CE = dyn_cast<ConstantExpr>(*I)) {
> > +        for (Value::use_iterator I = CE->use_begin(), E =
> CE->use_end();
> > +             I != E; ++I)
> > +          if (Instruction* Inst = dyn_cast<Instruction>(*I)) {
> > +            CallSite CS = CallSite::get(Inst);
> > +            if (isOnlyADirectCall(F, CS))
> > +              getOrInsertFunction(Inst->getParent()->getParent())
> > +                ->addCalledFunction(CS, Node);
> > +            else
> > +              isUsedExternally = true;
> > +          } else {
> > +            isUsedExternally = true;
> > +          }
> >        } else if (GlobalValue *GV = dyn_cast<GlobalValue>(*I)) {
> >          for (Value::use_iterator I = GV->use_begin(), E =
> GV->use_end();
> >               I != E; ++I)
> >
> >
>
> -Chris
>
> --
> http://nondot.org/sabre/
> http://llvm.org/
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