[LLVMdev] JIT and array pointers

[dummy1 at boxpl.com]

On Sun, 2005-04-10 at 22:23 -0500, Chris Lattner wrote:
> On Mon, 11 Apr 2005, dummy1 at boxpl.com wrote:
> >> There are many possible ways to do this, can you be a bit more specific
> >> about what you're trying to do?
> 
> > Here is a basic example:
> 
> Ah, ok, I see what you're trying to do.  Below is some *pseudo* code for 
> the basic idea:
> 
> > ============================================
> > unsigned int buff[4096];
> >
> > int main (void)
> > {
> >  buff[0] = 1;
> >
> >  // compile and execute code that will change buff[0] to 2
> >  Value *c0 = ConstantUInt::get (Type::UIntTy, 0);
> >  Value *c2 = ConstantUInt::get (Type::UIntTy, 2);
> >
> >  Module *m = new Module ("test_module");
> 
> Here, create an LLVM GlobalVariable 'BuffGV' of the appropriate type, and 
> insert it into m:
> 
> GlobalVariable *BuffGV = new GlobalVariable([4096 x uint], false, 
> GlobalVariable::ExternalLinkage, 0, "Buff", m);
> 
> >  Function *f = m->getOrInsertFunction ("test_function", Type::VoidTy,
> > 0);
> >  BasicBlock *b = new BasicBlock ("entry_block", f);
> >
> >  // Here is the problem.
> >  // I need to get the buff pointer into variable, which I can
> >  // pass to GetElementPtrInst
> >  // Value *pbuff = ??
> >  // -> %pbuff = external global [4096 x uint]
> 
>     pbuff = BuffGV;
> 
> >  Value *ptr = new GetElementPtrInst (pbuff, c0, c0, "ptr", b);
> >  // -> %ptr = getelementptr [4096 x uint]* %buff, int 0, int 0
> >  new StoreInst (c2, ptr, b);
> >  // -> store uint 2, uint* %ptr
> >  new ReturnInst (b);
> >
> >  ExistingModuleProvider *mp = new ExistingModuleProvider (m);
> >  ExecutionEngine *ee = ExecutionEngine::create (mp, false);
> 
> Tell the EE that buffGV -> buff:
> 
> ee->addGlobalMapping(BuffGV, buff);
> 
> Then you should be good to go!
> 
> -Chris
> 
> >  cout << "constructed module:\n\n" << *m << "\n\n";
> >
> >  vector <GenericValue> args;
> >  GenericValue ret = ee->runFunction (f, args);
> >
> >  printf ("buff[0] is now: %d\n", buff[0]);
> >  return 0;
> > }
> > ============================================
> >
> > I've been trying to do it with GlobalVariable. It seems like a
> > completely basic thing, but I just can't get it to work.
> >
> > _______________________________________________
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> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
> 
> -Chris
> 

Thanks for taking the time to answer. It's working now.

Paul