llvm dev - Feb 2011 - [LLVMdev] conversion from 'const llvm::Value*' to 'llvm::Constant*'

Oh, I thought that after "codegening" cos(0) would get me double 1.0
(assigment is working for anything like: global a = 1/3 + 2 /3 for
example)   What would be the best way to make assigments involving
functions, like  global a = cos(0);
without getting the assertion arising from  InitVal
cast<Constant>(Init->Codegen()); ?

I made some changes and now my code basically works, except in
assigments like the one above. It is a little bit frustrating because
is the main thing preventing me finishing my little silly scripting
language for monte carlo simulations.

Value *GlobalExprAST::Codegen() {
for (unsigned i = 0, e = GlobalNames.size(); i != e; ++i) {
  const std::string &GlobalName = GlobalNames[i].first;
  ExprAST *Init = GlobalNames[i].second;
  Constant *InitVal;
  InitVal = cast<Constant>(Init->Codegen());
  if (InitVal == 0) return 0;

GlobalVariable * globval = new GlobalVariable(*TheModule,
InitVal->getType(), false, llvm::GlobalValue::ExternalLinkage,
InitVal, Twine(GlobalName) );
}
}

Thank you very much for our help
Anton

2011/2/13 Duncan Sands <baldrick at free.fr>:
> Hi Anton,
>
>> But there are still some details I must be missing. I'm getting an
assertion
>> when I try the following assignment in my script:
>>     global c = cos(1);
>> Assertion failed: isa<X>(Val) && "cast<Ty>()
argument of incompatible type!",
>
> I think this is telling you that cos(1) is not a constant.
>
> Ciao, Duncan.
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On Sun, Feb 13, 2011 at 11:35 AM, Anton Skvorts <anton.skvorts at
gmail.com> wrote:
> Oh, I thought that after "codegening" cos(0) would get me double
1.0
Your codegen method looks like it will generate code to evaluate
cos(0).  There's no way in LLVM to run this code at global scope, it
has to be inside a function.  If you want to support running arbitrary
code at global scope in your language, you probably want to do
something like what C++ does for static initializers, where you run
code before main and fill in the values of global variables.
> (assigment is working for anything like: global a = 1/3 + 2 /3 for
> example)
The reason 1/3 + 2/3 works is because the IRBuilder recognizes these
as constants for you and folds them down to an LLVM Constant.

Reid

Hi Anton,
> Oh, I thought that after "codegening" cos(0) would get me double
1.0
> (assigment is working for anything like: global a = 1/3 + 2 /3 for
> example)   What would be the best way to make assigments involving
> functions, like  global a = cos(0);
> without getting the assertion arising from  InitVal >
cast<Constant>(Init->Codegen()); ?
the problem is that you are performing a function call (to "cos").  A
function
call is simply not a constant in the sense of LLVM (even if it is a constant in
the sense of mathematics): it needs to be executed to work out what the return
value is, and something that needs to be executed is not a Constant.

Probably you should have a constructor call "cos" and assign the
return value
to your global.  To work out how to do this I suggest you write the C code
corresponding to assigning cos(0) to a and stick it in http://llvm.org/demo to
see how it is handled.

Ciao, Duncan.

Hi Duncan and Reid,

Thanks for your comments and suggestions. I was puzzled because
assigning to a local variable in the tutorial example works. For
example:

var a = cos(1) in (
2 * a );

emits

declare double @cos(double)
define double @0() {
entry:
  ret double 0x3FF14A280FB5068C
}

and we get the right answer 1.08060461.



On Sun, Feb 13, 2011 at 5:09 PM, Duncan Sands <baldrick at free.fr>
wrote:
>
> Hi Anton,
>
> > Oh, I thought that after "codegening" cos(0) would get me
double 1.0
> > (assigment is working for anything like: global a = 1/3 + 2 /3 for
> > example)   What would be the best way to make assigments involving
> > functions, like  global a = cos(0);
> > without getting the assertion arising from  InitVal > >
cast<Constant>(Init->Codegen()); ?
>
> the problem is that you are performing a function call (to
"cos").  A function
> call is simply not a constant in the sense of LLVM (even if it is a
constant in
> the sense of mathematics): it needs to be executed to work out what the
return
> value is, and something that needs to be executed is not a Constant.
>
> Probably you should have a constructor call "cos" and assign the
return value
> to your global.  To work out how to do this I suggest you write the C code
> corresponding to assigning cos(0) to a and stick it in http://llvm.org/demo
to
> see how it is handled.
>
> Ciao, Duncan.
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev